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Amreica’s Enery Future: Technology and Transformation
aid in the deployment of large-scale wind generation and, potentially, solar generation by 2020;21 these energy sources are regional, intermittent, and often far away from major population centers. As the down periods for wind vary from region to region, long-distance transmission would help to pool such resources for transmitting the power to load centers. HVDC also is less expensive than AC if lines need to be underground—for example, when passing through pristine areas. Several HVDC lines already exist in the country, and, if planning is started within the next few years, several more large lines22 could be completed before 2020.
Further R&D on advanced materials and nanotechnology could lead to improved lightweight insulators, high-temperature low-sag conductors, and light-weight high-strength structures after 2020. In the longer term, breakthroughs in superconducting materials are needed for superconducting cable technology to become widespread. This is unlikely to occur until after 2030.
Cost-effective storage would be useful both on transmission and on distribution systems. Transmission systems require large-scale storage capacity with high power ratings (on the order of hundreds of megawatts) and long discharge times (hours to days). The variable power output of renewable resources is currently managed by standby generation, but as large-scale and remote wind or solar generation facilities are built, such storage technologies would be very beneficial for the transmission system that must deliver the power. Today, this type of storage is largely limited to pumped hydro storage, where water is pumped uphill into a reservoir and released to power turbines when needed. Another technology that has been demonstrated and is currently available for commercial deployment is compressed air energy storage (CAES).23 A CAES plant stores energy by using electricity (from off-peak hours) to compress air into an underground geologic formation (or potentially in aboveground tanks). The energy is recovered when a combustion turbine burns natural gas in this compressed air in lieu of operating
These electricity sources are discussed in detail in Chapter 6.
For example, lines might connect wind resources in Wyoming to California, or deliver wind power in the Dakotas to Chicago. Such lines might account for a large fraction of the cost of that electricity.
CAES has been demonstrated at a pilot plant in Alabama as well as at locations in Germany.