# Mainspring Energy

Startup profile on Capital Atlas: https://capitalatlas.ai/startups/mainspring-energy

- Industry: Power & Utilities
- Headquarters: Menlo Park, US
- Website: www.mainspringenergy.com
- Total disclosed funding: $656M
- Latest round: Series F (Apr 14, 2025)
- Investors on record: 30

## About

Founded in 2010 and based in California, US, Mainspring Energy, Inc., formerly known as EtaGen, Inc., operates as a provider of linear generators for commercial businesses. Shannon Miller is the Founder and current CEO of the company. In April 2025, Mainspring Energy, Inc. raised USD 258 million in series F funding led by new investor General Catalyst Partners, with participation from other new investors Amazon, Dcvc, Temasek Holdings, Marunouchi Innovation Partners, M&G Investments, and Pictet Group. Returning investors Lightrock, LGT Bank, Khosla Ventures, and Gates Frontier also participated in the round. The company produces a Mainspring Linear generator that delivers onsite power that increases resiliency and accelerates the transition to renewable fuels. The company product delivers fully dispatchable, fuel-flexible, near-zero NOx emissions, high efficiency, low capital & maintenance costs, and turn-key packaging. The Mainspring linear generators are used for commercial and industrial applications, grid infrastructure, and Microgrids. The company generates revenue by providing 2 purchase options for its users: Direct purchase and Energy services agreement. Direct purchase of linear generator option is for users looking to maximize cost savings and return on investment whereas Energy Services Agreement is for users where they can realize immediate cost savings, with no upfront costs, by only paying for electricity produced over the term of the agreement. The company plans to use the April 2025 funding to scale its linear generator business by expanding manufacturing and customer operations to meet growing global demand for flexible, low-emission power solutions.

## Funding rounds

- Series F, Apr 14, 2025, $258M — General Catalyst Partners, Temasek Holdings, Pictet Group, Khosla Ventures, LGT Bank, Lightrock, M&G, Amazon, Gates Frontier, Marunouchi Innovation Partners, Dcvc
- Series E, Sep 21, 2022, $140M — CPP Investment Board, Khosla Ventures, Lightrock, Shell Ventures, Princeville Capital, Trog Hawley Capital, Fine Structure Ventures, Hanwha Power Systems Co., Ltd.
- Series E, May 24, 2022, $150M — Alantra, Khosla Ventures, Fidelity Investments, Lightrock, Lineage, Inc., Alumni Ventures Group, Princeville Capital, Fine Structure Ventures
- Series D, Dec 16, 2020, $108M — Chevron Technology Ventures, Khosla Ventures, Devonshire Investors, American Electric Power, ClearSky Advisors LLC, KCK Group, Princeville Capital, Standard Investments, Equinor Ventures
- Series C, Jan 25, 2018 — Khosla Ventures, Centrica Plc, American Electric Power, KCK Group, Equinor Ventures
- Series C, Aug 29, 2017 — Khosla Ventures, ClearSky Advisors LLC, Gates Ventures
- Seed, Jan 1, 2010 — Khosla Ventures

## Investors

- Khosla Ventures (https://capitalatlas.ai/funds/khosla-ventures) — Seed, Series C, Series D, Series E, Series F
- ClearSky Advisors LLC — Series C, Series D
- Gates Ventures — Series C
- Centrica Plc — Series C
- American Electric Power — Series C, Series D
- KCK Group — Series C, Series D
- Equinor Ventures — Series C, Series D
- Chevron Technology Ventures (https://capitalatlas.ai/funds/chevron-technology-ventures) — Series D
- Devonshire Investors (https://capitalatlas.ai/funds/devonshire-investors) — Series D
- Princeville Capital (https://capitalatlas.ai/funds/princeville-capital) — Series D, Series E
- Standard Investments (https://capitalatlas.ai/funds/standard-investments) — Series D
- Alantra (https://capitalatlas.ai/funds/alantra) — Series E
- Fidelity Investments (https://capitalatlas.ai/funds/fidelity-investments) — Series E
- Lightrock (https://capitalatlas.ai/funds/lightrock) — Series E, Series F
- Lineage, Inc. — Series E
- Alumni Ventures Group (https://capitalatlas.ai/funds/alumni-ventures-group) — Series E
- Fine Structure Ventures (https://capitalatlas.ai/funds/fine-structure-ventures) — Series E
- CPP Investment Board — Series E
- Shell Ventures (https://capitalatlas.ai/funds/shell-ventures) — Series E
- Trog Hawley Capital — Series E
- Hanwha Power Systems Co., Ltd. — Series E
- General Catalyst Partners (https://capitalatlas.ai/funds/general-catalyst-partners) — Series F
- Temasek Holdings — Series F
- Pictet Group — Series F
- LGT Bank — Series F
- M&G (https://capitalatlas.ai/funds/m-g) — Series F
- Amazon (https://capitalatlas.ai/funds/amazon) — Series F
- Gates Frontier — Series F
- Marunouchi Innovation Partners (https://capitalatlas.ai/funds/marunouchi-innovation-partners) — Series F
- Dcvc (https://capitalatlas.ai/funds/dcvc) — Series F