Solar Cell Achieves 40% Efficiency 632
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.
Re:Cost is the issue (Score:5, Informative)
Re:Cost is the issue (Score:2, Informative)
Aren't the two related?
Also, FTFA:
where the facts? (Score:5, Informative)
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.
Re:Cost is the issue (Score:5, Informative)
No, not pale, pink-eyed mutants... (Score:1, Informative)
Here's the link [wikipedia.org] you forgot.
Re:transport losses? (Score:5, Informative)
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.
Re:Panels On The Roof (Score:5, Informative)
Re:where the facts? (Score:2, Informative)
Re:transport losses? (Score:2, Informative)
We don't?
Wait, we do. And that's the prime economic reason developing alternative energy strategies is in the US's (and everyone else's) best interests, despite our reliance on our current profits in the energy market.
Figures a bit out (Score:4, Informative)
13.9 trillion kW/h / 8776 (hours/year) = 1.58TW
This figure is comparable to the statement in the wikipedia that 2001 average world consumption was 1.7TW in 2001 [wikipedia.org]. So our sources agree within a reasonable margin.
According to the wikipedia, the energy density from solar energy reaching the surface as a global average is 170 W/m2 [wikipedia.org]. At 40.7% efficient, that's 69.2W/m2.
Using the lower figure of 1.58TW calculated above, you'd need 22.8 x 10^9 square meters, or approximately 8800 square miles of solar cells to meet 2001 world demand. (Or "just" 1900 square miles to meet the peak US demand of ~3 trillion kWh in the late 90s). Of course, these areas halve if sited in an area of the US where the solar energy density is 375 W/m2 (4000 square miles for world demand, 860 square miles for US demand).
Neither correspond to the whopping (265x265) 70000 square miles the article summary claims. Sorry kdawson, looks like you're a magnitude out!
Re:transport losses? (Score:5, Informative)
If you are just going to put bare panels somewhere it makes more sense to stick them on the top of existing poles instead of in some big facility since they act as discrete units anyway. Once they get rolled out there really isn't much that has to be done with them - the photovoltaics that existed when Einstein was young probably still work.
Personally I think we are already seeing the start of one of the major potential uses for photovoltaics - appliances that don't have to be plugged into the grid. If the prices come right down things like solar mobile phone chargers may well become mainstream.
Re:Cost is the issue (Score:5, Informative)
I don't know about how long ago you are talking, but the Energy return on investment [wikipedia.org] varies between a factor 4 and a factor 17 for current solar cells, rather than a number below 1 as you are suggesting.
Re:Cost is the issue (Score:2, Informative)
Gallium Nitride (Score:5, Informative)
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.
Re:transport losses? (Score:3, Informative)
Re:life span (Score:3, Informative)
http://en.wikipedia.org/wiki/Photovoltaic?section
I tried to calculate energy payback-time for different cells, and got results ranging from 8 months to 2 and a half years.
Even extreme PV-Cells bashers don't succeed in proving that payback-time exceeds 5 years, which still lefts you 3 times as much "free" energy.
Re:where the facts? (Score:5, Informative)
It's not necessary to do it that way. The way these multi-junction cells work is you have several layers of different semiconductor materials (with varying band gaps as the parent said). The material with the largest band gap is on top and the band gap of the material decreases as you go down the layers of the device. If a photon is not absorbed in the first layer (meaning the photon doesn't have very high energy, since, as the parent also said, the photon must have greater than the band gap energy to be absorbed), then it continues on to the next layer to be absorbed, then the next layer. This way, you are extracting the maximum amount of energy out of each photon.
That isn't a perfect explanation and any experts out there, please correct anything that's wrong.
Good point "National Security" (Score:3, Informative)
In Australia a few years ago there was a major disaster in the gas supply system that took a whole season to fix. The entire southern region was without gas for heating and cooking for weeks. Luckily the electricity system was still operational but a simultaneous failure would have resulted in a calamity.
Re:transport losses? (Score:5, Informative)
And even at low power levels, your fuel will keep fissioning merrily along, so in essence you're throwing away a finite resource. Also, your buffer will be significantly more expensive than the solar energy you're using as primary.
If you have an abundant source of renewable energy, you're better off using some of that to drive a buffer. Hydro buffer plants such as Dinorwig (see elsewhere in this discussion) have been shown to work well.
Re:transport losses? (Score:4, Informative)
Grid power would fall in price - because a) there is reduced demand for it (everyone is using their own panels) and b) supply would increase (people can sell the excess electricity from their panels back).
Re:Cost is the issue (Score:5, Informative)
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.
Re:transport losses? (Score:5, Informative)
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.
Re:transport losses? (Score:3, Informative)
1 Manufacturing solar cells is currently an extremely energy intensive process, it also creates a startling amount of toxic waste. Solar Cells need to be replaced on a regular basis as well.
2. Solar Cells are extremely expensive. I don't know about these 40% jobs, but something tells me they won't be a lot cheaper than our current top of the line cells. We're talking about a project in the trillions of dollars to do what you describe.
Re:transport losses? (Score:3, Informative)
Re:transport losses? (Score:3, Informative)
Right off the top you get $29,000 from other oregon and city taxpayers to buy your system. In any state without subsidies, that means over THIRTY YEARS longer payout period. Most solar cells degrade substantially by 20 years (10-20% less power output). Likewise, I'm betting like MOST states, that not just anybody can get those $29k in credits in Oregan. There is probably a fairly limited budget (a few million) and once that is gone each year, there are no more subsidies until the next calendar year.
I'm unclear how I'm supposed to use Federal Depreciation if it is not for a business or rent house. Granting that I can somehow use it for personal income taxes tho... it sounds like it would be a deduction, not a credit. That would mean it would lower your INCOME by roughly $3 grand a year- which would mean it would lower your TAXES by $1 grand a year at most. That lowers your savings from $13,000 to $5,000. That means your system costs $8,000 more --- that's 10 years more to cover costs. So you are up to 16 years, using your figures, and assuming you are lucky/smart enough to be one of the people that gets the subsidies.
Using your figures, for the 40 some-odd states where we only get the federal credits, the payout period is longer than the likely lifespan of the item.
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Now one thing we need to remember is this: Power is appreciating about as fast as inflation. That means your $813 bill today is going to be $1600 in 10 years and $3200 in 20 years. That works in your favor. It helps home buyers too. In 1995 my payment was $700 a month and rent was $655 a month. Today my payment is $700 a month and rent is $1100 a month. In 2015, my payment will be $700 a month and rent will be roughly $2200 a month.
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No.. It's not just an inverter. If you are connected to the grid you need a special circuit box that won't allow power to flow backwards into the grid unless the grid has power. I think it is called a reverse switchback circuit breaker.
The inverter converts DC - > AC.
The charge controller keeps the batteries charged and cycled at the proper levels so they have optimum lifespan.
The switchback? circuit box (can't remember the name exactly) keeps your 1.21 gigawatts of power from killing electric company linemen.
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No need to be insulting about the AC ideas. If solar power drops by an order of magnitude it is suddenly a very clever and reasonable way. $900 of solar power and a simple $200 window unit and you don't need to run your central AC during the day at all. No need to upgrade your electrical system. No need to have charge controllers, batteries, etc.
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There are several companies on the edge of dropping the price by an order of magnitude. Two of them basically print solar material with nano-particles. If any of them succeed and solar power does drop to 10% of the current price and becomes unbelievably easy to install (picture unrolling a 50'x3' long strip on your roof that costs about $3000 and produces 1.5 mw of power during the day with no clouds and it has a plug on one end to hook to another strip- no panels, no sun tracking arrays- nothing to break- no cells to be corrupted by water leakage. cool stuff)
As far as the other things- I'm already using efficient appliances, have a programmable thermostat, added radiant barrier, and use florescent lights.
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I'm pro solar power. It just isn't practical yet unless you can get other people to help you buy it through subsidies. That's only an option in some states.
Solar is already cheaper in some areas (Score:5, Informative)
Re:transport losses? (Score:3, Informative)
Carbon monoxide is highly flammable. It has the same NFPA rating as diesel (2). Burn it, recapture the energy. With a good countercurrent heat exchanger, you approach 100% efficiency. You can never reach 100%, and eventually it's not worth the effort to try for more, but you can get close.
It's less efficient than burning all of the natural gas to heat your water
Of course it's less efficient than burning the natural gas when you only consider the heat; you're getting hydrogen, too, and that's where part of the CH4's energy ends up. Burn the carbon monoxide, and your net result is:
H2
CO2
Heat
"Wasted" energy will end up as heat. Yes, there will be no perfect heat exchanger (which is why I said "almost"), but countercurrent heat exchangers can do a very good job.