SUN ROOF: Panels of cylindrical solar cells cover this roof in California and potentially offer a cheaper solution for photovoltaic power from rooftops.
Image: Courtesy of Solyndra
-
The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
Read More »
There are approximately 30 billion square feet (2.8 billion square meters) of expansive, flat roofs in the U.S., an area large enough to collect the sunlight needed to power 16 million American homes, or replace 38 conventional coal-fired power plants. By covering these roofs with large, flat arrays of cylindrical thin-film solar cells (think massive installations of fluorescent tubes, only absorbing light rather than emitting it), Fremont, Calif.–based Solyndra, Inc., hopes to harness that energy.
"With a cylinder, we are collecting light from all angles, even collecting diffuse light," says CEO Chris Gronet, who founded the solar cylinder company in 2005 based on an idea he had late one night while pondering less expensive ways to install photovoltaic panels. Because the arrays do not have to be angled or anchored into the roof, he adds, "we have half the installation cost and can install in one third the time."
Solyndra is now churning out copper-indium-gallium-selenide (CIGS) thin-film solar cells, wrapped into a cylindrical shape and encased in glass. This design not only seals out moisture but allows the glass to act as a sunlight concentrator, funneling photons onto the thin film, according to Gronet. He says the Fremont plant, which opened in the spring, will ultimately be capable of producing 110 megawatts worth of solar cylinders annually, but he declined to specify how many cylinders that is.
The company says that the solar cylinders—paired with a roof painted white to better reflect sunlight—can collect 20 percent more sunshine than their conventional flat counterparts. The estimate is based on 50 kilowatts worth of the tubular cells that the company installed on its own roof.
As it stands, Solyndra's CIGS solar cells convert as much as 14 percent of the sunlight that hits them to electricity and, all told, Gronet expects that a Solyndra system will deliver twice as many kilowatt-hours of electricity from a given rooftop.
The cylindrical design also allows Solyndra to lay its arrays flat and to space them so that the wind can flow through them, rather than lift them up like it can with angled arrays. This means that the solar cylinders can be installed without affixing them onto the roof—and still withstand up to 130 mile-per-hour (209 kilometer-per-hour) winds.
"Our test installation in Florida survived the recent hurricane," Tropical Storm Fay, Gronet says. "Because of the lower installation cost, we have a clear path to grid parity." In other words, the newly shaped cells have the potential of harnessing solar power at around the same price as electricity from coal-fired power plants, currently the cheapest generation option at around six cents per kilowatt hour. Typical solar photovoltaic installations, on the other hand, cost roughly 25 to 50 cents per kilowatt-hour of electricity, roughly one half of which is related to the expense of physically installing them.
Gronet declined to reveal the cost of manufacturing solar cylinders or the price tag of electricity it delivers—primarily because if they are able to deliver lower cost electricity they want to preserve that extra profit for their customers, he admits. The solar cylinders thrive in countries that set a minimum guaranteed price for solar electricity, such as Spain and Germany where the so-called feed-in tariff is as much as 44 Euro cents per kilowatt-hour.
As a result, Phoenix Solar, AG, a German company that installs solar power systems, is Solyndra's biggest customer to date—and the latter claims to have $1.2 billion in multiyear contracts, largely because the cylinders can be installed in days rather than weeks and do not require special supports. The company already has 10 prototype installations, located in Germany as well as in California, Florida, Pennsylvania, Utah and Washington, D.C.
The questions that remain include price and reliability in manufacturing, according to environmental engineer Vasilis Fthenakis, senior scientist at Brookhaven National Laboratory's National Photovoltaic Environment Research Center in Upton, N.Y., and Columbia University. "Companies have had difficulties producing CIGS without many defects," he says. "They may get more from deflected or reflected light but how much more? That needs to counterbalance the increased costs of production," due to the cylinder design and specialized thin-film materials.
That said, commercial rooftops are already among the most promising areas for installing solar power. "We envision large-scale photovoltaics in the desert but it's much easier for people to accept systems on the roof," Fthenakis notes. "It's cheaper to put them on roofs than on real estate."
See what we're tweeting about
8 Comments
Add CommentThis is a great idea. However, I think it can be improved substantially through the use of gradient index lenses... or rather, to turn the entire glass tube into a gradient index lens. Basically in GRIN lenses light is bent because the actual material varies in density from one side to the other, or from the outer edges to the center.
Reply | Report Abuse | Link to thisIf the inner side of the glass tube had a higher refractive index than the outer layer, the result would be to bend the light that hits the tube at odd angles towards the center. It might even "wrap around" inside the glass tube to strike the photoreceptor materials on the back side of the tube.
As it currently is set up, the light either does not change direction at all (its path is changed and then corrected by the curvature of the glass) or the light that hits at odd angles will be more likely to bend outwards and away from the photoreceptor. This is obviously not what the manufacturers intended.
The only disadvantage to this method is that it would increase production costs by requiring that ions be embedded in the glass to create this gradient index. However, the potentially drastic increase in efficiency could make it worth it to incorporate this very simple process as an extra production step.
The good news is that this company is suggesting that their solar cells are cheaper than the competition because they cost much less to install. Also, thin-film solar cells are supposed to be easier to mass produce and therefore should become cheaper as production ramps up. Adding this one extra step in production (which only require a bit of ion exchange) might increase the price, but I would imagine that they could still stay competitive with the larger photovoltaic arrays all the same.
1) The CIGS must get very hot in vacuum. One would expect both a degradation of performance and a decrease of life span of the material. Can anyone comment?
Reply | Report Abuse | Link to this2) Little mention was made of the manufacturing cost of Solyndra's article, however it appears to be costly, and not competitive with established crystalline and thin film solutions. One would expect Solyndra to tout its manufacturing costs at least as much as its installation costs if there is an advantage.
What happens when it snows? Wouldn't that cause a big decrease in energy?
Reply | Report Abuse | Link to thisI like the design!It occurred to me that a simple manifold of pipes to run air thru the middle of these tubes would allow them to become passive solar heaters at the same time they collect power.Reduce heat in the tube and provide heat for the building they are on.Could run the slow flow air fan by the collectors themselves.Only need it during daytime, anyway!Just a suggestion!Really like your product!David
Reply | Report Abuse | Link to thisI don't see how this design modification can decrease the price of solar energy from 25 to 50 cents/Kwhr of electricity to 6 cents/Kwhr, or equal to the present cost of electricity from coal fired plants. The explanations seem a little vague, esp. since the article is only talking about reducing the cost of installation (not production) by 50% with this new design.
Reply | Report Abuse | Link to thisIf the sale of these solar cells thrive in Europe where the feed in tariff is 44 Euro cents/Kwhr; that's fine. And any decrease in installation or production costs in solar cells is great; however, I don't think present day solar energy is cost competitive with other methods of energy production. It still requires the next generation of solar cells, which must be more efficient (greater than the 15 - 20% efficiency range of the present solar cells) and less expensive (solarbuzz.com shows industrial solar electricity rates at 21.3 cents/Kwhr for April 2008; naturally residential rates are significantly higher in the 35-40 cents/Kwhr range).
Great idea but will the glass be strong enough to survive a hailstorm?
Reply | Report Abuse | Link to thisGreat idea but would the glass tubes survive a hailstorm?
Reply | Report Abuse | Link to thisHow squirrel proof are they?
Reply | Report Abuse | Link to this