Energy Cache, which includes Bill Gates among its investors, has built a 50 kW prototype in Irwindale, Calif. There’s another large-scale prototype in Pennsylvania, involving dozens of lifts. An unnamed lift supplier is also said to be involved in these projects.

The concept of ski lift energy storage has been debated at energy storage conferences for several years. The idea is similar to water storage systems, which involve pumping water uphill, and then releasing that water to power a turbine located down the hill.

There are advantages in using gravel instead of water. For example, a system can be set up in more locations, including areas where water is a scarce commodity. And gravel/lift systems are easier to scale up. A utility-sized installation could include hundreds of lifts. By one estimate, a gravel-based system would be up to 40 percent less expensive than a water system, in part because the technology already exists in the mining and ski industries.

Will this come to pass? Stranger things have happened. However, it’s worth noting that one investor involved in the development of such systems calls this the most “out there” technology he has supported.