One of the largest US utilities is buying small, fuel-flexible generating units by the hundred megawatts. Mainspring Energy said on 13 October that American Electric Power has signed a sales agreement for up to 1.6 GW of its linear generators through 2034. AEP has already bought the first tranche of 190 MW, with deliveries starting in 2027. Mainspring calls it the largest procurement of linear generators so far.
How Big the Order Really Is
The 1.6 GW is a ceiling, not a firm figure. Utility Dive reports that AEP can take about 200 MW a year and that the agreement could be worth up to $4 billion if it is used in full. POWER magazine adds that AEP has not said whether the units sit inside its capital plan, and no deployment sites have been named. The order is also a first for Mainspring in another sense: until now it sold mainly to commercial and industrial customers and data centers, and this takes it into the investor-owned utility market.
AEP chief executive Bill Fehrman said in the release that the generators can add capacity quickly and efficiently. Mainspring's chief executive Tom Linebarger told Bloomberg, as quoted by Utility Dive, that the units are expected to be online within 12 months.
Not an Engine, Not a Fuel Cell
A linear generator has no crankshaft. According to Mainspring's product information, summarised by POWER, fuel and air are compressed until they react, and that reaction drives oscillators back and forth through copper coils, 13 times a second, which produces the electricity directly. The company describes the reaction as low-temperature and flameless. The units are sold as 2.5 MW packages made up of ten 0.25 MW units, so the first tranche works out at 76 packages.
They run on natural gas, biogas, hydrogen or propane, in any blend. The datasheet POWER cites gives 46 % electrical efficiency on a lower heating value basis and NOx below 1.5 ppm. Mainspring began commercial shipments in 2020 and says it has hundreds of megawatts in development and in the field.
Part of a Wider Buying Spree
The order landed in the same week as AEP's plan for a 702 MW Bloom Energy fuel cell plant near Cheyenne, Wyoming, built for Google under a 20-year power purchase agreement and costing about $4 billion. In July AEP said it had secured about 13 GW of gas turbines for deployment through 2031. Against roughly 69 GW of contracted load additions through 2030, its finance chief has said much of the demand is held back by a lack of generation.
For people who work with reciprocating gensets, the interesting part is the shape of the purchase. A utility is buying modular, distributed units in small blocks because they arrive in months rather than the years a turbine slot or a transmission line takes. That is the same argument that has put engine plants behind the meter at data centers, and it means more sites with many small units, gas supply on site and air permits written around frequent running.
Whatever the technology, the questions on site do not change much: who maintains dozens of units, what the gas connection looks like, and how the fleet is tested at commissioning before it carries real load. Those are worth asking early, when the delivery date is the only number anyone is talking about.
Sources: Mainspring Energy (press release), Utility Dive, POWER