The Ambri batteries mentioned in the last post are fine for storing some energy for a couple of days, but suppose you need a lot of storage for a week or more. That’ll be necessary when all the fossil fuel peaker plants have to closed in order to go 100% renewable.

This is where pumped-hydro comes in. It’s a dead-simple scheme – pump water uphill when there’s excess power, and let it flow down again through a generator when you need power. It’s been in use since 1907, and is far and away the largest form of storage, accounting for 1.6 terawatt-hours (TWh) worldwide, and 250 gigawatt-hours (GWh) in the US.

There’s a big pumped hydro system right here in Massachusetts – Northfield Mountain:

It was the largest in the world when it opened in 1972. It’s been upgraded over time, and can now generate 1.1 GW for up to 7 hours. That’s the same output as the Seabrook nuclear power plant, and is about 9% of the entire New England load. Its lower reservoir is on the Connecticut River. The pump / generators are in a vertical shaft beneath it, and a horizontal tunnel runs from there out to the river. The upper lake can store 21 million tonnes of water with a 210 m head, allowing it to store a theoretical peak of 12 GWh. It was actually built to store the nighttime output of the Vermont Yankee nuclear power plant, allowing it to run at the same rate all the time regardless of demand, but that reactor closed in 2014 due to low electricity prices from shale gas and constant protests. Doing this much storage with batteries at an aggressive price of $100/kWh would cost almost a billion dollars.

So pumped facilities like this are great for intermittent wind and solar power, but hardly any new ones are being built. This is mainly because high hills next to rivers are not common, and because tunnels are expensive.

A team at Australia National University in Canberra have been working on the first problem, and recently published a nice study on just where systems like this can be built: “GIS Algorithms to Locate Prospective Sites for Pumped Hydro Energy Storage” by Bin Lu et al, Applied Energy, July 2018. What they’ve done is to use Geographic Information Systems (GIS) to identify places that would be suitable to schemes like this. We now have data on the height and characteristics of every square meter of land on the planet, and so can use it to find places that:

• Are at least 300 m above another spot that is within a 1:15 slope nearby. If the slope is shallower than that, the tunnel between the reservoirs is too long.
• Could hold at least a million m³ of water.
• Have a height and volume that gives a storage capacity of at least 1 GWh
• Has an area of at least 10 hectares (300 m on a side, a small lake) for both the upper and lower reservoirs
• Is not in an already protected area such as a park
• Is not already under intensive use like residences
• Would need dams of limited height and limited amount of excavation
• Are near existing transmission lines

They then looked for sites to build two kinds of reservoirs:

a) Dry gullies – where there’s a slope that can be dammed. The dam should be no more than 40 m high.

b) Turkey nests – flat areas where excavated dirt can be piled up to form the dam. The sides should be no more than 20m high. Turkeys build their nests this way on flat ground.

The big difference between their work and previous efforts is that they did NOT assume there had to be a river nearby. In fact they call it STORES: Short-term Off-River Energy Storage. This greatly increases the number of available sites. This would be a closed-loop system – the water would be pumped back and forth between the reservoirs rather than flowing through. The reservoirs could be filled from a temporary pipeline, and then maintained by trucks or rain catchment arrangements on the slope between the reservoirs.

They applied this to the province of South Australia. It already gets over half of its power from solar and wind. It has a big transmission line to connect to the rest of the country, but when that goes down, they get blackouts. Having local storage would be a huge help to them, and let them go 100% green. The study found 190 sites like the above, with a total capacity of 276 GWh. Modern people consume an average of 1 kW each, so the two million people South Australia use an average of 2 GW. Give them 20 hours of storage and they need 40 GWh. The study found over 5X that!

They also applied the same GIS search to the US and found this:

There’s an embarrassment of riches! Basically all the hilly parts of the continent can do something. If we zoom in on western New England, more detail can be seen:

This map is centered on Mount Greylock in the Berkshires. Now you can see the reservoirs themselves and the tunnels needed. The red dots are the best. There are lots of good sites just north of Greylock in southern Vermont, and lots just to the west in New York. Eastern Massachusetts is too flat, but New Hampshire and Maine have good sites too.

So a surprising number of places could be used for pumped hydro. How about the second problem, the cost of tunneling? A lot of these sites have reservoirs that are quite far apart. Michael Barnard, a clean tech expert and author, proposed that Elon Musk Should Build Pumped Hydro With Tesla Energy, The Boring Co., & Coal Miners. Musk’s Boring Machine company aims to dig relatively small tunnels, ones only 4.3 m (14′) in diameter, for single lane underground traffic routes. That would also be a good size for these pumped hydro tunnels. The pumped hydro projects themselves would be a good addition to his solar projects.

Plus, there are a lot of pumped hydro sites in places like West Virginia and Wyoming, where laid-off coal miners could put their skills to use in a new industry. It needs people who can handle the machinery for tunneling and excavation, and doesn’t give you black lung while doing it. If we really do need to get 20 kWh of storage per person, then the US will need 6.8 TWh of it for 340M people. That’s 27 times what it has today. That sounds like a lot of good work for a lot of people!

So modern information systems in the form of GIS, and modern advances in technology like electric tunneling machines, could give us a way to really get 100% green. Just as the improvements in solar panels and wind turbines have made renewable electricity cheaper than coal, similar progress can give us a place to put all this cheap energy. We don’t have all that long to get going on this!