Learning Curves and Enhanced Geothermal (Part 2 of 2)

I recently listened to two podcasts by Dave Roberts both of which individually are well worth checking out. The first is on learning curves and their implication for renewable energy policy and the second is on enhanced geothermal power. In both, Roberts interviews authors of recent studies on the respective topics. After listening to them, I wondered how learning curves apply to enhanced geothermal power. To learn more, I dug into the studies covered in the podcasts and then turned to my colleague Yeh-Tang Huang to get the latest on geothermal. This, then, is the second in a two-part series on learning curves, enhanced geothermal power and speculating about what learning curves can tell us about the future of the cost of enhanced geothermal power.

Part 2: Will enhanced geothermal power be big and affordable if we move fast?

Coauthored with Yeh-Tang Huang

Enhanced geothermal power has been a potentially zero-carbon source of electricity for a little over two decades, but it might finally be ready to deliver on its promise. In fact, a recent study covered in another great podcast by Dave Robert suggests that enhanced geothermal systems (EGS) might be flexible in a way that would make them a valuable complement to wind and solar. How big a role enhanced geothermal systems (EGS) play in a clean energy future will depend on whether its costs follow a learning curve similar to wind and solar or one more like oil and gas. (For more on learning curves, see part 1 of this series.)

To avoid the worst impacts of the climate crisis, we need to eliminate carbon emissions from our electric grid by 2050. Removing the last 5 percent of greenhouse gases from the grid is going to be the most expensive step. (See the figure below from this recent helpful NREL release.) Wind and solar power are increasingly the least expensive and easiest to build sources of electricity, but once we get to very high levels of wind and solar deployment, it gets harder and harder to meet the needs for those times when the wind doesn’t blow and the sun doesn’t shine. The cost of storage is dropping—following a learning curve of their own—and batteries promise to play a big role in reaching 100 percent carbon-free power. However, having a zero-carbon source of electricity that can be dispatched anytime, day or night would be a game changer.

Enter, maybe, enhanced geothermal power. Unlike conventional geothermal power, which is only available where there’s hot water stored in permeable rocks below the ground, enhanced geothermal systems (EGS) can take advantage of a broader range of below-ground heat sources. This makes EGS potentially geographically available across much more of the country. The National Renewable Energy Lab has estimated that the technical potential is over 5TW, and in 2019 a Department of Energy (DOE) study put the economic potential over 100GW. Furthermore, some of the new approaches to EGS promise not only to be more widely available but also to be at least partly dispatchable.

If you want to know more about how EGS works, here are some resources. But the basic idea is to drill wells down into hot, dry rock and, using high-pressure water and maybe some acid, open up a path between the injection end and the production end. Once the connection is made, water can be pumped down the injection side, get heated by the rock, and then brought up on the production side, and the heat can be used to generate electricity. To be dispatchable, the production side is partially closed while water is pumped down the injection side, building up pressure and absorbing heat. Then when electricity is needed, the production side is opened.

Drilling the wells uses both technologies and expertise from the oil and gas industry. In fact, currently all the drilling rigs and teams currently available are primarily oil and gas rigs. Connecting the injection well and the extraction well requires fracking and also draws on oil and gas expertise. While this connection may initially give some pause, it creates a fantastic opportunity to deploy an already-trained workforce into an industry that could help secure our zero-emission electricity future.

While the fracking process is very similar, there is reason to be optimistic that the fracking involved with EGS will not cause water pollution or seismic activity as natural gas fracking has. Afterall, the goal of EGS is to effectively create a closed loop. Any leaking from that loop would effectively be lost heat and an increase in cost. In fact, there are companies developing technologies to prevent breaks such as Altarock. In other words, the interests of the developer and everyone who wants to drink clean water are aligned. Even should leaking occur, the impact on drinking water would likely be minimal because the reservoirs are typically much deeper than and thus disconnected from groundwater sources. As for induced seismicity, risks should be mitigated by avoiding major faults and strictly following seismicity protocols such as the DOE’s, which entails more seismic safety requirements than those imposed on oil and gas projects. Nevertheless, permitting agencies still need to require appropriate studies and monitoring to make sure EGS lives up to its potential.

Just being dispatchable would increase the value of EGS by about 60 percent based on the study covered in Dave Robert’s podcast, but for EGS to play a big role in getting to 100 percent clean energy it will have to come down in cost significantly. EGS is currently estimated to cost $450/MWh whereas new natural gas combined cycle turbines are estimated to cost between $45-$74/MWh. If the technology follows a learning curve similar to wind and solar, the faster we deploy EGS, the more money we will save.

On the one hand, the drilling and electricity generation technology involved in EGS systems will largely be the same from project to project allowing for more of a manufactured, streamlined system, similar to wind and solar, and offering the potential for learning-by-doing. On the other hand, as with oil and gas, the easiest and most understood geothermal resources will be tapped first. This may trap EGS in the same “running to stand still” phenomenon as oil and gas, where cost savings from learning just balance out higher costs from having to develop deeper and less well-explored resources. The bottom line is it’s too soon to know if EGS will have a consistent learning curve.

Add this uncertainty on top of questions that still need to be answered about water pollution, induced seismicity, and how broadly dispatchable EGS will be, and it becomes clear that we can’t bank on this exciting technology being a big part of the solution yet. Fortunately, the federal government has nearly $300 million for research, development and pilots of EGS and, around the world, there are at least 29 EGS projects that are generating power at an increasing rate. With a lot of hard work and some of the right kind of learning, EGS could prove to be another important tool in the fight against the climate crisis and another tool that saves us more money the faster we deploy it.