said Orbach, is to reduce the costs and increase the efficiency of the conversion process, which often requires understanding and controlling phenomena at the nanoscale level.

One drawback to the increased use of solar power and wind power is that they tend to be intermittent sources of energy, in that they can be generated only when the sun is shining or the wind is blowing. Taking full advantage of these technologies will require the development of both energy storage technologies and “smart grids” that can control the flow of electricity from energy producers to energy users.

Several energy storage technologies are being developed. Although current batteries are not suited for large-scale storage, advanced batteries and electrochemical capacitors offer potential for the future. An older technology that remains useful is to pump water to a higher level and subsequently use the stored potential energy to generate electricity. Another such technology is compressed air storage, in which air is pumped into underground caverns or aboveground storage areas and then drives electricity-producing turbines when it is released. “There’s some very good new technology on compressed air energy storage that can use existing gas turbine designs,” said Steven Specker. “There’s a plant in Alabama that has been operating for a number of years with compressed air energy storage. It works very well. [And] as wind power grows rapidly in certain parts of the United States and the world, we need a storage approach.”

Today, intermittent sources of electricity, such as wind or solar power, can make electricity grids unstable.1 To manage large amounts of renewable power generation, smart grids using advanced power electronics and electrical storage devices are needed to manage the transmission and distribution of electricity from where it is produced to where it is being used. Specifically, these grids must be able to “communicate” between utilities and electricity meters, enabling such advances as provision of power to the grid by plug-in hybrid automobiles and powering off of home appliances during peak load periods.

ENHANCED GEOTHERMAL ENERGY

Several speakers at the summit discussed sustainable sources of energy that are farther in the future than the expanded use of solar power and wind power. One is energy from engineered geothermal systems. As Dan Reicher pointed out, if a hole is drilled into the ground, it eventually will encounter rocks that are heated by Earth’s interior. If several such holes are drilled near each other and the rock between them is fractured, water can be injected into one well and returned from the others much hotter, and steam from that water could turn a

1

This depends on local grid characteristics, but in general grids are able to handle between 10 and 20 percent of intermittent renewables without requiring storage.



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