Development of a spectral dependent electrical & thermal model for high concentrating photovoltaic (HCPV) receivers

High concentrating photovoltaic (HCPV) systems employ III-V multijunction (MJ) solar cells. Such solar cells are monolithically connected in-series and therefore present a strong dependence on the solar spectrum variations. In addition, the concentrated solar flux contributes to the heat generation within the solar cells and, in combination with the current mismatch between the subcells, can force the device to operate in elevated temperatures. It is important therefore, to investigate the influence of the atmospheric parameters on the electrical performance of HCPV and also to quantify the cooling requirements based on the spectrum changes. In this thesis, a spectral dependent electrical model has been developed to calculate the electrical characteristics and quantify the heat power of a multijunction solar cell. A three-dimensional finite element analysis is also used to predict the solar cell's operating temperature and cooling requirements for a range of ambient temperatures. The combination of these models improves the prediction accuracy of the electrical and thermal behaviour of triple-junction solar cells. The convective heat transfer coefficient between the back-plate and ambient air is quantified based on input spectra. A theoretical investigation is performed to analyse the influence of air mass (AM), aerosol optical depth (AOD) and precipitable water (PW) on the performance of each subcell and whole. It has been shown that the AM and AOD have a negative impact on the spectral and electrical performance of 3J solar cells while the PW has a positive effect, although, to a lesser degree. In order to get a more realistic assessment and also to investigate the effect of heat transfer coefficient on the annual energy yield, the methodology is applied to four US locations using data from a typical meteorological year (TMY3). The integrated modelling procedure is validated experimentally using field measurements from Albuquerque, NM. The importance of the effect of atmospheric parameters on the solar spectrum and hence the performance of HCPV systems is highlighted in this work. The outdoor characterisation provides with useful insight of the influence of spectrum on the performance of a HCPV monomodule and the current CSOC and CSTC ratings are evaluated based on different spectral filtering criteriaESPR

Electrical-thermal analysis of III–V triple-junction solar cells under variable spectra and ambient temperatures

AbstractThe influence of the incident spectral irradiance on the electrical and thermal behaviour of triple-junction solar cells has been investigated. A spectral dependent electrical model has been developed to calculate the electric characteristics and quantify the heat power of a multijunction solar cell. A three-dimensional finite element analysis is also used to predict the solar cell’s operating temperature and cooling requirements for a range of ambient temperatures. The combination of these models improves the prediction accuracy of the electrical and thermal behaviour of triple-junction solar cells. The convective heat transfer coefficient between the back-plate and ambient air was found to be the significant parameter in achieving high electrical efficiency. These data are important for the electrical and thermal optimisation of concentrating photovoltaic systems under real conditions. The objective of this work is to quantify the temperature and cooling requirements of multijunction solar cells under variable solar spectra and ambient temperatures. It is shown that single cell configurations with a solar cell area of 1cm2 can be cooled passively for concentration ratios of up to 500× with a heat sink thermal resistance below 1.63K/W, however for high ambient temperatures (greater than 40°C), a thermal resistance less than 1.4K/W is needed to keep the solar cell operating within safe operating conditions

A theoretical analysis of the impact of atmospheric parameters on the spectral, electrical and thermal performance of a concentrating III–V triple-junction solar cell

The spectral sensitivity of a concentrating triple junction (3J) solar cell has been investigated. The atmospheric parameters such as the air mass (AM), aerosol optical depth (AOD) and precipitable water (PW) change the distribution of the solar spectrum in a way that the spectral, electrical and thermal performance of a 3J solar cell is affected. In this paper, the influence of the spectral changes on the performance of each subcell and whole cell has been analysed. It has been shown that increasing the AM and AOD have a negative impact on the spectral and electrical performance of 3J solar cells while increasing the PW has a positive effect, although, to a lesser degree. A three-dimensional finite element analysis model is used to quantify the effect of each atmospheric parameter on the thermal performance for a range of heat transfer coefficients from the back-plate to the ambient air and also ambient temperature. It is shown that a heat transfer coefficient greater than 1300 W/(m(2) K) is required to keep the solar cell under 100 degrees C at all times. In order to get a more realistic assessment and also to investigate the effect of heat transfer coefficient on the annual energy yield, the methodology is applied for four US locations using data from a typical meteorological year (TMY3)

Photovoltaic hotspots: a mitigation technique and its thermal cycle

In the rapidly evolving field of solar energy, Photovoltaic (PV) manufacturers are constantly challenged by the degradation of PV modules due to localized overheating, commonly known as hotspots. This issue not only reduce the efficiency of solar panels but, in severe cases, can lead to irreversible damage, malfunctioning, and even fire hazards. Addressing this critical challenge, our research introduces an innovative electronic device designed to effectively mitigate PV hotspots. This pioneering solution consists of a novel combination of a current comparator and a current mirror circuit. These components are uniquely integrated with an automatic switching mechanism, notably eliminating the need for traditional bypass diodes. We rigorously tested and validated this device on PV modules exhibiting both adjacent and non-adjacent hotspots. Our findings are groundbreaking: the hotspot temperatures were significantly reduced from a dangerous 55°C to a safer 35°C. Moreover, this intervention remarkably enhanced the output power of the modules by up to 5.3%. This research not only contributes a practical solution to a longstanding problem in solar panel efficiency but also opens new pathways for enhancing the safety and longevity of solar PV systems

Photovoltaic Cleaning Frequency Optimization Under Different Degradation Rate Patterns

Dust accumulation significantly affects the performance of photovoltaic modules and its impact can be mitigated by various cleaning methods. Optimizing the cleaning frequency is therefore essential to minimize the soiling losses and, at the same time, the costs. However, the effectiveness of cleaning lowers with time because of the reduced energy yield due to degradation. Additionally, economic factors such as the escalation in electricity price and inflation can either compound or counterbalance the effect of degradation. The present study analyzes the impact of degradation, escalation in electricity price and inflation on cleaning frequency and proposes a methodology than can be applied to maximize the profits of soiling mitigation in any system worldwide. The energy performance and soiling losses of a 1 MW system installed in southern Spain were analyzed and integrated with theoretical linear and nonlinear degradation rate patterns. The Levelized Cost of Energy and Net Present Value were used as criteria to identify the optimum cleaning strategies. The results showed that the two metrics convey distinct cleaning recommendations, as they are influenced by different factors. For the given site, despite the degradation effects, the optimum cleaning frequency is found to increase with time of operation

Photovoltaic Cleaning Frequency Optimization Under Different Degradation Rate Patterns

Dust accumulation significantly affects the performance of photovoltaic modules and its impact can be mitigated by various cleaning methods. Optimizing the cleaning frequency is therefore essential to minimize the soiling losses and, at the same time, the costs. However, the effectiveness of cleaning lowers with time because of the reduced energy yield due to degradation. Additionally, economic factors such as the escalation in electricity price and inflation can either compound or counterbalance the effect of degradation. The present study analyzes the impact of degradation, escalation in electricity price and inflation on cleaning frequency and proposes a methodology than can be applied to maximize the profits of soiling mitigation in any system worldwide. The energy performance and soiling losses of a 1 MW system installed in southern Spain were analyzed and integrated with theoretical linear and nonlinear degradation rate patterns. The Levelized Cost of Energy and Net Present Value were used as criteria to identify the optimum cleaning strategies. The results showed that the two metrics convey distinct cleaning recommendations, as they are influenced by different factors. For the given site, despite the degradation effects, the optimum cleaning frequency is found to increase with time of operation