Concentrator photovoltaics
Unlike conventional photovoltaic systems, it uses lenses or curved mirrors to focus sunlight onto small, highly efficient, multi-junction (MJ) solar cells.
[3]: 5 They enable a smaller photovoltaic array that has the potential to reduce land use, waste heat and material, and balance of system costs.
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.
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.
Diffuse light, which occurs in cloudy and overcast conditions, cannot be highly concentrated using conventional optical components only (i.e. macroscopic lenses and mirrors).
The annual CPV-x conference series has served as a primary networking and exchange forum between university, government lab, and industry participants.
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.
[26] 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.
In practice, the higher current densities and temperatures which arise under sunlight concentration may be challenging to prevent from degrading the cell's I-V properties or, worse, causing permanent physical damage.
Additionally, the cell design itself must incorporate features that reduce recombination and the contact, electrode, and busbar resistances to levels that accommodate the target concentration and resulting current density.
These features include thin, low-defect semiconductor layers; thick, low-resistivity electrode & busbar materials; and small (typically <1 cm2) cell sizes.
[27] Including such features, the best thin film multi-junction photovoltaic cells developed for terrestrial CPV applications achieve reliable operation at concentrations as high as 500–1000 suns (i.e. irradiances of 50-100 Watts/cm2).
[40] From concentrations of 100 to 300 suns, the CPV systems require two-axis solar tracking and cooling (whether passive or active), which makes them more complex.
[30] The solar cells require high-capacity heat sinks to prevent thermal destruction and to manage temperature related electrical performance and life expectancy losses.
[citation needed] Multi-junction solar cells, originally designed for non-concentrating PV on space-based satellites, have been re-designed due to the high-current density encountered with CPV (typically 8 A/cm2 at 500 suns).
[42] However, such standardized tests – as typically performed on only a small sampling of units – are generally incapable to evaluate comprehensive long-term lifetimes (10 to 25 or more years) for each unique system design and application under its broader range of actual – and occasionally unanticipated – operating conditions.
Reliability of these complex systems is therefore assessed in the field, and is improved through aggressive product development cycles which are guided by the results of accelerated component/system aging, performance monitoring diagnostics, and failure analysis.
[44][45] The tracker and module support structure for a modern HCPV system must each remain accurate within 0.1°-0.3° in order to keep the solar resource adequately centered within the acceptance angle of the receiver collection optics, and thus concentrated onto the PV cells.
More specifically, the cells are fabricated from a layering of thin-film III-V semiconductor materials having intrinsic lifetimes during operation that rapidly decrease with an Arrhenius-type temperature dependence.
The system receiver must therefore provide for highly efficient and uniform cell cooling through sufficiently robust active and/or passive methods.
By the end of 2015, the number of CPV power plants (including both LCPV and HCPV) around the world accounted for a total installed capacity of 350 MW.
Unfortunately, following a rapid drop in traditional flat-panel PV prices, the near term outlook for CPV industry growth has faded as signaled by closure of the largest HCPV manufacturing facilities: including those of Suncore, Soitec, Amonix, and SolFocus.
[63] The AC production capacity is specified as MWAC under IEC 62670 concentrator standard operating conditions (CSOC) of DNI=900 W/m2, AM1.5D, Tambient=20 °C, & Wind speed=2 m/s, and may include adjustments for inverter efficiency, higher/lower solar resource, and other facility-specific factors.
The largest CPV power plant currently in operation is of 138 MWp rating located in Golmud, China, hosted by Suncore Photovoltaics.
CPVT at high concentrations of over 100 suns (HCPVT) utilizes similar components as HCPV, including dual-axis tracking and multi-junction photovoltaic cells.
To maintain efficient overall operation and avoid damage from thermal runaway, the demand for heat from the secondary side of the exchanger must be consistently high.
These very low temperatures compared to CSP systems also make CPVT less compatible with efficient and economic thermal energy storage (TES).
For thermal applications having lower or intermittent demand, a system may be augmented with a switchable heat dump to the external environment in order to safeguard cell life and maintain reliable photovoltaic output, despite the resulting reduction in net operating efficiency.
[87] Minimizing the number of individual receiver units is a simplification that may ultimately yield improvement in the overall balance of system costs, manufacturability, maintainability/upgradeability, and reliability.
Third tier systems are distributed generators consisting of large arrays of ~20W single-cell receiver/collector units, similar to those previously pioneered by Amonix and SolFocus for HCPV.
