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Renewable Energy

Mandatory portfolio standards have different implications for different technologies.

Fortnightly Magazine - November 2004

energy is not available for collection in adequate quantities. Electricity available from the solar field in excess of the reliable capacity requirements could be sold at a lower price when storage is full and demand is available to be served.

The requirements of reliable source operation increase the investment required in solar generators to cover the cost of excess generation capacity to charge storage and the cost of the storage system and its operation. The reliance on storage also decreases net generation, as the result of losses experienced moving electricity to and from storage.

Hydroelectric Generation: Siting and Other issues

Hydroelectric generation is significantly more stable than wind or solar, and its output can be adjusted to follow changing loads if desired or required. On the other hand, when hydro is unavailable it tends to be unavailable for several months or even years at a time, as the result of droughts or low snow pack. This means that some portion of hydro generation capacity must be backed-up by conventional generation, which can be used to supply power while the hydro generator is partially unavailable. However, this conventional generation is typically not viewed as a component of reliable hydroelectric generation capacity.

Hydroelectric generation also is limited by the availability of major hydro sites and the reluctance of environmentalists to have additional hydro re-sources developed because of impacts on fish populations and other wildlife. Thus, it is unlikely that the hydro contribution to the U.S. generation mix will increase substantially in the future.

Biomass: Beware of Limits

Most biomass generating capacity is considered reliable, since there is ample unused biomass available to fuel the biomass generating facilities. However, the current and projected demand for biomass for the production of fuel ethanol may constrain the availability of biomass for the expansion of biomass-fueled electric generation. Biomass generation also may be constrained in the future by proposed CO 2 emission limits.

Geothermal: A Journey to The Center

Geothermal generators are the most reliable and predictable of the renewable sources of electric generation. Thus, geothermal generation will be the least affected by the transition to reliable-source status, since it has effectively achieved that status already. Potential geothermal resources are very large, and it is likely that geothermal generation will make a substantially larger contribution to the U.S. generation mix in the future, if access to drill hydrothermal resource wells is available; and, if the technology and market prices permit economic access to "hot dry rock" sources of geothermal energy. Hot, dry rock geothermal sources are projected to be adequate to provide all U.S. electric demand and consumption for tens of thousands of years. However, these sources require deep drilling into high-temperature rock formations, which increases project investment and thus project energy costs.

California's Experience With Reliable Renewables

The recent power availability problem in California was fundamentally the result of the combination of reduced capacity reserve margins within the total generation fleet serving the state and reduced availability of hydroelectric generation capacity as the result of both increased water demand and protracted drought. In the California electricity market