The Geysers Geothermal Energy Sustainability

I was recently asked about the renewable nature of The Geysers Geothermal steam field. I prepared a brief article for my Management and Sustainability Blog to respond to the question. I have updated it slightly to publish it here.

Both PG& E and the Steam Suppliers, mainly oil companies, depended upon analyses done by geological experts (university professors) for their judgment regarding the steam supply. The experts all agreed that the plants would be able to maintain full power output over their design life.

As I recall, the calculations were based upon about eighty percent of the steam condensate being evaporated in the cooling towers. Approximately 20-25% of the geothermal steam condensate was to be reinjected into the steam field in the form of cooling tower overflow. Occasionally, steam supply wells were expected to be drilled to replenish those with reduced flow and the total number of supply wells was generally anticipated to double over the life of the plant. It was further assumed that as reinjection wells plugged over time, they would sometimes be replaced. That was the design expectation, as I remember it. However, the world's experts were proved wrong in their analyses and, over time, the overall steam field pressure at the Geysers began to decline.

For about 15 years, the amount of steam available to fuel the geothermal plants decreased, as the reservoir beneath the Geysers dried up, a victim of over pumping. As steam pressure and flowrates decreased, energy production slipped and was in danger of grinding to a halt. Three older or less efficient power plants were decommissioned, including Unit 15, the Department of Water Resources Bottlerock plant. Apparently the California Energy Commission was miffed that it was discovered halfway through its construction that the plant would not have sufficient steam to operate. They passed new legislation to give the CEC the obligation to confirm steam supplies during NOI/AFC licensing for future plants. It is my memory that they always addressed this in the environmental licensing documents. They just did not have it written into law that they needed to independently verify. I think there were some politics at play here.

Solutions once deemed impractical were considered and plant operators at The Geysers partnered with local sewage water treatment plant operators to implement a somewhat innovative plan to restore and maintain adequate levels of underground water in order to ensure continued steam production. Since 1997, the Geysers steam field has been recharged by injecting treated sewage effluent from City of Santa Rosa and Lake County sewage treatment plants. This effluent, tertiary-treated wastewater, was originally dumped into rivers and streams but instead is now piped to the geothermal field where it is heated and eventually replenishes the steam produced and utilized for power generation. I believe about 18 million gallons per day of treated water is supplied by separate pipelines from the two Sanitation Districts. At The Geysers, secondary pipelines distribute injection water throughout the steam field.

These remedial actions resulted in stabilization of the overall geothermal system pressure. Apparently, the reinjection is working and compensating for the fact no natural recharge of the system occurs. It is assumed that the amount of heat available to produce the steam is essentially unlimited, but time will tell. The experts are not always right, even when they agree.

It makes one wonder though, with experts disagreeing on how much oil, gas and coal are in our reserves, how dependable are the estimates and to what degree will new innovative ideas supplement nature?

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