Photovoltaic Concentrator Cells

Photovoltaic Concentrator Cells: Electro-Thermal Modelling And Experimental Analysis

Boven, R.V.T.

Kuiper, J.M. (mentor)

Aerospace Engineering

Space Engineering

Space Systems Egineering

2017-05-30

An interesting concept related to photovoltaic energy is Concentrated Photovoltaics (CPV), in which sunlight is focussed on a PV cell through lenses and mirrors, thereby increasing the incident irradiance on the PV cell. Solar concentration is proven to not only increase the output power of PV cells, but also to increase the electrical efficiency of PV cells. This concept is expected to further push PV energy to the scale of MW power plants for large-scale energy production, and increase the power density of standalone PV modules on Earth and in space. Increasing the irradiation on a PV cell inevitably also increases the temperature of the PV cell due to thermal losses. Cell temperature has a negative effect on the output power and electrical efficiency of a PV cell, and given a high enough concentration ratio, may cause the PV cell to lose electrical efficiency and ultimately break down. Adequate cooling is therefore required for CPV systems to keep the PV cell in its optimal operating temperature range. For this purpose a model is proposed that simulates the output characteristics under influence of solar concentration and temperature variations, most notably the output power and electrical efficiency of a PV cell. The electro-thermal model is fundamentally based on the detailed balance model, which dictates that the absorbed and emitted photon flux must be equal in equilibrium conditions. From detailed balance, the absorption, recombination and photo-generation processes in a PV cell are determined, from which the Shockley-Queisser limit is deduced. This fundamental model is extended to the single-diode model, which serves as the ultimate baseline of PV simulation, taking into account cell temperature, concentration ratio and other internal PV cell factors. Sensitivity analyses on the single-diode model show that solar concentration indeed increases the output power and electrical efficiency. Taking into account solar concentration and temperature effects however, shows that the electrical efficiency drops by 4% points at a concentration ratio of 20, thereby confirming that without cooling, increasing the solar concentration on a PV cell will yield lower electrical efficiencies due to thermal effects. Laboratory experiments are conducted on an Emcore 3J gallium-arsenide PV cell (DUT) to verify the electro-thermal model. Baseline tests are conducted using a calibrated light source, and secondary tests involving a secondary light source are performed at controlled ambient and elevated temperatures. These results show that the model has a fit of 98.9% with respect to the verified specifications of the DUT PV cell at an ambient temperature of 25 ◦C. At an elevated cell temperature of 60 ◦C, discrepancies exist between the simulated single-diode model and test results. A new in-plane heat conduction concept developed by Airbus NL called Hiper is added to the test set-up to assess its suitability in conjunction with a heat radiator for PV cells. Hiper is a novel thin-film material particularly suited to spread heat effectively over a surface, from which it can be dissipated using a radiating material. Experimental results show that heat is spread slightly more effectively with Hiper, than in the same test set-up without Hiper, highlighting its heat spreading capabilities.

Photovoltaic concentrator cells

http://resolver.tudelft.nl/uuid:fde729b0-5a1b-4c68-87fd-3debc95c3179

Student theses

master thesis

(c) 2017 Boven, R.V.T.