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Pumped Hydropower Offers Potential for Greater Energy Storage Capacity

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Emily Folk's picture
Journalist Conservation Folks

Emily Folk is a conservation and sustainability journalist. She focuses primarily on green technology and the impact changes in technology have on climate change. On her blog, Conservation Folks...

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  • Jul 9, 2020

This item is part of the Energy Storage Insights - Summer 2020 SPECIAL ISSUE, click here for more

If you've ever worked with renewable energy, you know that storage is a major stumbling block. Unlike with a coal-fired or natural gas power plant, you can't adjust hydropower energy, wind energy and solar energy production based on grid needs.

Producing enough energy for a given area probably means overproducing when grid demand is low. You're also likely underproducing when grid demand is high, meaning your green energy source still relies on fossil fuels to keep the grid powered.

Batteries are available, and battery tech has come a long way in the past few years. While suitable for a home solar system, however, these batteries are expensive and not practical for long-term or grid-level storage.

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Energy storage startups have found a new way to store energy. They're pumping it underground. This is how green energy startups are using a new kind of pumped hydropower to store energy.

How Pumped Hydropower Stores Energy Underground

The technology works by effectively converting excess energy created by wind turbines and other green energy sources into potential energy that a company can later draw from.

In times of low energy demand, the system pulls excess energy from the grid to pump water up a hill from a lower reservoir to a higher reservoir. When energy production slows down, the water in the upper reservoir is released, flows downhill and spins a turbine, producing energy.

The tech isn't new — pumped hydropower accounts for about 95 percent of all stored energy projects in the U.S. Almost all existing hydropower projects are old, however — many were built in the 1970s and '80s. High costs, the limited utility of the projects in conventional energy applications and the difficulty of securing enough land has made new construction impractical.

Some startups behind the revival of pumped hydropower are taking a new, less land-intensive approach. Instead of pumping the water into an upper reservoir, they're pumping it underground. When energy demand is low, this system pumps water into an underground well, where it's stored under pressure. When energy demand exceeds the capacity of green sources, the well water is released, rushes back to the surface and spins a turbine.

The resurgence of the tech is part of a turn towards more eco-friendly construction and energy — like the increased popularity of water-filled cofferdams, which have a lower environmental impact than more conventional earth-filled cofferdams. The approach is a new one and hasn't been tested at scale yet. The first attempts at the project aim to store an estimated 10 hours of energy.

New Pumped Hydropower Projects Given the Go-Ahead

The rise of the underground hydropower approach has also been accompanied by renewed interest in traditional hydropower storage. One pumped hydropower company, Phoenix-based Pumped Hydro Storage, LLC, recently applied for a preliminary permit for a project that would create pumped hydropower storage along the Colorado River.

There are some concerns, however, about the potential environmental impacts the energy storage strategy may have. The proposed Colorado River project is an open-loop hydropower storage project, meaning water is pumped out of a natural body of water, not a reservoir, and released from the upper reservoir back into that body of water.

American Rivers, a nonprofit environmental protection charity, has already intervened in the project's approval process, citing potential environmental damage to the Colorado River.

Closed-loop, underground hydropower storage projects may not create the same environmental hazards, especially if they take advantage of existing underground structures like abandoned mineshafts and natural caverns to create reservoirs. However, it's likely that any hydropower storage project will have some environmental impact. This impact will need to be weighed against the utility the project provides.

Pumped Hydropower May Help Solve Green Energy's Storage Problem

The demand for renewable energy is likely to continue growing at a rapid pace in the coming years. Green energy companies will need to find some way to manage energy storage requirements.

Renewable energy systems are expanding rapidly, but they remain limited by the difficulty of scaling or storing the energy they produce. Stored hydropower is one potential solution that's picking up speed. However, even the most eco-friendly and least land-intensive version of the tech may come with an environmental cost. Energy professionals should keep these costs in mind when considering the technology.

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Mark Silverstone's picture
Mark Silverstone on Jul 15, 2020

Thanks for this information Emily.  This would certainly seem to be a better environmental alternative than new hydro projects from scratch.

I wonder how much energy is lost in the process of pumping water underground under pressure and then releasing it to generate? It would seem to be a lot, maybe even most.  Are there data on that?

Emily Folk's picture
Emily Folk on Jul 28, 2020

That's an interesting question, Mark! I haven't yet found any data on energy lost during the pumping and releasing process, which could partially be due to there only being a little over 40 facilities in the country.

The primary issues I've seen associated with pumped storage has been the high upfront cost (large scale can range from $1.3-$3.3 billion) and that it requires very specific topography (an area that can store massive amounts of water at a high elevation).

Audra Drazga's picture
Audra Drazga on Jul 26, 2020

Emily - great article.  I like Mark's question too.  This also seems more practical in places where water is in abundance.  The colorado river, I would think, presents issues because when the four corner states face droughts, the Colorado River is already taxed.  Curious about other projects that are being considered it the US?  Can you share?

Emily Folk's picture
Emily Folk on Jul 28, 2020

Thanks, Audra! Yes, pumped storage can present issues to areas that are stressed by drought. Interestingly, two of the projects that are being considered are in Mohave Country, AZ and Yvapai County, AZ. I'm not too familiar with Arizona's water management, but it will be interesting to see how they balance pumped storage with a drought-prone climate.

The other projects I'm aware of are one in Nevada and one in New York. About 20 states have looked into pumped storage over the past 5 or so years, but I'm not familiar with how many of them have plans to move forward with projects as of today.

John Simonelli's picture
John Simonelli on Aug 6, 2020

Well it may be somewhat dated but a few decades ago the efficiency loss was between 15 and 20% however technology as improved steadily especially with the use of variable speed pumps.  I assume the efficiency numbers are a bit better now a days. Let’s face it the biggest hurdles are going to be appeasing the environmentalists and getting the financial backing.  The article is spot on, this is not new, PSH has been doing the heavy storage lifting for the industry for over a half a century, basically since the big nuke build out of the 50’s and 60’s. It may take federal intervention to jump start building more PSH.

Bob Meinetz's picture
Bob Meinetz on Aug 9, 2020

"The U.S. Department of Energy's (DOE's) Water Power Technologies Office (WPTO) currently developing a research portfolio to evaluate and expand hydropower and pumped-storage’s contribution to grid resiliency and reliability."

The purpose of pumped storage in the days of early nuclear were to provide needed variability. Early nuke plants suffered from a phenomenon known as xenon poisoning - if they powered up or down too much, a buildup of xenon in the reactor core would reduce overall output for days or weeks.

Though Generation II+ reactors are far more flexible, the stigma they provide "baseload only" power persists.

Today, the Helms Pumped Storage facility in California is useful more for wasting energy than storing it. On sunny days, when CA solar overgeneration threatens grid reliability, CAISO engineers pump water in and out of Helms to serve as a giant resistor - to convert excess electrical energy into wasted heat. The "contribution of pumped storage to grid resiliency and reliability" could be more accurately rephrased "prevention of damage to the grid caused by unpredictable overgeneration from wind and solar sources."

The problem is not the inability to store energy, but inherent to renewable energy itself. Eliminate support for expensive, impractical solar and wind, and the problem goes away.

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