According to the Pew Center on Global Climate Change, the number of states that have adopted renewable portfolio standards stands at 26, with more states poised to jump on the bandwagon. These mandates require electric utilities to provide a percentage of their power from renewable sources like solar and wind. The mandates, accompanied by government subsidies and incentives, have companies scrambling to develop low-cost, highly efficient products to meet the demand for alternative energy sources. Three organizations hope to cash in on the green movement by developing new technologies -- technologies that may redefine the solar energy industry.

Thin and Flexible PVs

Mention “solar energy” and most people picture an array of roof-mounted solar panels, angled to capture the sun’s rays. Ascent Solar Technologies, Inc. (www.ascentsolar.com) plans to turn that perception on its ear.

There are many companies in the thin-film space, but most manufacture their products on glass, which requires a structure to hold the glass in place. Ascent Solar has developed a thin-film solar cell with a plastic backing, making it lightweight and flexible -- two features that open up a wide variety of possible applications. In addition, proprietary monolithically integrated processing techniques will allow the solar cells to be manufactured roll-to-roll. “We don’t have to cut up photovoltaics, test it, rewire it, test it again, and then package it into a module. The entire process is automated at the factory level,” says Joseph McCabe, vice president of business development for Ascent Solar. The result is lower production costs.

One of the first products using Ascent Solar’s patented technology is being developed in partnership with Norway-based Hydro Building Systems.

In the sunnier parts of Southern Europe, nearly all commercial buildings have louver-shaded windows. Hydro Building Systems’ louvers incorporate Ascent Solar’s technology to offer increased product value.

“These shading devices save electricity because the buildings require little or no air conditioning,” says McCabe. “We added a thin layer of encapsulated material for a much higher-value purpose: making electricity. Now the product not only saves electricity, it makes electricity. This is the true definition of building-integrated photovoltaics.”

Ascent Solar will be conducting demonstration projects in 2008 and plans to mass-market its product by 2010. In addition to the commercial and residential building markets, the company plans to provide products for space and near-space applications.

Tiny Technology, Big Results

Thin-film technology has certainly advanced the solar energy industry, but research scientists like Dr. Richard Bley believe the cutting-edge technology that will propel solar to the forefront of renewable energy sources is nanotechnology. Quantum dots, to be exact.

Bley is a senior chemist at Eltron Research, Inc. (www.eltronresearch.com), a private company that conducts research for government agencies and private companies. Bley’s vision is to make solar cells using quantum dots, which are semiconductor nanoparticles.

The theoretical efficiency of normal solar cells is around 43%. It has been estimated that if quantum dots are used in a solar cell, that efficiency will increase to as much as 60%. This is due to the fact that in quantum dots, a phenomenon called multiple excitations can occur.

“If a photon comes in that has an energy that’s some multiple of the band gap of the quantum dot, you can excite two electrons rather than just a single electron,” says Bley. “In fact, if the energy is high enough in the photon, you can excite three electrons.” This translates into greatly increased efficiencies in solar cells.

Quantum dots are relatively inexpensive to make; the problem lies in putting all the components of the solar cell together in just the right way. Currently, quantum dot solar cell manufacturing is not economically viable, but Bley hopes to change that. Eltron Research has submitted proposals solicited by the U.S. Department of Energy and the National Aeronautical Space Administration (NASA) to develop the technology. A decision on whether Eltron’s research will be funded is expected within the next year.

There are numerous public and private research firms, including the National Renewable Energy Laboratory (NREL), that are in a race to develop the process that can harness the powerful efficiencies of quantum dots within solar cells. “Different people are approaching the development of this process in different ways,” Bley says. “Some are focusing exclusively on solid-state, some are trying organic and inorganic mixtures, and each is obtaining different results. We don’t know who’s going to win.”

Although no one can predict when the breakthrough will occur, Bley is confident where the future of the solar energy industry lies. “There is no doubt about it. Quantum dots will some day be what we use in solar cells,” Bley states. “It’s just a matter of time.”

Intelligent Windows and Even Smarter Walls

RavenBrick LLC (ravenbrick.com) plans to manufacture windows and walls that regulate solar heat gain in buildings. The core of their technology is a thermoreflective filter, a material that is transparent at low temperatures and highly reflective at high temperatures.

How do their windows differ from currently available smart windows? One distinction is that RavenBrick’s windows offer a stand-alone solution. “Smart windows are electrically operated, meaning someone has to flip a switch in order to affect the transparency of the window,” says RavenBrick president Wil McCarthy. “It also means that the smart window must be connected to the building’s power system, and there’s a certain amount of infrastructure and overhead cost associated with that.” The technology used in RavenBrick windows operate automatically, with no power source or human intervention required.

Another limitation of smart windows is that they reduce the amount of light entering a building, but not the amount of heat. Smart windows block light by absorption. Once they are switched on, they become black or dark blue and filter the sunlight coming through. However, the heat is absorbed in the window and then reradiated into the building, forcing the building’s cooling system to compensate. The high reflectivity of RavenBrick windows greatly decreases their heat absorption.

RavenBrick’s wall product takes the window technology a step further. Because walls are opaque, the company can take advantage of additional materials and their unique properties. In cold weather, RavenBrick windows simply let heat and light in. The wall product, however, stores energy and releases it to warm the interior of the building at night, spreading out the thermal load. The temperature at which the wall begins to reflect solar energy can be set at the time of manufacture.

“In a typical office building, there is a huge thermal spike in the second half of the day. The building is absorbing a tremendous amount of solar energy, forcing the air conditioner to run,” says McCarthy. “After the sun sets, the building cools down and the heater kicks on. That’s not a very efficient system. If you can take the solar energy that you’re absorbing, store it for later, and then release it at night, the air conditioning and heating bills are both lowered.” The wall and window products are so efficient, in fact, a single-story, open-plan building like a warehouse can be taken completely off grid. The interior can be maintained within five or six degrees of room temperature year-round without any utilities at all.

“From our standpoint, the market is unbelievably vast,” says McCarthy. “We’re limited more by our own capacity than by customer demand.”

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