Coal mines’ rebirth as clean-energy source plotted in Appalachia

BEN CHAFIN Sees the future of clean energy in abandoned coal shafts.

The Virginia state senator, whose Appalachian district is pockmarked with empty mines, pushed through legislation in April that encourages companies to transform those tunnels into giant storage devices to hold vast amounts of renewable power.

The idea, which Dominion Energy Inc. has been studying, is to fill mines with water and then use electricity from wind and solar farms to pump it up to a reservoir on the surface. When utilities need power, operators open floodgates, letting water gush back into turbines on its way down.

“Voila-you have electricity,” said Chafin, a Republican. “These deep mines can act just like a giant battery.”

The technology Chafin is pushing is not new-its first use was for a Swiss hydroelectric plant in 1909. But it wasn’t until the 1960s and 1970s that the technology flourished, mostly to store surplus energy from nuclear plants. It has since been largely ignored-until now. As wind and solar boom, the need for grid- scale alternatives to lithium ion batteries has increased.

Unlike coal and gas generators, wind and solar farms don’t provide a steady flow of electricity-the sun doesn’t always shine and winds kick up and die down, defying forecasts. Giant batteries have long been considered the elusive solution to balancing clean energy’s ebbs and flows, allowing it to be more widely used.

The problem is that lithium ion batteries-the technology

The idea is to fill mines with water and then use electricity from wind and solar farms to pump it up to a reservoir on the surface. When utilities need power, operators open floodgates, letting water gush back into turbines on its way down.

used, for instance, in Tesla cars just can’t be built large enough to get the job done. That’s got developers scouting deep holes in the ground, reimagining this old technology that relies on little more than gravity and millions of gallons of water.

It remains to be seen whether pumped storage technology will actually work in old mines. Nonetheless, developers from Germany, to the UK, to the US are giving the idea a try.

High above the sand and sagebrush of southeastern California, a transmission line runs along Interstate 10, connecting solar farms in the Sonoran Desert to Los Angeles. From daybreak to nightfall, that line crackles with electricity as photovoltaic panels soak up the sun. It goes quiet just as millions of people turn on their lights.

“When the sun sets, that line goes empty,” said Steve Lowe, president of Eagle Crest Energy Co. “We want to do something about it.”

Eagle Crest is partnering with NextEra Energy, Inc., the US’ biggest clean energy developer, to build a 1.3 gigawatt, pumped-hydro facility near a sun-baked crossroads named Desert Centre. The US$ 2 billion project, already approved by federal regulators, could stockpile enough electricity to power nearly one million homes. It will utilise two pits left over from a defunct iron- ore mine dug into the side of a mountain. During the day-when solar power floods the grid-pumps will move water to the upper pit, ready for release at night. Lowe estimates it will take six years to build.

For all the talk of lithium ion as the future, pumped hydro is by far the most prevalent form of energy storage in the US, accounting for about 97 per cent of capacity. There are more than 40 existing facilities nationwide, with a combined capacity of more than 20 gigawatts. That’s enough to power all of New York City for several hours.

“They are the hidden story of the electricity grid,” said Jeff Leahey, deputy executive director of the National Hydropower Association. “But they are not sexy.”

Nor are pumped-hydro facilities easy or quick to build. The technology may be elementary, but it requires just the right spot, with a steep ascent and room for lots of water. Even a small project can cost US$ 1 billion, Leahey said. And since almost no one is building nuclear reactors these days, just a handful of pumped-hydro plants have been constructed in the Us over the last 25 years.

Renewables may change that.