High-Efficiency and Ultra-Low Emissions Linear Generator Demonstration Project in Southern California

High-efficiency, low-emissions linear generator for distributed generation applications using natural gas.

EtaGen, Inc.


Menlo Park, CA

Recipient Location


Senate District


Assembly District



Amount Spent



Project Status

Project Result

Mainspring Energy has successfully installed its linear generator at a Kroger Grocery Store in Colton, CA, and demonstrated 41.5% electric efficiency. The linear generator technology achieved ultra-low emissions and low operational and maintenance costs. Additionally, the linear generator demonstrated the ability to operate flexibly and provide reliable backup power. The successful demonstration attracted a $150 million agreement with NextEra Energy Resource to purchase linear generator units for 30 grocery stores.

The Issue

Existing CHP solutions generally provide the highest economic and environmental returns when the end-use facility has large and steady thermal and electricity loads. Commercial and light industrial facilities, however, typically have smaller and variable thermal loads in comparison to their electricity loads, which makes it difficult for CHP solutions that use existing prime movers (engines and microturbines) and costly fuel cells to provide sufficient economic and environmental returns in the 5 MW and under-size range to warrant the investment.

Project Innovation

Mainspring Energy (formerly EtaGen) is designing, building, and demonstrating an advanced linear generator with compelling economic, environmental, and operational attributes. The demonstration unit will be hosted by a major U.S. communications company. The Mainspring Energy technology, with high electric and high overall efficiencies in the CHP mode, will better fit the energy load characteristics of most commercial and light industrial applications. Intrinsic ultra-low air criteria pollutant emissions coupled with a high-efficiency drive and small greenhouse gas (GHG) footprint on natural gas make Mainspring's technology environmentally attractive. Capital cost and operating cost projections will be on the low side of the DG and CHP technology spectrum.

Project Benefits

Breakthrough enhancements include high electrical efficiency through direct conversion of linear motion into electricity generation; very low emissions through low-temperature combustion without spark, flame or oil; variable compression/expansion allowing for fuel flexibility; standard materials and manufacturing processes to keep capital costs low; and, only two moving parts, no spark plugs and oil-less operation result in low maintenance costs.

Lower Costs


The linear generator technology combines high electrical efficiency (>45%) with low installed cost (<2,500/kW). In terms of efficiency, it is similar to CHP-capable fuel cell technologies while pricewise it will be similar to standard internal combustion engines.

Key Project Members

Project Member

Adam Simpson

Project Manager



DE Solutions, Inc.


Montrose Air Quality Services, LLC


CoreStates Group


Conservation Technology


Match Partners


EtaGen, Inc.


Contact the Team