solar CPV

The paper presents the preliminary operational performance results of the of two 3.5 kWp Concentration PhotoVoltaic (CPV) devices. Each system consists of eight modules installed on a chassis for a total number of 1152 triple junction PV cells whose active area is 5.5 × 5.5 mm. The optics has a total geometrical concentration ratio of 476×. Two solutions for the primary PMMA Fresnel lens were tested, one with constant Fresnel pitch and one with variable pitch. The secondary optics is the same for both systems and consists of a truncated pyramid made of high reflective material. The two-axis tracking system is an azimuth-elevation device driven by two electrical motors and controlled by a sun sensor. Results allow to evaluate the efficiency of the plant as well as significant operational parameters under real outdoor operating conditions. The overall AC electrical efficiency is up to 31% and the power production peak is 2.54 kW. Electric power output has a linear dependency with the available Direct Normal Irradiation (DNI) while the Air Mass (AM) spectrum has a negligible effect on the performance. The system equipped with a variable pitch Fresnel lens performs slightly better (about 3.5% more power) with respect to the one with a constant pitch. The effect of lens fouling has a much higher impact: with a dirty lens the system generates over 12% less power and efficiency decreases by 3–5%, at equal solar irradiation. The performance ratio of the CPV system peaked at 82% and it has a monthly value over 70% in spring and summer months. The tracking mechanism has showed, in the worst scenario, an inaccuracy of 0.26° which is lower than the acceptance angle of the optics (0.4°).

As células solares fotovoltaicas (PV) que integram sistemas fotovoltaicos de concentração (CPV)
estão sujeitas a grandes valores de irradiância, levando a densidades de corrente elevadas e a um
possível sobreaquecimento. O aumento da temperatura de uma célula solar pode levar a uma redução
da sua eficiência, tornando-se por vezes necessário utilizar métodos de arrefecimento nos sistemas
CPV. Dependendo da configuração do sistema de arrefecimento, as células solares estão sujeitas a
diferentes perfis de temperatura, os quais afectam a sua eficiência de forma diferente.
O estudo da eficiência de uma célula solar quando sujeita a diferentes perfis de temperatura não
homogéneos é abordado neste trabalho através de estudos computacionais e experimentais. Foi
montado um setup experimental, que consiste num porta-amostras sobre o qual a célula será colocada,
de modo a produzir diferentes perfis de temperatura, assim como distribuições de temperatura
uniformes. A melhor configuração e os melhores materiais, de forma a produzir os padrões
pretendidos, foram estudados através de simulações CFD-FEA (Computational Fluids Dynamics –
Finite Element Analysis) usando SolidWorks.
Foram aplicados vários padrões de temperatura ao porta-amostras. Após a sua caracterização, foram
medidas curvas I-V para diferentes padrões de temperatura e assim analisado o efeito da nãouniformidade
térmica em parâmetros eléctricos da célula. Os melhores resultados foram registados
quando a célula foi submetida a menores temperaturas na zona da busbar. Os resultados obtidos serão
também utilizados para validação do modelo do díodo distribuído, o qual foi desenvolvido para o
estudo da influência de perfis não homogéneos de iluminação e temperatura em células CPV.

The necessity to find new forms of renewable energy is very important and urgent nowadays. The renewable sources of energy derived from the sun are one of the promising options. The photovoltaic cells as one of renewable energy sources have been largely studied in order to obtain cheap, efficient and secure PV cells. The conversion efficiency is the most important property in the PV domain. Indium gallium nitride (InGaN) alloys offer great potential for high-efficiency photovoltaics. We present numerical simulations of GaN/InGaN heterojunction solar cells by SCAPs simulation. The calculation of characteristic parameters: short-circuit current density, open-circuit voltage, and conversion efficiency. So, these simulations study the effect of indium content and thickness in these parameters. While the maximum efficiency of a p-n GaN/InGaN heterojunction solar cell with 0.2 indium composition is 2.78%, above an indium composition of 20%, the modeled heterojunction devices do not operate as solar cells.

Concentrated photovoltaic is a promising route to achieve high efficiency solar conversion. Concentration of sunlight increases the irradiation on panel along with its temperature. At higher temperature, the efficiency of the cells drops necessitating active cooling. However, flow of a coolant consumes pumping-power leading to reduction in net power output. These two counteracting factors lead to a two-stage optimization for designing an advection cooled concentrated photovoltaic (ACCPV) system. Here, we attempt developing a design methodology where standard numerical scheme for solving a multi-level conjugate heat problem is utilized to obtain optimal operating conditions in terms of the coolant flow rate, and the sunlight concentration ratio for a series of widely used photovoltaic materials: a-Si, m-Si, p-Si, CIGS, CdTe. For the chosen ACCPV geometry, the estimated concentration ratios are computed to be 7, 9, 9, 16 and 20 for m-Si, p-Si, CIGS, p-Si and CdTe cells, respectively. Even though the estimated values of optimal parameters depend on the choice of PV material, coolant and the geometry of the system, the methodology presented here is universally applicable for any such ACCPV system. The general intuition-higher the irradiation, better the performance-is demonstrated to be false through the present analysis.

The photocurrent produced by a multijunction III-V  cell is limited by the component cell of the union which  yields  the  lowest  photocurrent.  The  induced  energy  losses  are quantified  by  the  Energy  Matching  Factor
(EMF), defined as the ratio between the energy produced by a III -V multijunction cell and the energy that could be produced if the subcells were current matched at any moment. Accurate EMF estimations generally require accurate measurement of solar spectrum. An  alternative method is to measure the spectrum using three  “isotype”  cells,  or  single-junction  cells  that  have  the  same spectral  response  as  each  of  the  three
component cells in the multi-junction stack. That method is validated against photocurrents calculated from spectral  measurements  (by  spectroradiometer)  and  broadband  direct beam  measurements  (by
pyrheliometer). Those comparisons show agreement  in  the results  above 98% under  clear-sky conditions. The difference between the two independent EMF calculations is within 1% margin. That method enables to
characterize  the  photocurrent  produced  by  a  Concentrating 
Photovoltaics  (CPV)  module  with  a  sufficient accuracy  for  CPV  applications,  on  the  sole  basis  of measurements  of  the direct  beam  radiation  by  a
pyrheliometer and three photocurrents by three isotype cells. The application of this method to the spectral measurements achieved in Madrid in 2009 leads to estimate annual current spectral mismatching losses of some 5-10%.

The photocurrent produced by a multijunction III-V cell is limited by the component cell of the union which yields the lowest photocurrent. The induced energy losses are quantified by the Spectral Radiation Matching Factor (SRMF), defined as the ratio between the energy produced by a III-V multijunction cell and the energy that could be produced if the subcells were current matched at any moment. Accurate SRMF estimations generally require accurate measurement of solar spectrum. Another method is to measure the spectrum using three ``isotype'' cells, or single-junction cells that have the same spectral response as each of the three component cells in the multi-junction stack. That method is validated against photocurrents calculated from spectral measurements (by spectroradiometer) and broadband direct beam measurements (by pyrheliometer). Those comparisons show agreement in the results above 98% under clear-sky conditions. The difference between the two independent SRMF calculations is within 1% margin. The application of this method to the spectral measurements realized in Madrid in 2009 leads to estimate an annual current spectral mismatching of around 7%.

DoubleSun ® technology is a V-trough concentration system that makes use of commercial photovoltaic monocrystalline silicon modules. The system integrates a 2-axes tracking system and increases the amount of radiation falling upon the modules by using two flat mirrors. The purpose of the present work is to demonstrate the power and energy increase of commercial modules when integrated in a