As Boulder City leases more and more land for energy production on the outskirts of the city, questions about excess production and energy storage inevitably arise.

Last year, the City Council voted to approve an energy storage facility that would use large batteries to store energy. But in June, they voted 4-1 (over opposition from Councilman Matt Fox) to approve the first phase of a zoning amendment to allow an energy storage facility that would not use batteries. Fox opposed the site because he believes it is too close to areas that some of his supporters use for recreational off-road vehicle activities.

The proposal from Canadian company Hydrostor would be something no one has ever seen in Boulder City.

Let’s start with a brief overview of electricity generation in the engineering marvel that is the very reason for the city’s existence – the Hoover Dam.

The dam impedes the flow of the Colorado River and transforms a former desert valley into a reservoir that is over 360 meters deep when full.

The water continues to flow into the area, reaching the dam at a depth of nearly 900 feet and becoming a sort of giant indoor waterfall. As the water falls through large pipes to a point near the bottom of the dam where it is released back into the river, it drives huge turbines. An old turbine can be seen in Wilbur Square. The turbines spin a shaft, which in turn spins a series of magnets in a casing made of copper coils, and the fluctuations in the magnetic field are converted into electricity.

Most power generation plants, including wind power, use the same type of rotating arrangement. The difference is in the energy used to create the rotation. Solar power is the only exception here.

As more and more solar panels are installed to convert sunlight into electricity in a valley where the sun shines almost year-round, the point is quickly approaching where Eldorado Valley will produce more electricity during the day than the grid can absorb. The challenge is storing this “excess production” so it can be used after sunset.

Dean Tuel, Hydrostor’s vice president of origination for North America, recently spoke to the council to explain how the system works. In its simplest form, the technology uses excess solar energy and then the weight of water to compress and then release air in a way that drives the same turbines as in the Hoover Dam, only in the middle of the desert.

Hydrostor was co-founded in 2012 by Curtis VanWalleghem and Cameron Lewis. Together they developed the idea for A-CAES (compressed air energy storage) technology.

If the project does go ahead, Hydrostor plans to dig a large underground cave in a 300-hectare desert area. Above the cave, a reservoir and turbines will be built that will serve a dual purpose.

The cave would be filled with water (a “one-time” fill, as Tuel put it). During the day, excess solar energy would be used to drive turbines in one direction to compress air and force it into the cave. The air would be compressed so much that it would push the water up and then out of the cave into the reservoir. The air compression process would generate heat, which would be captured and stored to be used later in the process.

At night, when the air is no longer compressed and pumped into the cave, the weight of the water flows back into the cave, displacing the air and causing it to flow in the opposite direction, driving the turbines and generating electricity.

In short, it is not about storing electricity in the form of electrons, but about storing the electrical potential in the form of kinetic energy.

“We hope to bring an A-CAES facility to Boulder City and are excited to work with the Boulder City Council and the Boulder City community to make this a reality,” said Hydrostor President Jon Norman. “A-CAES facilities provide numerous economic benefits to the communities in which they are located and are built on a relatively small land footprint, which are significant advantages compared to traditional energy storage projects.”

While compressed air has been used to drive turbines before, it has always required a heat source, which in turn usually involves the combustion of natural gas, making the process less than zero in terms of carbon emissions. However, the heat capture technology used by Hydrostor eliminates this need.

“When power is needed from an A-CAES system, the compressed air in the underground cave is pushed back to the surface using the pressure of the water also stored in the cave,” said Emily Smith, Hydrostor’s head of media relations. “Once the air reaches the surface, it is reheated and pushed through turbines to generate power. This is necessary because a heat source is always required when using ambient air to drive a turbine. In the case of A-CAES, this heat source comes from the compressor for fuel-free operation, rather than an external source such as burning natural gas.”

It may sound like science fiction, but the company is already doing this in Canada. Hydrostor’s two-megawatt plant in Goderich began operation in 2019 and is contracted to Ontario’s independent power system operator.

The Goderich facility demonstrates the capability of the technology and forms the foundation for Hydrostor’s other projects, two of which are in the final stages of development in California and Australia and are expected to come online before the end of the decade. In addition to these two projects, Hydrostor has a global pipeline of more than seven gigawatts, which includes the planned project in Boulder City.