Sage Geosystems has pioneered a new way to store cheap energy, using the earth as a giant bellows to pump water into cracks in the ground and then letting the water spurt out with 70% efficiency. If heat energy is also harvested, the efficiency can reach 200%.
This method injects a liquid, usually steam, into shale oil deposits and leaves it there for several hours to heat the oil and lower its viscosity, making it easier to pump out.
Sage Company, on the other hand, uses high-density drilling mud deep underground in abandoned oil wells to push slender cracks open at high pressure, and then uses a high-pressure pump to pump water in to keep the cracks in an "inflated" state. The work is done using excess renewable energy collected during the day, then valves are closed to lock in the water.
When energy needs to be recovered, the valve is simply opened; formation pressure around the fracture squeezes the fractures back together and the water is forced back into the pipe, where it is run through a turbine to generate electricity. In fact, when the system is run in reverse, the motors and pumps that originally forced the water down the pipes become turbines and generators, pumping the energy back out.
This is the "EarthStore" system that Sage tested using an old oil well in Texas, with a round trip efficiency of 70-75%, measured fluid losses of only 1-2%, and no induced seismic activity detected. Sage said that if a single oil well is used as a load-following quick-release system, it can produce a maximum output power of about 3 million kilowatts; if it is used as a solar power generation system, it can release energy in a more precise way, providing more than 18 hours of power at night when solar power is not generating electricity.
But having access to old oil production wells deep in the earth has another benefit: heat. A system like EarthStore can be profitable enough as a grid or local energy storage system, but once you start factoring in heat, it starts to become extremely attractive.
The deeper the Earth, the warmer it gets, and reaching temperatures of 180-220°C (350-430°F) is relatively easy. Harvesting this geothermal energy is usually not cost-effective, but the "huff&puff" energy storage system significantly changes this number.
The EarthStore system holds water together with hot rock, bringing it into substantial contact with the surface and locking it there. So when the water is released, the heat not only increases the pressure on the water's return flow, making the turbines run more powerfully, but there's also an opportunity to capture the heat through the heat exchanger so that you end up getting more energy out of the "earth battery" than you put in.
That's not all; Sage suggests that if multiple geostorage wells are located next to each other and the drilling equipment does not need to be dismantled for transportation, thus saving costs, they could be combined to run as a multi-cylinder thermobaric engine.
The array pumps hot water from an underground reservoir, cools it using a heat exchanger to harvest electricity, and then immediately pumps the cooled water directly to a well next door for storage. Instead of storing liquid above ground, the entire process can run back and forth between the two cylinders.
According to Sage, installing 18-20 of these devices at one site would create a 50-megawatt renewable energy storage plant, effectively outputting twice the energy input. You can think of it as enhanced energy storage, or you can think of it as a way to make relatively shallow geothermal energy more economically viable, but it's a pretty neat idea.
Sage said that in terms of level cost of storage (LCoS), the EarthStore solution itself should be cheaper than lithium-ion batteries or pumped hydro storage - in fact, as a method of stabilizing the grid during peak periods, it is expected to cost as much as gas-fired peaking plants.
The six-month pilot program in Texas has now ended. The project utilized an exploration well to drill holes at depths of 7,920 ft and 11,140 ft (2,400 m and 3,400 m), creating a 3,200 ft (1 km) high and 200-300 ft (60-90 m) wide fracture.
The walls of this crack were only 0.1-0.2 inches (2.5-5 mm) apart, but by pumping and releasing water, and constantly maintaining enough pressure in the system to prevent the crack from closing, the volume of the crack expanded and contracted by a factor of 2, fluctuating between 7,500-15,000 barrels (1.2-2.4 million liters, 315,000-630,000 gallons).
"We've cracked the code to perfectly complement renewable energy, delivering reliable, cost-competitive power with lithium-ion batteries and natural gas peaking plants," Sage Geosystems CEO Cindy Taff said in a press release. alternative baseload. Our energy storage technology can provide large amounts of power - from remote mining operations to data centers to solving energy poverty issues in remote areas. We can interconnect to the grid or develop island/microgrids with proven and ready-to-scale energy solutions."
Sage, which has received investment from drilling specialist Nabors Industries and cleantech venture capital fund Virya, hopes to raise an additional $30 million in its current Series A round and continue validating, commercializing, optimizing and scaling the system.