Characterisation and impact of non-uniformity on multi-junction solar cells (MJSC) caused by concentrator optics

In this work, it has been developed a method to generate non-homogeneous light patterns on multi-junction solar cells. These patterns have been generated modifying the distance between the CPV receiver and the primary optics, which is based on a Fresnel lens. In order to diminish the impact of other variables, the incident spectrum, laboratory temperature and effective concentration have been kept constant: SMRtop-mid = 1 ± 0.02, 25 ± 0.5ºC and 380 ± 3 suns, respectively. The light patterns on the top and middle subcells are measured using a CCD camera and band-pass filters. Results show that the electrical performance of the solar cells depends on the spatial and spectral profiles. The present work introduces a procedure to characterise and evaluate the impact of non-uniformities on the output of multi-junction solar cells. Nevertheless, this work is not intended to predict the actual output of the cell as a function of the light profiles, but to provide indications for possible underlying mechanisms.This work is partially funded by European Regional Development Fund (ERDF) and Spanish Economy Ministry, grant number ENE2016-78251-

Optimum cleaning schedule of photovoltaic systems based on levelised cost of energy and case study in central Mexico

In this paper, the soiling impact on photovoltaic systems in Aguascalientes, in central Mexico, an area where 1.4GWp of new photovoltaic capacity is being installed, is characterised experimentally. A soiling rate of -0.16 %/day in the dry season for optimally tilted crystalline silicon modules, and a stabilization of the soiling losses at 11.2% after 70 days of exposure were observed. With this data, a first of its kind novel method for determining optimum cleaning schedules is proposed based on minimising the levelised cost of energy. The method has the advantages compared to other existing methods of considering the system investment cost in the determination of the optimum cleaning schedule. Also, it does not depend on economic revenue data, which is often subject to uncertainty. The results show that residential and commercial systems should be cleaned once per year in Aguascalientes. On the other hand, cleaning intervals from 12 to 31 days in the dry season were estimated for utility-scale systems, due to the dramatic decrease of cleaning costs per unit photovoltaic capacity. We also present a comparative analysis of the existing criteria for optimising cleaning schedules applied to the same case study. The different methods give similar cleaning intervals for utility-scale systems and, thus, the choice of a suitable method depends on the availability of information

Overview of the Fundamentals and Applications of Bifacial Photovoltaic Technology: Agrivoltaics and Aquavoltaics

Bifacial technology is attracting the attention of the photovoltaic community. Although considered premature, research and development activities still need to be carried out to improve bPV performance. In addition, the need for a standard test reference will aid bankability and increase confidence in this technology. This article describes the state of the art of bifacial technology, going through the bPV cell and its difference compared to conventional monofacial cells and listing the different sources of limitations, with an identification of different parameters that characterize the performance of the bifacial. Then, the paper reviews the different modeling methods that allow predicting the performance of bPV systems, and ends with the most important applications, whether for dual use of land to produce energy and food (agrivoltaic) or for placing bPV modules on water bodies instead of on the ground (aquavoltaics), or for vertical use as solar fences, acoustic barriers, or building-integrated photovoltaic modules

Quantifying the rear and front long-term spectral impact on bifacial photovoltaic modules

The demand for bifacial photovoltaic modules is continuously increasing. However, some aspects of their behaviour under realistic operating conditions still require more in-depth investigations. Indeed, the long-term analysis of the spectral impact on bifacial modules remains pending. This is particularly true for the rear incident spectrum, which changes depending on the ground type. In this paper, the rear and front long-term spectral impact on bifacial modules is analysed for three locations (Tabernas, Spain; Solar Village, Saudi Arabia; Alta Floresta, Brazil) and four ground types (light soil, white sand, green grass, and concrete slab) at daily, monthly and annual timescales. The SMARTS model is used to generate front and ground-reflected annual spectra. The investigation leads to the definition of a novel metric, called bifacial spectral factor, which quantifies the combined front and rear spectral impact. Results show that the annual bifacial spectral impact differs from the monofacial one due to the influence of the rear spectral irradiance. Green grass is found to have the higher bifacial spectral benefit, leading to yields in between 1.19% and 1.65% higher than in the monofacial case. However, thanks to its high albedo coefficient, white sand is the most convenient ground among the analysed types in terms of bifacial spectral energy gains. The rear spectral factor shows a great range of variation as a function of ground type (between 0.989 and 1.150). However, this is only a non-negiglible second order effect compared to the bifacial spectral factor, which is mainly influenced by the front spectral factor

A method for the outdoor thermal characterisation of highconcentrator photovoltaic modules alternative to the IEC 62670-3 standard

The IEC 62670-3 standard recommends the open-circuit voltage method to calculate the cell temperature inside high-concentrator photovoltaic (HCPV) modules. This method requires knowledge of the temperature coefficient of open-circuit voltage (b), and the same standard provides a procedure to get this parameter. In this paper, an alternative method for the thermal characterisation of HCPV modules is proposed. As an advantage, it allows obtaining both the b parameter and the internal thermal resistance (r) of the device from outdoor measurements. No internal sensor for measuring the cell temperature is required as in the case of the IEC 62670-3 standard. Knowing the r parameter allows a more accurate characterisation of the cell temperature. The proposed procedure is applied to a real HCPV module. An outdoor experimental campaign of two months in Jaen (Southern Spain) was carried out. The b value was underestimated in a 0.50% and the r value was overestimated in a 4.18%. When applying the estimated parameters for the prediction of the cell temperature, the open-circuit voltage method gave a root mean square error (RMSE) of 1.41 C, while the internal thermal resistance method gave a RMSE of 0.62 C