First demonstration of multi-junction receivers in a grid-connected concentrator module

A performance evaluation model of a high concentration photovoltaic module with a fractional open circuit voltage-based maximum power point tracking algorithm

Implementation of a modified circuit reconfiguration strategy in high concentration photovoltaic modules under partial shading conditions

Performance characterization of the optical elements of a high concentration photovoltaic (HCPV) module equipped with point-focus Fresnel lens as the concentrator, a plano concave lens as the secondary optical element and multileg homogeniser capable of uniformly distributing incoming rays onto four multi-junction solar cells have been investigated in this paper. To minimise the optical losses, the application of a singlelayer of Anti-Reflective Coating (ARC) on the optical elements was done, to investigate the effect this had on the optical efficiency of the HCPV module. A ray tracing technique using COMSOL Multiphysics was implemented to evaluate the optical performance of HCPV module. It was determined that the optical efficiency of the system without any ARC being applied was at 79.12% which increased by just under 3% to 81.87% when an ARC was applied to only the multi-leg homogeniser. Subsequently, by applying the ARC to the plano concave lens alone produced a further $\approx 2.7 \%$ increase in the optical efficiency to 84.61%. Finally, the highest increase in optical efficiency was observed when both the multi-leg homogeniser and plano concave lens had an ARC applied to them producing an optical efficiency of 87.48%. This shows that applying an ARC to the optical elements produces an increase of over 8% in the optical efficiency of the HCPV module.

Performance of multi-junction cells due to illumination distribution across the cell surface

Model for the prediction of the maximum power of a high concentrator photovoltaic module

High concentrating photovoltaic (HCPV) technology plays a more and more important role in solar power generation due to its extremely high efficiency. However, the efficiency of the HCPV module can be reduced by many factors. Especially, there are not enough researches and knowledge on the light intensity distribution and non-uniform illumination of different wavelengths of light concentrated by Fresnel lens. It is generally considered that the maximum power of multi-junction solar cell is achieved when the cell is placed on the focal plane of Fresnel lens. But it is proved to be incorrect by our research. When light beams of different wavelengths go through the Fresnel lens, their light spot distributions on the optical axis are not the same as those when they have different refractive indexes in Fresnel lens. At the same time, the triple-junction solar cell consists of three sub-cells which absorb light beams of different wavelengths respectively. Therefore, the performance of triple-junction cells would be influenced by the light distribution along the optical axis, this is exactly what we want to study in this work. The method of simulating the light tracing is used to calculate and analyze the light intensity distribution and non-uniform characteristics of different wavelengths of light concentrated by Fresnel lens. Combined with them from the circuit network model of a triple-junction solar cell, the electrical performances of triple-junction solar cell at different positions along the optical axis are studied. It is found from the simulation that the performance of cell does not reach the best state when cell is placed on the focal plane. The power of cell on the focal plane reaches only 0.41 W while the maximum point arrives at 0.69 W. The high non-uniformity of light on cell surface when cell is placed on the focal plane causes the decline of power. And an outdoor HCPV testing system with the ability to change the distance between Fresnel lens and the cell is conducted. The experimental results and the simulation results match well, therefore our simulation approach is verified. It shows that the module achieves the maximum power on either side of the focal plane, and the output power can increase more than 20% after optimization. It is a result after equilibrium between light intensity and uniformity on cell surface.

This paper presents an overview of the status of the high-concentration photovoltaic (HCPV) module technology and discusses the steps required to take it from to the production of gigawatts in the near future. The paper discusses the impact of the recent advances in multijunction cell technology on the economics of concentrator system.

Spectrally corrected direct normal irradiance based on artificial neural networks for high concentrator photovoltaic applications

Determination of the current–voltage characteristics of concentrator systems by using different adapted conventional techniques

Energy and exergy analyses of new cooling schemes based on a serpentine configuration for a high concentrator photovoltaic system

A 3-dimensinal simulator for concentrator photovoltaic (CPV) modules was developed using ray-trace and circuit simulators. By using this total simulator, we can calculate the operating characteristics of CPV modules composed of optical system and InGaP/InGaAs/Ge triple-junction solar cell. A typical flat Fresnel lens was adopted as a first lens and a homogenizer was adopted as a secondary lens. We used a ray-trace simulator ZEMAX. The generated photocurrent was obtained from ray-trace simulation and spectral response of InGaP/InGaAs/Ge triple-junction solar cell. By using the homogenizer, the uniformity of concentrated light was improved. A 3-dimensional equivalent circuit model for InGaP/InGaAs/Ge triple-junction solar cell can carry out calculations considering the in-plane distribution of the concentrated light. From the results of ray-trace, we could know the intensity distribution of photocurrent in each subcell. By using the ray-trace and circuit simulation, the operating characteristics of CPV modules were calculated totally. It was observed that the FF and cell efficiency could be improved by using the homogenizer. We can use the total simulator for the evaluation and optimization of CPV cells and modules.

Multi-junction solar cells can be economically viable for terrestrial applications when operated under concentrated illuminations. The optimal design of concentrator optics in high concentration photovoltaics (HCPV) systems is crucial for achieving high energy conversion. At a high geometric concentration, chromatic aberration of the primary lens can restrict the optical efficiency and acceptance angle. In order to correct chromatic aberration, multi-material, multi-element refractive elements, hybrid refractive/diffractive elements, or multi-element refractive and diffractive systems can be designed. In this paper, the effect of introducing a diffractive surface in the optical path is analyzed. An example two-stage refractive and diffractive optical system is shown to have an optical efficiency of up to 0.87, and an acceptance angle of up to ±0.55° with a 1600× geometric concentration ratio, which is a significant improvement compared to a single-stage concentrator system with a single material. This optical design can be mass-produced with conventional fabrication methods, thus providing a low-cost alternative to other approaches, and the design approach can be generalized to many other solar concentrator systems with different cell sizes and geometric concentration ratios.

The High Concentrator Photovoltaic (HCPV) technology, due to its high efficiency, is considered one of the most promising solutions for the exploitation of sun-irradiation-based Renewable Energy Sources (RES). Nevertheless, the HCPV production is strictly connected to the Direct Normal Irradiation (DNI) making this photovoltaic technology more sensible to cloudiness than traditional ones. In order to mitigate the power intermittence and improve production programmability, the integration between Energy Storage Systems (ESSs) and HCPV, resorting to forecasting algorithms, has been investigated. Specifically, a local weather forecasting algorithm has been used for estimating the daily time evolution of DNI, air Temperature (T), Wind Speed (WS), and Air Mass (AM). These data are subsequently processed by means of an accurate HCPV model for the estimation of one day-ahead daily power production profile. The processing of HCPV forecasted generation by means of a properly tuned filter-based algorithm allows one day-ahead the definition of power profiles of ESS and power plant respectively, considering also the ESS constraints and the characteristic of the implemented real-time control algorithm. The effectiveness of the proposed forecasting model and control algorithm is verified through a simulation study referring to the solar power plant constituted by HCPV and ESS installed in Ottana, Italy. The results highlight that the application of the proposed approach lessens the power fluctuation effect caused by HCPV generation preserving the batteries at the same time. The feasibility and advantages of the proposed approach are finally presented.

Since their inception, organic solar cells have been a cynosure of photovoltaic (PV) community, owing to their simplicity, affordability and mass-production capabilities. Research on organic solar cells has been propelled by advances in nanotechnology, polymer synthesis, and semiconductor processing; efforts to achieve high power conversion efficiencies (PCE) through refined device geometry, tailored synthesis and/or combination of new low-bandgap materials, and heuristic process optimization have fructified as ~10 % efficiency in single-junction organic solar cells. Recent PCE enhancement in organic solar cells has mostly attributed to the development of small bandgap materials that extend absorption of the sun into the red and infrared wavelengths.Utilizing tandem cells comprised of both large and small bandgap sub-cells enables light harvesting of different parts of the solar spectrum to be separately optimized, yielding higher PCE than single junction solar cells. But the challenges in achieving highly efficient organic tandem solar cells include optimal combination of materials for each sub-cell and interconnecting layers between sub-cells that are process compatible. Optimal combination of materials can be achieved by selection of two materials having complementary absorption windows. The interconnecting layer provides electrical and optical coupling between the two sub-cells and plays a key role in the performance of tandem cells. For the design of the interconnecting layer, electrical, optical, chemical and structural characteristics should be considered. Ideally, it should effectively facilitate charge transport between two sub-cells. Moreover, high transmittance and negligible absorption in the spectral region where two sub-cells absorb is desirable. Last but not least, the interconnecting layer should be designed to survive the subsequent solution coating and provide conformal surface coating for tandem cells with solution processed top cells. Here we evaluate some of candidate metal oxides for tunnel junction layers for organic tandem solar cells. Metal oxides are grown by Atomic Layer Deposition (ALD) for thin defect-free conformal layer to circumvent miscibility issues and negligible absorption. Normal and inverted interfaces are examined. The influence of annealing under different conditions and methods will be presented. Tunneling properties are qualified by J-V characteristics and optical properties evaluated by UV-Vis are contrasted to suggest optimal design tradeoffs of tunnel junctions for solution processed organic tandem solar cells.

High Concentration Photovoltaic (HCPV) power sources must compete with established energy sources such as fossil fuel or nuclear power, and must be as reliable and cost effective as other energy sources. HCPV manufacturers must address issues of technology viability, unique design requirements, immature manufacturing processes, quality control, and the impact these have on the reliability over a 25 year life. SolFocus is investing in proving the lifetime of its HCPV product and developing reliability assessment methods. This approach allows the company to provide an industry standard warranty with good knowledge of the financial risks involved and to set a cornerstone for product and company acceptance in the maturing solar industry. The SolFocus Reliability Program is divided into two major areas; panel and tracker reliability. This paper outlines the processes behind each program and summarizes current results.