Geothermal is too expensive, but Dig Energy’s impossibly small drill rig might fix that

On a farm near Manchester, New Hampshire, I was recently treated to a gusher of dirty water, not exactly the sort of thing that most startups will show a reporter. But for Dig Energy, the mud is a feature, not a bug, of its compact drilling rig.

The startup, which has been operating in stealth for the last five years, developed the water-jet drilling rig in an effort to make geothermal heating and cooling so inexpensive that it will displace fossil fuel boilers and furnaces. The rig is central to that, promising to slash drilling costs by up to 80%.

Dig has spent years refining the design of its rig, drilling test holes near its offices in New Hampshire. They’ve drilled through soil, gravel, clay, sand, and a range of different rock types, including sandstone, limestone, granite, slate, and shale. The team showed me test blocks of some very dense rock with neat holes blasted through the middle.

Today’s geothermal drill rigs can do the same, but they’re massive by comparison. The most commonly used versions sit on the back of large trucks. For easily accessible sites, they work well enough. But they are unable to squeeze through side lots into people’s backyards, and at crowded commercial building sites, they occupy precious free space.

While Dig’s prototype isn’t ready for commercial use, what I saw was substantially smaller than widely used geothermal drill rigs. The holes it drills are also straighter than those made by traditional rigs. Together, those two details mean that Dig’s bore holes can be placed closer together, a boon for any developer.

When it’s ready for its first commercial pilots — something this seed round will help accomplish — Dig’s rig will grow in size slightly, but it won’t require the large, double-axle trucks that currently dominate the industry.

The company is planning to sell the devices to drillers, giving them another option for existing projects and potentially opening avenues to new ones. Other companies are exploring the technology, too.

“We shouldn’t have to require people to buy a $2 million rig; it should be something that’s lower cost where they can get into the business,” Madden said. “Geothermal should be in 100% of buildings. It’s in 1% of buildings. So how do we close the 99%?” she added. “It’s effectively an untapped market.”