DE29813325U1 - Device for converting solar energy into electrical energy and / or thermal energy - Google Patents

Description

Device for converting solar energy into electrical energy and/or thermal energy

The invention relates to a device of the type specified in the preamble of claim 1.

Devices of this type are known in numerous variants (e.g. DE 34 19 797 Al, DE 41 20 943 Al, DE 42 06 931 Al, DE 296 05 277 Ul). The energy converter can contain a photovoltaic solar cell arrangement for generating electrical energy, a flow line through which a heat transfer fluid flows, also called a collector, for generating thermal energy by heating the heat transfer fluid or a combination of both.

In pure solar cell systems, a cooling device can be assigned to the energy converter, which consists, for example, of a cooling line carrying a heat transfer fluid into which a feed pump is connected. The heat transfer fluid is preferably circulated. In contrast, in a system with only collectors, the energy converter is part of a main circuit. In addition to the energy converter, this contains a storage unit for storing the heat obtained by converting solar energy into thermal energy and, except in the case of so-called thermosiphon systems, a circulation pump that causes the forced circulation of the heat transfer fluid. The flow lines are often arranged behind flat absorbers, which are used for

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ensure an improved conversion of the incoming solar rays into thermal energy. Finally, in combined systems, the energy converter can consist of a solar cell arrangement, whereby heat is extracted from the energy converter via the cooling line assigned to it, through which a heat transfer fluid flows, while at the same time the heated heat transfer fluid is passed through a storage unit, as in pure collector systems. Such hybrid modules are thus used to simultaneously generate thermal energy and electrical energy. The heat transfer fluid is usually a liquid, e.g. water or a water/glycol mixture, but can also be a gas such as air.

The problem with devices of this type is that the temperature of the energy converter and the heat transfer fluid can rise sharply depending on the operating conditions. This applies, for example, if the circulation pump connected to the main circuit fails or is switched off in order to prevent the storage tank from heating up or charging too much, or if no energy is drawn from the storage tank, which is unavoidable, for example, with a device mounted on a building during holiday periods. If the energy conversion takes place with the help of collectors, the maximum temperatures of 150 ⁰ C and more that occur during such downtimes lead to strong thermal stress, e.g. due to the different thermal expansions of the materials forming the energy converter, which can result in a reduced service life.

If, however, photovoltaic solar cells are also or only used for energy conversion, there is not only the risk of thermal stress but also the well-known disadvantage that the efficiency of solar cells decreases sharply as the cooling effect decreases. In general, when using modern solar cell modules, it is expected that there will be a loss of performance of around 0.45 % for every 1 ⁰ C increase in temperature (average value when using crystalline solar cells), so that at a module temperature of 70 ⁰ C the performance is reduced by around 20% compared to the manufacturer's specifications, which are usually based on an operating temperature of 25 ⁰ C. If the electrical energy obtained with the solar cell modules is therefore to be fed into the public power grid, the operator of the device will incur considerable losses in the cases mentioned due to insufficient cooling performance.

In contrast, the invention is based on the object of designing the device of the type described at the outset in such a way that undesirable temperature increases in the area of the energy converter do not occur or can at least be effectively reduced.
5

To solve this problem, the characterizing features of the claim

The invention has the advantage that when a preselected temperature is reached, the feed pump in the cooling line is automatically switched on, thereby cooling the energy converter. The energy converter can thus be effectively protected from high thermal loads.

Further advantageous features of the invention emerge from the subclaims.

The invention is explained in more detail below in conjunction with the accompanying drawings using exemplary embodiments. They show:

Fig. 1 shows schematically a device according to the invention for converting solar energy into thermal energy and/or electrical energy according to a first embodiment of the invention;

Fig. 2 and 3 further embodiments of the device according to the invention; and

Fig. 4 shows a particularly preferred embodiment of a solar cell arrangement according to the invention in cross section.

According to the rough schematic representation in Fig. 1, a device for converting solar energy into electrical energy and thermal energy contains, for example, an energy converter 1, which is exposed to solar radiation indicated by arrows, a storage tank 2 and a circulation pump 3, which are connected in series by flow lines and connected to one another to form a closed main circuit in which a heat transfer fluid, e.g. water, circulates in the direction of the arrows shown. The

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Energy converter 1 consists, for example, of an upper section la exposed to solar radiation, which is covered with solar cells (not shown in detail), and a lower section Ib, which has a cooling line Ic (not shown in detail), which has an inlet 4 and an outlet 5 and is formed in a cooling body, through which the heat transfer medium, which also flows in the main circuit, flows to cool the solar cells. The connections and components used in the photovoltaic circuit are known and are therefore not shown. The storage tank 2 is, for example, a conventional hot water storage tank, which is heated by the heat transfer fluid heated in the energy converter 1 and stores the thermal energy supplied to it until it is used by a consumer, e.g. a household.

According to the invention, a cooling circuit intended for cooling the energy converter 1 is connected in parallel in the manner of a bypass. This cooling circuit contains the cooling line Ic and a feed pump 6 and is designed so that it is automatically switched on when an undesirably high temperature is detected at a preselected point in the main circuit. The cooling circuit is also designed so that a heat transfer medium guided in it is circulated in the direction of the arrow when the circulation pump 6 is switched on and thereby flows through the energy converter 1 in a similar way to the heat transfer fluid in the main circuit. The cooling circuit is preferably provided with a heat exchanger 7 through which the heat transfer fluid flows, which is, for example, an air/liquid heat exchanger, the liquid passages of which are flowed through by the heat transfer fluid, while a fan 8 pushes cooling air through the air passages.

A particularly practical and simple arrangement is one in which the heat transfer fluid is the same in both circuits, i.e. the two circuits are connected to the cooling line Ic. For this purpose, the inlet 4 and the outlet 5 are each connected, for example, to an electrically, pneumatically or otherwise controllable switching valve 9 or 10, whereby the switching valve 9 has two outputs that can be optionally connected to the two circuits and the switching valve 10 has two inputs that can be optionally connected to the two circuits. Both switching valves 9, 10 are also connected to a switching device 14 via control lines 11, 12. This can be connected via further control lines to temperature sensors arranged at preselected locations, whereby a

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Temperature sensor 15, for example, measures the temperature of the heat transfer fluid at the outlet 5 of the cooling line Ic and another temperature sensor 16, for example, measures the temperature in the storage tank 2. Additional control lines 17, 18 and 19 are connected to the circulation pump 3, the feed pump 6 and the fan 8. Alternatively, the temperature sensor can also be arranged at a preselected location on the energy converter 1 and measure its temperature directly.

The switching device 14 is set up, for example, using microprocessor control means, so that if one of the temperature sensors 15, 16 indicates an undesirably high temperature of, for example, 70 ⁰ C, the two changeover valves 9, 10 are switched via the control lines 11, 12 so that the energy converter 1 or the cooling line Ic is connected to the cooling circuit but no longer to the main circuit. At the same time, the circulation pump 3 is switched off via the control lines 17, 18 and 19, while the feed pump 6 and the fan 8 are switched on.

This activates the cooling circuit, which now remains switched on until the temperature at the location of the relevant temperature sensor 15, 16 has fallen below a critical value, whereupon the changeover valves 9, 10 are switched back to the main circuit, the circulation pump 3 is switched on and the feed pump 6 and the fan 8 are switched off.

If the two circuits are separate circuits, it is sufficient to switch on the feed pump 6 and the fan 8 and switch off the circulation pump 3 or vice versa, i.e. the changeover valves 9, 10 are not required in this case.

The switching device 14 can also be provided with additional sensors, which signal undesirable states and cause the pumps 3, 6 and/or the changeover valves 9, 10 to switch over.

The invention provides the advantage that, in the event that the energy converter operates with solar cells, a loading of the storage tank 2 up to a maximum storage temperature of e.g. 70 ⁰ C is ensured in the normal case with the help of the permanently connected main circuit, while in addition with the help of the cooling circuit

it can be avoided that the energy converter 1 or parts thereof, such as the solar cells, are damaged or destroyed due to very high thermal loads. In addition, the cooling circuit ensures that the energy converter 1 always works with a more favorable efficiency even under changed conditions. In contrast, in a device that works exclusively with solar collectors used to generate heat, the cooling circuit mainly serves to protect the device from thermal loads. The cooling or protective effect caused by the cooling circuit is generally better the closer the heat exchanger 7 is to the energy converter 1, i.e. the shorter the connecting lines are.

According to a particularly preferred embodiment of the invention, the switching operations effected by the switching device 14 take preselected temperature conditions into account. If, for example, a temperature T ₁ is measured at the location of the temperature sensor 15 and a temperature T ₂ is measured at the location of the temperature sensor 16, a maximum value T _2max can be assigned to the temperature T ₂ and it can be required, for example, that the circulation pump 3 is switched off or remains switched off if and as long as T ₂ > T _2max in order to avoid discharging the storage tank 2 with certainty. At the same time, a maximum value T _lmax could be assigned to the temperature T ₁ and it can be required that the feed pump 6 and possibly also the fan 8 are switched on if T ₂ > T _2max and at the same time T ₁ > T _lmax in order to ensure that the energy converter 1 is cooled as soon as its temperature T ₁ exceeds a preselected maximum temperature. Furthermore, it could be specified that when T ₂ < T _2max the feed pump 6 is or remains always switched off in order to give priority to a possible loading of the storage tank 2 in any case, and the circulation pump 3 is switched on if at the same time T ₁ - T ₂ > T _B.

A particularly advantageous circuit diagram is shown in the following table:

Ongoing
number temperature
gradient Temperature T ₂ Temperature T ₁ Circulation pump
3 Feed pump
6 1 T ₁ -T ₂ ST ₈ T ₂ ST ₂ ^ T ₁ ^T _1n , OUT OF A 2 T ₁ -T ₂ ST ₈ T ₂ ST _2n ^ t^t,^ OUT OF OUT OF 3 T ₁ -T ₂ ST ₈ T ₂ < T _2n ^ T ₁ ST _1n ^ A OUT OF 4 T ₁ -T ₂ ST ₈ Tj<T _2mi Ti<T _la « A OUT OF 5 _{T1 -T2} < _T8 T ₂ ST _2n ^ T,ST _lmt OUT OF A 6 _{T1 -T2} < _T8 T ₂ ST _2n ^ _x &tgr;,<&tgr;_{11&Igr;&Bgr;&Igr;} OUT OF OUT OF 7 _{T1 -T2} < _T8 T ₂ < T _2n ^ T ₁ ST _11111x OUT OF OUT OF 8th _{ΔΓΔΔ2 < Δβ T2} < T^ T^T^ OUT OF OUT OF 9 _T2 < _T2 ^ ₁
Due to
Pump failure
or manual
Shutdown
no feed
securing T ₁ ST _lmax+ OFF, e.g.
Failure/manu
elle switch
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This means:

T ₁ = temperature at the location of the temperature sensor 15; T ₂ = temperature at the location of the temperature sensor 16; = maximum desired temperature at the location of the temperature sensor 15;

= maximum desired temperature at the location of the temperature sensor 16; T _B = preselected temperature difference between T ₁ and T ₂ .

For example, if the temperature T _2max = 70 ⁰ C, then the value T _lmM could be set to 50 ⁰ C and the value T _B to 8 ⁰ C.

The numbers 1 to 8 in the table above show the different circuits.

The above circuits do not take into account, for example, the case where the circulation pump 3 is switched off accidentally or intentionally or has failed due to a defect when T ₂ < T _2max . In this case, the above table shows that the feed pump 6 is always switched off. This could in turn result in the temperature Tj rising far above the desired value of T _lmax in strong sunlight. According to the invention, a higher-level control is therefore additionally provided which, when a preselected temperature T _lmax+ of e.g. 110 ⁰ C is reached, switches on the cooling circuit even if the storage tank 2 is at a temperature T ₂ which is below the value T _2max (cf. serial numbers 3, 4, 7, 8 in the above table).

In terms of circuitry, this higher-level control can be implemented using AND or OR functions, as shown schematically in Fig. 1. Within the switching device 14, for example, two comparators 20, 21 are connected to the output of the temperature sensor 15, while the output of the temperature sensor 16 is connected to the input of a comparator 22. The outputs of the comparators 21 and 22 are connected to two inputs of an AND gate 23, while the output of the comparator 20 and the output of the AND gate 23 are connected to two inputs of an OR gate 24, whose output leads to the feed pump 6.

The comparator 22 gives an output signal (e.g. logic "1") when T ₂ >: T _2mM . The comparator 21 gives a corresponding signal when T ₁ >: T _lmai . As a result, the feed pump 6 is only supplied with a signal that causes it to switch on (e.g. logic "1") (see table above) when T ₂ > T _2max and at the same time T ₁ ^ T _lmax . In all other situations, there is no output signal (e.g. logic "0") at least at one output of the comparators 21, 22, so that the feed pump 6 is or remains switched off.

The comparator 20 checks, for example, according to serial number 9 in the table above, whether T ₁ > T _lmax+ applies. If this is the case, it generates an output signal (e.g. logical "1"), whereby the feed pump 6 is switched on via the OR gate 24, although the AND gate 23 does not emit a corresponding output signal. At the same time, the signal at the output of the comparator 20 can be used to switch on an alarm device that signals a fault.

Furthermore, as is usual with controls of the type described, different T _lmax values can be defined for switching on and off processes and recorded using hardware or software. This means that for switching on the pumps 3,6, for example, the values given above, T _lmax = 50 ⁰ C or T _lmax+ = 110 ⁰ C, are used, while for subsequent switching off processes, for example, values of T _lmax = 45 ⁰ C or ⁼ 100 °C are used as a basis.

Fig. 2 shows an embodiment in which the cooling circuit is directly assigned to a single energy converter 1 or is integrated into it. In contrast, in the embodiment according to Fig. 3, several solar cell modules 21 to 23 are connected in parallel to a single cooling circuit. Otherwise, in Fig. 2 and 1, the same parts are provided with the same reference numerals as in Fig. 1.

Fig. 4 shows a particularly preferred solar cell arrangement which contains at least one solar cell 24 which is manufactured, for example, using a technique that is common today and consists, for example, of an essentially plane-parallel plate with a size of approximately 120 mm x 120 mm in plan view and a thickness of a few millimeters. Any number of such solar cells 24 can be combined in electrical parallel and/or series connection to form a so-called module. 20

On their upper or front broad side, the solar cells 24 are covered with a transparent cover 25, which consists, for example, of a plane-parallel glass plate and covers all solar cells 24 that may be present. Each solar cell 24 is attached to the cover 25, for example, by means of a layer 26 consisting of an elastic adhesive that compensates for the different thermal expansions of the solar cells 24 and the cover 25.

A heat sink 27 according to the invention is attached to the lower or rear broad sides of the solar cells 24, through which the heat transfer fluid can flow, for example in the direction of the arrows shown in Fig. 1. The heat sink 27 contains a large number of individual strips 28a, 28b, which are arranged one behind the other and parallel in the direction of flow and extend transversely to the direction of flow. The strips 28a, 28b are corrugated in a meandering shape transversely to the direction of flow, so that they have lower sections 29a and 29b, upper sections 30a and 30b and webs 31a and 31b located between them.

The rear sides of the sections 29a, 29b and the front sides of the sections 30a, 30b are preferably located essentially in planes that are parallel to one another and at a distance from one another that corresponds to the length of the webs 3la, 31b. The corrugations of successive strips 28a, 28b are also preferably offset from one another transversely to the flow direction.

The heat sink 27 is preferably manufactured in one piece, with the strips 28a, 28b being made from a sheet metal by a rolling process using profile rollers or by a punching process. The sheet metal consists of a preferably thin, highly heat-conducting material, in particular metal sheets (e.g. copper, aluminum). The heat sink 27 expediently extends over all of the solar cells 24 present. However, several heat sinks 27 of the specified type can also be used, arranged in parallel or in some other way, which are, for example, assigned optionally to the main circuit or the cooling circuit according to Fig. 1.

The connection of the heat sink 27 to the solar cells 24 is expediently carried out by the front sections 30a, 30b of the strips 28a, 28b being attached to the latter by means of a layer 32 made of a preferably elastic and highly heat-conductive adhesive which compensates for the different thermal expansions of the heat sink 27 and the solar cells 24.

Due to the described design of the heat sink 27, the sections 29a, 29b, 30a, 30b and the webs 31a, 31b form a plurality of passages or through-holes running in the direction of flow, which within the individual strips 28a, 28b alternately delimit areas 33 that are open to the front or top and to the back or bottom. The areas 33 that are open to the front are directly opposite the backs of the solar cells 24, so that a heat transfer fluid flowing through these areas 33 comes into direct contact with the back walls of the solar cells 24 and causes intensive heat dissipation.

The areas 34 are open downwards or backwards, but their front sections 30a, 30b are adjacent to the rear sides of the solar cells 24, so that a heat transfer fluid flowing through them can be transported away via these sections 30a, 30b.

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λ m φ ·

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Heat is involved. Overall, the corrugations result in a very large heat exchange surface even with short webs 3la, 3Ib or flat heat sinks 27 and thus a good cooling effect, which is further increased by the offset of the strips 28a, 28b and the resulting intensive turbulence of the heat transfer fluid flowing through the heat sink 27.

A rear wall 35 is attached to the rear of the heat sink 27 or to the sections 29a, 29b, which is connected to the cover 25, for example, by frame parts and seals, so that a housing is created that surrounds the heat sink 27 and is closed on all sides and is provided with the inlet 4 or the outlet 5 according to Fig. 1. In addition, in this case the housing could be provided with sections free of the heat sink 27 in the area of the inlet 4 or outlet 5, which form collecting chambers for the heat transfer fluid and improve its distribution across the width of the heat sink 27.

The invention is not limited to the described embodiments, which can be modified in many ways. This applies in particular to the basic circuit diagram shown in Fig. 1. For example, it would be possible to provide an energy converter 1 in Fig. 1 consisting exclusively of solar cells, to which only the cooling circuit is assigned, i.e. the main circuit would be completely omitted in this case. In this variant, the cooling circuit would be switched on or off when preselected temperatures at the location of the temperature sensor 15 are exceeded or not reached and would only serve for cooling. In addition, the cooling line Ic could be arranged in an open circuit, since the heat transfer fluid flowing in it now only serves for cooling, but not for heating up a storage tank. The same applies if the cooling line Ic is present in addition to a collector or the like connected to the main circuit. In addition, the design of the solar cell arrangement can also be different from that shown in Fig. 4. Conventional plate or shell heat exchangers can be used in particular as heat exchanger 7. Furthermore, the storage tank 2 does not necessarily have to be a conventional hot water storage tank, e.g. arranged in a building. Alternatively, the storage tank 2 could also be a swimming pool, for example. According to a preferred development of the invention, the device should also be designed in such a way that the for operating the switching device 14, the circulation pumps 3, 6 and the fan 8

The electrical energy required is generated in whole or in part by an energy converter 1 in the form of a solar cell arrangement contained in the device. Furthermore, the changeover valves 9, 10 could be designed as thermostat valves which, when preselected temperatures are reached, open the auxiliary circuit and simultaneously close the main circuit, or vice versa. Finally, it is understood that the various features of the invention can also be used in combinations other than those shown and described.

Claims (12)

&bull;-&bull;13 «· Claims 1. Device for converting solar energy into electrical energy and/or thermal energy with an energy converter (1) and a cooling line (lc) associated therewith, carrying a heat transfer fluid and having a switchable feed pump (6), characterized in that a switching device (14) connected to the feed pump (6) is provided for automatically switching on the feed pump (6) when a preselected temperature (T ₁ ) is exceeded in the energy converter (1) and/or in the cooling line (lc). 2. Device according to claim 1, characterized in that it contains a main circuit having the energy converter (1) and a storage device (2) and carrying a heat transfer fluid, and the cooling line (Ic) is connected in parallel to the energy converter (1). 3. Device according to claim 1 or 2, characterized in that the cooling line (Ic) is arranged in a cooling circuit. 4. Device according to one of claims 1 to 3, characterized in that the switching device (14) is assigned at least one temperature sensor (15) arranged at a preselected point of the energy converter (1) and/or the cooling line (Ic) for determining the preselected temperature (T ₁ ). 5. Device according to one of claims 2 to 4, characterized in that the switching device (14) is assigned at least one further temperature sensor (16) assigned to the storage tank (2) and the switching device (14) is also designed to switch a circulation pump (3) arranged in the main circuit on or off when preselected temperatures (T ₂ ) in the storage tank (2) are exceeded or not reached. &bull;&Mgr;' 6. Device according to one of claims 1 to 5, characterized in that the switching device (14) is designed such that it switches the feed pump (6) and/or the circulation pump (3) on or off when preselected temperatures and/or temperature differences (T ₁ - T ₂ ) are exceeded or not reached. 7. Device according to one of claims 3 to 6, characterized in that the cooling circuit contains a heat exchanger (J) . 8. Device according to claim 7, characterized in that the heat exchanger (7) is an air/liquid heat exchanger. 9. Device according to one of claims 1 to 8, characterized in that the cooling line (Ic) is connected to the main circuit by switching valves (9, 10), by means of which the energy converter (1) can be switched optionally into the main circuit or into the cooling line. 10. Device according to one of claims 1 to 9, characterized in that the energy converter (1) contains at least one solar cell (24). 11. Device according to claim 10, characterized in that the energy converter (1) has a solar cell arrangement with a cooling body (27) mounted on the back of the solar cell (24) and through which the heat transfer fluid flows. 12. Device according to claim 11, characterized in that the cooling body (27) consists of a lamella with a plurality of corrugations which form regions (33, 34) through which the heat transfer fluid flows or channels which are open on sides extending parallel to the flow direction of the heat transfer fluid and which border directly on the solar cells (24) with these open sides.