Mainspring Energy co-founders (L-R) Adam Simpson, Matt Svrcek, and Shannon Miller with the company’s linear generator.Photo: Mainspring Energy
In January 2018, Gates invested in Mainspring Energy’s $83.3 million Series C, according to PitchBook, which led the company to a $208.3 million valuation.
Mainspring’s linear generator uses chemical energy to convert motion along a linear line into clean electricity at any scale, according to the company. The linear generator continuously adjusts compression and expansion to different fuel quality and fuels, so it can use fuels such as biogas and green hydrogen.
The linear generators can match power output with demand, and integrate on-site solar and energy storage. The technology can also continue providing power if an energy grid is down.
Gates was a follow-on investor in Mainspring’s $108.1 million Series D funding round, according to PitchBook, which led the company to a $458.1 million valuation in May 2021.
He invested again in Mainspring’s $290 million Series E funding round in September 2022, which led the company to a $1.04 billion valuation, according to PitchBook.