DE112006003417T5 - Optimization of the efficiency of a photovoltaic electrolysis device - Google Patents

Abstract

A method of operating a hydrogen producing electrolyzer powered by two or more available photovoltaic modules irradiated by sunlight, namely an array of modules, the electrolyzer comprising two or more electrolytic cells and a DC operating voltage and an operating voltage, one or more photovoltaic modules in a parallel or series circuit arrangement are interconnectable to form different arrays of a module / modules for delivering DC power to the electrolysis cells, wherein a given array of modules / modules may comprise less than the total number of available modules, the method includes that:
Maximum power operating voltages for representative arrays of one module / modules are predetermined;
determining an operating current and an operating voltage for the electrolyzer for a desired hydrogen production rate; and
a photovoltaic array is selected from a module (s) as a currently operating array and is applied to operate at its maximum power point voltage to deliver the particular operating current and voltage to the electrolyzer.

Description

TECHNICAL AREA

These This invention relates to hydrogen production by electrolytic Decomposition of water. More specifically, this invention relates to the optimized Use of photovoltaic modules to power for electrolytic production supplied by hydrogen from water.

BACKGROUND OF THE INVENTION

As disclosed in the above parent application is solar hydrogen production by photovoltaic electrolysis device systems (PV electrolysis device systems, PV from engl. "photovoltaic") a renewable and for the environmentally beneficial energy source for fuel cell vehicles and other applications that use hydrogen as fuel. The photovoltaic system and the hydrogen-producing electrolysis device are however separate and differently working devices, their use and work processes have to be coordinated to achieve appropriate operating efficiencies for each, if they be used in combination.

A photovoltaic system typically comprises a group of individual planar solar cells arranged in rows and columns in a flat panel called a module. Each cell in a module is typically made of the same chemical material that has the property of converting incident solar radiation into electrical potential. Materials for such photovoltaic cells include, for example, crystalline silicon, amorphous silicon, copper indium selenium (CuInSe ₂ ) or cadmium tellurium (CdTe). For example, a representative cell membrane could produce a DC electrical potential of 0.6 V at a cell membrane temperature of 25 ° C when idle, when receiving solar radiation of 100 mW / cm ² (an irradiation from a sun). The plurality of cells in a planar module may be configured and electrically connected to produce a specified operating voltage and current at a specified temperature and under specified solar irradiation and operating load conditions. Two or more modules may be interconnected in an electrical series or parallel connection to a group of modules called arrays.

It There are also known electrolysis device systems for the electrolytic Dissociation of water to hydrogen and oxygen. Examples include alkaline electrolyzers, proton exchange membrane electrolyzers (PEM electrolysis devices), steam electrolysis devices and high pressure electrolysis devices. For many Applications may prefer an alkaline electrolyzer be. The electrolyzer typically consists of a Group of individual cells that are electrically interconnected to a desired Hydrogen production rate using specified electrical To obtain performance parameters. The single alkaline water electrolysis device For example, an electrolyte of aqueous potassium hydroxide (5 M KOH), a platinum or nickel cathode (for hydrogen) and a suitable comprising a catalyst provided with an anode for oxygen generation.

at the design of a specified hydrogen production becomes the operation the electrolysis device for a desired one Hydrogen production rate designed and scheduled. The electrolysis device design becomes a fixed number of electrolysis cells with a DC voltage / cell of about 1.6 volts and an electrical power requirement for the planned Hydrogen production rate and the operating temperature range of the Systems have. The multiple electrolytic cells may be in be arranged an electrical series or parallel connection. Then a photovoltaic system with the ability to electric power provided efficiently to the electrolyzer.

It has been recognized that a given PV system of cells and modules has a maximum power point voltage for the system to be found from a predetermined relationship between an actual voltage and an actual current under load. It has been recognized that improved efficiencies are achieved by modifying the number of electrolyzer cells so that a PV system can operate at its maximum power point voltage. In contrast, the number of modules in the PV system may be changed such that the load required by the electrolyzer fits the revised and unconfigured PV system. However, the operation of the PV system and the electrolyzer system may vary. For example, the operation of the PV system is particularly susceptible to variations in ambient temperature and solar radiation Lich. In this example, there is a continuing need to be aware of the changing operating characteristics of the PV system and to adapt the overall operation of the PV electrolysis devices to such changes in order to maintain the operating efficiencies of the combined systems.

Accordingly there remains a need for Practices for optimizing the operation of a group of photovoltaic modules (Arrays) in combination with an electrolysis device with a Group cells for the electrolysis of water to hydrogen and oxygen.

SUMMARY OF THE INVENTION

It will be procedures for the design and / or operation of a solar powered photovoltaic electrolyzer system for one efficient production of hydrogen from water provided. The methods are generally on electrolyzer systems and photovoltaic systems applicable. The goal of the procedure is to do it each separate system, namely photovoltaic and electrolysis device, to allow, in their combination to work efficiently.

The electrolyzer is sized based on a design rate of hydrogen production. The hydrogen production rate will allow calculation of a _DC operating _current (I _oper ) and a determination of a number of series connected electrolytic cells. Some electrolyzer cells may also be arranged in electrical parallel connection. The operating voltage (V _oper ) is estimated from the number of cells in an electrical series circuit. The testing of the system will provide an accurate confirmation of the operating current and operating voltage values for the electrolyzer and a suitable operating temperature or range of operating temperatures for the most efficient operation of the electrolyzer. An object of the practice of this invention is to provide a photovoltaic system (PV system) for charging the specified electrolyzer so that the PV system is able to operate at a most efficient voltage level in delivering DC power to the electrolyzer.

One PV system is organized such that it is an array of individual Includes modules in series or parallel electrical connections can be arranged. For example, an array of PV modules with some in series switched modules to a suitable operating voltage for the electrolyzer to be provided, and organized in parallel, for a suitable operating current for the required hydrogen production rate provide. The maximum power point for each module is determined and recorded, and its operating fluctuation with the temperature is determined and recorded.

voltage and current sensors are connected to the operating voltage and the operating current of the photovoltaic electrolysis device system to measure, and temperature sensors are built-in to the operating temperature to measure the photovoltaic modules. Furthermore, a control system that logical systems, control algorithms, electronic controllers and Switch (solenoid or other) to the voltage, current and temperature sensors to be connected to the operation and the Efficiency of the photovoltaic electrolysis device system control the basis of the sensor readings. The tax system acts around the system operation and the system efficiency constantly under Use of signals from the sensors to optimize the number of solar cells or modules connected in series and parallel are arranged in the photovoltaic system to rearrange, as it necessary to obtain the optimum output voltage of the PV system, the same the desired Operating voltage of the electrolyzer is to maintain. Different arrays of the modules are formed to make an efficient Maintain system operation.

alternative System operation and system efficiency can be used of signals from the control system are constantly optimized to the Number of electrolysis cells connected in series and parallel are switched in the electrolysis device to control, and thus to maintain the optimum system operating voltage. alternative can the system operation and the system efficiency constantly using signals be optimized by the control system to the output voltage of a DC / DC converter or a charge controller, and thus the optimum system operating voltage to maintain. One or a combination of the alternatives Tax scenarios can / can used to operate the PV electrolysis device to control.

Frequently, the operating temperature of photovoltaic modules increases during operation and reduces their electrical output. The cooling of the modules (by spraying a cooling liquid or the same) can be used to keep their operation at the desired maximum power point.

aims and advantages of the invention will become apparent from a detailed description of the preferred Practices and embodiments, the consequences, be understood.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a schematic representation of a PV-Elektrolysevorrichtungssystems with a direct connec tion between the PV modules and the electrolyzer.

2 is a schematic representation of a PV electrolysis device with a DC / DC converter, which is arranged between the PV modules and the electrolysis device.

3 is a graph of current (A) or power (W) for a typical photovoltaic module showing the maximum power point (MLP). MLP is the point on the graph of the PV current output above the voltage at which the power output is maximum. The corresponding curve of power (P = V × I) across the voltage is also shown.

4 Figure 12 is a graph of the estimated efficiency of the electrolyzer for a 20 cell PEM electrolyzer connected directly to the PV modules with a range of MLP voltages.

5 Figure 10 is a graph illustrating the effects of current and temperature on the efficiency of a PEM electrolyzer. The efficiency of the electrolyzer in percent was plotted over the operating current at temperatures of 22 ° C and 39 ° C.

6 FIG. 10 is a simplified schematic of a variable load tester with an internal voltmeter and ammeter (using a Hewlett Packard Electronic Load Model 6060A) used to sense current-voltage curves of photovoltaic modules to measure solar electrical efficiency to determine the maximum power point. Using a temperature sensor (thermocouple), the device can also measure the effect of module temperature on solar electrical efficiency (temperature coefficients of current, voltage and power).

7 FIG. 12 is a graph of power and current output sampling over current for a Sanyo HIP-190 PV module (a layered crystalline and amorphous silicon material) at 41 ° C. FIG.

8th is a graph illustrating the effect of temperature on the efficiency of the Sanyo PV module HIP-190, where a data adjustment of the results of the measured efficiency has been made on a straight line (linear temperature coefficient of -0.3% / ° C) ,

9A Figure 4 is a schematic representation of a real-time system for continuous operation and continuous control of a three-module PV system in parallel for delivering DC power at a predetermined operating level of 50 V to an electrolyzer. In this embodiment, operating voltage switches are employed to switch between direct connections of the PV modules to the electrolyzer and the onset of a DC / DC converter for better match between operation at the maximum power point of the PV module array and the electrolyzer. Voltage, current and temperature readings are used by a programmed computer to control the operation of the switches when using the transducer.

9B Fig. 12 is a schematic representation of a real-time system using computer controlled electrical switches to generate different arrays of a group of PV modules to maintain operation at the maximum power point of the modules in delivering power to a hydrogen producing electrolyzer. The system controls the number of PV modules connected in series and in parallel to optimize the efficiency of the PV electrolysis device.

9C FIG. 10 is a schematic representation of a real-time system using computer controlled electrical switches to control a parallel / series arrangement of electrolysis cells in an electrolyzer for efficient joint operation of PV array arrays and the electrolyzer and to optimize the efficiency of the PV electrolysis device.

10 is a normalized expression of the efficiency of the PV module and other variables used to predict PV efficiency at V _oper .

11 is a normalized expression based on a computer model for easy calculation of PV efficiency by interpolating new values of V _oper / V _mlp .

12 _{Figure 4} is a graph _showing a comparison of the electrical efficiencies of each type of PV cell at its V _mlp and at 32 volts, the ordinary V _{oper of} the electrolyzer system.

13 is a plot of percent efficiency versus power input (W) for DC / DC converters used in PV-E systems.

14 _{Figure 4} is a graph of solar hydrogen _efficiency (%) _versus V _mlp (volts) of PV systems comparing a measured efficiency and predicted solar hydrogen production efficiency by directly connected PV electrolyzer systems.

15 _{Figure 4} is a graph of solar hydrogen _efficiency (%) _versus V _mlp (volts) of PV systems comparing the measured efficiency and predicted solar hydrogen production efficiency with PV electrolyzer systems using DC / DC converters.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the practice of this invention, two methods of electrical interconnection of photovoltaic (PV) modules with an electrolyzer for the production of hydrogen are used. In one of these methods, the PV system is wired directly in series with the electrolysis system ( 1 ). In the second method, a DC / DC converter in the circuit is wired in series between the PV system and the electrolyzer device (FIG. 2 ), a process called tracking of the maximum power point.

In the schematic representation of 1 For example, a multi-module photovoltaic system (box labeled with Optimal PV system) is directly connected to a multi-cell electrolyzer for the electrolytic separation of water into hydrogen and oxygen using a proton exchange membrane (box labeled with PEM electrolyzer). An ammeter (box A) and a voltmeter (box V) are used to constantly monitor the DC electrical potential and current flow from the PV system to the electrolyzer. Oxygen (O ₂ ) is produced at the cathodes of the electrolyzer cells, and the separate streams are collected and led out of the electrolyzer for the desired use. Hydrogen (H ₂ ) is produced at the electrolysis device anodes. The evolution of hydrogen is violent and entrains liquid. In this embodiment, the streams of water from the plurality of cells are collected into a common stream which is washed with deionized water. The water is separated from the hydrogen product in a gas / liquid separator or separator and pumped back into the PEM electrolyzer.

Preferably, the operating temperatures of the optimum PV system and the PEM electrolyzer are determined by thermocouples or the like disclosed in U.S. Pat 1 not shown, constantly measured.

In this embodiment In the invention, the PV system is directly with the electrolyzer connected. The PV system is constantly changing for one efficient joint operation with the electrolyzer without optimizes the use of an intermediate DC / DC converter. The PV system is constantly changing electrically configured so that its maximum power point voltage is close to the operating voltage of the electrolyzer.

In the schematic representation of 2 For example, a DC / DC converter is arranged in electrical connection between a non-optimal PV system and the PEM electrolyzer. The other elements of the working PV electrolysis apparatus are as shown in FIG 1 described. In this embodiment of the invention, the DC / DC converter is used to compensate for differences between the maximum power point voltage of the non-optimal PV system and the operating voltage of the electrolyzer.

In the practice of this invention, a predictive model is used to estimate the efficiency of each PV electrolyzer system based on the electrical characteristics of the switch Determine circular elements and select the optimum electrical specifications for the PV modules, electrolyzer, and DC / DC converter (if any) for use in designing a system for optimal hydrogen production. The predictive model is used to devise a practical, step-by-step procedure for the optimized design and operation of a PV electrolyzer system. The models and optimization procedure can be used to optimize any PV electrolysis system, including those with PEM, alkali, steam, high pressure and other types of electrolysis devices, and to provide optimal design specifications to build PV solar hydrogen systems.

A PV powered PEM electrolyzer is a more efficient means of hydrogen production when the two units are integrated to optimize their combined efficiency. Notably, the maximum power point (MLP) of the PV system must match the characteristic operating voltage of the electrolyzer to maximize the efficiency of the PV electrolyzer system. If the PV system has an MLP voltage (V _mlp ) that is different from the operating voltage (V _oper ) of the electrolyzer, the PV modules operating at a non-optimal voltage will produce less power for the electrolysis process Operating efficiency (whose electrical energy output divided by its solar irradiation input) will be reduced. The farther _away V _mlp of V _oper along characteristic IV of the particular PV modules used in the system, the lower will be the percent efficiency of solar energy conversion to hydrogen energy.

V _mlp is the voltage at MLP. 3 is a graph of the current (A) or power (W) for a typical photovoltaic module showing the maximum power point (MLP). MLP is the point on the graph of PV current output over voltage where the power output is maximum. The corresponding power curve (P = V × I) is also shown.

V _oper is a characteristic stress at which the electrolyzer _operates on account of its electrode and membrane materials, its catalyst _coatings and its electrolyte (in a PEM electrolyzer, the water-flooded membrane acts between the electrodes as the electrolyte). The _{operatability of} the electrolyzer is the sum of the normal water _{splitting voltage} plus the electrolysis device overvoltage multiplied by N, the number of electrolysis cells in series within the electrolyzer _circuit (Equation 1). All values are in direct current (DC).

Equation 1:

• V Opera = N × (1.23 volts / cell + overvoltage / cell)

The overvoltage in a 20 cell PEM electrolyzer used in several tests was 0.4 volts / cell, so V _{oper was} 32-33 volts.

Gleichung 3:

wobei H₂-Strömung = die gemessene Strömungs- oder Durchflussrate in L/h bei einer Atmosphäre und 298 K ist, H₂LHV = H₂ unterer Brennwert = 33,35 kWh/kg, H₂-Dichtefaktor = 0,002 kg/24,45 L bei 298 K und 1 Atmosphäre, und Sonnenbestrahlung = Sonnenenergie in W/m² × aktive Zellenfläche eines PV-Moduls in m².The overall efficiency of the PV electrolyzer system can be measured directly, as measured in this study, by measuring the solar irradiation and the area of the PV solar cells to obtain the input energy and the current flowing through the electrolyzer using an ammeter low voltage is measured in the circuit, which is then multiplied by the standard voltage for electrolysis of water to determine the energy of the hydrogen produced. Hydrogen energy production was also calculated from the volume of hydrogen measured with a calibrated flow or flow meter as a test of results. All of these methods reported the same system efficiency (solar hydrogen production efficiency) within ± 4%. The methods of calculating the system efficiency from the operating stream and the hydrogen flow or flow are shown in Equation 2 and Equation 3. Equation 2:

Equation 3:

where H ₂ flow = the measured flow or flow rate in L / h at one atmosphere and 298 K, H ₂ LHV = H ₂ lower calorific value = 33.35 kWh / kg, H ₂ density factor = 0.002 kg / 24, 45 L at 298 K and 1 atmosphere, and solar irradiation = solar energy in W / m ² x active cell area of a PV module in m ² .

However, understanding the efficiency and optimization of PV electrolysis is complicated by the fact that at least two units, a PV system (the power source) and an electrolysis device (the operating load), must be integrated to produce hydrogen. Each unit has its own efficiency, and instead of having a single independent efficiency level, the two units interact so that the PV system affects the efficiency of the electrolyzer and the electrolyzer affects the efficiency of the PV system. The results of modeling the PV efficiency of the electrolyzer in a direct connection system are shown in Table 1 which, for each PV system tested, shows the voltage at the MLP under Standard Test Conditions (STC, 25 ° C) Data used to calculate the efficiency of each PV system at V _oper , the efficiency of the electrolyzer, and the resulting system efficiency under operating conditions, including effects of PV temperature (which often rises well above STC) and the operating voltage of the electrolyzer (Last), which may force the PV system to operate above or below the MLP voltage. Equation 4 is the basis for the model of direct junction PV electrolysis device in Table 1: the system efficiency is the product of the PV efficiency corrected for temperature effects times the efficiency of the electrolyzer.

Equation 4:

• System efficiency = (electrical PV efficiency at V Opera  - PV temperature correction) × efficiency the electrolyzer at V Opera

If The DC / DC converter PV electrolysis is used in the Model an additional term (Equation 5).

Equation 5:

• Efficiency of the system = (electrical PV efficiency at V Opera  - PV temperature correction) × efficiency the electrolyzer at V Opera  × efficiency of the DC / DC converter

In Both models (equations 4 and 5) assume that line losses due to the resistance in the wiring connecting the circuit elements connects, by using a sufficiently thick wire for the Transport of the expected operating current are minimized, according to standard rules, the for electrical DC systems are used. Because resistance losses in the wiring and connections are low (<1%), is in these Models no term for contain these losses.

The efficiency of the electrolysis device ( 4 ) can be calculated from the measured value of V _oper under the actual conditions existing during operation of the PV electrolyzer system (Equation 6).

To determine the efficiency of the electrolyzer, we used the theoretical standard electrolysis _voltage (1.23 volts / cell) divided by the measured V _{oper of} the electrolyzer with N electrolysis cells in series.

Equation 6:

If desired, the efficiency of the electrolyzer may be measured in advance in a range of operating currents and operating temperatures ( 5 ). The efficiency of the electrolysis device can then be calculated from the measured temperature and the efficiency curves in 5 be predicted. The electrolyzer efficiency values calculated from the measured V _oper (column G in Table 1) were used in the model because they were readily available and more accurate than any predicted values.

The 20 cell PEM electrolyzer (referred to above), which had an operating voltage of 32-33 volts, was operated using a number of different commercial photovoltaic modules, numbered (e.g., # 3) in column A are identified from Table 1. The V _mlp at 25 ° C of the particular module or combination of modules arranged in series or parallel electrical connection is shown in column B of the table. Various operating characteristics and efficiencies obtained using the above equations of the PV module (s) and the electrolyzer are shown in several columns of Table 1. It can be seen that some modules do not generate sufficient voltage to operate the specific electrolyzer.

The preceding section of this description has described how the operating efficiencies ei a multi-module PV system and a multi-cell electrolyzer for optimizing practices of this invention. Now attention is focused on the optimization process.

Step by step procedure optimization

It A series of nine steps is used to increase the efficiency to measure and optimize a solar-powered PV electrolysis. The complete Step by step optimization procedure, which illustrates example cases 2-4 is given below.

The Gradual procedure begins by the electrolysis device is characterized. The first step requires that the electrolyzer with the desired Hydrogen generation rate is operated until the electrolyzer a stationary one Temperature reached, and then the operating current, the Operating voltage and operating temperature are measured:

Step 1 -

wobei 26806 Ampere pro kg pro Stunde gleich der Faradaykonstante ist (96500 Coulomb/g Wasserstoff) und N die Anzahl von Elektrolysezellen in Reihe innerhalb des Elektrolysevorrichtungsschaltkreises ist.The electrolysis _current (I _oper ) required for the desired hydrogen generation rate is calculated using Faraday's law (Equation 7). Equation 7:

wherein 26,806 amps per kg per hour equals the Faraday constant (96500 coulombs / g hydrogen) and N is the number of electrolysis cells in series within the electrolyzer circuit.

The electrolyzer is connected to a variable DC power supply and the power output is increased until the current flow (I _oper ) is equal to the desired hydrogen production rate determined using Faraday's law. A constant operating temperature is necessary because increasing the temperature in the allowable temperature range of the electrolyzer increases its efficiency and hydrogen generation rate. The temperature reaches a stationary state (a constant temperature), which depends on the power input and the cooling water flow or flow rate and the cooling water temperature. In practice, the steady state temperature is determined by measuring the temperature of the electrolyzer stack using a temperature sensor (thermocouple or thermometer) attached to the stack plates and electrolysis cells. When a stationary state is established (the temperature no longer changes), the operating current in the electrolysis circuit is measured using an ammeter in series with the electrolyzer, and the operating voltage is measured using a voltmeter connected in parallel with the electrolyzer (as it is in the 1 and 2 is shown). A procedure that includes recording and plotting the operating voltage, operating current, and operating temperature until the electrolyzer reaches a steady state at the desired target hydrogen generation rate may help determine the steady state current and temperature.

Example Case 1 -

In a hypothetical example of optimizing a PV electrolyzer system, we need 0.5 kg of hydrogen per day to run a single fuel cell vehicle, and the PV electrolyzer system works for 6 hours in daylight. The hydrogen production rate will be
0.5 kg / 6 hours = 0.083 kg / hour.

Out Equation 7: steady state current in an electrolyzer with 20 cells becomes 0.083 kg / hr x 26806 amp / kg / hr / 20 = 111 amps.

Of the Electricity in stationary Condition after warming up becomes at 21 ° C held. The measured operating voltage is 40 volts.

Case 2 - Control Example (not closed) optimize):

All Conditions were as in case 1.

We will be up to four cases with various modifications in the design of a PV electrolyzer system Consider, in each case, the same sequence of calculations accomplished is the effect of the modifications on the efficiency the PV electrolyzer systems.

Step 2 -

Of the Efficiency of the electrolyzer under steady state conditions (constant temperature, voltage and current at the desired Hydrogen flow rate or flow rate) is calculated using Equation 6, d. H. Efficiency = 1.23 volts × 1 / (operating voltage per electrolytic cell).

In example case 1

From equation 6, the efficiency of the electrolyzer is Efficiency = 100% × 20 × 1.23 volts / 40 volts = 62%

Case 2 - Control Example (not closed) optimize):

All Conditions were the same as in case 1.

The measured efficiencies of the electrolyzer for 17 examples of PV electrolyzer systems are in FIG 4 applied. When V _{mlp of} the PV system was less than 30 volts, the PEM electrolyzer lacked sufficient energy to split the chemical bonds of the water, no current flowed, and zero efficiency. At a V _mlp of 30 volts, the current started to flow, but both the current and the volume of hydrogen produced indicate that the efficiency of solar hydrogen production is only 6.8%, and therefore, from equation 4, the efficiency is the electrolyzer only 56% (0.56). When the V _{mlp reached} 33 volts, the electrolyzer delivered its maximum efficiency (78%) and maintained an approximately constant efficiency at that level (76-79%) in the other PV electrolysis tests where the ambient temperature (20-23 ° C) C) was held.

The Use of a gas flow or flow meter connected to the hydrogen outlet the electrolysis device is connected, is an alternative or supplementary Means for measuring the hydrogen production rate. The efficiency the electrolysis device can from the hydrogen flow rate Using equation 8 can be calculated.

Equation 8:

In example case 1: the measured hydrogen production rate is 0.0833 kg / hour:

From equation 8: Efficiency = 100% × 0.083 × 33.3 / (111 × 40/1000) = 62%

Case 2 - Control Example (not closed) optimize):

• Efficiency = 100% × 0.083 × 33.3 / (111 × 40/1000) = 62% (equal)

Step 3 -

In some cases For example, the operating efficiency of the electrolyzer during the Hydrogen generation as part of a procedure to optimize a solar-powered hydrogen production can be increased. This is an optional one Step that should be considered.

Under circumstances # 1, if the present hydrogen generation rate is greater than necessary to produce the required hydrogen for fuel or other desired purposes, choosing an alternative, lower target hydrogen production rate by reducing the operating current of the electrolyzer. As it is in 5 is shown, reducing the operating current improves the efficiency. The estimated improvement in the efficiency Δ _T WG (%) = 0.17% / ampere × I _oper.

Under circumstances # 2, when the operating temperature of the electrolyzer is below the maximum operating temperature allowed by the durability and safety requirements of the electrolyzer, increasing the steady state operating temperature by reducing the flow rate or flow rate of the circulating water, or by artificial means is used to heat the electrolyzer (such as heating the circulating water). As it is in 5 As shown, increasing the operating temperature of the electrolyzer improves the efficiency. The increase in efficiency is Δ _T WG (%) = 0.13% / degree C x .DELTA.T. [Note: Water or an electrolyte mixture, such as water and KOH, is circulated through the electrolysis cells of electrolyzers to supply water for conversion to hydrogen and oxygen. The circulating water also passes through a cooler, such as a cooler, and serves to cool the electrolyzer, which heats up during operation due to the overvoltage that must be applied.]

Reducing the operating current to improve efficiency also reduces the hydrogen production rate of the PV electrolyzer system. There is a trade-off between lower hydrogen production (and higher cost per kg of hydrogen) versus improved efficiency. If the decrease in hydrogen production is unacceptable, N, the number of electrolysis cells in series, can be increased to compensate for the loss. The hydrogen production rate from Equation 7 is: Hydrogen rate = I Opera / (N × 26,806 amps / kg / hour).

The Number of cells can be increased up to 50% or more to the practical Design limits of electrolysis devices.

In example case 1:

We increase the efficiency of the electrolyzer by raising the temperature from 21 ° C to 50 ° C and reducing the current from 111 amps to 89 amps. After these changes: Δ T WG (%) = 0.13% / degree C × ΔT = 0.13 × 29 = 3.8% Δ I WG (%) = 0.17% / Amp × I Opera = 0.17 × 22 = 3.7%

The new efficiency will be: Efficiency of the electrolyzer = 62% + 3.8% + 3.7% = 70%

The new hydrogen production rate will be (from Equation 7): Hydrogen rate = I Opera / (N × 26,806 amps / kg / hour) = 89 × 20/26806 = 0.066 kg / hour

Although the efficiency of the electrolysis apparatus has been increased by the current was lowered, it may be that the total hydrogen production is too low: 0.066 kg / hour produced only 0.4 kg of hydrogen in 6 hours and full sunlight (1000 W / m ² radiation) per Day.

The hydrogen output can be brought back to 0.100 kg / hour (0.6 kg / 6 hours of sunlight) by increasing N, the number of electrolysis cells in series from 20 to 30. Again from equation 7, Hydrogen rate = 89 x 30/26806 = 0.100 kg / hour.

In our example, Case 1, (from Equation 6), the operating voltage of the electrolyzer is also increased from 20 to 30 due to the increase in the number of electrolysis cells:

Case 2 - Control Example (not closed) optimize):

• Hydrogen rate = 111 x 20/26806 = 0.083 kg / hour.
• Electrolysis apparatus efficiency = 62%

In tests ( 5 ), in which a much higher current (up to 70 amperes) was applied to the electrolyzer of large DC power supplies, the efficiency of the electrolyzer gradually decreased to about 72% while the operating current was increased. However, the efficiency of the electrolyzer increased with increasing temperature. These dates ( 5 ) can be used to predict the efficiency of the electrolyzer.

The Solar power for operating the electrolysis apparatus for production of hydrogen fuel is produced by photovoltaic modules (PV modules) provided that convert solar radiation into electrical power. The efficiency of a PV system that is used to load one to apply (an electrolysis device or any electrical device) depends on the operating voltage of the load and the operating temperature of the PV modules from. An increase the operating temperature of a PV module causes a decrease in its electrical efficiency. The changes the voltage, the current, the power and the efficiency per Degree of temperature increase in a PV module are expressed as temperature coefficients.

First, the PV modules are characterized by tests to determine their maximum power point in the following steps of the optimization procedure. Alternatively, the voltage, current, power, maximum power point, efficiency, and temperature coefficients can be estimated from manufacturer specifications and product literature for the PV modules under test that could be used to construct the PV electrolyzer. If the available PV specifications do not include the coefficients for the temperature-induced changes in voltage, current, and power, averages for the PV semiconductor material may be used. Crystalline silicon is the dominant PV semiconductor used today. The operating temperature of the PV modules can be continuously measured using a temperature sensor attached to the back of the module (the simplest method). The operating temperature could also be predicted since it is a function of the ambient temperature, the wind speed and the sunshine (W / m ² ).

Step 4 -

An electronically adjustable load device (with a voltmeter and an ammeter) is connected to the PV module and is used to measure the voltage, current, maximum power point, efficiency and temperature coefficients of the PV module. The circuit for a variable load is in 6 shown schematically.

The module (or group of interconnected modules) of solar powered photovoltaic cells is connected to a variable load as part of a procedure for optimizing solar powered hydrogen production. A temperature measuring device is mounted on the modules to continuously measure the operating temperature, and the modules are positioned with light receiving surfaces facing directly toward the sun. The temperature is constantly measured until the modules reach a steady operating temperature. The sun exposure (W / m ² ) is constantly using a calibrated Sonnenbestrah lung sensor measured.

A variable load (such as the Hewlett Packard 6060A Electronic Load Model) is connected in series with the module or modules. The variable load device is an electronic device that operates as a variable resistor, a low resistance ammeter in series with the electrical circuit to measure the input current, and a voltmeter in parallel with the electrical circuit to measure the input voltage. acts ( 6 ). In addition to measuring the current and voltage, the variable load device also measures the power. Using the variable load test system, the load applied to the module or modules is varied across the current range of the PV system from zero to the short circuit current (I _sc ), while the loads are the current, voltage, power and temperature under the expected operating conditions during the planned solar powered hydrogen production (usually steady-state operating conditions).

It is helpful to next apply the power over the voltage, where the power is defined as voltage × current to measure the maximum power (P _max ) (see 3 ). The application of current and power over voltage makes it possible to observe the maximum power point of the power curve and the point on the IV expression where the voltage is the maximum power voltage (V _mlp ) and the current is the maximum power current (I _mlp ) is what corresponds to the maximum power (P _max = V _mlp × I _mlp ).

7 shows the results of the sampling and the application of the voltage, current and power from a high efficiency PV module to find the maximum power point and P _max , V _mlp , I _mlp , the maximum PV efficiency using a system for a variable Load (tested under bright, natural sunlight in Warren, Michigan).

The effects of PV module temperature on voltage, current and maximum power and efficiency can also be measured using the variable load system and the results used to determine the module's temperature coefficients. In 8th For example, the effect of operating temperature changes on the electrical efficiency of a PV module at maximum power point (its optimal operating voltage) was determined by sampling a PV module six times with a range of operating temperatures. The change of 0.06% efficiency per degree C corresponds to a temperature coefficient of -0.3% / degree C, ie the efficiency of 18.8% At STC (25 degrees C) falls by -0.3% × 18.8% = -0.06% for each degree C increase in temperature due to solar heating. When the temperature reaches 40 degrees C, the efficiency will drop to 18.0%. The temperature coefficient for the PV power output is the same size as that for the efficiency (-0.3% / degree C) because efficiency = power output / P _max , where P _{max is} a constant (the maximum power under STC).

Example Optimization Case 1:

For the PV module (Sanyo HIP-190), which was tested using the system with an electronic variable load, as described in the 7 and 8th shown, we found the following results:
Voltage at the MLP (V _mlp ) = 52 volts at 41 ° C [off 7 ]
[the V _mlp at STC, 25 ° C, was 54.8 volts according to the manufacturer's _{specifications} ]
Power at MLP (P _max ) = 180 watts 41 ° C [off 7 ]
[the P _max at STC was 190 W according to the manufacturer's specifications]
The maximum power current (I _mlp ) of each PV module will be 180 watts / 52 volts = 3.46 amps at 41 ° C.
The temperature coefficient of P _max (% of total P / ° C) = -0.30% [out 8th ]
[the coefficient was also -0.30%% of the total P / ° C according to the manufacturer's specifications]
Temperature coefficient of V _mlp (volts / ° C) ≈ 0.3% × 180 VA / 3.46 A = 0.16 volts / ° C.

Case 2 - Control Example (not closed) optimize):

All PV module parameters were the same as in case 1.

Step 5 -

Next, the effect of the operating voltage of the electrolyzer on the efficiency of solar powered photovoltaic electrolyzer systems to generate hydrogen optimized by the following procedure.

The method in steps 1 and 2 is used to measure the operating voltage and efficiency of the electrolyzer under steady state conditions required to produce the target flow or rate of hydrogen production. _Thereafter , the method of step 4 is used to measure the maximum power point voltage (V _mlp ) and the efficiency of multiple sample photovoltaic modules or groups of interconnected modules under the expected operating conditions during the planned solar energized hydrogen production. The most appropriate module or groups of connected modules are chosen that have a V _mlp equal to the operating voltage of the electrolyzer to obtain the maximum efficiency from the photovoltaic system. This selection of the most appropriate module (s) will be made by _plotting photovoltaic _{module performance} and photovoltaic module efficiency _versus V _oper / V _mlp for the modules under the expected hydrogen production operating conditions, or alternatively a module or group of interconnected modules Power or efficiency _curve plotted against V _oper / V _mlp , indicating that the solar powered photovoltaic system maintains a desired percentage of maximum efficiency at the steady state operating voltage (V _oper ) of the electrolyzer.

At our optimization case 1:

The PV module (Sanyo HIP-190), which we characterized in step 4, produces an output voltage of 54.8 volts (the V _mlp ) at its maximum power output at 25 ° C (the MLP under standard _operating conditions of 25 ° C). Since the electrolyzer optimized in step 3 requires 53 volts (the operating voltage V _oper ), the PV output voltage can be considered a good choice for use in the PV electrolyzer system. For the PV modules to deliver 53 volts to operate the electrolyzer with high efficiency, the modules must either be designed to have a V _mlp of 53 volts at the steady state operating temperature, or the stationary operating temperature of the PV modules must be nearby of 25 ° C (see step 7 below). The small excess of PV output voltage over the operating voltage, 54.8 volts - 53 volts = 1.8 volts (3% excess) is helpful because the output voltage will drop as the operating temperature rises above 25 ° C, and it will fail due to Resistance in wiring can give low "copper" losses that reduce the voltage.

The PV modules will all be configured in parallel, ie connected positive to positive and negative to negative, and will be connected directly to the electrolyzer. The number of PV modules will be:
Number of modules = 89 amps / 3.46 amps / module = 26.
Total power at MLP (P _max ) = 26 × 180 watts = 4680 watts at 41 ° C
[Performance coming out of the 7 calculated maximum power point is calculated]

Case 2 = control example (not to be optimized):

The PV modules will all be configured in parallel, ie connected positively to positive and negative to negative, and will be connected directly to the electrolyzer. The number of PV modules will be:
V _oper = 40 volts

Out 7 :
PV power at V _oper = 150 watts per module
Current (I _oper ) at V _oper = 150 watts / 40 volts = 3.75 amps
Number of modules = 111 amps / 3.75 amps / module = 30
Total power = 30 × 150 watts = 4500 watts

Under these non-optimized conditions use more PV modules, but which yield less power than Case 1.

Step 6 -

It may be an alternative method of estimating the maximum power point voltage and efficiency of a module or modules of solar powered photovoltaic cells having a variab are used as part of a method for optimizing solar-powered hydrogen production by using the photovoltaic module specifications specified in the product literature by the manufacturer for maximum power point voltage and maximum power at 25 ° C (standard test conditions), and a temperature measuring device attached to the module or modules to measure the steady-state operating temperature by the method of step 4. The temperature coefficients (or average temperature coefficients for the semiconductor and type of photovoltaic material) provided by the manufacturer, obtained from this literature, can be used to estimate the maximum power point voltage and the maximum power at the operating temperature (using the temperature coefficients and the operating temperature used to correct the maximum power point voltage and the maximum power at 25 ° C).

Step 7 -

Next, the following procedure for increasing the efficiency of a photovoltaic module or photovoltaic modules may be used as part of a procedure for optimizing solar-powered hydrogen production. First, a greater or lesser number of modules are connected in series to modify the output voltage of the entire photovoltaic system to make it equal to the stationary operating voltage of the electrolyzer by the direct connection method (see step 5). Second, during the procedure of step 5, a flow of cooling water or other fluid, gas or liquid impinging on the module or modules may be used to reduce the steady-state module operating temperature. Alternatively, fluids carried in cooling loops, vanes, or vents that contact or are brought to the modules are used to reduce the steady state operating temperature. We tested the effect of periodically spraying cold water (21.4 ° C) on a PV module and found that the module temperature was effectively reduced. Reducing the operating temperature during step 5 increases the P _max and the efficiency of the PV module.

In addition there it circumstances, among those the only one available PV system no output voltage close enough to the operating voltage the electrode for an efficient operation of the PV electrolysis device by the Direct connection method has (see step 5). Under these circumstances be DC / DC converters or charging controllers in series between the modules and the electrolyzer switched to the output voltage of the entire photovoltaic system to make it equal to the stationary operating voltage to make the electrolyzer. Because DC / DC converter the resistance of the circuit, the maximum efficiency with DC / DC converters is lower than that maximum efficiency of PV electrolysis with direct connection, although both methods can be used to equal a voltage to supply the operating voltage. Therefore, become DC / DC converters not used when using the procedure in step 5 can, in order to set up the output voltage of the PV system, that it matches the operating voltage of the electrolyzer.

When optimizing Case 1:

The stationary Operating temperature of the PV modules during a cool windy Period is 35 ° C air.

In subsequent weeks, as the ambient temperature increases, a cooling liquid or cooling gas is used to maintain the PV operating temperature of 35 ° C whenever the ambient conditions of sunlight and wind speed heat the module beyond this temperature. Holding the PV modules 10 degrees above the standard temperature of 25 ° C will hold the V _mlp at 53 volts, the optimum level equal to the V _{oper of} the electrolyzer. If no cooling system is used, solar radiation will heat the modules to over 40 ° C on cold sunny days and to more than 50 ° C on warm sunny days, causing a drop in voltage and reduced efficiency. V mlp at 35 ° C = V mlp at 25 ° C + (temperature coefficient × ΔT) = 54.8 volts + (-0.16 volts / ° C × 10 ° C) = 53.2 volts

Case 2 - Control Example (not closed) optimize):

It nothing is done to the voltage, the current output or to change the temperature of the PV system.

When optimizing Case 3:

The steady operating temperature in another cool sunny period is 41 ° C. All of the electrolyzer parameters are the same as in Case 1, except that the redesigned electrolyzer in this case (Case 2) has 25 electrolysis cells connected in series, giving a V _oper of 45 volts.

The PV module has been redesigned to have 83 solar cells in series to produce a V _mlp of 45 volts at 41 ° C. [The original PV module in Case 1 had 96 solar cells connected in series to give 52 volts at 41 ° C.]

When optimizing Case 4:

All Electrolysis apparatus parameters are as described in Case 1.

At the PV operating temperature, the only PV modules available for use have a V _mlp of 36 volts.

The PV modules are connected to a DC / DC converter or to a charge controller system connected to an input voltage range of 36 volts (for example 30-40 Volt) and he amplifies the voltage to an output voltage of 53 volts at the expected PV operating temperature.

Of the DC / DC converter has an efficiency of 90% and causes a Efficiency loss of 10% in case 3 compared to the system with direct connection in case 1.

Step 8 -

The Optimization procedure in steps 1-5 can be used to an optimal design to build an optimized solar impact Photovoltaic electrolysis device system for generating hydrogen to produce. The optimal design parameters are used the method of step 1, to the stationary operating voltage of the electrolyzer to measure, and using the method of the steps 2 and 3, the operating efficiency of the electrolyzer in the range of allowed Operating current and permissible Operating temperature to be measured, calculated. Next, the method of Step 3 used to, if possible, to improve the efficiency of operation of the electrolyzer, and it will be the desired one Operating current (and the resulting hydrogen generation rate and the corresponding efficiency of the electrolysis device) is selected. When next become steps 4-6 used to optimize the efficiency of the PV system.

There is a trade-off between high hydrogen production and high efficiency. It should be noted that increasing the hydrogen generation rate by increasing the operating _current I _oper leads to reduced efficiency.

In case 1:

Of the Efficiency of the electrolyzer is 70%.

Of the Efficiency of the PV system is 18.2%.

Of the Overall efficiency of the conversion of solar energy into hydrogen is 12.7%.

The Hydrogen production rate is 0.10 kg / hour.

The PV cell area is 26 × 1.027 m ² = 26.7 m ² . (measured area of PV cells usually available from the manufacturer)

In case 2 - control example (not to optimize):

Of the Efficiency of the electrolyzer is 62%.

Of the Efficiency of the PV system = 150 watts / 190 watts × 19% = 15%

The overall efficiency of the conversion of solar energy into hydrogen is 9% Hydrogen rate = I Opera / (N × 26,806 amps / kg / hour) = 111 × 20/26806 = 0.083 kg / hour

The PV cell area is 30 × 1.027 m ² = 30.8 m ² .

There the electrolyzer and the PV system are both not optimized case 2 requires a larger number, area and costs of PV modules, but produces less hydrogen per hour.

In case 3:

Of the Efficiency of the electrolyzer is 70%.

Of the Efficiency of the PV system is 18.2%.

Of the Overall efficiency of the conversion of solar energy into hydrogen is 12.7%

The Hydrogen production rate is 0.10 kg / hour.

The PV cell area is 26 × 1.027 m ² = 26.7 m ² .

In case 4:

Of the Efficiency of the electrolyzer is 70%.

Of the Efficiency of the PV system is 18.2%.

Of the Efficiency of the DC / DC converter is 90%.

Of the Overall efficiency of the conversion of solar energy into hydrogen is 11.4%

The Hydrogen production rate is 0.09 kg / hour.

The PV cell area is 26 × 1,027 m ² 26.7 m ² .

Step 9 -

It For example, a method based on steps 1-5 may also be used become the solar powered photovoltaic electrolyzer system to optimize and operate hydrogen production. voltage and current sensors are connected to the operating voltage and the operating current of the photovoltaic electrolysis device system to measure, and temperature sensors are built-in to the operating temperature to measure the photovoltaic modules. Then there is a tax system the logical systems, control algorithms, electronic controllers and switch (solenoid or other), to the voltage, Current and temperature sensors connected to the operation and the efficiency of the photovoltaic electrolyzer system based on the sensor readings. The tax system acts to constantly increase system operation and system efficiency optimize by using signals from the sensors to the number of solar cells connected in series and parallel in the photovoltaic modules are switched to control the optimal Output voltage of the PV system equal to the desired operating voltage of the Keep electrolysis device.

alternative can System operation and system efficiency are constantly optimized by: Signals from the control system can be used to determine the number of Electrolysis cells, in series and parallel circuits in the Electrolysis device are connected to control to the optimum Maintain system operating voltage. Alternatively, the System operation and system efficiency are constantly optimized by Signals from the control system are used to control the output voltage a DC / DC converter or charge controller to control the optimal Maintain system operating voltage. One or a combination The alternative control scenarios can be used to control the Operation of the PV electrolysis device to control.

A system of control circuits and algorithms used for system control is in 9A shown schematically. This control system is designed to switch between two modes of photovoltaic device operation: (a) direct connection operation in high sunshine periods (giving high current and high voltage) and (b) DC / DC converter operation to control the Increase operating voltage in periods of partial clouding when the PV output voltage is too low for efficient direct connection operation. The direct connection mode usually results in higher power and higher efficiency PV electrolyzer operation since the addition of a DC / DC converter to the circuit increases the resistance. The increase in resistance when using the DC / DC converter mode causes a decrease in the maximum power delivered to the electrolyzer and a decrease of 5% -10% of the hydrogen produced.

In 9A _{For example} , the electrolyzer is operated at 50 volts (V _oper = _50V ). Three photovoltaic modules, each operating at their maximum power points V _mlp = 50 V, are arranged in parallel to deliver a sufficient operating _current to the electrolyzer for the required hydrogen production. The system is operated by a pre-programmed controller (controller algorithms). The controller may consist of a computer or other electronic control system with sufficient memory. The algorithms that govern the controller and decide when the controller will enable switches to make a direct connection from the PV array to the electrolyzer, or to use the PV array instead with the DC / DC converter will become one Performance database or efficiency model for the electrolyzer and the multiple PV modules derived. The direct connection mode of the PV electrolyzer system may be considered the default mode. In the direct connection mode, the V _{oper of} the system is equal to the output voltage of the PV array (V _PV ). The algorithm requires that, when the operating voltage (V _oper and V _PV ) of the PV electrolysis _{device fall} below the lower limit of the optimum voltage range of the PV array (V _opt ) in the direct connection mode, the controller will disconnect the connections of the PV array. Arrays with the DC / DC converter (the mode with DC / DC converter) and the mode with direct connection (default) will switch away.

A voltmeter and ammeter monitor the performance of the PV system and their respective data is monitored by the controller system. The voltmeter monitors when V _{oper drops} below the preset value of V _opt , which is a characteristic value for the particular PV array used in the PV electrolyzer. The database for the performance and the efficiency model for the electrolysis apparatus and the plurality of PV modules are used to V _opt, V _MLP or V _PV of the PV array or V _oper the electrolytic device under any temperature conditions or current conditions for use by the controller logic to put. Electric switches, controlled by the controller algorithms, allow automatic change from direct connection mode to DC-DC converter mode. If the V _{PV is coming} from the controller in 9A u is monitored, rises again to V _opt, the controller will automatically return to the mode with a direct connection (Standard) will switch. In this example, a DC / DC converter may be switched into the PV power _{delivery system} in the event that the voltage (V _mlp ) _output from the three PV modules falls below the operating voltage of the electrolyzer, and depending on that Current levels from the sun's rays are taken out of the circuit again.

9B illustrates a second embodiment in which an electrolyzer has a predetermined V _oper and a predetermined I _oper for producing hydrogen. The optimal values of V _oper and I _oper are _{predetermined} by the mathematical model for optimizing PV electrolysis (see Table 1). A PV array is provided to provide DC power for operation of the electrolyzer. Voltage, current and temperature sensors are built in to monitor the operation of the array of photovoltaic cells. The PV array is connected to electrical switches to obtain combinations of electrical series and / or parallel connections between the respective modules. The mathematical model for optimizing PV electrolysis (see Table 1) is based on data obtained with a number of PV modules, DC / DC converters, and electrolyzer conditions. The performance curve of each array of PV modules is thus predetermined and stored in the database of a programmed controller (the controller may consist of a computer or other electronic control system with sufficient memory). An initial arrangement of some or all of the modules is established by the control of the switches to deliver power (I _oper and V _oper ) to the electrolyzer, the array of modules _operating at their V _mlp . Should the solar irradiation change or the temperature of the PV array change, or the operating temperature or current of the electrolyzer change, or the like, the controller may have a different _{Command switching arrangement} for a new array of PV modules, while still working at the V _{mlp of} the new array. The controller algorithm of the system in 9B controls the connections of the PV modules and cells in the PV array so that the V _{mlp of} the PV array will be equal to V _oper , the operating voltage of the electrolyzer. This condition gives the maximum efficiency and maximum hydrogen production.

9C illustrates another embodiment of the invention. In this embodiment, it is the number of electrolyzer cells that are arranged in series and / or parallel, which can be varied for a desired change in hydrogen production rate or for compensation with the PV array. This figure is similar to that of 9B with the exception that, as illustrated schematically, the change is made in the organization of the electrolyzer cells. The controlling controller algorithm in this embodiment requires that the V _{oper of} the electrolyzer cells be equal to the V _{mlp of} the PV array determined by the efficiency model as shown in Tables 1 and 4 under the operating conditions.

PHOTOVOLTAIC KÜHLEXPERIMENTE

Tests were conducted on the effectiveness of cooling PV modules on a sunny day in October. Cool tap water (21.4 ° C) was applied to the surface of the PV modules for 3-5 minutes using a hose and a fine spray nozzle. A sensor attached to the back of each module was used to monitor the temperature. The current-voltage-power curves of the modules were sampled before and after the cooling process. The results of the tests are summarized in Table 2. Table 2. Photovoltaic cooling experiments PV module Initial temperature (° C) Final temperature (° C) Initial power (W) Final power (W) Increase in P _max (%) Sanyo HIP-190 41 24 181 191 5.5 SunPower 36 23 81 88 8.6

OPTIMIZATION MODEL

An overall model of the efficiency of a PV electrolysis device was constructed and tested in our database by comparison with the measured hydrogen production efficiency. This efficiency model was also the basis for establishing the step-by-step procedure for optimizing the efficiency of PV electrolysis. The steps of the procedure were chosen by analyzing the terms used to model the efficiency. To estimate the efficiency of each PV system at V _oper , a typical IV expression for a crystalline silicon PV module (Sharp Solar NT-185U1) was normalized to a relative efficiency of 1.0 to a V _mlp of 1.0 that is, the PV module would deliver full power at an irradiance of 1000 W / m ² if its V _{mlp is} exactly equal to V _oper for the electrical load ( 10 ). The fraction of V _{mlp represented} by the V _oper was obtained for each PV module and by drawing a vertical line from the V _oper / V _mlp value on the X axis to the efficiency _curve it was possible to estimate the fraction of the full PV electrical efficiency available at V _oper . For example, if V _{mlp is} 64 volts for module A and V _{oper is} 32 volts, the fraction V _oper / V _{mlp is} 0.5. Using the graph, a value of 0.5 (V _oper / V _mlp ) on the X axis corresponds to an efficiency of 0.58 on the Y axis. Then, multiplying the cell efficiency by 0.58 (at the MLP) of module A (about 14%) would give an estimated electrical efficiency of 0.58 x 14% = 8.1% at V _oper .

A mathematical model for predicting the efficiency of PV modules was developed by adding a curve to our experimental data presented in Tables 1 and 2 10 using a regression model developed using SAS software ( 11 ). To more easily estimate the predicted efficiency using this mathematical model, a "clickable" Microsoft Excel ^™ model (based on the SAS regression model) for interpolating new V _oper / V _mlp values into this file was presented as Table 3 locked in. To interpolate any desired value of V _oper / V _mlp and find out the corresponding efficiency of the PV system: double-click with the cursor positioned in the table, then insert a line, enter the V _oper / V _mlp value and press Tab Key to that by the Model predicted efficiency read out. V _oper / V _mlp Efficiency Model (SAS) 0 0.00 0,050 0.06 0,100 0.12 0,150 0.17 0,200 0.22 0,250 0.27 0,300 0.33 0,350 0.39 0,400 0.45 0,450 0.51 0,500 0.56 0,550 0.61 0,600 0.66 0,650 0.71 0,700 0.76 0,750 0.82 0,800 0.88 0,850 0.93 0.900 0.97 0.950 1.00 1,000 0.99 1,050 0.96 1,075 0.94 1,100 0.92 1,120 0.89 1,140 0.86 1,160 0.81 1,180 0.73 1,200 0.61 1,220 0.41 1,240 0.07 1,245 -0.04 Table 3. Clickable Microsoft Excel model (based on a regression model with 8 variables) to interpolate new V _oper / V _mlp values. To interpolate: Double-click with the cursor positioned in the table, then insert a line, enter a new V _oper / V _mlp value and press the Tab key to read out the modeled predicted efficiency.

The efficiency of each PV system at its V _mlp and V _oper is in 12 applied. In 12 For _example , the PV efficiency _curves for V _mlp and V _{oper coincide} in the range where V _{mlp of} the PV module is 33 to 36.2 volts, since this range is approximately _{equal to} the V _oper (32 volts) of the electrolyzer. This is the area where the efficiency of the PV modules is optimized and therefore the area where most hydrogen is produced and system efficiency is highest. The optimal V _mlp range (33 to 36.2 volts) is in 12 marked with bold brackets.

Solar radiation heats the PV modules during daylighting when working hotter than the ambient temperature, and this reduces its power output and electrical efficiency. While the V _mlp and other specifications of the PV modules are measured under standard test conditions (STC), which is 1 kW / m ² at a spectral distribution of AM1.5 (global spectral irradiation) and cell temperature (PV T) of 25 ° C , the PV modules often operate in hotter conditions such as Nominal Operating Cell Temperature (NOCT), which is ~ 47 ° C, which under standard operating conditions (ambient temperature of 20 ° C, solar irradiation of 0.8 kW / m ² and Wind speed of 1 m / s) occurs. In hot sunny conditions, temperatures rise even higher than 47 ° C. Thus, it is necessary to correct the predicted efficiency by subtracting a temperature coefficient (0.45% per ° C) times the number of degrees of temperature increase to obtain the temperature corrected value for the predicted efficiency (Equation 9).

Equation 9:

• corrected efficiency = not corrected Efficiency - (PV T ° C - 25) × 0.45% / ° C

Of the Temperature coefficient for six PV modules (Solarex, Shell Solar, Astropower, Siemens, BP Solar and Sanyo) ranges from 0.33% / ° C to 0.52% / ° C, with most materials have a coefficient close to the average of 0.45% / ° C exhibit. The predictive model was the average PV coefficient of 0.45% / ° C used (Table 1).

In the PV electrolysis model with a DC / DC converter for optimization shown in Table 4, an additional term must be added to account for the loss of efficiency due to the resistance provided to the circuit by the DC / DC converter will be added. The predicted efficiency of the PV electrolyzer must be multiplied by the measured efficiency of the DC / DC converter to obtain the corrected predicted efficiency of the overall system of DC / DC converter and PV electrolyzer (Equation 5). The measured efficiencies of DC / DC converters, ie the output power of the converter (I _out × V _out ) divided by the power input (I _in × V _in ), for two types of DC / DC converters, a Solar Converters Ltd. Model 48-10 Linear Current Booster (LCB) and a Solar Converters Ltd. Charge Controller Model 48-20, are in 13 shown. The efficiency values of the DC / DC converters used in Table 3 were exhausted 13 estimated: 95.2% for the LCB; for the charge controller 97.2%.

14 _{Figure 10} shows the solar hydrogen production model efficiencies of 15 PV electrolyzer _tests estimated from the predictive model for direct connection PV electrolyzers (Table 1) and based on the efficiency of the electrolyzer and PV efficiency at V _oper , including the effects of Interactions between the two systems and the PV temperature effects. The two curves are generally quite close. The biggest difference between the two sets of values is an efficiency of only 0.1%. 15 compares the predicted and measured efficiencies of DC / DC converter systems and PV electrolysis systems as described in US Pat 4 are modeled. The 14 and 15 demonstrate that the models can predict system efficiencies with an average accuracy of <± 0.1% for a direct connection and ± 0.4% for PV electrolyzers with DC / DC converters.

The Practices of the invention have been illustrated by way of example. These examples are meant for the Be illustrative and not limiting the scope of protection.

Summary

An array of photovoltaic (PV) module (s) is arranged in electrical series and / or parallel connection to deliver DC electrical power to an electrolyzer for producing hydrogen. The electric power is output through the array at its maximum power point (V _mlp ) to deliver an I _oper at V _oper for the electrolyzer. The array of PV modules in the array, or the array of cells in the electrolyzer, is constantly monitored and controlled by an automatic controller system to operate the PV and electrolyzer systems at or near their respective maximum efficiencies. A DC / DC converter can be used to set the V _mlp to the operating voltage of the electrolyzer.

Claims (15)

Method for operating a hydrogen-producing Electrolysis apparatus available through two or more, through Sunlight irradiated photovoltaic modules, namely an array of modules, is applied, wherein the electrolysis device two or more Electrolysis cells and a DC operating current and an operating voltage having one or more photovoltaic modules in a parallel or series circuit arrangement are interconnectable to different Arrays of a module / modules for delivering DC power to form the electrolysis cells, wherein a given array of a Module / modules less than the total number of available modules may comprise, the method comprising: Maximum power point operating voltages for representative Arrays of a module / modules are predetermined; one Operating current and an operating voltage for the electrolyzer for one desired Hydrogen production rate can be determined; and a photovoltaic array selected from a module / modules as a currently operating array and is applied to with its maximum power point voltage to Delivery of the specific operating current and operating voltage to work on the electrolyzer. Method for operating a hydrogen-producing The electrolyzer of claim 1, wherein the method further includes that: the operating voltage of the currently working Photovoltaic arrays of modules constantly monitored becomes; and a new array of modules is selected and is applied to at its maximum power point voltage to Delivery of the specific operating current and operating voltage to work on the electrolyzer when the currently operating Array of modules not at its maximum power point voltage is working. Method for operating a hydrogen-producing An electrolyzer according to claim 2, wherein a currently operating Array of modules by switching electrical connection between two or more modules is converted into a new array of modules. Method for operating a hydrogen-producing An electrolyzer according to claim 2, wherein a currently operating Array of modules by replacing one or more different ones Modules is converted into a new array of modules. Method for operating a hydrogen-producing The electrolyzer of claim 1, wherein the method further includes that: a DC / DC converter between a currently operating one Array of a module / modules and the electrolyzer is switched to the adjustment between the maximum power point voltage of the present working arrays and the operating voltage of the electrolyzer to improve. The method of operating a hydrogen producing electrolyzer of claim 1, the method further comprising: continuously measuring the operating temperature of the module (s) in the currently operating array, and cooling the modules in the currently operating array as the operating temperature increases and the maximum power point voltage of the array decreases. Method for operating a hydrogen-producing An electrolyzer according to claim 6, comprising a flow of a cooling fluid on the module or modules is used to the stationary module operating temperature to reduce. Method for operating a hydrogen-producing An electrolyzer according to claim 2, wherein the new array comprises Modules more modules in series than the previous array comprising modules. Method for operating a hydrogen-producing Electrolysis device passing through an array on photovoltaic modules, which is irradiated by sunlight, is applied, wherein the Electrolysis device has a plurality of electrolysis cells in a parallel or series arrangement can be switched and a DC operating current and an operating voltage, wherein the photovoltaic modules in a parallel or series arrangement are switchable to different Arrays for delivering DC power to the electrolyzer to form, the method comprising: Maximum power point operating voltages for representative Arrays are predetermined from the modules; a first operating current and a first operating voltage for the electrolyzer for one desired hydrogen production rate be determined; a first array of photovoltaic modules selected is at its maximum power point voltage to deliver the certain operating current and the specific operating voltage to work the electrolysis device; and then the hydrogen production rate the electrolyzer by changing its operation to a second operating current and to a second operating voltage is changed; and a second array is selected from the photovoltaic modules, at a second maximum power point voltage of the array for Output of the second operating current and the second operating voltage to work on the electrolyzer. Procedure for permanent Optimizing the operation of a solar powered photovoltaic electrolyzer system for generating hydrogen, wherein the electrolyzer by a group of two or more available photovoltaic modules, which are irradiated by sunlight, is applied, wherein the electrolysis device has two or more electrolysis cells, in series or parallel with variable DC operating current values and variable operating voltage values are switchable, wherein the Photovoltaic system includes one or more photovoltaic modules, the are switchable in a parallel or series circuit arrangement, to different arrays of a module / modules for delivery of DC power to form the electrolysis cells, wherein a given array less than the total number of available modules may include; the method comprising: the operating voltage and continuously measuring the operating current of the photovoltaic electrolyzer system become; the operating temperature of the photovoltaic modules constantly measured becomes; and a pre-programmed computer control system is used, the one mainframe or microprocessor and associated circuits, switches and wiring involves to constantly current Values of a system operating current and a system operating voltage and receive a photovoltaic module temperature, and the values to use a current one Photovoltaic array of a module / modules with a maximum power point close at the present Select operating voltage of the electrolysis device system and with the computer having a database of maximum power point values, with operating temperatures for available Photovoltaic arrays of a module / modules are related. Procedure for permanent Optimize the operation of a solar powered photovoltaic electrolyzer system according to claim 10, wherein the preprogrammed computer control system, the one host or microprocessor and associated circuits, Switches and wiring, the number of photovoltaic modules, which are connected in series and parallel circuits, controls, to maintain the optimum operating voltage. Procedure for permanent Optimize the operation of a solar powered photovoltaic electrolyzer system The apparatus of claim 11, wherein the preprogrammed computer having a Host or microprocessor and associated circuits, switches and wiring, replacement of a current array of modules a new photovoltaic array of modules by switching electrical Instructs connections between one or more modules. Procedure for permanent Optimize the operation of a solar powered photovoltaic electrolyzer system The apparatus of claim 11, wherein the preprogrammed computer having a Host or microprocessor and associated circuits, switches and wiring, replacement of a current array of modules a new photovoltaic array of modules by replacing one or more modules instructs several different modules. Procedure for permanent Optimize the operation of a solar powered photovoltaic electrolyzer system according to claim 10, wherein the preprogrammed computer control system, the one host or microprocessor and associated circuits, Switch and wiring includes the output voltage of a DC / DC converter controls to the maximum power point voltage of the currently operating one Arrays of modules closer to adjust the operating voltage of the electrolyzer. Procedure for permanent Optimize the operation of a solar powered photovoltaic electrolyzer system according to claim 10, wherein the preprogrammed computer control system, the one host or microprocessor and associated circuits, Switches and wiring, the number of electrolysis cells, in series and parallel circuits in the electrolyzer are switched to the optimum system operating voltage to maintain.