This Dezeen guide to solar energy, part of our Solar Revolution series, explains the different types of photovoltaics, from the established to the more experimental.
Solar power is a clean, renewable, and relatively cheap source of energy that is expected to become more widespread as the world weans itself off fossil fuels.
When people talk about solar energy, they are often referring to the photovoltaic process in which the sun’s rays are captured and converted into electricity.
Particles of light, called photons, strike a semiconductor surface and cause their atoms to release electrons, thereby creating an electric current.
Solar cells, which contain semiconductor materials, capture the sun’s energy in this way, but there are several different types.
Here is an explanation of the different types of solar cell technology, compiled in collaboration with Theo Hobson, a post-doctoral researcher in solar physics at the University of Liverpool:
silicon
Silicon-based solar cells are by far the most widespread, accounting for around 95 percent of the commercial photovoltaic market.
They are made from crystalline silicon, which is extracted from sand, although they also require some rarer elements such as silver.
Silicon solar cells are currently the most efficient solar cells available, converting about 24 percent of the energy from the sun’s rays that strike them into electricity. A silicon solar panel in the right place can typically recoup the energy expended to manufacture it in less than two years with a lifespan of around 25 years.
Because silicon solar cells are rigid, they are typically assembled into flat panels that are placed on rooftops or set up as solar farms. These formats are expected to continue to dominate the solar energy market in the near future.
Examples of buildings where silicon solar cells have been integrated in interesting ways include Shigeru Ban’s La Seine music complex near Paris (pictured) and BIG and Heatherwick Studios’ Google Bay View campus in Silicon Valley.
thin film
Thin-film solar cells, which make up the bulk of the remaining five percent of the photovoltaic market, are typically made from either cadmium telluride or copper indium gallium selenide (CIGS).
Cadmium and tellurium are both by-products of the mining industry, so they’re relatively accessible and cheap — although it’s predicted that supplies of the rarer tellurium could become less readily available in the future.
The elements used to make CIGS solar cells are harder to come by as they are also used in touch screens and are therefore much more in demand.
Scientists are exploring thin light-absorbing alternatives to cadmium telluride and CIGS like kesterite, which is made up of common elements like copper, tin, zinc and selenium.
Thin-film solar cells are less efficient than silicon cells, with a maximum power conversion of about 19 percent, even though they require less energy to manufacture. Their main advantage is that they are much more flexible than silicon cells and thus have a wider range of possible applications.
Projects previously used on Dezeen that use thin-film solar technology include Marjan van Aubel’s solar panel skylight designed for the Dutch Pavilion at Dubai Expo 2020 (pictured) and Pauline van Dongen’s windbreaker jacket with integrated solar panels .
Organic Solar Cells
The production of solar cells from organic, carbon-based molecules is also possible – although this technology is still in the research and development stage.
If they become commercially viable, organic solar cells would have the advantage of requiring much less energy to manufacture and not relying on finite elements, potentially making them cheaper to manufacture.
In addition, it is possible to tune organic solar cells to different wavelengths of light, such as infrared, so that they are transparent but still capture the sun’s rays. However, the technology remains relatively inefficient and unreliable.
Most often, organic solar cells are made from polymers such as plastics, although some researchers have taken the idea further. In 2020, engineering student Carvey Ehren Maigue won a James Dyson Award for his AuReus system, which turns waste plants into a disguise that harvests energy from light.
tandem cells
A rapidly developing area of solar technology is the concept of tandem cells.
Here solar cells – as described above – are used in combination with each other, optimized to absorb different light waves. This allows a single solar panel to use the solar spectrum more effectively.
The goal is to break the 24 percent efficiency frontier and harvest much more energy from the sun, making solar power even more competitive compared to fossil fuels.
Tandem technology could also make organic solar cells practical, by stacking the transparent cells on top of each other to capture different wavelengths of light.
In the past, tandem solar cells were so expensive to manufacture that they weren’t cost-effective, but new designs are emerging that could change that. For example, Oxford PV, a company affiliated with the University of Oxford, is stacking thin-film perovskite over conventional silicon solar cells to create a product that it says could have efficiency levels in excess of 30 percent.
solar thermal
The term solar energy can sometimes also refer to solar thermal energy. While photovoltaics generate electricity from the sun, solar thermal uses the sun’s rays to generate heat.
It’s a less sophisticated technology that generally involves heating a liquid, usually water, directly with sunlight.
In a domestic environment, solar thermal collectors can be installed on a sun-facing roof to heat water stored in a cylinder, which can then be used for hot water and heating.
Examples include UK company Naked Energy’s VirtuHOT, a solar thermal tube product that can heat water up to 90 degrees Celsius.
Solar Revolution
This article is part of Dezeen’s Solar Revolution series, which explores the diverse and exciting uses of solar energy and how people can take full advantage of the sun’s incredible power.
The top photo is by Anders J via Unsplash.
