But Seriously: Can You Use Gravel to Store Renewable Energy?
Maybe. A recent white paper concludes that “‘mountain gravitation energy storage’ [MGES] could be a viable alternative to long-term energy storage, particularly, in isolated micro-grids or small islands demanding storage capacities lower than 20 MW.”
Engineering website Hackaday broke it down like this: “MGES involves storing excess energy from the grid by raising sand or gravel to a higher elevation. This is achieved using a pair of cranes, which load the material into storage containers, before pulling them up to height on a cable. The material can then be held in storage at higher elevation until power is requested by the grid. At this stage, the material can be reloaded into storage containers, and lowered to the bottom storage site, with gravity doing the work to pull the weight back down, turning a generator in the process. Interestingly, the same electric motors that lifted the gravel in the first place can also be used as the generators.”
It’s a lot like pumped hydroelectric installations, Hackaday points out, only instead of water, the process uses, um, rocks.
Reaction from engineers and others about the idea’s efficacy ranged from mild interest to outright skepticism. As one noted, comparing the idea to hydroelectric plants, “Rocks don’t evaporate, but sometimes you get extra bonus energy/water from the sky. When it’s raining rocks, you’ve got other problems.”