Intermittency, Part II


by Mark Heinicke

This article is a continuation of the discussion began in Why Intermittency Matters, Part I: Germany's Faltering Experiment in Renewable Energy Generation.

For starters, you will want to check out this site’s previous article on battery storage: Battery State-of-the-Art. It’s a quick read and packs a wallop.  The comments are very informative, too.  This present article and the one to follow (WHY INTERMITTENCY MATTERS, PART III: BATTERIES AT WORK) expand on a few of its salient points. 

Batteries by the ton: AES Energy Storage facility in Moraine, Ohio

In this installment, I discuss (1) the need for storage due to the intermittent generation of electricity from solar and wind, and (2) lithium-ion batteries, the current leader in commercially available rechargeable battery technology. In the next installment, I discuss the deployment of lithium-ion batteries in two wind energy facilities.

There’s little doubt that massive storage of some kind is required to support high penetration of intermittent energy sources into an electric energy grid.  This contravenes renewable energy proselytizers who envision a super-smart grid capable of balancing multiple intermittent sources to deliver reliable power when the contribution of wind and solar add up to more than 40% of the total. Possible?  Yes. Possible in time to head off climate catastrophe?  No. There’s the rub: we don’t have 25—50 years to tinker with a network that might work as advertised as we continue to burn fossil fuels at a furious rate, when we have more trustworthy options.  

I’ll get to the vision of a perfectly orchestrated, near-future distributed grid later.  For now I’m talking storage.  Chemical batteries first, not because they are necessarily the most effective storage technology, but because of familiarity. We’ve all held a battery in our hand. It’s likely that mechanical forms of storage such as pumped hydro and compressed air have the best chances of being scaled up to the demands of a local or regional grid, and I’ll get to those in future posts.  Also, I’ll get to hydrogen, flywheels, and more exotic possibilities, but for now let’s give batteries their due.  Batteries are highly portable, ubiquitous, and are evolving quickly. 

A Miracle Waiting to Happen

Let’s listen to Bill Gates, no stranger to technology, in his Gates Notes blog with the title We Need a Battery Miracle: To reduce the impact of climate change and meet the world’s energy demand, we need a reliable source of energy that’s cheap and emits no carbon. Many of the possibilities today involve intermittent energy sources such as wind and sun. The only way these can become primary sources of energy is if we develop inexpensive energy storage systems on a massive scale. Without this, renewable energy sources like wind turbines and solar cells will never approach the scale or affordability that is necessary.
“Over the last 50 years, the technology associated with generating wind and solar power has advanced, but not the technology to store it. Hopefully, that’s changing.”
(Full blog post here.)

When Gates says “miracle,” presumably he means something less than the intervention of a supernatural agency.  But how much less?  A miracle is by definition improbable.  Gates goes on to lament the inadequacies of current storage technology in active use.  Then the punchline: “Hopefully, that’s changing.”

Hopefully, the miracle will occur. This may give you pause when you think about the feasibility of an electric grid highly dependent on wind and solar energy.  If one of the world’s smartest and most foresighted people sounds so tentative about electric energy storage, while saying it is essential to the operation of the grid of the future, you might want to think about how much of a risk we take ramping up solar and wind to the neglect of more thoroughly tested solutions.  Bill Gates can afford to throw a few million dollars at an enterprise with iffy chances of success.  As for the rest of us, Gates says: “The only way [solar and wind] can become primary sources of energy is if we develop inexpensive energy storage systems on a massive scale.” 

For another tech-savvy voice, lend an ear to Tesla’s Chief Technical Officer J.B. Straubel.  In an interview published in energybiz magazine, last spring, Straubel spoke of the major role storage would play in a “100 percent renewable grid.”

Straubel talks about being “a few tens of years away from seeing a major shift.  It’s still early for stationary storage [such as would be used at a power plant].  It’s a small part of our business.”  So, a guy with prospective zillions to make selling batteries for a renewably powered grid, is taking a wait-and-see approach.  Looks like a case of smart money trumping smart grid.

For the full interview, with its unbounded optimism for a 100% renewable grid eventually, look here.

Whether for electric vehicles (EVs) or stationary storage, Tesla has taken the plunge on lithium-ion technology.  This makes sense, since lithium-ion—for the moment—leads the pack in rechargeable batteries.  (I oversimplify, since there are several varieties of lithium-ion batteries, with trade-offs between various characteristics, but the performance of all in commercial use is in the same ballpark.) Some of lithium-ion’s comparative advantages are: high energy density, scalability, long life, low maintenance, tolerance for hot operating conditions, and a solid track record going back to 1991.  Nearly all new EVs use lithium-ion for these reasons.  For more on lithium-ion fundamentals, check out the link to “Battery University” at the end of this article.  (For those who have feared lithium-ion car batteries biting the dust in eight years, there’s a link at the end of this article to some research indicating a lifetime of 20 years, if properly treated—which is what you’d expect in a for-profit power plant, with its cooling system, another energy drain, for keeping batteries at optimum temperature.  Note the A/C units in the photo of AES Energy Storage facility.)

Owing to space, I’m going to narrow my battery discussion to lithium-ion in this article and the next, which looks at operational deployment.  There might be (and in time there will be) better batteries, but for a rough idea of scale, lithium-ion should suffice.

Lithium-ion battery production has a particular environmental sore spot that may see a shift from conventional production to a cleaner production process that does not use N-methyl-pyrrolidone: cleaner lithium ions?.

A few words on energy density, since lithium-ion is touted to be especially strong in this regard.  The density of lithium-ion batteries has a range from .20 up to .75 kilowatt-hours (KWh) per kilogram. Gasoline, about 12 KWh per kilogram.  Coal, 6-9 KWh per kilogram.  Uranium?  For natural uranium, approximately 45,000 KWh per kilogram. So it would take 64 tons of the best lithium-ion batteries to store the electric energy extracted from a kilogram of natural uranium, a volume slightly larger than a golf ball you could lose in a tote bag.

As for storing wind energy:  a 100-megawatt (MW) farm operating at peak output generates enough energy in an hour to occupy 135 tons of the best-performing (.75 KWh/kg) lithium-ion batteries. (That leaves aside the question of charging rate and the charge threshold for any particular setup. I’m sticking to raw numbers for a sense of scale.) The facilities discussed next generate at that order of magnitude, so we’re likely to be considering tens of tons of batteries to handle the output of wind farms.   We look at batteries in operation in our next installment, Why Intermittency Matters, Part III: Batteries at Work.

Lastly, I recommend using Google Chrome to comment on these articles.  Please Ctrl-C or save comments before clicking send or preview.

A couple of informational links:
2. Life of present-day EV batteries can be up to 20 years (from a meeting of the American Chemical Society): EV battery lifespan


  1. I couldn't manage to edit my article at the moment, so I'm posting a correction to it here.

    When I compared the energy density of nuclear to other sources, I neglected to take into account the roughly 30-33% thermal-to-electric efficiency in a nuclear plant. I should not have said "electric" energy for the nuclear equivalency. Therefore, if we were to expect a 90% "round trip" efficiency for the lithium ion batteries, it would take only 24 tons of batteries to store the electric energy produced from a kilogram of natural uranium.

    Nevertheless, the ratio should make pretty clear that battery storage is inadequate to back up intermittent generating sources apart from dampening small fluctuations.



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