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Will "two lined swimming pools connected by a pipe" help us get rid of natural gas?

Uploaded: Jul 19, 2020
A Montana-based clean energy developer described his proposed pumped hydropower facility as “two lined swimming pools connected by a pipe”. Could this possibly be the key to reducing our natural gas dependency? California seems to think so.

Earlier this year, California’s Public Utilities Commission (CPUC) released planning guidance for utilities. It suggests we add the following resources to our grid in the coming decade (1).

CPUC’s resource buildout guidance, given a 46 million metric ton emissions target (Source: CPUC)

In addition to a big increase in solar power and battery storage plus a modest increase in wind, we see a first-time need for “long-duration storage”. Traditional lithium-ion batteries can provide energy for a few hours, but this type of storage is designed to last for most of a day. In a more aggressive scenario in which we decommission some of our natural gas plants, CPUC suggests even more long-duration storage:

CPUC’s resource buildout guidance, given a 38 million metric ton emissions target (Source: CPUC)

As solar and wind displace gas on our grid, we need to handle extended cloudy or windless periods. The graph below (highlighted in a recent talk by previous Secretary of Energy Steven Chu) shows this general relationship. When a grid has a relatively low penetration of renewables (e.g., less than 40-50%), short-duration storage like batteries suffices to cover gaps in renewable energy. For grids up to about 80% penetration, storage for up to a day’s worth of energy is needed. That is where solutions like pumped hydropower come in. (2)

Once a grid is more than 50% or so solar and wind, longer duration storage is needed (Source: Joule)

Pumped storage hydropower (PSH) is a pretty simple technology. When renewable energy is plentiful, water is pumped uphill from a lower reservoir to an upper reservoir. When renewable energy is scarce, water flows downhill, spins a turbine, and generates electricity. The effect is not to create energy. In fact, these facilities are net consumers of energy. But by making renewable energy available when it is most needed, PSH helps renewables better match demand, reducing the need for gas on the grid.

This diagram shows the basic components of a pumped storage hydropower facility (Source: US Dept of Energy). (3)

The greater the height difference between the two reservoirs, and the larger the pipes (aka penstocks), the more power can be produced. The bigger the reservoirs, the more energy can be produced (the longer the power can last). These facilities can be pretty flexible. Newer ones can switch between generating a small amount of power for a long period or a larger amount for a shorter period. And most can switch between pumping and generating energy in minutes, reacting quickly to changes in demand. Moreover, they are pretty efficient, generating about 80% of the energy that they take in. (4)

This isn’t new. Pumped hydropower has been around since the late 1800s, but it took off in the United States in the 1960s and 1970s with the development of large, inflexible coal and nuclear power supplies.

Pumped storage hydropower capacity by initial operating year (Source: EIA)

The flexible hydropower resource was ramped up and down to better meet the demand curve. Today it serves a similar purpose, helping to fill in gaps when our inflexible renewables fall short. You can see how that works in the chart below. This type of flexible hydropower makes up around one-third of Palo Alto’s power supply.

Pumped hydropower on California’s grid ramps up to meet early morning and evening demand, when solar is insufficient (Source: US Dept of Energy)

Today over 95% of electricity storage in the US is in the form of pumped hydropower, but there’s just not that much of it. The 40-odd facilities we have cover only 2% (22GW) of our total power capacity (1 TW). (5) It’s not for lack of trying. The Department of Energy reports that 55 new PSH projects were in the development pipeline at the end of 2018, totalling about 30 GW. (6)

Hydropower projects in the pipeline in the US at the end of 2018, with pumped storage in light blue (Source: US Dept of Energy)

But some of these applications have been lingering. In fact, as you can see in the bar chart above, only one PSH system has been built since 2010. The problem is that big projects in remote areas have long permitting times and large upfront costs. Permitting complications include impacts on free-flowing rivers, harm to fish and wildlife, flooding of scenic areas, additional transmission requirements, and use of increasingly scarce water resources. And although PSH is cheaper than batteries for these long durations (7), the capital costs can be several billion dollars for a large facility. How can we mitigate these problems?

It can simplify things if you are adding a pump to an existing hydropower dam, as is being proposed for the Hoover and Glen Canyon Dams. But even so you need to identify and connect to an upper reservoir. Most developers now are proposing “closed loop” facilities that recycle water between the two reservoirs rather than taking in fresh water from a river. This can reduce environmental impact. You can further reduce costs and impact by developing the reservoirs in existing features like old mines.

An open pit mine that is one of Eagle Mountain’s two reservoir sites (Source: GEI Consultants)

The proposed 1.3 GW Eagle Mountain project near Joshua Tree National Park in Southern California is proposing closed-loop PSH with each reservoir located in an open pit mine. This has helped with permitting (they have a license to construct), as has its proximity to a major transmission line. But concerns remain about the use of an underground aquifer to fill and replenish the reservoirs, and they are still working on financials.

Another relatively promising project is the 400 MW Gordon Butte project in Montana. It is also a closed-loop facility on private land located near transmission, though it requires construction of two reservoirs.

Proposed Gordon Butte reservoir in Montana (Source: Absaroka Energy)

Goldendale in southern Washington is yet another closed-loop proposal on private land, with two man-made reservoirs near ample transmission. The site is an old aluminum smelter, so the proposal includes cleanup of the site as well. It would use water from the Columbia River for the initial fill and replenishment. With an impressive 2400 vertical feet between reservoirs, they are aiming for 1.2 GW of power and hope to be operational by 2028.

Depiction of the Goldendale project (Source: Rye Development)

A different approach is to use the ocean. Below you can see a small closed-loop system on an island, using the ocean as the lower reservoir.

Pumped storage hydropower in the Canary Islands (Source: Idom)

But some projects are more difficult. A plan to build pumped storage at Lake Elsinore in southern California has been on the books since 1997. The lake would serve as the lower reservoir and an upper one would be built nearby. This is a recreational lake in the middle of a small town, with residents concerned about impacts on recreation use and water quality. Furthermore, a new 32-mile transmission line is needed that will route through local forest, and residents are concerned about fire. Lake Elsinore residents and lake users continue to organize in opposition.

Even the best large, custom designs are expensive and slow, so the US Dept of Energy has looked into small modular systems. But it’s not clear that the reduction in overhead would be enough to offset the much smaller size of the projects. Other developers are looking at using tunneling machines to expedite construction and reduce costs. Quidnet Energy is looking to drill into underground rock layers for the lower reservoir.

Standard parts and oil and gas expertise can be used to create an underground reservoir (Source: Oil and Gas)

These ideas can save time and cost. Leasing is another possibility to help with large upfront costs that may otherwise deter buyers. The CPUC’s new signal confirms a market, which can reassure buyers. Will one of these projects get over the finish line by 2026? Or will a cheaper or lower-impact option take hold, like compressed air or flow batteries? It will be interesting to see what innovators come up with and whether our government is able to streamline the path from invention to deployment as we accelerate our efforts to clean up our power grid.

Notes and References
0. The City of Palo Alto Utilities has recently started a sustainability e-newsletter for kids. You can find the first two issues with fun educational activities to help your kids learn about environmental sustainability here.

1. The chart below shows how CPUC’s guidance evolves today’s energy mix over the coming decade.

2. With 80% or more renewables, we need to handle multi-day or even multi-week periods without sun or wind, which might involve hydrogen or something new. But what’s reassuring is that we can have a lot of renewables on the grid without zero-emission seasonal storage.

3. Here is a photo of a pumped storage mechanism from hydropower developer Andritz. The reversible pump-turbine is on the bottom and the motor-generator is on top.

Here is diagram of a recent PSH installation in China, also from hydropower developer Andritz.

4. Plants with larger vertical drops (called “heads”) are more efficient, and may be as high as 85%.

5. This data is from 2017. For comparison, by the end of 2018, we had less than 1GW of battery storage.

6. The LA Times reports FERC applications for 51 GW of pumped storage hydropower.

7. Section 4.3.8 of this lengthy report on storage cost and performance for the US Dept of Energy has a lot of information about the costs associated with PSH and technical innovations.

8. The Global Energy Storage Database inventories energy storage facilities around the world.

9. A team in Australia has identified potential sites for pumped storage hydropower. It’s fun to play around with. They have suggestions for flooding various portions of Wunderlich County Park, Portola Valley, and Pescadero, to name a few....

10. Stanford’s Global Energy Forum hosted a conversation with Steven Chu, Nobel Prize-winning Professor of Physics at Stanford and the twelfth Secretary of Energy. It is jam-packed with information about long-duration storage technology and government programs to encourage it. Chu is also pretty funny -- worth watching!

Current Climate Data (June 2020)
Global impacts, US impacts, CO2 metric, Climate dashboard (updated annually)

The first half of 2020 was the second warmest in the 141-year record, with combined land and ocean surface temperatures at 1.93F above average.

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Posted by Concerned About Costs, a resident of Cuesta Park,
on Jul 19, 2020 at 8:17 am

How much would such an undertaking cost & would the expenses involved be passed along to consumers?

My utility bills are already high enough as it is and no one wants to pay more for the lousy PG&E service that we already receive.

As far as alternative sources of 'natural gas' go, how about finding a way to harness the methane gas expelled by humans & animals?

Posted by Energy Dude, a resident of Barron Park,
on Jul 19, 2020 at 4:00 pm

Sherry, excellent post as always. Very informative and thorough. Thank you for the time you put in to these articles.

I'm a big proponent of these types of projects, particularly for their attributes when compared to other solutions to the same problem: storing excess renewable energy, and therefore allowing for more carbon-free generation.

Batteries are getting cheaper every year, and can be placed closest to where they are needed, but I can't see them scaling as efficiently as a large, centralized pump storage facility. Doubling the size of a battery bank requires double the lithium/cobalt, etc. whereas pump storage simply requires a bigger hole, bigger pumps, and bigger generator. That said, we will never unlock these benefits without the political will to allow these projects without requiring 10 years and tens of millions of dollars to permit them. If we get over that hurdle, it would likely make sense to have very large, central storage facilities that store energy from even distant renewables, because the efficiency of the storage would make up for the transmission losses.

I like both solutions more than using electrolysis to " store " excess generation as hydrogen, because the physics of the conversion process give away about 60+% of the energy I believe. This seems to have been getting some traction in Asia where it is subsidized by the government, and is being pushed here by the Bloom Energy types who want to portray their methane fueled fuel cells as emission free by having wind and solar displace the step in their process where they strip methane into CO2 and H2. I suppose if hydrogen can be used directly to offset gasoline, it may have a place, but I can't think of any worse way to "store" electricity than pay the huge efficiency price of converting it to hydrogen and back.

Which brings us back to pumped storage. Energy is a unique beast. All we are really doing, is turning a gigantic crank that really doesn't want to be turned, and requires a lot of force to do so (putting aside PV solar for this analogy). As is often the case, the simplest solution is the most efficient, and I think this type of storage is just that. I'm curious if you think there is a breakthrough coming in distributed batteries that will allow them to scale to the size needed? You asked it as an open-ended question, and I'd be inclined to guess "no" because of the sheer simplicity of the physics involved. It's difficult to invent a revolutionary new way to turn a giant crank. We are up against physics more so than lack of creativity and ingenuity. So that being said, let's find some big (spots of) holes, and start building transmission lines to them.

Posted by Sherry Listgarten, a PleasantonWeekly.com blogger,
on Jul 20, 2020 at 2:35 pm

Sherry Listgarten is a registered user.

Terrific comments, thanks! Here are a few thoughts.

@Concerned: Yes, a critical issue with storage is cost. A recent paper estimates the cost of pumped storage to be about $0.18/kWh, though there is still much discussion about how to assess cost. You can’t compare storage cost with energy cost directly, but I imagine you could look at the difference in the time-of-use rates, which is maybe $0.10, to see how it compares. The Dept of Energy would like for long-duration storage to be $0.05/kWh, and it’s not there yet. If you are interested, here is one example of costs for pumped storage hydropower, but these vary significantly between instances, particularly transmission.

This doesn’t have to mean your utility bills will go up as we add more renewables. Other related costs might go down, or government could decide to offset any additional cost with proceeds from elsewhere that have been allocated for addressing climate change.

Your suggestion to use biogas at scale is an interesting one, and something people are looking into. You can read about a plan to capture gas from hog manure here. Palo Alto gets about 12% of its power from landfill gas, which is related. But afaik there is no way to capture biogas at scale in a cost-effective fashion.

@Energy, you raise a great question about small-and-distributed energy vs large-and-centralized. Which is cheaper? Which is more resilient, and how do you value that? I used to think rooftop solar was very inefficient and a bad idea. But one thing I was struck by in California’s guidance for utilities (see graph in note 1) is how much of the new solar is “customer solar” rather than centralized solar. No land acquisition or new transmission is needed, and it can provide resiliency against blackouts if paired with a battery. Maybe small allows us to scale faster while also adding more resiliency. Wouldn’t it be nice if big tech companies could have their own underground pumped storage or compressed air facility beneath each data center to use for backup power, selling it for peak shaving at other times?

Re hydrogen, yes, it seems like a very inefficient way to store electricity, and it is expensive. That said, if we have sufficient excess renewables, hydrogen can work for seasonal storage unlike most other options. It’s also one of the better options for long-haul transportation. So, we’ll see...

Re energy storage, to your point, one thing that Chu mentioned is that electro-mechanical systems tend to be more efficient than others, and that is one reason why he likes pumped hydro and compressed air for long-term storage. Hopefully we can find good places for these facilities and continue to push down on costs.

Thanks again for the great comments.

Posted by Concerned About Costs, a resident of Cuesta Park,
on Jul 21, 2020 at 9:12 am

>"But afaik there is no way to capture biogas at scale in a cost-effective fashion."

^ That is unfortunate given the amount of biogas expelled at our house (two parents, a father-in law, three children and a dog).

Posted by Alan, a resident of Menlo Park: Belle Haven,
on Jul 21, 2020 at 9:43 am

Alan is a registered user.

When I was a kid, I remember visiting the newly completely "Ludington Pumped Storage Power Plant", on the eastern shores of Lake Michigan. At the time (1973) it was the largest pumped storage facility in the world, used to store excess power generated by local nuclear power plants. It's recently been modernized and stores some power generated by local wind farms. Web Link

Posted by Gard, a resident of Cuesta Park,
on Jul 21, 2020 at 2:23 pm

Gard is a registered user.

It was at least 10 years ago we visited Raccoon Mtn. Pumped Station Reserve. It used spare TVA power to pump to a lake at least 600' above the river and run 4 400MegaWatt generators during the day. Very impressive.

Posted by Sherry Listgarten, a PleasantonWeekly.com blogger,
on Jul 21, 2020 at 4:37 pm

Sherry Listgarten is a registered user.

@Alan/Gard -- Thanks for sharing. I've never visited one!

@Concerned -- Ha, I feel for you :) This biogas though is more burps. You've heard the old adage that if cows were a country, they'd have the third-most emissions? It's mostly from their burps and from growing their food, though also processing their manure. This has some good info. This article describes a gas capture device they are testing for cows. Maybe you could rig up something similar for your family :)

Cow wearing a methane-capture mask developed in the UK (Source: Bloomberg Green)

Posted by Concerned About Costs, a resident of Cuesta Park,
on Jul 21, 2020 at 5:15 pm

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