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Iron pyrite is the top material picked by a University of California at Berkley and Lawrence Berkeley National Laboratory to replace silicon in solar cells. While modestly less efficient than crystalline silicon, its dramatic cheaper in processing costs and very abundant. Adopting it as a replacement to silicon or thin films could dramatically cut costs and enable enough production to supply the world's power needs, according to the team.  (Source: Crystals Guide)
Search for more abundant, lower cost materials should help improve solar cost efficiency

Solar power is an incredibly promising alternative energy technology.  However, the problem with converting solar energy directly to solar power via photovoltaics or other designs is that the cost of producing power is simply not cost competitive with nature's designs -- coal or petrol.

The cost issues are not for lack of efficiency.  Scientists have milked very high efficiency out of the cells, iteratively raising the yield year by year.  However, the high cost of silicon, the primary material for solar panel cells, keeps the costs high even as efficiencies experience dramatic gains.

In order to make solar cost competitive, researchers at University of California, Berkeley, and the Lawrence Berkeley National Laboratory (LBNL) are spearheading the search for a silicon replacement for the solar industry. 

The team surveyed 23 promising semiconducting materials and then pared the field down to the 12 that are abundant enough to meet or exceed the world's yearly energy needs.  From there 9 were selected, which exhibited significant cost savings in raw material costs over crystalline silicon.

Daniel Kammen, UC Berkeley professor of energy and resources, and colleagues Cyrus Wadia of LBNL and A. Paul Alivisatos of UC Berkeley's Department of Chemistry discovered that some superior solar choices may have been overlooked due to the desire to keep the status-quo of silicon.  They believe before solar power can be deployed on a broad scale, the basic science must be reevaluated to ensure that the industry is using the best possible materials, rather than blindly proceeding. 

Wadia states, "The reason we started looking at new materials is because people often assume solar will be the dominant energy source of the future.  Because the sun is the Earth's most reliable and plentiful resource, solar definitely has that potential, but current solar technology may not get us there in a timeframe that is meaningful, if at all. It's important to be optimistic, but when considering the practicalities of a solar-dominated energy system, we must turn our attention back to basic science research if we are to solve the problem."

Today's top solar materials are crystalline silicon and thin film CdTe (cadmium telluride) and CIGS (copper indium gallium selenide).  Silicon is abundant, but costs a great deal to process.  The exotic metals like indium used in thin films are cheaper to process, but less abundant.  If the world switched to all solar, they would quickly run out.  States Professor Kammen, "We believe in a portfolio of technologies and therefore continue to support the commercial development of all photovoltaic technologies.  Yet, what we've found is that some leading thin films may be difficult to scale as high as global electricity consumption."

Wadia adds, "It's not to say that these materials won't play a significant role.  But rather, if our objective is to supply the majority of electricity in this way, we must quickly consider alternative materials that are Earth-abundant, non-toxic and cheap. These are the materials that can get us to our goals more rapidly."

The team's top candidates for a replacement material are iron pyrite, copper sulfide, and copper oxide.  Of them, iron pyrite is the cheapest, being plentiful and easy to process.  While nanoscale science has shown that cells of such unconventional materials will experience modest efficiency losses, the researchers say that these costs will be easy offset by the decrease in raw materials and processing costs.

Professor Kammen concludes, "As the U.S. envisions a clean energy future consistent with the vision outlined by President Obama, it is exciting that the range of promising solar cell materials is expanding, ideally just as a national renewable energy strategy takes shape."

The team's research was funded by the U.S. Environmental Protection Agency, the Energy Foundation, the Karsten Family Foundation Endowment of the Renewable and Appropriate Energy Laboratory.  It appears in the journal Environmental Science & Technology.

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RE: How modest is modest?
By Solandri on 2/20/2009 2:12:25 PM , Rating: 2
The Volt is supposed to have a 16 kWh battery pack.

Sunlight at noon has an energy density of about 800 W/m^2. Figure you can cover the surface of a Volt with 2-4 m^2 of panels. Furthermore, assume they're the latest high-efficiency panels which convert 40% of the sunlight to electricity. That would yield 0.64-1.28 kWh per hour. So you'd need 12.5 to 25 hours of noon-time sun to fully charge a Volt's battery.

If you take more realistic figures of sunlight at a 45 degree angle, 2 m^2 of panels, and 15% efficiency, you get 0.17 kWh per hour. It would take you 94 hours, or over a week to fully charge a Volt's battery.

People vastly overestimate the power they can get from sunlight. Solar energy is abundant, but it's very low density.

RE: How modest is modest?
By JasonMick (blog) on 2/20/2009 2:25:35 PM , Rating: 2
Kudos, couldn't have calculated it better myself :)

One other tiny point to raise is that only the best lab cells are 40 percent efficient and if I recall that's concentrated solar. Top of the line commercial photovoltaic is around 20 percent so with your calculations it would take 25 to 50 hours for a volt to charge in OPTIMAL sunlight conditions.

An average hour in the sun might return about 1/100 of the battery charge needed. I don't see this as being cost effective for an installation costing $2,000 plus dollars and cutting down on your aerodynamics.

Solar farms are a great idea if solar can become cheaper by new materials and efficiency/manufacturing/installation improvements. Like you said, the energy is plentiful, just not dense.

Solar power for cars is about equally as much fun as flying cars and equally as practical.

RE: How modest is modest?
By ayat101 on 2/21/2009 1:20:09 AM , Rating: 2
... another thing to consider is how much the added weight of the solar cells and charger adds to the energy use of the car.

RE: How modest is modest?
By highlandsun on 2/21/2009 5:54:28 PM , Rating: 3
All negligible. You wouldn't sue crystalline silicon cells on a car, they're too fragile. You'd use thin-film cells, which would add less mass than a coat of paint. And on that score you'd make the car lighter because you wouldn't be painting the surface where the cells are mounted.

As for a charger: you're taking the DC output from a solar array and feeding it to a DC battery. You're not getting anywhere near an amp of output from the array, and if you arrange the parallel/series connections correctly you don't even need to do any voltage conversion. As such, the complexity here is also negligible.

But as already pointed out, none of this is worth doing because the amount of power you can collect from this surface area is also negligible.

Personally, I would still do it, because I drive a black car in Southern California, and it gets way too hot sitting out in the summer. A rooftop mounted solar array to drive the car's ventilation system while it's parked would be excellent. The array itself would keep things cooler simply by absorbing sunlight and turning a fraction of it into electricity instead of directly into heat. I used to have a contact at Sanyo Solar who sold me thin-film amorphous-silicon cells, but they seem to no longer be selling products to individuals, otherwise I would have done this already. And no, none of the clip-on-the-window solar powered fans are large enough/move enough air to keep the car cool, I've tried several.

RE: How modest is modest?
By MrTeal on 2/21/2009 11:38:36 AM , Rating: 2
You can get the latest and greatest triple-junction cells and get 40% efficiency for normal light. Of course, covering 2 m^2 would triple or more the price of the car, but what's several tens of thousands of dollars between eco-friends?

Thanks for posting a realistic number for solar conversion. I see people posting way too often that they'll cover their roof in 100 m^2 of 40% efficient PV cells, seeming to think that they can just go to wal-mart and pick them up, instead of the millions it would actually cost. Monocrystalline Si can get into the low 20s. Standard poly Si that almost all home installations use are stuck in the mid teens.

Alright, enough ranting.

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