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

F I g u r E 1 . 1 8
Simplified Load Curve with Typical Fuel Sources 
Source | Authors.
Solar/Wind
Hydro
Geothermal
Time of Day (Hours)
Load
Fossil Fuels
system demand throughout the entire year. For example, suppose a country’s system demand is 
normally above a given level over a given timeframe (one year), according to data from the power 
regulator or utility. However, every year during a three months period, the demand happens to fall 
significantly below that normal level. In this example, geothermal power capacity for such a country 
should not exceed the capacity that is required to satisfy the demand during the three months 
period that reflects the lowest point of the load curve. This is the system demand that can always be 
maintained by the system and therefore installed geothermal capacity should not exceed this level at 
any time. Other power sources should be deployed to satisfy the remaining demand for electricity.
Besides the level of system demand, the other major factor influencing the size and capacity of 
a planned geothermal power plant is the reservoir’s potential. International best practice is to 
develop geothermal plants in steps depending on the estimated potential (which is based on 
scientific exploration) and on the results of test drillings. For high temperature geothermal power 
projects, common steps are between 30 and 60 MW per power unit (genset) installed. This means 
that geothermal power projects cannot be regarded as a quick fix for any country’s power supply 
problems, but should rather be part of a long term strategy. Operating the initial unit for some years 
will provide valuable information about the reservoir’s dependable potential and thereby facilitate fact-
based planning for future expansions of the power facility.

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