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 3 . 8
Parallel Development of Two or More Geothermal Fields Reduces Resource Risk
Source | Authors.
Geothermal 
Field 3
Geothermal 
Field 4
Geothermal 
Field 5
Portfolio Exploration
Phases 1-4
Parallel
Development
Phases 4-7
Geothermal 
Field 1
Geothermal 
Field 2
Total
100 MW
Total
200 MW
Total
300 MW
+
+
+
MW
Step 1
MW
Step 2
50
+
+
50
50
MW
Step 3
50
+
+
50
50
Step 1
MW
Step 2
MW
Step 3
MW
Stepwise Field Expansion

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110
G e o t h e r m a l H a n d b o o k : P l a n n i n g a n d F i n a n c i n g P o w e r G e n e r a t i o n 
Of course, parallel development could be extended to additional geothermal fields in the country 
based on the same principle. One 50 MW plant built in each of three geothermal fields, for example, 
could make 150 MW of geothermal power available to the country’s power system within the period of 
time it takes to install a 50 MW project in just one field. 
In contrast, committing the entire geothermal development budget of the country to a 150 MW plant 
built in a single geothermal field would be a riskier proposition and could take more time for reasons 
mentioned earlier.
B O x 3 . 1 1
Experience from Application of the Stepwise Expansion in Kenya
The Kenyan Olkaria geothermal power project is an example of stepwise development. The field is located in 
Kenya’s Rift Valley, about 120 km from Nairobi. The first power plant, Olkaria I, was commissioned in 1981 
with a capacity of 15 MW, then enlarged to 45 MW. The Olkaria II plant followed in the 1990´s with two 35 MW 
generators; it was enlarged in 2009 by another 35 MW. An IPP generates 12 MW at the Olkaria III site with a 
binary bottoming cycle. KenGen, the generating company, has plans to enlarge the Olkaria field from 170 MW to 
over 400 MW in the coming years, by deploying 4 new 70 MW power plants. Parallel to these activities, at least 
two other fields are expected to provide several hundred megawatts each.
Source | Magnus Gehringer based on Mwangi 2005.