Is energy storage really the “Holy Grail” of the electric smart grid, as some pundits claim? Let’s hope not—since customers and utilities will need more than a mythical technology to ensure safe, reliable, and affordable service in years to come.
Utility-scale energy storage offers numerous potential applications, as NEXT100 recently outlined in a report on PG&E’s pilot tests with sodium sulfur battery technology. Energy storage can help integrate intermittent renewable energy onto the power grid, defer costly upgrades of transmission and distribution infrastructure, and take advantage of gaps between peak and off-peak energy prices by storing energy when prices are low and releasing it when prices are high.
While enthusiasts abound, storage technology has yet to prove itself in widespread use. Skeptics like Davis Swan, president of Debarel Systems, Ltd., insist “Utility scale storage is not close and saying that it is will only make people complacent.”
‘A lot of research going on’
To get an objective take on the future of energy storage, I had a long talk with Haresh Kamath, a senior expert at the Electric Power Research Institute, one of the major R&D arms of the utility industry.
The good news, Kamath said, is “There’s a lot of research going on and a lot of exciting things are happening.” The bad news is that owing to immature technology and limited market size, costs remain too high for most applications. “There’s hope for a path to cost reduction, but it’s tough,” he allowed.
The most proven technology is pumped hydro, of which PG&E’s Helms plant is a prime example. Another proven but more rarely deployed technology is compressed air energy storage, an approach that PG&E is studying with help from federal and state grants. In their current forms, however, both require unusual geological formations (mountain reservoirs, underground caverns) that limit their application.
Some startups are exploring ways to repurpose those concepts more generally. For example, Gravity Power is looking at ways to mimic pumped hydro by drilling deep holes to hold water that can be forced up or down through a pipe to run a turbine.
Others are exploring the possibility of storing compressed air in above-ground chambers or tanks, freeing that technology from any limits of geography or geology. EPRI has been looking for partners to test a variant of that approach, using oil or gas pipelines as inexpensive storage facilities, Kamath told me.
Gravel, salt and flywheels
A more off-beat approach, championed by British startup Isentropic Energy, is to store energy in separate large containers of hot and chilled gravel. An efficient heat pump linking them generates electricity on demand.
For small-scale applications, some technologists are still betting on flywheels, ultra-fast-spinning disks or cylinders. They are great for helping to stabilize power grids on a second-to-second basis, but the Chapter 11 bankruptcy of Beacon Energy in 2011 suggests they aren’t yet economic.
A few large players in the concentrated solar power market are planning to use molten salt to store solar energy at mid-day for release during shoulder hours when the sun is setting but demand remains high. PG&E recently announced a deal with Solar Reserve LLC for such services.
Most bleeding edge of all is hydrogen storage technology. Surplus energy can be used to split water into oxygen and hydrogen. The stored hydrogen can then be converted back into electricity through a fuel cell. Unfortunately the cumulative inefficiencies of each step combined with the equipment cost make it a potential player only some years into the future.
Much focus on batteries
Kamath said most of the research into storage these days is focused on batteries, partly because they have multiple markets, including plug-in vehicles. That expands the market size, offering the promise of production efficiencies that drive down costs.
The big push today is on lithium ion technology, the favorite of electric car makers and many consumer electronics manufacturers. Such batteries are probably too expensive for most big grid applications, Kamath indicated, but there may be cases on the distribution system where batteries are more cost-effective than upgrading electric lines and transformers to meet peak customer loads.
“There’s a lot of room for lithium ion battery costs to come down,” Kamath said. “However, there is a price floor, set by some of the basic materials costs. Manufacturing these precision components is fairly expensive, too.”
Another promising approach is flow batteries, which pump big tanks of liquid electrolytes into a chemical cell to generate electricity. They’ve been studied for years but suffer from limited sales potential outside the utility industry. One of the benefits of flow batteries is that their storage capacity can be increased without a large increase in overall costs. A claimed breakthrough by researchers at the Massachusetts Institute of Technology marries lithium and flow battery technology to get the best of both worlds, if it can be commercialized.
Also promising are zinc-air batteries, which have generated recent news from companies such as Zinc Air Inc. and Fluidic Energy. “You can get a lot of energy in a small package,” Kamath said, “but there are major engineering challenges and we aren’t quite there yet.”
Automated demand response
One dark horse candidate that can potentially meet some of the same objectives as storage is automated demand response—using control technology to regulate customer demand in near real time. Demand response could in theory be used to match the irregular output of wind power—for example, by remotely instructing thousands of electric vehicles to charge faster or slower depending on power availability. If it works, Kamath agreed, “the cost will be much lower than a piece of capital equipment” like a huge battery.
With so many options to consider, utilities across the country have at least three dozen pilot studies underway or in the planning stages to help them assess the feasibility of storage, including performance, cost, and operational challenges. At the same time, of course, PG&E and other utilities continue to assess other possible ways of providing safer and more reliable service to customers, as affordably as possible.
PG&E believes in a technology-neutral approach, where all resources, including energy storage, compete on equal footing to meet the needs of the grid. In addition to developing the technologies, PG&E seeks to build operational experience with them through collaboration on pilot projects with technology companies, developers, grid operators and other utilities.
Bottom line: electrical energy storage technologies are still emerging and are not ready for mass deployment in most utility applications. But they’re a lot more real than the Holy Grail, and a lot more worth exploring.
By Jonathan Marshall
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