Just as in the oil industry, drilling and engineering for geothermal projects is an expensive proposition. To help buy drilling rigs and develop its services, ThermaSource has taken a hefty funding of $41.5 million.

The Santa Clara, Calif. company employs 210 people, but plans on doubling in size by the end of this year.

Riverstone Holdings, US Renewables Group and Rustic Canyon Partners provided the funding. ThermaSource has taken $93 million to date, counting both equity and debt.