Concentrator photovoltaics (CPV), also called concentrating photovoltaics or concentration photovoltaics, is a photovoltaic technology that generates electricity from sunlight. Unlike conventional photovoltaic systems, it uses lenses or curved mirrors to focus sunlight onto small, highly efficient, multi-junction (MJ) solar cells. In addition, CPV systems often use solar trackers and sometimes a cooling system to further increase their efficiency.
Systems using high-concentration photovoltaics (HCPV) possess the highest efficiency of all existing PV technologies, achieving near 40% for production modules and 30% for systems. They enable a smaller photovoltaic array that has the potential to reduce land use, waste heat and material, and balance of system costs. The rate of annual CPV installations peaked in 2012 and has fallen to near zero since 2018 with the faster price drop in crystalline silicon photovoltaics. In 2016, cumulative CPV installations reached 350 megawatts (MW), less than 0.2% of the global installed capacity of 230,000 MW that year.
HCPV directly competes with concentrated solar power (CSP) as both technologies are suited best for areas with high direct normal irradiance, which are also known as the Sun Belt region in the United States and the Golden Banana in Southern Europe. CPV and CSP are often confused with one another, despite being intrinsically different technologies from the start: CPV uses the photovoltaic effect to directly generate electricity from sunlight, while CSP – often called concentrated solar thermal – uses the heat from the sun's radiation in order to make steam to drive a turbine, that then produces electricity using a generator. , CSP was more common than CPV.PV-insider.com How CPV trumps CSP in high DNI locations , 14 February 2012
History
Research into concentrator photovoltaics has taken place since the mid 1970s, initially spurred on by the energy shock from a mideast oil embargo. Sandia National Laboratories in Albuquerque, New Mexico was the site for most of the early work, with the first modern-like photovoltaic concentrating system produced there late in the decade. Their first system was a linear-trough concentrator system that used a point focus acrylic Fresnel lens focusing on water-cooled silicon cells and two axis tracking. Cell cooling with a passive heat sink and use of silicone-on-glass Fresnel lenses was demonstrated in 1979 by the Ramón Areces Project at the Institute of Solar Energy of the Technical University of Madrid. The 350 kW SOLERAS project in Saudi Arabia – the largest until many years later – was constructed by Sandia/Martin Marietta in 1981.
Research and development continued through the 1980s and 1990s without significant industry interest. Improvements in cell efficiency were soon recognized as essential to making the technology economical. However the improvements to Si-based cell technologies used by both concentrators and flat PV failed to favor the system-level economics of CPV. The introduction of III-V Multi-junction solar cells starting in the early 2000s has since provided a clear differentiator. MJ cell efficiencies have improved from 34% (3-junctions) to 47.6% (4-junctions) at research-scale production levels. A substantial number of multi-MW CPV projects have also been commissioned worldwide since 2010.
In 2016, cumulative CPV installations reached 350 megawatts (MW), less than 0.2% of the global installed capacity of 230,000 MW. Commercial HCPV systems reached instantaneous ("spot") efficiencies of up to 42% under standard test conditions (with concentration levels above 400) and the International Energy Agency sees potential to increase the efficiency of this technology to 50% by the mid-2020s. As of April 2026, the best lab cell efficiency for concentrator MJ-cells reached 47.6% (four or more junctions). Under outdoor, operating conditions, CPV module efficiencies have exceeded 33% ("one third of a sun"). System-level AC efficiencies are in the range of 25–28%. CPV installations are located in China, the United States, South Africa, Italy and Spain.
Challenges
Modern CPV systems operate most efficiently in highly concentrated sunlight (i.e. concentration levels equivalent to hundreds of suns), as long as the solar cell is kept cool through the use of heat sinks. Diffuse light, which occurs in cloudy and overcast conditions, cannot be highly concentrated using conventional optical components only (i.e. macroscopic lenses and mirrors). Filtered light, which occurs in hazy or polluted conditions, has spectral variations which produce mismatches between the electrical currents generated within the series-connected junctions of spectrally "tuned" multi-junction (MJ) photovoltaic cells. These CPV features lead to rapid decreases in power output when atmospheric conditions are less than ideal.
To produce equal or greater energy per rated watt than conventional PV systems, CPV systems must be located in areas that receive plentiful direct sunlight. This is typically specified as average DNI (Direct Normal Irradiance) greater than 5.5-6m kWh/m2/day or 2000 kWh/m2/yr. Otherwise, evaluations of annualized DNI vs. GNI/GHI (Global Normal Irradiance and Global Horizontal Irradiance) irradiance data have concluded that conventional PV should still perform better over time than presently available CPV technology in most regions of the world (see for example ).
CPV Strengths CPV Weaknesses High efficiencies under direct normal irradiance HCPV cannot utilize diffuse radiation. LCPV can only utilize a fraction of diffuse radiation. Low cost per watt of manufacturing capital Power output of MJ solar cells is more sensitive to shifts in radiation spectra caused by changing atmospheric conditions. Low temperature coefficients Tracking with sufficient accuracy and reliability is required. No cooling water required for passively cooled systems May require frequent cleaning to mitigate soiling losses, depending on the site Additional use of waste heat possible for systems with active cooling possible (e.g.large mirror systems) Limited market – can only be used in regions with high DNI, cannot be easily installed on rooftops Modular – kW to GW scale Strong cost decrease of competing technologies for electricity production Increased and stable energy production throughout the day due to (two-axis) tracking Bankability and perception issues Low energy payback time New generation technologies, without a history of production (thus increased risk) Potential double use of land e.g. for agriculture, low environmental impact Optical losses High potential for cost reduction Lack of technology standardization Opportunities for local manufacturing – Smaller cell sizes could prevent large fluctuations in module price due to variations in semiconductor prices – Greater potential for efficiency increase in the future compared to single-junction flat plate systems could lead to greater improvements in land area use, BOS costs, and BOP costs – Source: Current Status of CPV report, January 2015. Table 2: Analysis of the strengths and weaknesses of CPV.
Ongoing research and development
CPV research and development has been pursued in over 20 countries for more than a decade. The annual CPV-x conference series has served as a primary networking and exchange forum between university, government lab, and industry participants. Government agencies have also continued to encourage a number of specific technology thrusts.
ARPA-E announced a first round of R&D funding in late 2015 for the MOSAIC Program (Microscale Optimized Solar-cell Arrays with Integrated Concentration) to further combat the location and expense challenges of existing CPV technology. As stated in the program description: "MOSAIC projects are grouped into three categories: complete systems that cost effectively integrate micro-CPV for regions such as sunny areas of the U.S. southwest that have high Direct Normal Irradiance (DNI) solar radiation; complete systems that apply to regions, such as areas of the U.S. Northeast and Midwest, that have low DNI solar radiation or high diffuse solar radiation; and concepts that seek partial solutions to technology challenges."
In Europe the CPVMATCH Program (Concentrating PhotoVoltaic Modules using Advanced Technologies and Cells for Highest efficiencies) aims "to bring practical performance of HCPV modules closer to theoretical limits". Efficiency goals achievable by 2019 are identified as 48% for cells and 40% for modules at >800x concentration. A 41.4% module efficiency was announced at the end of 2018.
The Australian Renewable Energy Agency (ARENA) extended its support in 2017 for further commercialization of the HCPV technology developed by Raygen. Their 250 kW dense array receivers are the most powerful CPV receivers thus far created, with demonstrated PV efficiency of 40.4% and include usable heat co-generation.
A low concentrating solar device that includes its own internal tracker, is in development by ISP Solar which will enhance the efficiency of solar cell at low cost.
Due to several challenges CPV face, a novel ray tracing method is applied to better characterize the overall performance of CPV systems. This method is based on the propagation of inhomogeneous waves in absorbing media, enabling the materials' characterization, using their complex refractive indices.
Efficiency
According to theory, semiconductor properties allow solar cells to operate more efficiently in concentrated light than they do under a nominal level of solar irradiance. This is because, along with a proportional increase in the generated current, there also occurs a logarithmic enhancement in operating voltage, in response to the higher illumination.
To be explicit, consider the power (P) generated by a solar cell under "one-sun" illumination at the earth's surface, which corresponds to a peak solar irradiance Q=1000 Watts/m2. The cell power can be expressed as a function of the open-circuit voltage (Voc), the short-circuit current (Isc), and the fill factor (FF) of the cell's characteristic current–voltage (I-V) curve:
Upon increased illumination of the cell at "χ-suns", corresponding to concentration (χ) and irradiance (χQ), there can be similarly expressed:
where, as shown by reference:
and
Note that the unitless fill factor for a "high quality" solar cell typically ranges 0.75–0.9 and can, in practice, depend primarily on the equivalent shunt and series resistances for the particular cell construction. For concentrator applications, FF and FFχ should then have similar values that are both near unity, corresponding to high shunt resistance and very low series resistance (<1 milliohm).
The efficiencies of a cell of area (A) under one-sun and χ-suns are defined as: and The efficiency under concentration is then given in terms of χ and the cell characteristics as:
where the term kT/q is the voltage (called the thermal voltage) of a thermalized population of electrons – such as that flowing through a solar cell's p-n junction – and has a value of about at room temperature ().
The efficiency enhancement of ηχ relative to η is listed in the following table for a set of typical open-circuit voltages that roughly represent different cell technologies. The table shows that the enhancement can be as much as 20–30% at χ = 1000 concentration. The calculation assumes FFχ/FF=1; an assumption which is clarified in the following discussion. +Theoretical Cell Efficiency Increase Due to Sunlight Concentration CellTechnology Multi-crystalSilicon Mono-crystalSilicon Triple-junctionIII-V on GaAs ApproximateJunction Voc 550 mV 700 mV 850 mV χ = 10 10.8% 8.5% 7.0% χ = 100 21.6% 17.0% 14.0% χ = 1000 32.5% 25.5% 21.0%