Over the past decade, Mainspring Energy has been at work on a novel "linear generator" that it says can provide on-site electricity with lower emissions than fossil-fueled engines and microturbines, and greater flexibility than fuel cells.
On Tuesday, Mainspring's vision garnered a vote of confidence from U.S. utility and renewables giant NextEra in the form of a $150 million agreement with its business services arm NextEra Energy Resources to purchase, finance and deploy Mainspring's devices across the country.
Mainspring started testing its linear generators last summer with an unnamed national supermarket chain, which has agreed to expand its use to up to 30 grocery stores, according to Tuesday’s announcement. The Menlo Park, Calif.-based startup, formerly called EtaGen, has also shipped products to big-box retailers and utility customers, and it is in discussions with other Fortune 500 companies.
The core concept behind Mainspring’s generator — capturing the back-and-forth motion of pistons, or oscillators in Mainspring’s terminology, to generate energy — is shared by a wide class of devices, ranging from Stirling engines to linear alternators and motors. But Mainspring’s system differs in several key ways from the variety of similar technologies developed over the decades, CEO Shannon Miller said in an interview.