By combining the heavy rig drilling technology and the power of earth’s gravity, Gravity Power is testing a unique renewal energy storage mechanism which will have the storage capacity running into gigawatts. The test is being conducted at a site in Santa Barbara. The project begins with underground drilling of thousands of feet to provide space for 18 ft diameter storage shaft and six feet diameter return pipe.
Procedure
The procedure involves a large concrete piston, ‘weight stack’, fitted at the bottom of the shaft. A return pipe that runs parallel to the shaft is also bored into and is connected to the top and bottom ends of the main shaft. The entire apparatus is filled with water before being sealed tight.
The process of energy storage begins at off-peak electricity hours during which the return pipe pushes the water down with the power supplied by a pump, and raises the weight stack. The position of weight stack determines the amount of energy stored. During the peak hour, the stack is released which is pulled downwards by the gravitational pull and pushes the water back into the return pipe that reverses the direction of the pump, resulting in power generation.
Cost and efficiency
A 7 acre site has the capacity to produce 2 GW of energy at a cost of $150/kWh for a system that can store 200 MWh, which a bit higher than the pumped hydro. The Gravity Power Module has a conversion efficiency of anywhere between 75 and 80 per cent.
Eco-friendly system
Pumped hydro installation, with installation cost of $100/kwh, do not conform to the renewable energy standards as the system negatively impact natural habitat for aqua life. With increasing power need, Gravity Power could be the ultimate solution.
Source: cleantechnica
