Taking long-term energy storage to the mountaintop

Mountains could help supply long-term energy storage using simple, inexpensive, readily available technology, according to an article published November 6 in the journal Energy.

Julian Hunt, a postdoctoral research scholar at the International Institute for Applied Systems Analysis, led the research. (IIASA is an independent international research institute.)

Hunt refers to his proposed system as mountain gravity energy storage, or MGES. Here's how it would work:

When energy is abundant, an electric motor (which will later double as a generator) hauls sand or gravel in big buckets from the bottom of a mountain and dumps them into a storage site on the mountaintop. The buckets hang from a continuous-loop cable. The apparatus resembles a ski lift or the sky rides that offer bird's-eye views to visitors at amusement parks.

When the stored energy is needed, the system fills the buckets with sand at the top and lets gravity pull them down to the bottom, spinning the motor-turned-generator to produce electricity.

"Regions with high mountains—for example, the Himalayas, Alps, and Rocky Mountains—could therefore become important long-term energy storage hubs," Hunt said in an IIASA news release.

"Other interesting locations for MGES are islands, such as Hawaii, Cape Verde, Madeira, and the Pacific Islands with steep mountainous terrain."

The system operates like pumped-hydropower storage. That technology involves pumping water to a higher-elevation reservoir, then letting it spin a generator as it flows back down to a lower reservoir.

The difference is that mountain gravity storage uses sand or gravel, which doesn't evaporate. Sand or gravel is also cheap and plentiful. In some areas, water can be a scarce resource that's needed for irrigation or drinking.

Technical issues limit pumped hydro to height differences of no more than 1,200 meters (almost 4,000 feet). The mountain storage system could have a height difference of more than 5,000 meters (16,400 feet).

Mountain gravity storage could also incorporate hydropower. Water from mountain streams could be diverted into the buckets at any point on the mountainside and stored at the top along with the sand or gravel.

Hunt and his colleagues envision mountain gravity storage as filling long-term gaps in energy generation. For example, it could fill in during seasonal lulls in the availability of wind or solar power or conventional hydropower. It could provide supplementary power on islands for heavy tourism seasons. Batteries or other nimble storage devices could take up the slack for shorter-term needs, such as supplying electricity overnight in lieu of solar power.

"It's important to note that the MGES technology does not replace any current energy storage options," Hunt said, "but rather opens up new ways of storing energy and harnessing untapped hydropower potential in regions with high mountains."