Question: How long does it take for the sun to radiate more energy onto the Earth's surface than society consumes in one year (about 4.1 x 1020 joules)?
Anyone? Yes, you in the back.
“About an hour”
Correct. And that is why photovoltaic (PV) energy is the fastest growing electricity generation technology in the world. Market statistics show the steady progress solar energy is making in the U.S. and the notably faster pace of development in Europe and Japan.
For instance, the European Photovoltaic Industry Association (EPIA) has published a report that put global PV generation growth in 2010 at approximately 16 GW (gigawatts). The total installed capacity has now reached at least the 37 GW mark and could be as much as 40 GW.
In Europe PV is the leading renewable energy technology in terms of new capacity growth--almost 13 GW. Germany continues to the global PV market leader, adding over 6.5 GW of new installations to the already existing 9.8 GW of PV systems in place, according to EPIA. At the end of 2010, the cumulative installed capacity of PV in the EU amounted to more than 28 GW, with an energy output that equals the electricity consumption of around 10 million households in Europe.
According to EPIA estimates, over 3GW of new PV installations were outside Europe last year with the main contributors coming from Japan, where almost 1GW MW was installed, followed by the US with around 700- 800 MW.
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Looking ahead, in the U.S. the PV market will rise almost tenfold, from less than half a gigawatt in 2009 to more than 4 GW in 2014, according to the market research firm iSuppli.
An even more optimistic forecast comes from the Washington-based Solar Energy Industries Association. According to a report issued by the trade group conmsisting of 21 associations from around the world and presented at the COP16 climate summit in Cancun, global development of photovoltaic and solar thermal power projects could reach 980 GW by 2020, cutting emissions of carbon dioxide by about 570 million tons, the equivalent of taking 110 million cars off the road. The same report predicts an increase in total U.S. solar capacity U.S. to 139 GW.
To be fair, the report does not address where the capital needed to manufacture that much capacity would come from-- critics characterize the cost as “staggering”—and would also require a significant shift in U.S. energy policy.
Technical progress, too
To get anywhere near to that target, the production of solar cells will need to be ramped up by a few orders of magnitude, while their costs must remain sufficiently low.
The problem is, solar’s efficiency/cost/production practicality equation reads a bit like the Heisenberg Uncertainty principle In quantum mechanics. The Heisenberg uncertainty principle states that certain pairs of physical properties, such as position and momentum, cannot be simultaneously know with precision. That is, the more precisely one property is measured, the less precisely the other can be measured.
The solar conundrum is that seemingly revolutionary cell architectures or record-breaking cells tend to be produced in an unconventional way, so while they are technologically interesting, they are also highly unlikely to be manufactured on a large scale anytime soon. For instance, while the best efficiency reached for silicon cells stands at close to 25 per cent now, this record figure was achieved using small-scale cells not suitable for volume manufacture at reasonable cost.
While we are on the subject of physics the Shockley–Queisser limit refers to the maximum theoretical efficiency of a solar cell using a p-n junction to collect power from the cell. It was first calculated by William Shockley and Hans Queisser in 1961. The limit places maximum solar conversion efficiency around 33.7% assuming a p-n junction band gap of 1.1 eV (typical for silicon).
Put another way, of all the power contained in sunlight falling on a silicon solar cell (about 1000 W/m²), only 33.7% of that could ever be turned into electricity (337 W/m²). Modern commercial single-crystalline solar cells produce about 22% conversion efficiency,
Thin film PV panels, made of such materials as copper indium gallium diselenide (CIGS) applied to a backing such as glass, flexible metallic foils or high-temperature polymers, are manufactured in a different way to traditional crystalline silicon PV panels; the manufacturing process is faster, uses less energy and requires fewer raw materials. As a result thin film panels potentially could be less expensive.
I said potentially less expensive because unfortunately thin film PV panels are also less efficient..In its recent report “Tracking the Sun III: The Installed Cost of Photovoltaics in the U.S. from 1998-2009” Lawrence Berkeley Laboratories researchers found the efficiency gap of thin-film modules, even if lower cost, would tend to engender higher balance of system costs. The study shows that thin-film systems in several size ranges had average installed costs higher than comparably-sized crystalline systems ($0.8/W higher among ≤10 kW systems and $0.4/W higher among 10-100 kW systems).
By shrinking the thickness of solar cells down toward the nano-scale, researchers think that energy outputs could grow significantly. Scientists at Stanford University, for instance, have found a way to trap light in organic solar cells. The idea is that the longer light is in the solar cell the more electrons will be generated. We know that very thin solar cells can absorb sunlight more efficiently than the thicker silicon cells used today, because light behaves differently at scales around a nanometer (a billionth of a meter).
Researchers have calculated that by making the organic layer much thinner than the wavelength of light and by roughing it up so that light is trapped and has to ricochet around inside the film of a solar cell the film could absorb as much as 10 times more energy from sunlight than was previously thought possible.
Thin solar cells are also the object of research at Belgium’s IMEC, which is targeting solar cells that eventually will be only 40µm thick with efficiencies above 20% for large-area silicon solar cells. At the 2010 European Photovoltaic Solar Energy Conference and Exhibition (EUPVSEC) an IMEC team showed how relatively simple changes had delivered crystalline silicon cell efficiencies of up to 19.4 per cent. IMEC’s progress results from changing the contact material, replacing the silver screen-printed contacts with plated copper contacts to raise the conversion efficiency from 19.1 per cent to 19.4 per cent. The improvements were obtained at IMEC’s new solar cell process facility in Leuven, Belgium, where the institute is aiming to bridge the gap between pilot-scale and industrial-scale production.
