A Gravity based energy storage system stores energy using weights
As the generation of renewable energy is increasing, demand for new ways of storing this energy has also started to rise. This is required because the main source of this renewable energy is either sun or wind and when they are not available, there must be a way to ensure an uninterrupted power supply.
Gravitricity, a Scottish Company, is making a big leap in this direction. The company is building a demonstrator facility for a new system that stores energy using gravity.
The concept is quite simple and this makes the innovation highly scalable. The weights are pulled & held aloft at a place using powerful cables and winches. These weights thus store huge amounts of potential energy.
When the energy is needed, the weights can be lowered down to spin the winch and generate and feed electricity into the grid.
The weights in the range of 500 – 5000 tonnes are suspended in a deep shaft using a number of cables, each of which is attached with a winch capable of lifting its portion of the weight. Electrical power is then consumed or generated by raising or lowering the weight. To prevent the weights from swinging and ultimately damaging the shaft, a system of tensioned guide wires guide the weights. To ensure the stability of weights in the holes, the winch system is accurately controlled through the electrical drives.
Output Power & Efficiency
According to the company, the peak power output from these units is in the range of 1 and 20 MW.
This giant mechanical battery is recharged using electricity from renewable sources that power the winches to lift the weights back to the top. The overall efficiency of the system is between 80 and 90 percent.
The concept of lifting weights and storing energy is not new and is currently being attempted by other companies too. The true innovation of Gravitricity is the combination of creative approaches that it has adopted:
- using the depth instead of the height for raising and lowering the weight. The constraints associated with the height, limit the system’s power generation capacity. Also with increasing height, safety becomes a critical parameter due to the involvement of large weights.
- The swinging of weights is prevented through the company’s unique patented system of tensioned guide wires.
- The energy storage capacity of their system can be increased to a great extent if the shaft is used as a pressure vessel, enabling a compressed air energy storage to run alongside the gravity (weight) based energy storage system. This requires adding a pressure-tight “lid” to the top of the shaft and lining the shaft to prevent leakage. The ground provides the resistance except at the very top of the shaft.
The company is constructing a 16m tall tower for hoisting & dropping two weights of 25-tonne each for generating 250 kW of power.
“In one test we’ll drop the weights together to generate full power and verify our speed of response,” says Miles Franklin, lead engineer at Gravitricity. “We’ll then run tests with the two single weights, dropping one after the other to verify smooth energy output over a longer period, alongside a program of other tests to demonstrate and refine the full capabilities of the system.”
Capabilities of the Innovation
This extremely effective way of storing energy offers many capabilities and advantages:
- Can function for up to 50 years with no cycle limit or loss of performance
- Response time – zero to full power can be obtained in under a second. The system can quickly release its power payload in just 15 minutes or slow it down to last for up to eight hours.
- Versatility – can be designed to supply any amount of power (ranging from low to high)
- Simplicity – The system is easy to construct near networks
- Cost-effectiveness – The Levelized cost of the system is well below lithium batteries. It stores energy at a cost that is lower than other grid-scale energy storage systems, like Tesla’s huge lithium-ion battery in Australia.
To Wrap Up
The value proposition offered by the company is quite promising for network-constrained users and generators, and major power users seeking a long term, fast response, and reliable means of energy storage.
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