DAVIS, California, US, April 12, 2006 (Refocus Weekly) Outage rates for geothermal facilities in California are lower than at a conventional natural gas generating unit, while solar values are 79% and wind is as low as 25%.
The Renewables Portfolio Standard in the state requires a ‘least-cost best-fit’ strategy for selecting new generation projects to fulfill its supply goals from renewables, explains a report prepared for the California Energy Commission by the California Wind Energy Collaborative. That strategy explicitly includes indirect integration costs in the bid evaluation process, and the report documents a multi-year analysis of integration costs for the period from 2002 to 2004.
The capacity credit analysis uses a conventional gas unit as benchmark, and shows that biomass has outage rates comparable to the gas benchmark unit, with a resulting capacity credit of 98%. With lower outage rates, geothermal facilities in both the north and the south of the state were assigned a rating of 109%.
Solar values wee relatively high, given the natural tendency to track load and auxiliary gas generators, with a rating of 79% relative to rated nameplate capacity and 75% relative to annual peak generation. Wind values ranged from 27% to 44% based on annual peak generation, and from 24% to 39% based on nameplate capacity, with higher rates in the north and lower at San Gorgonio and Tehachapi.
The report says the levels are reasonable given wind's variable nature, and the results were verified using an alternate method.
The multi-year analysis, ‘California Renewables Portfolio Standard: Renewable Generation Integration Cost Analysis,’ provided opportunities to verify consistency of methodologies used and to study the impact of renewables on integration costs over several years. Besides the California Wind Energy Collaborative, authors included the National Renewable Energy Laboratory, Oak Ridge National Laboratory and Dynamic Design Engineering.
An analysis of regulation indicates that total system costs were $0.39 per MWh in 2004, with total load costs at $0.36. Geothermal was $0.02, biomass was $0.12, solar was $0.37 and wind ranged from $0.33 in the north to $0.58 at San Gorgonio, with an average for wind of $0.47/MWh.
“The resources studied have fairly minor impacts on total system regulation requirements,” the report concludes. “Because of the sheer size of total load, its regulation cost is consistently very close to that of the total system requirement.”
Geothermal had fairly flat output and low regulation cost, while regulation costs for solar and wind are higher than biomass and geothermal but are still quite modest, it explains. “The solar results are consistent with the minute-to-minute variability in its generation data; the regulation costs imposed by wind are reasonable given that there are no apparent mechanisms that tie wind plant performance to the power system's needs either favorably or unfavorably in the regulation time frame.”
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