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

risk of Oversizing the Power Plant
Commitment of investment resources to a geological resource of uncertain production capacity is 
always risky: the results will be suboptimal when a geothermal power plant is either too large or too 
small in relation to the underlying geothermal reservoir. This could be considered part of the resource 
risk discussed earlier. The risk of oversizing the power plant needs to be specially mentioned for two 
reasons. First, oversizing the power plant magnifies the resource risk by concentrating investment 
resources in a given location instead of spreading it by building smaller plants in several geologically 
independent fields. Second, excessive plant capacity in relation to the productive capacity of the 
underlying geothermal field can cause extraction rates that are unsustainable. Pressure drops or even 
reservoir depletion may result. The best way to mitigate this risk, as discussed in Chapter 3, is to limit 
the development in a single geothermal reservoir to increments of about 50 MW sequentially, adding 
subsequent increments as data about the resource are collected over time rather than immediately 
developing a single, large power plant. To accelerate the build-up of the overall geothermal 
development program in the country or region, developing multiple independent reservoirs in parallel 
is recommended.