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Oh come now. You repeated essentially exactly the same statement as GP and then claimed GP was wrong?!?!

If the OP's statement was true, most panels would need to be replaced by the 25 year mark, since the standard panel guarantee is a minimum of 80% at the 25 year mark. Very few panels are replaced as most do much much better.

And it's not a "guarantee". Nobody guarantees anything for 25 years.

Solar panel makers do exactly that. see http://us.sunpowercorp.com/support/warranty/

Solar panels are warrantied for maybe 1-3 years against manufacturing defects if you're lucky, and that's about it.

OK, I'm done with you. You clearly have never read a solar panel guarantee. Just follow the link.

no one would be building solar plants yet, . . .

That's odd, I just worked on a small project for a new solar power plant in Chicago, so, obviously, someone is building solar plants already.

Photovoltaics routinely exceed 20%.

No that is wrong, please don't disseminate this sort of misinformation. The most efficient PV panels you can buy today are rated less then 20% efficiency, and that's per cell, a whole panel will be several percent lower. That's in ideal conditions - heat, inverters, charge controllers, batteries all knock a big chunk of that efficiency.

No, you are wrong...well, not exactly wrong, but you too are spreading mis-information. My solar panels on Monday produced energy for the day at ~900 Wh/m^2, and that is AC watts, so not your "ideal" number, a real number complete with conversion losses. My city's 30 year maximum flat panel solar radiation exposure for the month of January (from here) was 5.6 kWh/m^2-day. So let's assume Monday matched that maximum, that means my system hit 16% real world efficiency. I don't have the most efficient panels you can buy today, today's most efficient panels outperform mine by over 15%. That's now approaching the 20% quoted by the grandparent. I agree, it is incorrect to state "photovoltaics routinely exceed 20%" in the context of AC watts, but it is correct to state panels approach 20% and therefore cells exceed 20%.

And as I stated in another post, it sure looks to me like economically my panels are kicking the tar out of this idea in terms of cost and production.

$38K? That seems expensive to me, but I don't know how big his system is. I'm putting one my house (waiting on electrical inspection) that is 4 kW, and it cost $22k.

Tracking down the original specs, he put in "27 Sunpower panels, each rated at 225W, for a total 6.1KW system." With various ancilliary installation features, such as the monotoring system, sounds like the price is about the same.

Sunpower makes very high end panels, for what it's worth-- he quotes 18% efficient.

If this were the case, there would be capitalists all over the world assembling massive solar arrays for electricity production.

*coughs*

No, suppose there aren't any companies like that that you can invest in that go around and build massive solar arrays for clients.

There is a physical limitation on the efficiency of any particular photovoltaic material, due to the fact that sunlight is a broad spectrum, and the bandgap of the semiconductor is a fixed quantity. For silicon-based PV, the theoretical maximum efficiency is something like 25-30% (sorry, I don't have specific figures). You can improve things by ganging several materials, with different bandgaps, together. Those are the so-called multijunction cells that get upwards of 40% efficient in the lab.

Quality silicon solar cells on the market today, without going to the extreme high end (in cost and efficiency), are more like 15% efficient. That might creep up some; for instance, you can pay a bit more and get 18%-20% efficiency. But, by and large, without some fundamental breakthrough, the efficiency isn't going to go much higher. Your best bet is to try and reduce the cost and increase the durability, so that they can become ubiquitous.

Solar Panels: 22% efficiency SunPower
Electrical Transmission: 92.8% efficiency (by jtoomim (217124) Alter Relationship on Thursday June 12, @06:10AM (#23761407))
Battery Charging: 85% efficiency John W. Stevens and Garth P. Corey
Electric Motor: 90% efficiency

78% loss -> 7.2% loss -> 15% loss -> 10% loss = 15.6% efficiency, not 2.5%.

If you don't factor in the "loss" in the efficiency of the panel to collect the rather amazing amount of energy produced by the sun (of which the Earth only intercepts a tiny fraction), the efficiency is in the 70% range.

The price would be pretty much the same whether it was US companies or French companies doing the drilling.

But it makes a big difference to both French and US companies who gets the money.

scale up solar cell production to the same level (and with the requirement that they be completely replaced every few years). Solar cells have gotten a lot cleaner than they used to be, but we're still talking about a LOT of them.

Solar cells last more than a "few years". You can find solar panels with warranties longer than 20 years. SunPower's panels have a 25 year warranty. As does some BP panels. Here are more panels with 20 or 25 year warranties. And those were just the first 3 results from googling "solar panels" warranty.

That's being done now... see sunpower: http://www.sunpowercorp.com/ 22% efficient pannels and amazing per watt pricing.

There is, as the article mentions, the problem of electron-hole recombination.

Another difficulty with semiconductor photovoltaics, not addressed by this new development, is that the semiconductors make poor use of energetic photons. There are limitations, derivable from solid-state physics, that limit the maximum light-->electricity efficiency of photovoltaics. A little background:

Depending on the chemistry, the bandgap energy of the semiconductor corresponds to a photon of a certain minimum energy. A photon with less energy (longer wavelength) than the bandgap energy will not have enough umph to create an electron-hole pair, while a photon with energy >= the bandgap energy can create an electron-hole pair. In silicon-based semiconductors, the bandgap energy corresponds to a photon in the very near infrared, almost a visible red.

The electrical energy you get from the electron-hole pair comes from those charges being separated by the electrical potential at the semiconductor junction. Unfortunately, it doesn't matter if the electron-hole pair was created by a red photon, a blue photon, or ultraviolet. You'll get the same amount of electrical energy out of the solar cell from any of these photons.

However, the red, blue, and UV photons have significantly different energies due to their different wavelengths. The UV photon, though more energetic, will produce the same electrical energy output as the less energetic red photon. If you were to shine only red light on the solar cell, it would make quite efficient use of them. Unfortunately, red is only one component of the solar spectrum. The solar cell makes poor use of the higher-energy photons in the solar spectrum, and thus has a seemingly poor light-->electricity conversion efficiency.

If everything else went perfectly, the solid state physics at work limit the maximum efficiency for silicon solar cells to about 25%. Good cells mass-produced today top out at about 21%. One can create multiple junction cells to capture different segments of the spectrum at higher efficiency. Consider this chart of maximum efficiency under lab conditions.

There is, as the article mentions, the problem of electron-hole recombination.

Another difficulty with semiconductor photovoltaics, not addressed by this new development, is that the semiconductors make poor use of energetic photons. There are limitations, derivable from solid-state physics, that limit the maximum light-->electricity efficiency of photovoltaics. A little background:

Depending on the chemistry, the bandgap energy of the semiconductor corresponds to a photon of a certain minimum energy. A photon with less energy (longer wavelength) than the bandgap energy will not have enough umph to create an electron-hole pair, while a photon with energy >= the bandgap energy can create an electron-hole pair. In silicon-based semiconductors, the bandgap energy corresponds to a photon in the very near infrared, almost a visible red.

The electrical energy you get from the electron-hole pair comes from those charges being separated by the electrical potential at the semiconductor junction. Unfortunately, it doesn't matter if the electron-hole pair was created by a red photon, a blue photon, or ultraviolet. You'll get the same amount of electrical energy out of the solar cell from any of these photons.

However, the red, blue, and UV photons have significantly different energies due to their different wavelengths. The UV photon, though more energetic, will produce the same electrical energy output as the less energetic red photon. If you were to shine only red light on the solar cell, it would make quite efficient use of them. Unfortunately, red is only one component of the solar spectrum. The solar cell makes poor use of the higher-energy photons in the solar spectrum, and thus has a seemingly poor light-->electricity conversion efficiency.

If everything else went perfectly, the solid state physics at work limit the maximum efficiency for silicon solar cells to about 25%. Good cells mass-produced today top out at about 21%. One can create multiple junction cells to capture different segments of the spectrum at higher efficiency. Consider this chart of maximum efficiency under lab conditions.

Microsoft already has solar power on its campus.

Something seems odd about installing solar panels in a city famous for grey overcast skies, but the panels work nonetheless. :)

Given the success of NASA in this area, I don't really see how anyone can compete with that braintrust and bankroll. Given the same requirements, I could likely build something similar to Atair's attempt in my garage. I'm very unimpressed. Plus, TFA seems like a weak PR attempt from a fringe, wannabe defense contractor.

Thankfully, there has been building interest in renewables, principally photovoltaics and wind power. At this point, the lifetime cost of a wind power installation (of size greater than, say, 1 MW) is on par or even less than traditional energies like gas and coal-fired plants. Meanwhile, the market cost of 20% silicon-based solar cells is down to something like $3-4/W, depending on how the market for semiconductor-grade silicon goes.

One of the major setbacks in the deployment of such energy is the physical infrastructure in the capital cost. While the solar cells are becoming rather cheap, the structure to support/protect them, and the electronics to interface them with the grid cost at least as much. In both the case of wind and solar, since there is low maintenance and basically no consumables, the lifetime cost of and installation is 90% upfront capital cost. For a coal or gas fired plant, or nuclear, the upfront capital cost is something like 40% of the total cost of running the plant over its lifetime, while maintenance and the cost of consumables take up the rest.

The end result is that people balk at the huge upfront costs of renewable power installations, even though the lifetime costs are nowadays comparable with traditional electrical power generation facilities. However, there are two situations that can give renewables an edge. The first we are already experiencing: the cost of consumables and maintenance are on the rise. Natural gas costs are increasing, coal-fired plants have to run cleaner, and nuclear is an ever-increasing headache.

The second, and more relevant, situation that favors renewables (and the point of TFA), is that there are some situations where one really, really needs electrical power, and is faced either with the choice of an expensive installation cost for renewable power, or a really expensive cost for shipping in the consumable fuel (and someone who can work the power generator itself, which ain't as easy as it sounds). In the case of remote power generation (for relay stations on the side of a mountain, for instance), in very rural areas with little or no road access (developing nations like Afghanistan), or in a disaster situtation where the usual delivery infrastructure has completely gone to hell, the scales tip away from things like petroleum, gas, and coal fired generators and squarely into the arena of renewables.

What these guys are doing is demonstrating that not only is the technology mature enough for long duration, high capacity, low maintenance remote power generation, but that it is rugged enough to be deployed anywhere, anytime, where it is needed. Bravo!

Indeed, I took the cell numbers as functionally equivalent to module efficiency (ie mirrors can be 98+% efficient). But reading the literature, It's clear that cheap is the goal (cheap focusing elements). In fact, the production price for multijunction concentrators being discussed is 12-50 cents/Wp. WOW! $0.12/Wp for 30 years is $0.0015/kWh! (of course this doesn't include BOS, but even with, its amazing)
Commercial Efficiencies:
Entech - 30% net concentrator efficiency, 33% cells (2001)
Sharp - 28% net concentrator efficiency (FYI-uses non imaging optics)
Sharp - 17.4% MODULE efficiency (not cell)
Sunpower - 16.5% MODULE efficiency (21.5% cells)

Now take into consideration that the spectrapower cells Entech is using are now up to 37.3% (2004) efficiency, which will increase module efficiency to 33.5% from their 2001 announcement (which is in line with a claims of the VC I spoke with).

So at 30% efficiency (using published value) we need to increase our land base values by 33%. So All US ENERGY Needs from 13,491 Mi^2 or 5% of TEXAS (including shading at an average of 1800 kwh/m^2/year).

Thanks for calling that one, I'll update my database of facts. I haven't been reading the solar journals very closely over the last 4-5 years as the company I am working for is developing storage technologies, so I put most my time that technology and market trends therein (which we will get to).

People are already doing this of course - the Helios project is one that comes to mind, as an unmanned craft intended to be capable of flying for six months without landing - a cheap atmospheric alternative to satellites. not particularly informative link