Solar and wind get most of the attention, but the most consequential thing about Kenya's generation mix is that a large share of it comes from a resource that does not care whether the sun is up or the wind is blowing. Understanding why that is possible here, and why it is not possible in most places, is worth a few minutes.
Three things have to occur together#
A geothermal field needs a heat source, rock that water can move through, and water to move through it. Any two without the third produces nothing useful.
The East African Rift supplies the first condition unusually well. The crust is being pulled apart, magma sits closer to the surface than it does under stable continental interiors, and the result is a band of anomalously hot rock running through the region. Volcanic centres along the rift floor concentrate that heat further.
The second and third conditions are why fields are drilled in specific spots rather than anywhere along the rift. Fractured volcanic rock lets water circulate; dense unfractured rock does not. Rainfall and groundwater recharge keep the system supplied.
From steam to megawatts#
The physical chain is short. A production well brings up a mixture of steam and hot brine under pressure. A separator splits them. Dry steam is piped to a turbine, spins it, and the turbine drives a generator. The steam is then condensed and, together with the separated brine, injected back into the reservoir through separate wells.
Reinjection is not an environmental afterthought. It is what keeps reservoir pressure up. Fields that produced without returning fluid have declined faster than fields that did, which is now standard practice rather than good behaviour.
Where the resource is hotter, direct steam turbines work. Where it is cooler, a binary plant uses the geothermal fluid to boil a second working fluid with a lower boiling point, and that vapour drives the turbine. Binary units extract useful power from resources that would otherwise be marginal.
The money is in the drilling#
The economics are the opposite of solar. A solar plant's costs are almost entirely known before construction: panels, inverters, mounting, land. A geothermal project spends heavily on exploration and drilling before anyone can be certain what the field will produce.
| Stage | Cost profile | Risk |
|---|---|---|
| Surface exploration | Low | Low |
| Exploration drilling | High | Very high |
| Production drilling | High | Moderate |
| Plant construction | High | Low |
| Operation | Low | Low |
A dry or under-performing well is a sunk cost. This is why geothermal development has historically depended on state entities and development finance willing to carry drilling risk that commercial lenders will not, and why "resource risk mitigation" facilities exist as a distinct category of energy finance in the region.
What it means for the grid#
A geothermal-heavy system has a different shape from a solar-heavy one. Output is steady, so the grid needs less storage and fewer fast-ramping units to stay stable overnight. The flip side is that geothermal plants are not good at following load; they run best flat out, so demand that swings sharply still needs something else alongside them.
Solar changes what you generate during the day. Geothermal changes what you can rely on at three in the morning.
That reliability is the reason the resource keeps attracting investment even though the drilling risk is real and the lead times are long.
Sources and further reading
