Why photovoltaics

Photovoltaic systems are quiet and visually unobtrusive. Small-scale solar plants can take advantage of unused space on rooftops of existing buildings. PV cells were originally developed for use in space, where repair is extremely expensive, if not impossible. PV still powers nearly every satellite circling the earth because it operates reliably for long periods of time with virtually no maintenance.

Solar energy is a locally available renewable resource. They can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination.

One way to get around this limitation is to use two or more different cells, with more than one band gap and more than one junction, to generate a voltage.

These are referred to as "multijunction" cells also called "cascade" or "tandem" cells. Multijunction devices can achieve a higher total conversion efficiency because they can convert more of the energy spectrum of light to electricity. As shown below, a multijunction device is a stack of individual single-junction cells in descending order of band gap Eg. The top cell captures the high-energy photons and passes the rest of the photons on to be absorbed by lower-band-gap cells.

As an example, the multijunction device below uses a top cell of gallium indium phosphide, "a tunnel junction," to aid the flow of electrons between the cells, and a bottom cell of gallium arsenide.

Aug 6, Recommended Articles. Globally, the U. Most modern solar cells are made from either crystalline silicon or thin-film semiconductor material. Silicon cells are more efficient at converting sunlight to electricity, but generally have higher manufacturing costs.

Thin-film materials typically have lower efficiencies, but can be simpler and less costly to manufacture. A specialized category of solar cells - called multi-junction or tandem cells - are used in applications requiring very low weight and very high efficiencies, such as satellites and military applications.

All types of PV systems are widely used today in a variety of applications. There are thousands of individual photovoltaic panel models available today from hundreds of companies. Compare solar panels by their efficiency, power output, warranties, and more on EnergySage. Photovoltaics Share. How to compare solar inverters How to compare solar panels How does PV technology work? Solar cell researchers at NREL and elsewhere are also pursuing many new photovoltaic technologies—such as solar cells made from organic materials , quantum dots , and hybrid organic-inorganic materials also known as perovskites.

These next-generation technologies may offer lower costs, greater ease of manufacture, or other benefits. Further research will see if these promises can be realized. Photovoltaic research is more than just making a high-efficiency, low-cost solar cell. Homeowners and businesses must be confident that the solar panels they install will not degrade in performance and will continue to reliably generate electricity for many years.

Utilities and government regulators want to know how to add solar PV systems to the electric grid without destabilizing the careful balancing act between electricity supply and demand.