NL2012583B1 - Helio-energic concentrator unit and device for gaining solar energy. - Google Patents

Abstract

Een helio-energetische conversie-eenheid omvat primaire refractiemiddelen voor het invangen van een bundel zonlicht en reflectiemiddelen met een gebogen reflectie-oppervlak waarop een van de primaire refractiemiddelen ontwijkende bundel zonlicht wordt ontvangen en wordt gereflecteerd naar ten minste één doeloppervlak van een geringere omvang dan het intreedvenster. Zowel de refractiemiddelen als de reflectiemiddelen zijn roteerbaar en zelfstandig gekoppeld aan verplaatsingsmiddelen om daaraan een gecontroleerde rotatie op te leggen teneinde deze delen voortdurend ten opzichte van elkaar en ten opzichte van een actuele stand van de zon aan de hemel te richten. Het reflectieoppervlak omvat een aantal naast elkaar gelegen segmenten, die elk een deel van de bundel zonlicht concentreren op een daarmee geassocieerd intreedvenster van secundaire refractiemiddelen. De secundaire refractiemiddelen concentreren de zonlichtbundel op een secundair doeloppervlak, waar energetische omvormmiddelen zijn voorzien, in het bijzonder een zonnecel en meer in het bijzonder een III-V zonnecel met meervoudige pn-overgangen, die in staat en ingericht zijn om aan het daardoor ontvangen zonlicht energie te onttrekken en in een gewijzigde vorm af te staan.

Description

Helio-energic concentrator unit and device for gaining solar energy Introduction

Back in 2007, a novel kind of concentrator system with integrated tracking was introduced by applicant. While nowadays most CPV systems make use of an external structure to track the sun, some concepts have been developed to integrate tracking functionality in the module. This avoids the need of bulky external tracking structures and allows compact designs.

The device according to the invention uses two rotating concentrator optics in order to integrate sun-tracking into the module and still achieve a high concentration ratio: primary refraction means, specifically a Fresnel prism, and reflection means comprising a parabolic mirror featuring multiple facets, particularly four facets or segments. The prism first refracts incident sunlight onto the mirror, which then concentrates the light onto a stationary hybrid PV/thermal receiver (Fig. 1).

As the apparent position of the sun changes through the day and the year, the rotation angles of both elements have to be varied accordingly to keep concentrating light on the receiver (Fig. 2). According to the invention, the latter consists of a secondary optical element (SOE) with an entrance for each mirror segment, i.e. 4 entrances (one per mirror facet) in the embodiment of figure 1, which increases the concentration ratio up to 870 times.

The secondary optical unit concentrates the incident sun light and directs it onto conversion means which are capable of gaining energy there form and to deliver it in an altered, more useful form, specifically a III-V multi-junction solar cell as in the embodiment of figure 1. The secondary optical element used according to this embodiment of the present invention is shown in figures 3 and 4 in further detail at a frontal and back face respectively.

The cell is directly attached to a bulk copper substrate that conducts excess heat onto a water circuit, thus increasing the overall system conversion efficiency. A validation of the optical system through ray-tracing simulations and its optical performance has been thoroughly studied in terms of optical efficiency, spectral sensitivity, angular tolerance and irradiance map on the cell.

Optical modelling and results

Optical simulations were carried out using the commercial software Trace Pro for Monte Carlo ray tracing. At first, it has been studied the optical performance of the concentrator under ideal on-axis conditions: a light beam with an angle of 60° from the prism plane. Typical PMMA, silver and BK7 glass properties were assumed for the prism, mirror and SOE, respectively. Light rays were given a broad AM1.5D spectral irradiance. Irradiance maps for this particular case are presented in Fig. 5 and Fig. 6 at both the SOE inputs (4 heads) and output (solar cell), see also Fig. 3 and 4.

The mirror is capable of illuminating the 4 SOE inputs well within their optical aperture and the output on the cell is reasonably homogeneous, although the Peak to Average Ratio is still around 3. The optical efficiency in this particularly case is close to 70%. The simulation allows as well establishing a breakdown of losses per optical stage: 87% eff. through the prism, 93% at the mirror and 86% at the SOE, which become the theoretical objectives for each component.

This study has been repeated for 90° and 70° tilt angles and it will be extended to significantly sample the sun course throughout the year, in order to estimate the average efficiency of the integrated tracking strategy. Moreover, the effect of rotation errors has also been evaluated. At 90° tilt, for a power loss lower than 10%, a maximum ±1° prism rotation error is allowed.

As the system uses III-V multi-junction (MJ) cells, the spectral balance delivered by the optics (light available for every subcell) has been studied to assess current mismatch losses. However power losses, can be higher if the current mismatch between subcells is locally higher than the average due to series resistance. This is the case here, as it can be seen in Fig. 7.

Finally, to improve the predictive capabilities of the simulations, typical optical non-idealities (roughness, waviness, overall geometry errors or transmission absorption) will be added to each element. Studying the impact on efficiency of these defects will provide relevant feedback for defining specifications for these components.

Although the invention has been described herein before in substantial detail referring to merely a single embodiment it will be clear that alternative embodiments are very well conceivable for a skilled person without departing from the scope and spirit of the present invention which emanates from the following claims (conclusies), in maner that would require him to exercise any inventive skill.

Claims (12)

A heli-energetic concentrator unit for extracting energy from sunlight, comprising primary refraction means with an entrance window for catching a beam of sunlight and comprising reflection means with a curved reflection surface in a path of a sunlight bundle escaping from the primary refraction means, sunlight beam is thereby reflected to at least one target surface of a smaller size than the entrance window of the primary refraction means, the refraction means being rotatable about a first axis of rotation and being coupled to first displacement means to impose a rotation thereon about the first axis of rotation, the reflecting means are rotatable about a second axis of rotation and are coupled to second displacement means to impose a rotation thereon about the second axis of rotation, wherein control means are provided which are capable and adapted to dispose of the primary refraction means and the reflection means directing each other and relative to the sun by a rotation of at least one of the refraction means and the reflection means depending on a current position of the sun in the sky, characterized in that the reflection surface comprises a multiple reflection surface of a number of side by side segments with separate main optical axes, that each of the segments concentrates a portion of the sunlight received from the refraction means received therefrom on an associated primary target surface of a number of primary target surfaces, that secondary refraction means are provided with optical entry windows which substantially coincide with each of the primary target surfaces and which concentrate a part of the sunlight beam received thereby on a common secondary target surface, and that at least substantially at the location of the secondary target surface, conversion means are provided which are capable and adapted to receive received energy from sunlight and give it in a modified form. 2. Concentrator unit as claimed in claim 1, characterized in that the reflection surface is composed of four at least substantially contiguous segments arranged in quadrants and which are each provided with secondary refraction means with an entry window in an optical focal point of the relevant segment. Concentrator unit according to claim 1 or 2, characterized in that each of the segments comprises a parabolic reflection surface. Concentrator unit according to one or more of the preceding claims, characterized in that the secondary optical refraction means comprise a spherical lens at the location of each of the primary target surfaces. Concentrator unit according to one or more of the preceding claims, characterized in that the secondary refraction means are combined in a common secondary optical unit, in particular in a common monolithic optical body. A concentrator unit according to claim 5, characterized in that the secondary optical unit is arranged, at least in projection, at a distance from an outer edge of the reflection surface at least near a dividing line of adjacent segments. Concentrator unit according to claim 5 or 6, characterized in that the secondary optical unit is tightly connected to the reflection means through the interposition of at least one mounting arm. A concentrator unit according to claim 7, characterized in that the at least mounting arm extends at least substantially on a north side of the reflection means. Concentrator unit according to one or more of the preceding claims, characterized in that the primary refraction means comprise a lens on an entry side and a flat lens with a stepped structure on an exit side. Concentrator unit according to claim 9, characterized in that the lens comprises a prismatic lens with a stepped sawtooth profile on the exit side, in particular a Fresnel lens. Concentrator unit according to one or more of the preceding claims, characterized in that the converting means comprise at least one photovoltaic cell body, in particular a photovoltaic cell body comprising an III-V semiconductor substrate, more in particular an II-V galium arsenide (GaAs) substrate. A helio-energetic device comprising a series of concentrator units according to one or more of the preceding claims in a common housing and with at least one common energetic output.