Improving Solar Energy

While standard solar cells are good at generating electricity, they aren’t as good at generating heat.  However, a researcher at Michigan Technological University has created a solar cell that is good at both making electricity and capturing heat in order to warm your home and your water.  Joshua Pearce, an associate professor of materials science and engineering, teamed up with Kunal Girotra from ThinSilicon in California and Michael Pathak and Stephen Harrison from Queen’s University in Canada to create the cells.

Solar photovoltaic thermal energy systems (PVTs) are capable of generating both electricity and heat; however they are much less efficient at generating heat than a stand-alone solar thermal collector.  This is because the crystalline silicon that makes up these solar cells generates the most electricity at low temperatures, a problem for capturing heat.  And although solar thermal applications are effective in capturing heat, the PVT systems can take up most of the space on a roof and leave no room for the thermal devices.

Pearce and his team have created new solar panels out of amorphous silicon, or thin-film silicon, instead of the standard crystalline silicon.  This type of silicon does not have the capability of creating as much electricity; however they are lighter, flexible, cheaper and have a greener footprint.  The problem with using this material in the past has been its vulnerability to something known as the Staebler-Wronski effect.

“That means that their efficiency drops when you expose them to light—pretty much the worst possible effect for a solar cell,” Pearce explains.

But by incorporating thin-film silicon into a new type of PVT, Pearce and his team were able to figure out a way around the effect.  They found that by heating the material to temperatures near the boiling point of water, they were able to create thicker cells that overcame the Staebler-Wronski effect.  After applying the silicon to solar thermal energy collectors, they were able to increase the electrical efficiency by more than 10%.  This means that a PVT system made with thin-film silicon would have increased thermal and electrical capture, so both types of energy could be generated with one system.

“They give you the most usable solar energy per square foot of roof space,” Pearce said.  “I think that 20 years from now, every roof will be made of integrated PVT.”

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