Photovoltaic and Solarthermal hybrid technology: MIT and Boston College

Researchers at Boston College and the Massachusetts Institute of Technology (MIT) have produced a single technology that accomplishes what is currently only accomplished with two separate units: thermoelectric and photovoltaic solar electricity generation.

As we have pointed out previously in the Solar Choice blog, solar hot water systems are one of the most effective ways to reduce home energy costs; water heating accounts for 30 to 40% of the average household’s energy bills by using the sun to pre-heat water for showers, baths, and basins. Solar hot water systems absorb heat from the sun and concentrate, heating the water inside. Thermoelectric technologies, a broader category that encompasses solarthermal technologies, can utilise heat from the sun, fires or elsewhere to generate electricity. Solarthermal generation can be similar in principle to concentrating solarthermal electricity generation, except that concentrating solar thermal generation typically requires large swathes of land for mirrors and giant towers to spin turbines to generate power (much as in a conventional coal generation plant). Solarthermal of the type and scale developed under the MIT/BC project would not generate enough power to do so.

Solarthermal technologies have not been deployed as widely as photovoltaic technologies have. Photovoltaics solar panels convert sunlight directly into electricity, which can then be used by appliances in a home or fed into the electricity grid.

Solarthermal and photovoltaic technologies have always been manufactured in separate units. The combination of these methods of generation in the technological development at Boston College and MIT has the potential revolutionise the way that the power of the sun is utilised in homes and elsewhere. The team of researchers used nanotechnology (nanostructuring) to combine into one flat-bodied panel materials that have thermoelectric properties with photovoltaic materials that selectively absorb certain parts of the spectrum of light. The technology promises efficiencies up to 8 times higher than the previous record for solarthermal, and would not require large arrays of high-precision tracking devices to aim mirrors and concentrate sunlight, as is the case with many solarthermal technologies that are currently deployed, such as the solar towers in Spain and parts of the US.

There are a number of potential benefits associated with the use of solar photovoltaic/solarthermal technology: a panel would not require as much material to manufacture, and would not be affected so significantly by orientation with regard to the sun. It could also be integrated with a solar hot water system: water inside the panel would be heated by incoming light, whilst the exterior materials absorb the sunlight and convert it to electricity. This dual-action effect greatly increases the overall sunlight-to-useable energy efficiency of the unit, promising payback periods of up to one third shorter than those of conventional solarthermal panels, according to Zhifeng Ren, a co-author of the paper on the technology.

The hybrid technology would not be a replacement for solar hot water or solar photovoltaics, but instead would be “another way” of utilising the massive amount of solar power with which the earth is inundated on a daily basis, according to says Gang Chen, MIT’s Carl Richard Soderberg Professor in Power Engineering and director of the Pappalardo Micro and Nano Engineering Laboratories. œWith the use of other or new thermoelectric materials that can operate at a higher temperature, the efficiency may be improved further to be competitive with that for state-of-the-art amorphous silicon solar cells. This can potentially provide a different approach to realizing the $1-per-watt goal for solar-electricity conversion, says Li Shi, associate professor of mechanical engineering at the University of Texas, Austin.

Written by James Martin

Solar Choice Analyst

© 2010 Solar Choice Pty Ltd

Sources and Links:, “MIT and Boston College researchers develop hybrid solarthermal technology”

MITnews, “Solar power, with a side of hot running water”

Boston College office of news and public affairs, “BC researchers report on solar-thermal flat panels that generate electric power” (top image also from this website)

Previous related Solar Choice blog entries: Solar Hot Water: an introduction : What type of solar panel is best for you? : What is grid parity and what does it mean for solar power? : Tilt angle and orientation for solar panels in Australia

James Martin II