Northern California Power Agency (NCPA) and SPG Solar, announced that they will together to build a 1 megawatt (MW) single-axis solar tracking system that will provide renewable energy to an existing pump station that supplies the NCPA Geysers Geothermal Energy Plant.
The array will be used to collect solar power to pump wastewater into the geysers, which is in turn used to generate geothermal power. The photovoltaic array will start generating clean renewable power beginning in September 2008.
The $8.2 million installation consists of 6,300 solar modules that will produce 2.2 million kilowatt hours of electricity annually. The solar plant will supplant PG&E-provided grid power that had been powering the pumps.
NCPA operates two geothermal plants at the Geysers producing approximately 132MW gross, and 120MW net of electricity. In the late 1990’s, in an attempt to regain pressure in the rapidly declining Geysers field, NCPA and other operators at the Geysers entered into an agreement with Lake County to reclaim the treated waste water, pipe it to the Geysers, and reinject it into the reservoir. This is necessary because nearly 70% of the mass extracted from the reservoir is released into the atmosphere during operations of the power plants and natural recharge was not matching the pace of extraction.
The good news is this scheme to replace mined mass has worked; so much so, that Calpine followed suit and created a similar agreement with Santa Rosa. The bad news is, it takes power to move the millions of gallons of water from Lake County to the injection wells. The pipeline is about 30 miles (50 km) and gains nearly 2,000 feet (600 m) in elevation over the course of its run. The load to run the pipeline operations is about 8MW, or two-thirds of the parasitic load borne by the NCPA plants.
So, in practical terms, the application of solar energy to power some of the pumping operations should be characterized as an experiment in multi-dimensional harvest. The other opportunities NCPA and the other Geysers operators have (given the location and transmission infrastructure) are straight-forward bottom cycling using the new generation units from UTC power further harvesting heat from the steam exhaust from the turbines and wind turbine installation. This is the approach Montara Energy Ventures is taking with its Sou Hills Prospect.
