Solving the Green Energy Storage Problem

By Jessica Meyer

A variety of ways to store excess electricity produced by solar and wind power, to be used when the sun isn’t shining and the wind isn’t blowing, have been and are being developed and tested, and scientists are anxious to find new, better, cheaper ways.  Academic departments, businesses, and public energy research labs have been bursting with innovation and have seen steep increases in enrollment in electrical and environmental engineering programs.  The outlook for education and research on the excess wind and solar electricity problem looks more promising than ever: MIT, Stanford, and others have recently started to tap into the power of the web by offering engineering courses for free online; and accredited PhD online programs in a variety of engineering disciplines are currently in development.

Electricity generated by the use of conventional fossil fuels and nuclear power has not generally been stored; plants endeavor to produce the correct amount to power the grids. Widespread future use of renewable energy sources such as sun and wind seems dependent on the development of effective, affordable means to store excess electricity. Those who advocate continued primary reliance on fossil fuels, such as former U.S. Energy Secretary James Schlesinger, point to the intermittence problem with renewables, to say the future contribution of power by solar and wind will be minimal. The development of storage methods, however, is moving in a promising direction.

Another argument from critics of solar and wind power has been that it is far more expensive to produce than conventional power, such as coal or nuclear. But, according to Jon R. Luoma in “The Challenge for Green Energy: How to Store Excess Electricity,” wind power is nearly at “grid parity”—the cost of generating electricity from wind is about the same as that of generating it from coal—and solar power should reach grid parity in a few years.

It remains vital to find ways to store the massive amount of excess electricity sun and wind produce for the “down times” when it’s dark and the air is still. Some of the methods in use today are huge batteries, converting electricity to liquid air, and in-home storage.

Improving battery technology has been an approach, but a 1,300 metric ton battery larger than a football field that can generate 40 million watts of power, currently deployed in Fairbanks, Alaska to protect against blackouts, could only, in 2003-4, provide enough electricity for about 12,000 residents for seven minutes (Luoma). It would take hundreds of units the size of the Fairbanks unit to store electricity from solar and wind to equal the power generated by one coal plant.

Other types of batteries have been developed, but some have low “round-trip efficiency”—they lose energy as it is stored and comes out of storage. Lithium ion batteries have high “round-trip efficiency” but are very expensive, and a lithium metal-air battery, when it absorbs moisture from the air in addition to the oxygen it needs, can explode.

According to NewScientist, a promising type of power plant cools excess energy and stores it in the form of liquid air, or cryogen. The Highview 300-kilowatt pilot plant supplies energy to the UK National Grid. The process warms the cryogen when electricity is needed; it recovers only about 50 percent of the electricity fed into it, but cryogen plants can be located anywhere, costing far less to operate per kilowatt than batteries.

Excess energy from wind power can also be stored in the home, raising the temperature of an energy customer’s water heater or storing the heat in ceramic bricks in a nearby space heater. These devices, run by microchips and remote-controlled by the power administration, then act as a battery, giving back power when needed. The customer’s tap-water and room temperature are said not to fluctuate noticeably. The New York Times reported on a pilot program in the Pacific Northwest where energy customers do have to pay to participate.

Scientists are working on still other methods of storage, and constantly on the lookout for new ones. There certainly seems to be a serious commitment to making renewable energy sources an integral component of future electricity consumption.

[Image credit: Scamper Girl, Flickr]

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One response

  1. This is simply wishful thinking. The linked post by  Luoma simply states that wind power is nearly at grid parity but fails to offer any evidence. The latest cost-leveled estimates from DOE only show (on shore) wind achieving parity to coal in 2016 and make some rather generous assumptions to achieve even that by including carbon taxes. Luoma goes on to talk about battery storage by seriously offering up various lithium chemistries while admitting that cost is an issue. Beyond that, cell lifetime and sufficient energy storage dominate the problem and with battery technology improving at an anemic 7-8% per annum it’s going to be a long time until those solutions are practical and cost effective. Flow batteries, essentially a kissing cousin of fuel cells, do offer some potential, but again cost and capacity are problematic.

    Next, Luoma offers up that perennial poster child: hydrogen. Aside from the fact that the efficiencies of splitting hydrogen from water either through electrolysis or other techniques are generally low, hydrogen happens to be a very difficult gas to store. To get any significant energy density it needs to be stored cryonically or under very high pressure. Hydrides have been hyped but their storage capacity remains underwhelming. Being a very small molecule hydrogen is notorious for leaking, and hydrogen embrittlement is yet another issue.

    Finally, Luoma offers up compressed air storage. Certainly there are various natural formations that can be used to store compressed air, but the efficiency of compressing and expanding this air is quite poor, on the order of 50%. That means that half of the energy you’re trying to store is gone and you need to significantly oversize your nameplate capacity to account for this loss. Still not a compelling alternative.

    The reality remains that the most efficient energy storage medium known today remains pumped water storage. Recovery efficiencies are excellent (>80%) and the energy can be stored indefinitely in an enclosed environment. Unfortunately, if so called renewables –anyone who understands the second law of thermodynamics understands the impossibility of such a thing– are to become a significant fraction of US baseload electricity, say 20%, there is simply not enough pumped storage or other cost effective energy storage technologies of the scale required to support this.

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