First polymer solar-thermal device heats home, saves money

April 4, 2011, Wake Forest University

A new polymer-based solar-thermal device is the first to generate power from both heat and visible sunlight – an advance that could shave the cost of heating a home by as much as 40 percent.

Geothermal add-ons for heat pumps on the market today collect heat from the air or the ground. This new device uses a fluid that flows through a roof-mounted module to collect heat from the sun while an integrated solar cell generates electricity from the sun's visible light.

"It's a systems approach to making your home ultra-efficient because the device collects both solar energy and heat," said David Carroll, Ph.D., director of the Center for Nanotechnology and Molecular Materials at Wake Forest University. "Our solar-thermal device takes better advantage of the broad range of power delivered from the sun each day."

Research showing the effectiveness of the device appears in the March issue of the peer-reviewed journal Solar Energy Materials and Solar Cells.

A standard, rooftop solar cell will miss about 75 percent of the energy provided by the sun at any given time because it can't collect the longest wavelengths of light – infrared heat. Such cells miss an even greater amount of the available daily solar power because they collect sunlight most efficiently between 10 a.m. and 2 p.m.

"On a rooftop, you have a lot of visible sunlight and heat from the infrared radiation," Carroll said. "The solar-cell industry has for the most part ignored the heat."

The design of the new solar-thermal device takes advantage of this heat through an integrated array of clear tubes, five millimeters in diameter. They lie flat, and an oil blended with a proprietary dye flows through them. The visible sunlight shines into the clear tube and the oil inside, and is converted to electricity by a spray-on polymer photovoltaic on the back of the tubes. This process superheats the oil, which would then flow into the heat pump, for example, to transfer the heat inside a home.

Unlike the flat solar cells used today, the curve of the tubes inside the new device allows for the collection of both visible light and infrared heat from nearly sunrise to sunset. This means it provides power for a much greater part of the day than does a normal solar cell.

Because of the general structure and the ability to capture light at oblique angles, this is also the first solar-thermal device that can be truly building-integrated – it can be made to look nearly identical to roofing tiles used today.

Tests of the solar-thermal device have shown 30 percent efficiency in converting to power. By comparison, a standard solar cell with a absorber has shown no greater than 8 percent conversion efficiency.

The research team will build the first square-meter-size solar-thermal cell this summer, a key step in getting the technology ready for market.

Explore further: Solar-powered process could decrease carbon dioxide to pre-industrial levels in 10 years

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not rated yet Apr 04, 2011
Am I correct in assuming that the effect is based on the photovoltaic polymer being put on a half-pipe surface so that the light coming at it would be perpendicular to at least some part of the surface throughout the day?

Because the problem of ordinary solar panels is that the photovoltaic effect doesn't work very well if the light is coming in at an angle. (or it partially reflects off the panel, I forget which)

In that case, wouldn't a similiar effect be had if you put ordinary solar panels into narrow strips and then arranged them in V shaped throughs? They'd be more efficient at turning light to electricity than polymer panels, and you could still put infrared-absorbing oil in the same channel to carry away the heat.
not rated yet Apr 04, 2011
That's great...

too bad you can actually do better than that, for the purpose of heating water or air, through a few hundred dollars worth of materials and a few hours of your spare time.

Homemade Solar forced air heaters and water heaters are already doing better than that using black paint and some corrugated metal, or even cardboard painted black.

It's cheaper, low tech, durable, and doesn't require paying a 50% to 100% mark-up for someone else's brand name.
not rated yet Apr 04, 2011

It's cheaper, low tech, durable, and doesn't require paying a 50% to 100% mark-up for someone else's brand name.

But it makes no electricity.
not rated yet Apr 06, 2011
Here's my Mark 2-verion:
Half-tubes with mirror surface inside, reflecting back up on to a center-beam designed as article concept sun-catcher. This is a better and cheaper version, as it requires less suface PV to total solar area, while using the same principle.

A circulating gas inside panel-displacement is cooled towards liquid medium radiators on top, to reduce heat-loss from system, and heat wear on parts.

Top surface of panel are vacuumed double glass, and sides/bottom insulated with glass-wool. Roof window frame could form outer visual structure, for better looks.

Combined, inexpensive domestic solar el./heat may be an important component for tomorrow's energy and grid structure. Low production energy-and-resource inputs are paramount in these appliances, along with low maintainence and long life, since output pr. item is low.

Nice to see that people with credetials are looking into it.

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