Gravity-based energy storage, like pumped-hydro, is based on simple principle: use energy during the charging phase of the system to transport a solid mass from a lower location to an higher level and discharge energy by releasing the mass to rotate an electric generator.
The higher the mass in question is transported, the more energy will be released upon its descent and on that basis, Austrian researchers have proposed a ‘mountain gravity energy storage’ (MGES) system. The scientists claim such a storage system could be combined with hydropower and would be ideal for locations with low demand for energy storage capacity – they suggest around 1-20 MW – plus long-duration cycles of anything from seven days to three years.
In the paper Mountain Gravity Energy Storage: A new solution for closing the gap between existing short and long-term storage technologies, researchers from the International Institute for Applied Systems Analysis, said the technology – which is already said to be used in sectors including construction, recreational sites and mining – could cost $50-100/MWh of stored energy and $1-2 million/MW of installed capacity.
Long storage cycles
The technology would involve two cranes on the edge of a mountain from a storage site at the base and an electric motor on an upper storage site to transport a solid mass of sand or gravel. “The horizontal bar of the crane in the upper and lower storage sites moves up and down according to the level of the storage sites to maximize efficiency of the system and to maintain the cables as stretched so that the process can function properly without having to change the length of the cable in the system” state the researchers.
MGES plants, the researchers say, could be designed to store energy for months and to generate a small but constant amount of energy for long periods. “This small but constant electricity generation could be combined with other storage technologies such as batteries, to balance the short-term variations of electricity demand, solar and wind generation,” the research team stated, adding: “Mountainous regions where the potential for MGES is higher favor wind power in detriment to solar power projects.”
The authors of the paper claim the technology has limited visual and environmental impact due to the restricted area required for the cranes and storage sites.
This year, U.S. company Energy Vault has unveiled gravity-based storage technology relying on a crane working with 35-ton concrete bricks. The crane orchestrates the energy storage tower and electricity charge/discharge and accounts for factors including energy supply and demand volatility, weather, and inertia, according to the company, which SoftBank backed with $110 million in August. “Energy Vault will be demonstrating the first 35 MWh storage tower, in the north of Italy, in 2019,” said the Japanese conglomerate at the time.