Geothermal handbook: PlanninG and Financing power Generation t e c h n I c a L r e p o r t 2 / 2

B O x 1 . 2
 
Lessons to Learn from The Geysers Field in California
In the 1970s, The Geysers field in California was drilled by four independent private companies who failed to 
properly coordinate exploitation activities. The combined installed capacity of all power plants built during this 
decade surpassed 2,000 MW. Too many wells were drilled, reservoir pressure dropped precipitously, and still 
more wells were needed to supply enough steam to the turbines at the required pressure. This led to a severe 
reduction of power capacity at The Geysers. Subsequently, the steam pressure decline was abated by increasing 
the reinjection percentage to its maximum and adding sewage water from nearby cities, only to stabilize it at about 
half of its historic peak. 
Source | Calpine 2010.
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The problem is known in economic theory as the “Tragedy of the Commons.”
Exceeding productive capacity may also result from a lack of coordination among the developers of a 
shared geothermal reservoir.
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Several projects, the best example being “The Geysers” in California, 
U.S. (Box 1.2), have faced this problem. In some of those examples of poor coordination, the outcome 
was partial or total loss of the investment due to loss of the productive capacity of the resource.
Subsequently, geothermal developers have learned to utilize a more judicious approach. To minimize 
the risks of pressure drops or reservoir depletion, geothermal plant capacity should be expanded in 
increments of about 30 to 60 MW at a time. If the investment budget allows, several geothermal power 
projects can be developed in parallel, exploiting different fields. This approach increases the supply 
faster, more economically, and with less geological risk than does an attempt to capture the entire 
capacity of a field in one go (as discussed further in Chapter 3).