Power outages can cripple businesses and back-up generators are often diesel fuelled, expensive, noisy and dirty. Enter the 220- 250kw fuel-flexible "linear generator". Mainspring's generators can run on natural gas, propane, biogas or hydrogen, and are designed to ramp up and down to fill gaps in power supplies, either on their own or as part of a microgrid with renewable energy & battery storage. The simple (compression) design, with no flame/spark or spinning elements, also means it should be lower cost, lower maintenance and lower emissions to other traditional generators.