GE has agreed to invest up to $40 million in eSolar, a California-based developer of large solar thermal power systems. The investment follows a licensing agreement that GE struck with eSolar in June that will see the two companies supplying technology that combines solar-thermal and natural-gas power systems. The hybrid technology reduces carbon emissions and pollutants that would otherwise come from a stand-alone natural-gas plant.

GE wants to package eSolar's solar-thermal technology, which uses a large field of mirrors to focus the sun on a central tower to produce steam, with a new line of natural-gas plants known as "combined cycle" systems because they capture their own waste heat to power a steam cycle. This process increases the plant's operating efficiency. The combined-cycle plants achieve up to 61 percent efficiency and use a new type of gas turbine that can more quickly adapt to the variability of some renewable energy sources, such as solar.

Adding eSolar's technology could boost that efficiency even further. Its precisely positioned mirrors achieve temperatures of up to 580 °C and produce enough heat to turn water into steam. When the sun is shining, the steam augments the steam cycle of GE's natural-gas plant, increasing overall plant efficiency to around 70 percent.