Our Solar Future

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Carbon-neutral energy sources, especially the “Big 3”—solar, wind, and nuclear power—have the potential to relieve our dependence on fossil fuels and lessen our impact on global warming. However, for any of these possibilities to surpass fossil fuels as a real, widespread solution, the price must be right.

Nuclear power has great promise, but it comes with significant roadblocks. To accommodate our world’s estimated energy needs by the year 2050 through nuclear power alone, 10,000 new nuclear power plants would have to be constructed. To put this in perspective, only 436 plants exist worldwide, less than one-fourth of which are in the US. Considering the generally negative feelings in our country toward nuclear power, and the cost associated with constructing the plants, this kind of expansion is unlikely.

When it comes to wind power, the problem lies not in safety or price but in volume. There is a finite amount of appropriate land on which to construct windmills, and only so much wind to turn them. Even if all of this land were used optimally, experts estimate the energy produced could only provide, at most, 10% of our world’s total needs.

With all of these restrictions in mind, solar energy stands out as our best bet. Without a doubt, the sun’s rays can provide more than enough energy—it’s just up to us to harvest it. This presents two key problems. First, to accommodate our national energy needs, we would need 60,000 square miles worth of solar cells—this is equivalent to the entire highway and road system in the United States. To put this in perspective, the US only produces 700 square miles of carpet per year. So, these solar cells must be very easy to manufacture.

The other problem, of course, is cost. Current solar energy technology is expensive. Traditional solar cells are made of silicon, which is derived from common sand. While sand is cheap, the manufacturing process is not, requiring temperatures of more than 3000ºF. Then, the silicon must be formed into large, highly pure crystals. This whole process, aside from being expensive, also requires a lot of energy. In fact, it can take up to 4 years before the cells produce as much energy from the sun as it took to make them in the first place.

Researchers are now working on several alternative forms of solar cells with cost and scalability in mind. One option is to use a less pure version of silicon—multicrystalline silicon—which is cheaper and less energy-intensive to manufacture. Traditionally, it has also been less efficient, converting only 15% of the energy it absorbs from the sun into usable power, versus the 20% efficiency of the more expensive version. However, researchers are now testing new versions of cells using multicrystalline silicon, and have nearly hit the 20% mark.

Other metals under investigation include thin sheets of cadmium telluride and nanocrystals of copper indium gallium diselenide. Both have been made into solar cells that are about 10% efficient, which is the minimum for commercialization. While this is much lower than silicon cells, the benefit lies in price. Two companies that produce these cells, First Solar and Nanosolar, claim to manufacture them at a cost of only $1 per watt, a unit of energy, which is about 20% the cost of traditional silicon cells.

Our research group works on another exciting alternative, known as organic photovoltaics. In chemistry, "organic" means that something contains only lightweight atoms such as carbon, nitrogen, oxygen, and hydrogen. These atoms link together in long chains known as polymers, making their products very flexible. Learn more about the science of organic photovoltaics.

Because of this flexibility, organic solar cells can be constructed using a roll-to-roll processing method (think of the large machines that assemble newspapers or magazines). They can also be created by dissolving the polymer to form an “ink,” which is then inkjet-printed onto a flexible metal film. This could enable the mass production necessary to meet our nation’s energy needs.

Organic solar cells also have the potential to become a true mainstream solution for the everyday consumer, in that an expensive, specialized expert may not be needed to install the technology. For example, cells could be incorporated into building materials such as wall siding or shingles. Some scientists have even proposed “solar paint," which could be applied to almost any surface to harvest the sun’s rays. Imagine picking that up at your local hardware store!

It is this versatility that stands to make organic photovoltaics truly revolutionary. Much like other solar cell alternatives, their efficiency may never match silicon. Current versions are about 5% efficient, and we expect this to reach 10%. However, organic solar cells require much less energy to produce, lowering their costs. We estimate they’ll eventually be produced more cheaply than even the cadmium telluride and copper indium gallium diselenide versions.

It is important to remember that commercially competitive organic photovoltaics are still 5-10 years in the future, and that there are other obstacles in place. Even with solar cell shingles on homes and businesses, a great expanse of solar cell “power plants” will be needed to power the entire country. In fact, researchers estimate they’ll need land equivalent to the size of the state of Oklahoma. Which states will contribute this land? And, when these plants are built, efficient ways of channeling the power back to cities across the country will need to be constructed.

While these obstacles are significant, they are not insurmountable. With the right buy-in from consumers, business owners, and our nation’s leaders, a carbon-neutral energy solution just might be on the horizon.

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