To cut greenouse gas emissions 80 percent by 2050, California and the nation have three main technological options, according to a leading California Institute of Technology scientist: carbon capture and sequestration, nuclear energy, and solar power. Other technologies and strategies--including energy efficiency and wind power--can help meet interim greenhouse gas reduction goals. But they cannot successfully achieve the 80 percent mark that state’s climate protection law, AB 32, calls for in 2050, according to Caltech chemist Nathan Lewis. In a presentation to the California Air Resources Board February 23, Lewis pointed out that two of the three options--carbon capture and sequestration and nuclear power--are riddled with problems. For instance, the places to pump carbon dioxide into the ground without contaminating water are limited. Also, the supply of uranium is too limited to build enough reactors to cut greenhouse gases 80 percent unless breeder reactors are used, but that would cause the proliferation of nuclear weapons. This leaves solar energy. “But we have to find a way to make it really cheap and store it,” Lewis said. To make enough power to cut emissions 80 percent with the sun’s energy, Lewis said photovoltaic technology must become like paint and carpet that you simply spray on or unroll to make energy. The most promising way to achieve such a breakthrough is to pour research money into developing nanotechnology materials for photovoltaic systems. Lewis said the optimal solar cell would consist of a layer of inorganic material at the base topped with a layer of nano brushes and covered on top with a thin layer of organic material that lets in the sun’s light. The cell would be about 300 nanometers thick, invisible to the human eye at about the thickness of a virus. However, while such technology could provide power during the day, to have electricity at night energy would have to be stored economically. Also, to meet the 80 percent greenhouse gas reduction mark, solar energy would have to be stored to meet transportation needs. Hydrogen offers promise for energy storage, Lewis said, but the materials used today in fuel cells, which convert the gas into usable energy, are too expensive and rare to be of much use. Platinum is commonly used as a catalytic material in fuel cells, Lewis noted, but it is extremely expensive. The amount of platinum in a fuel cell-powered school bus, he said, costs $500,000. Moreover, he said, there is not enough platinum in the world to create enough fuel cells to cut greenhouse gas emissions by 80 percent. Therefore, he suggested that research should focus on how to create catalysts that use iron, which is cheap and abundant. Despite these materials science challenges, Lewis said he is confident that economical solar and energy storage technologies can be developed. But it will take a massive and sustained effort to do so, he quickly added.