100 GW Of US Geothermal Power Will Push US Past Gas

July 18th, 2014 by Tina Casey

Natural gas has been having a field day in the US energy profile for the past dozen years or so, but it looks like the sleeping giant of US geothermal power is being nudged out of its stupor. Yesterday, the Energy Department announced that it is plunking down $31 million to rev up a cutting edge geothermal demo project that could enable the US to tap into an estimated 100 gigawatts of geothermal power.

The new geothermal project, called FORGE for Frontier Observatory for Research in Geothermal Energy, is just one of a package of clean energy investments that President Obama has been rolling out in recent days.

US Geothermal vs. Natural Gas

Earlier this week the US Energy Information Agency released a new futurecast in which the base scenario calls for almost 75% of all new generating capacity to be from gas-fired power plants. In consideration of the new geothermal announcement, which comes on top of stunning gains in wind and solar power, it looks like EIA has a bit of revising to do.

Here’s the Energy Department enthusing over FORGE:

The FORGE initiative is a first-of-its-kind effort to accelerate development of this innovative geothermal technology that could help power our low carbon future…This field observatory will facilitate the development of rigorous and reproducible approaches that could drive down the cost of geothermal energy and further diversify our nation’s energy portfolio.

Just one caveat. When you check out the details, the words “fluid” and “underground” come to mind, which conjures up fracking, so we’re going to temper our enthusiasm for now.

The FORGE project basically involves finding ways to “effectively stimulate large fracture networks” (so yeah, kind of like fracking). The idea is to tap into areas underground where the rocks are hot, but the heat doesn’t have a natural way up to the surface.

In industryspeak that’s called an Enhanced Geothermal System. Ideally, an ESG would create pathways that enable fluid to circulate efficiently through rock, and return to the surface piping hot.

That means drilling a well into the target area, and then injecting water at high pressure and/or heat to split the rock. You keep doing that until you have a “fracture network” large enough to sustain a reservoir in terms of heat and flow rate.

All that’s left to do is drill a production well into the reservoir. The returning water should be hot enough to transition to steam at the surface. Alternatively, it could be used to heat another fluid to produce vapor. Steam or vapor, there’s your energy for running a turbine.

Here’s a nifty infographic from the Energy Department:

That infographic looks awfully clean but as described above the process of building an ESG is pretty messy.

However, it’s not likely that a boom in ESG construction would lead to the kind of widespread environmental impacts that have characterized the natural gas industry in states with weak regulations for fracking, including the disposal of fracking wastewater.

We’re thinking that’s the case partly because unlike the wildcatting, all-over-the-place nature of the natural gas (and oil) fracking boom, ESG lends itself to the kind of large scale, centralized installations that could fall under federal jurisdiction.

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