Energy and the Environment

Increased Efficiency, Solar Power Key

Editor's note: This is the first of seven stories covering each of the sessions at the recent Summit on the National Academy of Engineering Grand Challenges March 1-3 in Durham. Each article also has a link to the corresponding video.

Watch the session.

"At a certain point, the risk becomes so high we have to act," said Paul Alivisatos, referring to the risk of advanced climate change and geopolitical conflict as a result of the way humans are currently using energy.

Alivisatos is Interim Laboratory Director at the Lawrence Berkeley National Laboratory and Professor of Chemistry and Materials Science and the Larry and Diane Bock Professor Nanotechnology at the University of California, Berkeley.

In his talk at the Grand Challenges Summit on March 2, Alivisatos focused on energy efficiency and solar energy technology as two strategies for reducing our dependence on fossil fuels, which emit carbon dioxide—a greenhouse gas—when burned.

"We have a tremendous opportunity in the area of energy efficiency," he said. As an example, he pointed to electricity use in California. From 1973 to 2008, electricity use grew steadily in the U.S.—except for California. Electricity use per person there held steady, even though the gross domestic product per person doubled. The reason?


California instituted standards for new refrigerators and offered rebates for discarding old inefficient ones. The rebates encouraged people not just to buy better refrigerators but also to actually unplug and get rid of the old ones. Over the years, the size of efficient refrigerators has grown and the price has fallen, all while using less energy per month than the inefficient variety. Alivisatos estimated that California’s refrigerator standards have prevented the need to build 40 power plants (1-gigawatt each).

Alivisatos also pointed out another area that’s ripe for an efficiency overhaul: buildings. Almost 40 percent of the energy used in the U.S. is used in residential, commercial and government buildings, and this energy use accounts for almost half (48 percent) of the country's carbon emissions. With good planning and technology, new buildings can get by on just 10 to 20 percent of the energy used in traditional buildings, he said.

But energy efficiency alone cannot solve energy problems. On the supply side, renewable energy will play a role. Much of Alivisatos’s research is related to improving solar energy technology.

He said that it’s a myth that the technology is all ready and just waiting to be implemented. “We don’t have all the knowledge that we need,” he said. “New energy technologies are possible and necessary.”

Currently, renewable energy accounts for only 7 percent of the energy consumed in the U.S., and solar accounts for only 1 percent of that. Engineers have many problems to solve before that number can be ramped up. Solar cells need to be cheaper to produce and install. They need to be durable and easy to maintain. They need to wring more usable energy out of each photon of sunlight. They need to be made of materials that are available in mass quantities.

Alivisatos said that in the 1960s, engineers were exploring many different compounds for use in photovoltaic solar cells, but that after the oil shock of the early 1970s, engineers began to focus solely on the handful of elements and compounds that were already showing promise. Alivisatos said scientists need to go back and look at some of the other alternatives because there aren’t enough of the workable compounds available worldwide to make widespread solar applications practical. "We need transformative solutions," he said.

Alivisatos and his colleagues are looking into making solar cells using nanocrystals. "The smaller the crystal, the less total energy to make a perfect crystal," he said. A question with nanocrystal solar cells is whether the electric charges generated would be trapped in the gaps between the tiny crystals.

Alivisatos hopes to solve this problem by using a material whose electron wave-length is larger than any of the "traps" between the nanocrystals. He made an analogy to potholes on a highway: "Your car will drive right over a pothole that is 1 millimeter wide."

Another intriguing possibility, according to Alivisatos, is investigating is artificial photosynthesis. Plants produce fuel for themselves by using water, carbon dioxide and energy from the sun to produce hydrocarbons. Engineers are trying to figure out how to do the same thing. One advantage would be that the resulting hydrocarbon fuel could be used when needed, in contrast to current solar technology, which produces electricity that must be used right away or stored in expensive and unwieldy batteries.

Alivisatos said it’s an exciting time in energy research because environmental awareness is attracting people to science and engineering. "We have a generation of young students who are energized," he said.