Updates on Solar Energy

Stephen DeAngelis

August 29, 2008

Yesterday, Barack Obama accepted the Democratic Party’s nomination to run for the office of the President of the United States. Nothing surprising there — he has been the presumptive nominee for some time. In political advertisements leading up to his nomination, Obama trumpeted that he is the candidate of change and the champion of alternative energy. Last night during his acceptance speech he reiterated his claims that if elected president he will create 5 million new jobs in the alternative sector by investing $150 billion dollars in that sector over the next decade. Voters remain wary of such political promises knowing that they are often hyperbole. What sounds good during the election season is often difficult to implement once the campaign ends. With the price of oil frightfully high and analysts predicting it will remain there, politicians from both major U.S. political parties have been declaring their support for “energy independence.” With the airwaves filled with such talk, one would think that the politicians would have rushed build up their alternative energy credentials before the election, but they have dithered instead [“Freezing the Sun,” The Economist, 28 June 2008 print edition].

“It seemed so promising—mirrors sprawled across desert land in the scorching south-west delivering clean electricity and helping to wean Americans off imported fossil fuels. Some scientists and industry developers claim that Nevada’s empty and sun-drenched expanses alone could supply enough terawatts to power the entire country. Now even the optimists fear this wonderful prospect may be a mirage. Congress has been dithering over extending a valuable investment tax credit for solar-energy projects, which solar advocates say is critical to the future of their industry but which is due to expire at the end of the year. The latest attempt failed in the Senate earlier this month: prospects for a deal before November’s presidential and congressional elections now look dim. Uncertainty has led some investors to delay or abandon projects in the past few months. Rhone Resch, the president of the Solar Energy Industries Association, said if the tax credits are allowed to expire at the end of the year, ‘it will result in the loss of billions of dollars in new investments in solar.’

Just as surprising as the lack of concern in Congress, was the fact that in June the U.S. Government put a freeze on using federal lands to produce solar energy.

“Further dampening hopes for a big solar-energy boom, the federal Bureau of Land Management (BLM) has abruptly slapped a moratorium on new applications to put solar collectors on federal land. The agency says it has a backlog of more than 130 applications and needs to conduct a region-wide environmental-impact study on the industry before it will accept any more. The study will take 22 months to complete, however. Few argue against trying to preserve precious water sources and protect desert tortoises and other creatures that might not enjoy cohabiting with sprawling fields of mirrors. But many solar advocates wonder why the government is not acting as cautiously when it comes to drilling for oil and gas.”

The Bush administration is not known for taking positions favoring the environment, which made this action all the more curious.

“Senator Maria Cantwell, a Democrat from Washington state, wants a congressional probe into the proposed moratorium. ‘The fact that the BLM pops this out without people even knowing about it, especially when solar thermal looks extremely promising as a baseload [power source], is not right,’ she says. Harry Reid of Nevada, who is the majority leader in the Senate, also condemns the BLM’s freeze, saying that it could ‘slow new development to a crawl’. The BLM is not without its supporters, however. At a public meeting on June 23rd in Golden, Colorado, Alex Daue, of the Wilderness Society, said that his organisation supports renewable-energy development as long as it doesn’t damage other important resources. The message is clear: no rubber stamps, even for renewable energy.”

The BLM’s action is unlikely to salvage any lasting legacy for the Bush administration, but it is surely going to get additional attention as the campaign heats up. Fortunately, research into solar power has not stopped just because the federal government has declared a moratorium on using public lands for fields of solar panels. According to The Economist, scientists have discovered “another new way of turning sunlight into power” [“Guiding Light,” 12 July 2008 print edition].

“The main impediment to the widespread use of solar power—clouds and nightfall aside—is the cost of the silicon cells that actually convert the sun’s rays into electricity. To keep the expense down, people have been searching for ways to minimise the size of solar panels relative to the amount of light they can harvest. Often, this is done using clunky pieces of kit called solar trackers, which tilt an array of mirrors so as to direct large amounts of sunlight onto small, high-performance cells. Such trackers, however, are expensive to install and run, and are prone to heat the cells up too much, which reduces their efficiency and may damage them. That, in turn, means the cells have to be fitted with pricey cooling systems. An alternative now being tested is called the luminescent solar concentrator (LSC). Instead of focusing the sun’s rays on a cell, as a solar tracker does, an LSC first traps them, wherever they have come from, and then delivers them to the cell using what is known as a waveguide. No moving parts are involved.”

One of the reasons that the BLM put a moratorium on solar fields on federal land, you recall, was the fact that huge solar arrays require water for the cooling systems — and water is precious and scarce in the deserts of the southwest. If I am reading the article correctly, the LSC approach reduces or eliminates the need for pricey cooling systems and the water they need.

“Many researchers around the world are working on LSCs. The latest group to report, in a paper in this week’s Science, is led by Michael Currie and Jonathan Mapel of the Massachusetts Institute of Technology. They reckon they can triple the efficiency of such devices, and thus launch them on the path to success. A standard LSC is made of a sheet of plastic containing molecules of dye and stretched within a frame that is, in effect, a single long, thin solar cell. The dye absorbs incoming sunlight, and then re-emits it. The re-emitted light is trapped inside the plastic sheet by a process called total internal reflection, which causes it to bounce between the sheet’s surfaces without being able to escape, and thus guides it towards the circumferential solar cell. (Optical fibres work in a similar way.) Alas, this approach, too, has its limits. In particular, some of the light is reabsorbed as it bounces around, and is lost as heat. The more dye molecules there are, the more light is lost. On the other hand, you want a lot of dye molecules in order to absorb a lot of light in the first place. A difficult balance has to be struck. Dr Currie and Dr Mapel think they have found a way round this problem and, as a bonus, one that will also make LSCs easier to manufacture. Their answer is to get rid of the plastic sheet. Instead, they spray a sheet of glass with a mixture of dyes combined with a substance called tris(8-hydroxyquinoline) aluminium. In combination, the dyes and the glass act as the waveguide, preventing light from escaping. Meanwhile, the interaction between the different dye molecules and those of t
he tris (8-hydroxyquinoline) aluminium allows a quantum-mechanical phenomenon, called Förster energy transfer, to come into play. This eliminates the reabsorption loss by ensuring that light is re-emitted at a frequency which the dye molecules cannot then reabsorb.”

Pretty cool trick, but the Currie and Mapel have one more trick up their sleeves.

“On top of this—literally—Dr Currie and Dr Mapel have come up with another trick: placing a second sandwich of dye and glass over the first. The upper layer of dye intercepts high-energy light, such as ultraviolet. The lower one captures longer wavelengths that have passed unperturbed through the upper, and also any lower-energy light that has been re-emitted within the top layer and somehow escaped. The upshot is a device that, even as a prototype, converts ten times more of the incident light into electricity than a conventional solar cell—and another contestant in the increasingly crowded race to replace old-fashioned power generation with electricity from the sun.”

A ten-fold increase in power from solar cells while reducing their production costs is impressive. Such cells could make wider use of solar panels more than political hyperbole. The question is whether the U.S. utility system is ready for a big increase in alternative energy production. The answer may be that it is not [“Wind Energy Bumps Into Power Grid’s Limits,” by Matthew L. Wald, New York Times, 26 August 2008].

“The dirty secret of clean energy is that while generating it is getting easier, moving it to market is not. The grid today, according to experts, is a system conceived 100 years ago to let utilities prop each other up, reducing blackouts and sharing power in small regions. It resembles a network of streets, avenues and country roads.”

Wald’s article focuses on wind generated electricity rather than solar power, but the transmission problems are the same.

“While the United States today gets barely 1 percent of its electricity from wind turbines, many experts are starting to think that figure could hit 20 percent. Achieving that would require moving large amounts of power over long distances, from the windy, lightly populated plains in the middle of the country to the coasts where many people live. Builders are also contemplating immense solar-power stations in the nation’s deserts that would pose the same transmission problems. The grid’s limitations are putting a damper on such projects already. … ‘The windiest sites have not been built, because there is no way to move that electricity from there to the load centers,’ [Gabriel Alonso, chief development officer of Horizon Wind Energy] said. The basic problem is that many transmission lines, and the connections between them, are simply too small for the amount of power companies would like to squeeze through them. The difficulty is most acute for long-distance transmission, but shows up at times even over distances of a few hundred miles.”

If Barack Obama’s dream of increasing the use of alternative sources of energy is to come true, there will have to be a major investment in upgrading the transmission grids across which such energy must flow. President Eisenhower changed the face of the nation when he proposed and starting building the interstate freeway system. The next president will have the same opportunity to invest in America’s infrastructure and its future by creating the “superhighway” electrical grid system that will be needed to keep the country’s economy progressing.