The Hoover Dam was undoubtedly one of the greatest construction achievements of the 20th century. Built in the 1930s, this supersized arch dam measures 221m from top to bottom, and 379m across the crest. It generates an average of 4 billion kWh of hydroelectric power each year, enough to serve 1.3 million people.

The dam has always had multiple uses – flood and silt control, agricultural irrigation and domestic water supply, to name a few. Now a new project has been proposed, which would effectively turn the Hoover Dam into a gigantic battery.

Under the $3bn proposal, a renewable-powered pumping station would be built 20 miles south of the dam, serving to regulate the water flow through its generators. Water would be pumped from downstream back up to the top, and released for power on demand. In essence, the dam would be able to store renewable energy as well as produce it.

As advocates see it, the project could massively increase the dam’s productivity, adding at least 500MW of potential output. More than that, it would solve one of the West Coast’s trickiest energy problems: balancing energy production against demand.

“Solar energy is produced when the sun is shining and wind energy is produced when the wind is blowing, and we don’t have much of a say in when it’s produced,” says Peter Gleick, co-founder of the Pacific Institute think tank. “We’ve been trying to figure out how we can better integrate renewable energy into our bigger energy system, so that’s the idea here – if there was some way to store excess energy, then we can use it later when the demand is higher.”

If the Hoover Dam were used for this purpose, less of California’s energy production would go to waste.

Balancing the energy mix

Aptly nicknamed the Sunshine State, California is a major producer of renewable energy. Last year, renewables accounted for 27% of the state’s energy mix, and it looks to be on course to achieve its goal of hitting 50% by 2030. Solar energy especially is booming, surging from 0.5% of the mix in 2010 to 10% in 2017.

On very sunny days, however, the state’s solar panels produce more energy than is possible to use. For instance, on 5 March this year, production was 50% higher than demand. Much of it is passed on to neighbouring states to avoid overloading California’s own power lines.

Since the state has limited ability to store this power, other forms of energy production are still necessary. Perhaps counterintuitively for a state with an oversupply problem, it relies on imports for around a quarter of its energy needs.

The Hoover Dam proposal, then, would be instrumental in helping the state improve the reliability of its energy supply. This is a particularly loaded topic following the signing of the SB 100 bill, which saw California commit to 100% carbon-free power by 2045.

An economic white elephant?

Earlier this year, the Los Angeles Department of Water and Power (LADWP) pitched the concept to interested parties, including groups across the Southwest that receive power from the Hoover Dam. It has subsequently been reported in New York Times, prompting scepticism and excitement in equal measure.

This does not mean, however, that the proposal will necessarily go ahead. As Gleick points out, there is a big difference between considering an idea and moving forward with it.

“I think any proposal that tries to address Western US energy challenges is worth consideration, but this is really just an early-stage idea at this moment,” he says. “While I think it’s worthy of evaluation, I’m somewhat sceptical that it would address the core of the problems that we face.”

He adds that the proposal needs to be evaluated from multiple angles – technological, economical and environmental.

“Because this is such an early idea, there really is no definitive engineering design that we can look at,” he says. “There is no economic assessment of the true costs of doing this compared to the costs of other things, there is no assessment of the environmental impacts of the project. We just don’t know enough at this point to say whether this project makes any sense compared to the other options that are available to us.”

The proposal may also face political hurdles, and will require an enormous amount of cooperation between federal, state and local agencies. To take just one piece of the problem, the Colorado River is politically fraught, wending its way through seven US states along with Mexico. There just isn’t enough water in the river to meet everyone’s desired demands.

“Another important point is that building a project like this will take many years, and during that time other options for energy storage are going to be developing,” says Gleick. “We might decide that this project might make sense today and we may build it, but ten years from now it may turn out to be an economic white elephant.”

The possibilities ahead

A storage solution is needed – that much is not in doubt. However, it’s hard to say at this stage whether or not the Hoover Dam is the right choice. Other options include large-scale battery storage systems, similar to Tesla’s 100MW lithium ion battery, installed in Australia in 2016. This is certainly a possibility, insofar as the underlying technology is continuing to improve and prices are falling.

Another option simply comes down to better investment in wires, improving the interconnections between different regional energy systems.

“If we had excess solar energy in Southern California during the day, that could be shipped to another part of the country where the demand is still higher than production, and trade energy back and forth,” says Gleick. “If we were better at building those grid connections it would be much easier to move energy around – right now we’re not very good at it.”

For the time being, there are many unknowns. Certainly, the Hoover Dam proposal is being taken seriously – LADWP is doing some initial engineering assessments, and Los Angeles Mayor Eric M. Garcetti has described it as a “once-in-a-century moment”.

“So far it looks really possible,” he said. “It looks sustainable, and it looks clean.”

If the project goes ahead, it could be completed as soon as 2028, which would give California an early push towards meeting its 100% renewables target. It would likely inspire similar efforts across the US.

While remaining somewhat sceptical about the proposal, Gleick is heartened that California is even having this conversation.

“One of the pieces of this problem is the fact that California now has a huge amount of renewable energy production, so we’re actually talking about how to use it most effectively,” he says. “And we’re building more and more every day – that’s a dramatic change from 10 years ago.

“The minor problem that sometimes we’re producing a little more renewables than we can use – I think that’s a small challenge in the face of the much better news that renewables have become economically attractive.”