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Geothermal power has the potential to be cheap, reliable, and abundant—running off the heat of the Earth 24 hours a day, seven days a week. That’s especially true thanks to a new generation of home-grown geothermal plants, which don’t run off the steam of natural hot springs and geysers. No need to find those hydrothermal gems; today, geothermal engineers are making their own reservoirs by drilling down into hot rock and pumping in water.

The catch? Engineers can’t see what’s happening underground. Drilling wells in just the right spot can be like playing golf blindfolded: Even if someone faces you in the right direction, you could still hit the ball way off the green. But tiny fragments of DNA dropped into the wells could soon help engineers follow the path of water underground, helping them sink their putts every time.

In a basic geothermal plant set-up, engineers actually have to drill two types of wells. The first kind, which goes down two or three miles, carries cold water down deep, where it fractures the hot rock and creates new paths for water to move. It’s kind of like fracking, but without the chemicals.

The second set of wells, called production wells, intersects with those fractures to carry the (now hot) water back up to the surface—hot water that produces the steam to turn the turbines and create electricity.

Now, for a drilled geothermal plant to produce a maximum amount of energy, engineers have to place its multiple production wells very carefully, making sure that each new well has the best chance of delivering that steamy hot water. A good production well hits just the right places—crossing fractures that are deep, big, and long, so water flows into it really easily.

But engineers don’t have a device that can show them where the initial wells opened up fractures, or how long they are. So they’re trying to map them by tracking the flow of water underground.

Right now, engineers can test the path of water with a range of tracers from chemicals to radioactive elements to fluorescent dyes. But those methods can produce muddled results. Scientists mix the tracers with water flowing into the injection well and then monitor the production wells, where they should show up after about a month. But the tracers could get trapped or destroyed; they could be leftover from a test that happened six months ago, or they could go completely haywire—as one research group experienced. They presented their results at the World Geothermal Congress this year.

The group had put a few tracers into a well, and one of the tracers seemed to disappear altogether. The tracer that did eventually appear happened to be one that the group hadn’t even introduced to the well—so they concluded that a chemical reaction had transformed it from one material to another.

“That’s the kind of complication that happens in field practice that we want to avoid by using DNA,” says Roland Horne, a geothermal engineer at Stanford University. With specific DNA tags—even if you lose some of them—you would be able to know exactly where you injected a tag and at what time.

Building on work by scientists trying to preserve long DNA codes, Horne’s geothermal team used short, synthetic DNA fragments to track moving water. The DNA has a unique pattern of about a hundred base pairs, and it curls around a tiny silica ball. (Our genetic code is pretty clingy, curling around the ball on contact.) Then, the team puts a silica shell around the DNA to protect it. Horne is presenting the lab results at the Annual Geothermal Resource Council conference in Reno this week.

“It’s a very neat idea, because the unique signature of these silica balls would give you a lot of information,” says Michael Bartl, a chemist who works on geothermal tracers at University of Utah. “The big question when it comes to DNA will be temperature.” In underground fractures, the environment is very harsh, with intense pressure and temperatures that hover around 600 degrees Fahrenheit.

So far, the DNA silica balls have survived six hours in 300 degrees in the lab, but they haven’t been field tested. Horne and his team still have to work to safeguard the DNA for the long field trials. And that will be the next step—more endurance under more heat—as part of the race happening all over the world to find tough, reliable and accurate tracers.

If the tags do succeed in field tests, knowing the locations of the biggest fractures and best wells will allow plants to invest resources wisely. And once they have that figured out, geothermal really could go anywhere.

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Balls of DNA Could Fix Geothermal Energy’s Biggest Problem

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