photovoltaic panels, courtesy of DOE/NREL


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Photovoltaic power systems
Roof top photovoltaics

The sun's heat and light provide an abundant source of energy that can be harnessed in many ways. Photovoltaic power systems convert sunlight into electricity directly. Research and development efforts are under way to improve efficiency and reduce cost of photovoltaic power systems in applications ranging from roof-top residential to large industrial or electric utility sites. Topics covered include:

  • The solar resource: irradiation, tracking or fixed installations, concentrators, site evaluation (NREL PV Watts performance calculator), economics of PV systems
  • Applications: standalone residential, grid-connected residential, industrial, utility
  • Technology of photovoltaics: monocrystalline and multicrystalline silicon wafers, thin film solar cells, models and voltage-current characteristics
  • Power electronics in photovoltaic systems: system architectures, DC-DC converters, peak power tracking, batteries and charge controllers, DC-AC inverters and grid interface

Photovoltaic shingles

Smart roof top photovoltaic shingles with integrated power electronics

Solar cell

Solar cell circuit modelSolar cell characteristic

Thin film solar cells

Thin film solar cells may lead to significantly reduced costs by employing thin layers of semiconductor materials in low-cost manufacturing processes.


Semiconductor material absorbs photons and converts photons having sufficiently high energy into hole-electron pairs. A standard electrical circuit model consists of a photogeneration current Io proportional to solar irradiation in paralel with a diode. The cell short circuit current Isc is proportional to the number of absorbed photons. The cell open-circuit voltage Voc depends on the semiconductor diode characteristic. The maximum output power is obtained when the cell operates at the peak power point (Vpk, Ipk).