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Solar Cell Achieves 40% Efficiency
Fysiks Wurks found on the U.S. Department of Energy website news of a breakthrough in solar energy efficiency. From the article: "...with DOE funding, a concentrator solar cell produced by Boeing-Spectrolab has recently achieved a world-record conversion efficiency of 40.7 percent, establishing a new milestone in sunlight-to-electricity performance." A page linked from Wikipedia's article on solar energy calculates the land area that would need to be covered by solar collectors at 8% efficiency to meet the world's energy needs (using 2003 figures). At 40% efficiency, it looks like a square 265 miles on a side in the American southwest would do it.
So it's a bit unclear what the article means by 40% efficient as the article seems to confuse the concentrator part of the solar cell with the multi-junction part. The concentrator doesn't make the device more efficient at converting solar radiation into electrical power, it just concentrates the light so you don't have to use as large of a device. The idea being that the solar cell material is expensive but the optics are relatively cheap, so you might as well focus as much light on the device as it will absorb and still function.
The multi-junction part comes from the idea that you can, using a solar cell, only extract as much energy from a photon as the size of something called the band gap of the material that the cell is made from. At the same time, a solar cell can only absorb photons with energies higher than the band gap. If the bandgap is small, as it is in silicon, then you can absorb most of the suns rays, but you can only get about 1 electronVolt of energy out of each one no matter how much energy the photon has. Since the bulk of photons emitted by the sun have more than 1 electronVolt of energy Si solar cells waste alot of the energy in sunlight as heat. If you make the solar cell out of a semiconductor with a larger bandgap then you absorb fewer photons (more of the solar spectrum lies below the critical energy for absorption) but you extract more energy from each photon. So, for a solar cell made from one material there is a sweet spot in terms of the bandgap that maximizes the energy extracted. Multi-junction cells try to overcome this by combining multiple devices with different bandgaps so that you can maximize both the total number of photons converted to electricity and the energy extracted from each photon.
In addition, 40.7% is just a bump up from 39%, which (apparently) Spectrolab has been achieving for the better part of the year. They may be very close to high-volume production. Direct photovoltaic solar generation is an immediate revenue source, but solar energy can be directly applied for other processes, the most notable being desalination.
And hydrogen transports just as easily as oil via the same infrastruture.
Bzzt! Wrong answer. Hydrogen requires a completely different infrastructure that has never been massively developed. Transporting hydrogen trapped in a hydrocarbon is feasible and could use the same infrastructure, but hydrogen itself is a much more complicated issue. You either need to cryogenic cooling or you need to build infrastructure that has low hydrogen diffusion and low hydrogen embrittlement (and probably very high pressure to move a significant energy density of hydrogen around if you go the gaseous path). People who want hydrogen for various industries tend to steam reform it from hydrocarbons instead of using this oil infrastructure you think can transport hydrogen.
Contact your local power company. Many (such as LIPA) will pay for a large percentage of your costs.
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I don't know about how long ago you are talking, but the Energy return on investment varies between a factor 4 and a factor 17 for current solar cells, rather than a number below 1 as you are suggesting.
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A student at The Univ. of California, Santa Barbara just presented research showing the use of multi-junction devices using Gallium Nitride. This is awesome because Nitride materials are very well suited for a HUGE amount of the sun's radiation, and since he managed to perfect a way of sticking several layers of differently absorbing Nitride Materials together in ONE device, we could theoretically see solar cells that absorb the Entire spectrum of the sun's rays in the near future!
u ll-spectrum-solar-cell.html
e /2005/11/28/review07.pdf
Here's some links:
Indium-Gallium-Nitride can be made to absorb the entire spectrum of solar rays:
http://www.lbl.gov/Science-Articles/Archive/MSD-f
Tunnel Junctions - this is how you stick together many different layers of material, each layer with their own optimal absorption range (in terms of wavelength, aka. color):
http://www.hitachi-cable.co.jp/ICSFiles/afieldfil
(sorry, this is the best I could do, there was no simple paper explaining a tunnel junction. "tunnel" is for electron tunneling...)
In essence, you have different layers that absorb only one range of wavelengths (colors of light), and whatever isn't absorbed goes straight through, and the next layer absorbs another range, etc. etc.
As an aside, did you ever wonder how blue LEDs & lasers finally managed to get working? Nitrides paved the way for emission (and absorption) in a range of visible wavelengths, including blue. This is also why they're great for this application.
At current prices, you'll need a little more than 6 months on your mortgage. Assuming you're in Britain, which by the usage of your language is probably reasonable...
I bought an 80 watt peak solar panel in the summer, basically as a fun project and to investigate the practicality of generating some of my own electricity. Here is how it works out, using a monocrystalline panel (the most efficient panel commercially available at present):
Peak power is produced only within about an hour or so each side of mid day on a bright, cloudless, hazeless sunny day.
Three hours before or after mid day, the unit produces about 50% of peak.
Five hours before or after mid day, the unit produces around 10-15% of peak
At mid day, summer time haze with 10 miles visibility will cut output to around 80% of peak
At mid day, with thin cirrus clouds (still bright sunshine), output is around 50%
At mid day, on a bright cloudy day where shadows are still cast, output is around 15%
At mid day, on an overcast day, output is generally 5% or less.
In the winter, I've never seen the unit capable of producing more than about 25% of peak on the brightest winters day.
All in all, the average output even in the summer will only be 5% of peak (because of night time, and cloudy days). Winter time is even worse. So if you want to make sure you have an average of 200 watts - which really isn't a lot, but if you can store it or put it back on the grid it'll make your house more or less neutral in terms of the electricity you use, if you have the normal domestic cycle of being out and not using much electricity during the day. To get that average of 200 watts, you'll need 4000 watts peak of solar panels.
80 watt panels cost (in quantity) around £250 a piece. That'll cost you £12,500 *just* for the panels, without a grid tied inverter and storage system or installation (probably another 4 to 6 grand) - to get a measly average of 200 watts - i.e. just enough to power one Pentium 4 computer continuously. It's simply not worth doing at all unless you can put it back on the grid (not many electricity companies let you do that - yet), or store it in batteries - since if you have a normal domestic cycle, while your solar panels are producing near peak you will be away from the house and letting three or four thousand watts go wanting. You'll probably need three grand's worth of batteries if you can't sell back to the grid - and even deep cycle leisure batteries are going to need replacing at least once every 10 years. This is for a system which will only work reasonably well in the summer. In the winter, when the days are short and you need the most power, it'll hardly contribute anything - perhaps you'll get 50 watts average from £12,500 worth of solar panels.
If solar panels were 1/10th of the price they are now - yes, it'd be worth it. I'm waiting for the breakthrough in price, not efficiency (if the efficiency brings the breakthrough in price all the better). Even a moderate sized south facing roof - I've calculated just my shed roof replaced with solar panels could produce 1kW peak - is large enough for a decent peak output using current monocrystalline panels. Price is everything. If I could get the panels at 10% of what they cost now, you bet my shed roof (my only south facing roof) would be covered by the spring. But at the current price point? It's simply not affordable for the meagre amount of electricity you get. It's a shame because the panels aren't visually intrusive and they are silent and almost maintenance free, unlike wind turbines. I really really want solar panels to be worthwhile - but at the moment - at current prices, they simply aren't.
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I'll get about a quarter of the cost back in refunds from the power company right up front. The remaining cost (around $25k) will roll into my mortgage, which will increase it by around $100 per month (30 year mortage at 6%). My monthly electricity bills should be reduced by at least $150. It just makes sense.
The fact that I care about the environment just makes it an even better deal.
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