Gravity Power is testing a novel kind of energy storage with potential gigawatt-scale capacity – that uses simple mechanics and gravity underground – at a first test site in Santa Barbara.
Their Gravity Power Modules would marry traditional heavy rig drilling technology with renewable energy storage.
At utility-scale, the pumped storage would begin with drilling thousands of feet underground, large enough to accommodate an 18 foot diameter storage shaft and a 6 foot diameter return pipe.
Here’s how it works, in the elegant words of Powermag
“At the bottom of the shaft is a large concrete piston fitted to the shaft, called the “weight stack.” Also bored into the ground is a parallel but smaller-diameter “return pipe” that is connected to the main shaft at the top and bottom.
Finally, the entire volume is filled with water and tightly sealed—air is compressible and its presence reduces the system effectiveness. In essence, the position of the weight stack in the shaft determines the amount of energy stored.
During the energy storage process, off-peak electricity is used to power a pump that pushes water down the return pipe that will raise the weight stack from the bottom of the deep storage shaft.
During a peak electricity demand period, the weight stack is released, which pushes the water up the return pipe, reversing the direction of rotation of the pump-turbine and producing electricity, much as in a typical pumped storage hydroelectric plant.”