By Matt Owens July 10, 2013
This is what we usually hear about solar and wind: "the sun doesn't always shine and the wind doesn't always blow...so it's not enough to replace fossil fuels." But what if there was a cheap way to store the copious amounts of energy generated when the wind does blow and when the sun does shine? And what if that stored energy could provide a constant and reliable source of power? What if I told you that such a way exists, and has even been in continuous, large-scale, global use for a century? It's called pumped storage hydro, and power generators love it because it makes their operations more efficient (which probably has something to do with why they've been using it for so long).
Above: The Taum Sauk facility in Indiana is just one example of design configurations currently in use for pumped storage hydro. Image credit: Wikipedian Kbh3rd.
Around the world, there are at least 50 such pumped storage hydro plants that have a capacity above 1,000 MW (which is pretty large), and many more with smaller capacities. And as a matter of fact, Virginia is home to the world's largest, the Bath County Pumped Storage Station. It went into operation in 1985 and has a capacity of over 2,700 MW. There's also the Smith Mountain Dam in Virginia, with a capacity of 560 MW, in operation since 1979. From an energy capacity perspective, pumped storage is about 2.5% of global total electrical power capacity.
Before I get too far ahead of myself, let me explain what pumped-storage is. It's really simple: First, two reservoirs are needed, with one being higher in elevation than the other. Second, some conduits need to connect the two. And then, the final step is to add a few hydro turbines and water pumps. Water flows downhill, generating electricity and filling the bottom reservoir. Then, the same water gets pumped back uphill for storage. Basically, it's a giant battery, capacitated by gravity.
The whole system looses a bit of energy in the pumping process, and through evaporation. This varies by system design, and is usually about 20%. But that's better than a 100% loss - which is the situation when there's excess energy production that would otherwise be lost.
In the past, the reason for building these hydro storage plants was for storing the excess energy from slow-responding coal power plants. It made economic sense around the world to build these stations, to the scale of over 2.5% of global power capacity! But this type of plant can also be used to store excess solar and wind production.
This potential combination would be versatile too. A substantial amount of water is needed for the hydro element, but the system is a closed-loop, so losses are fairly small. Once established, little replenishment is needed. A height difference between the upper and lower reservoirs is also needed, but the Ludington Pumped Storage Power Plant on the shores of Lake Michigan pumps water up just 363 feet in height. And by using lake water, the Ludington station has no problem getting water. The Taum Sauk facility in Missouri (pictured above) was built with concrete walls - like a giant inflatable swimming pool, and at an affordable cost. And there are many more engineering variations already in use, each suited to its own region, but I'll leave it there for now.
Perhaps the real beauty of pumped storage is that if it were widely integrated with renewables, the grid operators could distribute energy storage when and where they needed to. Even areas that were remotely located from any renewable energy plant could have a pumped storage hydro plant providing a guaranteed and stable local power supply.
From an ecological perspective, the standard dam concerns don't apply. The reservoirs don't need to dam waterways at all. And most don't under current practice. The primary issue is one of changing a terrestrial habitat to an aquatic one. The best system would have low organic content, meaning plants and possibly top soil would need to be cleared away before flooding. That would keep methane emissions from the new lakes at zero, and provide a healthy lake ecosystem.
And the areas flooded by these reservoirs (if we are successful in going 100% renewable) wouldn't be huge - but they would be noticeable, and they would require displacing land owners in some cases. Unfortunately, the easiest and cheapest sites on the US East Coast would probably coincide with Appalachian natural areas set aside as protected land (although this land is often leased out for agricultural or mining uses). But the footprint of flooded land could be offset by expanding healthy habitats elsewhere - which is something we'll need to do anyway as the inertia of climate change increasingly stresses habitats in the coming years.
I did a quick run of the numbers based on construction, maintenance, and financing costs (using available data on existing plant construction costs): it looks like these facilities would "add" about $10 per monthly household electric bill (assuming average American consumption and prices). That's a pretty modest price for an alternative to fossil fuels. And if we factor in "externalities" like the loss of Miami to sea level rise, well - it's hard to argue against $10 a month. [Of course in the big picture, there's the cost of the renewable energy itself to factor in. For wind, that comes to about as much (or less) than coal costs according to levelized costs by the US EIA. Solar costs are more variable, and still about 50% more expensive than conventional energy. But even with solar, would an extra $50 per average monthly electric bill really crush this nation?]
I'm not the first one to realize the potential of pumped storage. Voith, a leading global manufacturer of industrial machine parts states: "Pumped storage power plants play a vital role for future energy supplies. Without these huge power stores, the energy shift will not succeed." Voith manufactured upgraded turbines for the Bath County station in 2009, and they've been making hydro turbines since the 1800's. But they also supply products for coal, oil, and gas extraction, so their outlook on pumped storage hydro can't be entirely biased.
As for other takes on pumped storage, there's a small but growing number of research papers on the topic, especially focusing on Europe. Greece in particular has been looking at the option for providing cheaper, cleaner, and more reliable energy to its many islands. Under the current system of regulation and incentives, research indicates that many islands should be able to replace more than 40% of their fossil fuel energy sources with the combination of renewable generation and pumped hydro storage.
Based on my assessment of geology and topography, pumped hydro storage could be implemented in virtually every country. Some areas are better suited it's true, but the same is true for any energy source. The only critical element is modest foothills and adequate amounts of water (just think about the massive runoff and flooding problems around the world lately - this could be captured and stored).
According to a 2010 paper by Chi-Jen Yang, China has recently identified 247 potential sites with combined capacity of 310,000 MW (that's about 1/3 of China's current total generation capacity)! As for the potential expansion and limits, he makes the point of Japan: "[a]lthough Japan already has the highest density of PHS installation in the world, Japanese power companies are continuing to develop more PHS plants. The share of PHS in the total hydroelectric power capacity in Japan is still growing."
From the Yang paper is this table of leading countries with installed capacity:
|Table 1. Installed PHS capacities.|
|Country||Installed PHS Capacity (MW)|
Here in the US, there is a lot of flat terrain in the middle of the country that would make storage difficult locally; but wind and solar are abundant there, and those plains states could easily be major generating sources of renewable energy for the rest of the country. That would mean an electricity supply far in excess of local demand on a virtually constant basis. With a grid-scale integration of renewable energy production and transmission, a state like Kansas wouldn't go a day or night without enough wind and solar power to keep their batteries charged.
So pumped storage is looking good! We've got to make the change to clean energy ASAP - and this technology is affordable and available on a global scale. It already accounts for about 2.5% of global electricity capacity. If we expand it and couple it with renewables, it sure looks like it would do most of the work to power us through the coming dark doldrums.
A final note on correcting the record: The Economist published an article a few years ago that said pumped-hydro storage has very limited expansion potential because there are too few sites. It does not go beyond that brief statement of dismissal. Perhaps it's because it's just regurgitating a paper by Chen et al., "Progress in electrical energy storage system: A critical review," which states: "[t]he major drawback of PHS lies in the scarcity of available sites for two large reservoirs and one or two dams." This is simply not true if the word "available" is replaced with the phrase "feasible considering the current social ambivalence towards global warming." The word choice may have been poor, and further elaboration on the meaning of "available" in the Chen et al. paper is not given. My analysis and review of the existing examples of pumped storage plants and potential for expansion finds the exact opposite to be true: sites are abundant. The 247 sites recently identified in China support that view.
I can only speculate that the Chen et al. paper maybe have been defining "availability" in the context of a political environment where public land would not be made available. Considering the urgency of the climate crisis, what is deemed available is changing. In the paper I cite below by Margeta and Glasnovic, they reference the Chen et al. paper specifically, and refute that point (as well as 2 others regarding pumped storage), saying "the construction of storages for daily or weekly balancing of production and consumption of energy is very realistic at numerous locations."
Yet Margeta and Glasnovic also seem to agree about "large storages," saying that "[a]cceptable locations for large storages are hard to find." If they mean on the scale of Three Gorges Dam, then perhaps they're right, but they do not elaborate on "large storages." However, the topographical prerequisite formations are abundant for facilities of several square kilometers surface area. And as the Taum Sauk facility demonstrates, even an entirely built-reservoir can be cost-effective. And as the Ludington Pumped Storage facility shows, even a small rise of just under 400 feet can be employed.
The limiting factor however, and definitely worth taking note of, is fill time. Bigger projects - which for comparison, would be far below the Three Gorges scale, would require lots of water. Along the US East coast for example, figuring out the fill time can be done by looking at local river flows and estimating needed reservoir volumes, surface areas and evaporation rates, and potential diversion fraction of usable waterways. By my own investigation, the result for the East Coast is that such reservoirs, when filled with fresh water (i.e. not seawater), would take several years to fill up - which is typical for most dam projects; but in some cases it would take 10 years to fully charge a new reservoir. And if several plants were built at once, it would further divide the available water supply. For projects located on the shores of existing lakes however, the fill-time would be limited only by the installed pumping capacity. In other words, fill times would be measured in days or weeks. So, lakeside locations like the Ludington station or seaside locations may be prime real estate in the short-term, until inland stations can be filled. The time scale over which we need to act on reducing emissions to zero is incredibly short - ASAP - in fact. So fill rates are quite important.
Also see this new article: "California's Bold Move: Energy Storage" (November 13, 2013)
Anagnostopoulos and Papantonis; 2012: "Study of hybrid wind-hydro power plants operation and performance in the autonomous electricity system of Crete Island." Recent Advances in Energy, Environment and Economic Development.
Margeta and Glasnovic; 2011: "Role of Water-Energy Storage in PV-PSH Power Plant Development." Journal of Energy Engineering.
"Electric Energy Storage Technology Options: A White Paper Primer on Applications, Costs, and Benefits." EPRI, Palo Alto, CA, 2010. 1020676.
Yang; 2010: "Pumped hydroelectric storage." acedido a, 20.
Correction: The original version of this article made reference to two articles without providing citation information. One was from the Economist and the other from New Scientist. The New Scientist article could not be located after a recent search for it. The other citation is:
The Economist [no author identified]: "Packing some power;" March 3, 2012.