As the global economy attempts to further distance itself from fossil fuels, renewable sources of energy are receiving increasing attention.
Yet for all the potential of green energy sources – be it solar or wind power – there remains the unavoidable problem of intermittency. Wind power generation is contingent on windy conditions, just as solar is reliant on it being sunny, meaning predictable energy generation is never a given.
In order to ensure the grid has enough energy in its system – and avoids blackouts – long-term energy storage is required. Only then will there be enough power to keep the lights on in the event of a sunless or still day.
While traditional lithium ion batteries are able to store energy for short amounts of time, they are insufficient when it comes to long-term energy storage. And while there is evidence to suggest pumped hydro-storage might be able to store energy for longer periods, with large generation capacities, it remains incompatible with grids with smaller demand.
However, a new paper to come out of the Austria-based International Institute for Applied Systems Analysis (IIASA) has proposed a new concept that could be the answer to the storage service question. And the system is based upon that most awe-inspiring of topographical features: the mountain.
Going off-piste: introducing MGES
Known as mountain gravity energy storage (MGES), the technology works by simply transporting sand or gravel from a lower storage site to an upper elevation, storing potential energy from the upward journey and releasing it on the way back down. The higher the height, the greater the amount of stored energy, claims the research.
The paper’s writer is Julian Hunt, who headed up the IIASA team of researchers. It also proposes that MGES could be combined with hydropower in the case of river streams on a summit, whereby water, in periods of high availability, could replace sand and gravel in the storage vessels.
Yet, the concept of gravitational energy is not entirely new, says Hunt, who has published previous papers on its potential. He also alludes to an attempt by Bill Gates back in 2012 to create an energy storage system by transporting gravel on ski lifts. The project was later abandoned.
“He spent several million dollars trying to develop the technology, but gave up in the end,” says Hunt. “But if you want storage for the long term, it’s a still a viable alternative.”
Advantages: Longer storage and cheaper
On paper, MGES carries several benefits. For instance, unlike pumped hydro-storage plants – which tend to be limited to height differences of approximately 1,200 metres as a result of high hydraulic pressures – MGES could extend past 5,000 metres, allowing for greater long-term storage.
“This could certainly benefit mountainous regions, such as the Himalayas, the Alps or the Rockies,” says Hunt. “Even in the UK, it could perhaps work in Scotland or Wales, although I doubt England is mountainous enough.”
The use of sand also carries an innate economic advantage. “Sand is cheap, and unlike water, it doesn’t evaporate, meaning you never lose potential energy and it can be reused again and again. This makes it particularly interesting for dry regions.”
According to Hunt’s calculations, the cost of MGES ranges from $50- 100 megawatt hours of installed capacity. The system, he argues, could make a good fit with micro-grids, in the region of 20MW, which have smaller energy demands in tandem with seasonal storage requirements. This, says Hunt, means MGES could be well suited to small islands and remote locations.
The end of lithium ion batteries?
Could MGES really provide a viable alternative to lithium ion batteries, which have been subject to drastic cost reduction in recent years, making them much more affordable than in the past?
“The answer is yes,” says Hunt. “Lithium batteries tend to only really be used for one-day storage, costing something like $200 MWh. If you use them every day for a year, it’s still $200 MWh, but 365 times more expensive, requiring 365 different batteries. That’s not a good solution for long-term storage.”
Hunt’s research stresses that while MGES could bridge the gap between pre-existing short-term and long-term energy storage systems, it wouldn’t be utilised for storing energy across daily cycles. That said, the technology would be able to store energy on a monthly basis and then generate power in the following months.
Hunt is hopeful his research will be picked up and developed into a commercial project, although he has no plans publish any further papers on MGES in the immediate future. He does, however, “remain committed to proposing solutions for long-term energy storage.”