Enel put a generator down Cove Fort's injection well to make power from returning brine

Ars Technica reported in December 2016 that Enel Green Power, which bought the defunct Cove Fort geothermal plant in Utah in 2007, saw it had 'an exponential amount of hydraulic energy' in water re-injected after use. With oilfield service firm Baker Hughes it installed a downhole generator in the injection well, opposite the production well that pumps brine up. A turbine above spins as the brine falls and a generator converts that to electricity.

Enel says the addition produces an extra 1,008 megawatt hours, improving efficiency by 8.8 percent at a plant making 160,000MWh a year. Senior operations manager Brian Stankiewicz said it also controls how fast brine returns to the aquifer, limiting damaging 'turbulent vortexes'.

Enel had converted the old steam plant to a binary cycle design that uses pentane, reopening it in 2013. The 25MW plant powers about 13,000 homes for the Salt River Project in Arizona.

Brine dropping down an injection well carries unused gravitational energy.

A turbine in the well captures it without changing the main generation process.

Controlling flow protects the underground rock and aquifer.

Cove Fort's geology gave enough head pressure and flow to make it worthwhile.

Look for waste energy in a process's return path, not only its main loop, and add a harvester that also solves a side problem.

A correction notes that a Northern California Power Agency project predated Enel's geothermal-hydro combination, so it was not the first. Enel said the idea could likely work at other sites with the same geology, but each injection well needs analysis to confirm there is enough head pressure and flow.