Getting Energy From The Energy Store

Guest Post by Willis Eschenbach

Inspired by an interesting guest post entitled “An energy model for the future, from the 12th century” over at Judith Curry’s excellent blog, I want to talk a bit about energy storage.

The author of the guest post is partially right. His thesis is that solving the problem of how to store city-sized amounts of electricity would make a very big difference, particularly for intermittent sources like wind and solar. And he’s right, it would. But he’s wrong not to point out how devilishly difficult that goal has been to achieve in the real world.

Storage of electricity is a very strange corner of scientific endeavors. Almost everything in a 2013 car is very different from what was in a 1913 car … except for the battery. Automobile batteries are still lead-acid, and the designs only differ slightly from those of a hundred years ago.

Figure 1. Elements of a lead-acid car battery. SOURCE 

Now, we do have nicads and such, but the automobile storage battery is the bellwether for the inexpensive storage of electricity. Cars need a surprisingly large amount of energy to start, particularly if they are balky. If there were a cheaper way to store that big charge, it would be on every car on the planet. Given that huge market, and the obvious profits therein, people have been busting their heads against the problem since before Thomas Edison made his famous statement about automobile batteries.

And despite that century-long huge application of human ingenuity, in 2013 the lead-acid battery still rules. It’s an anomaly, like fusion energy, a puzzle that has proven incredibly hard to solve. Potential solutions have all fallen by the wayside, due to cost, or capacity, or energy density, or dangerous components, or long-term stability, or clogging, or rarity of materials, or a habit of exploding or melting down, or manufacturing difficulties, the number of pitfalls is legion.

So I’ll get excited when we have something other than lead-acid batteries in our cars. Because that will be evidence that we’ve taken the first step … but even that won’t be enough. The other problem is the huge amount of energy we’re talking about. Here’s some back-of-the-envelope figures.

New York City’s electricity consumption averaged over a 24/7/365 basis is on the order of 5 gigawatts (5E+09 watts) continuous. Let’s take a city a tenth of that size, there’s plenty of them on the planet, China alone has dozens and dozens of cities that big, and lets consider how much storage we’d need to provide three days of stored electrical energy for that city. The numbers look like this

5.0E+08 watts continuous times

72 hours equals

3.6E+10 watt-hours of storage times

3.6E+03 seconds/hour gives

1.3E+14 joules of storage needed

So that means we’d need to store 130 terajoules (130E+12 joules) of energy … the only problem is, very few people have an intuitive grasp of how much energy 130 terajoules is, and I’m definitely not one of them.

So let me use a different unit of energy, one that conveys more to me. That unit is “Hiroshima-sized atom bombs”. The first atomic bomb ever used in a war, the Hiroshima bomb released the unheard of, awesome energy of 60 terajoules, enough to flatten a city.

And we’re looking to store about twice that much energy …

I’m sure that you can see the problems with scalability and safety and energy density and resource availability and security for that huge amount of energy.

So while I do like the guest author’s story, and he’s right about the city-sized storage being key … it’s a wicked problem.

Finally, as usual, Judith has put up an interesting post on her interesting blog. I don’t subscribe to a lot of blogs, but hers is near the top of the list. My thanks for her contribution to the ongoing discussion.

w.

PS—Edison’t famous statement about automobile batteries? He was offered big money in those days, something like ten grand from memory, to design and build a better battery for electric automobiles than the lead-acid battery. He took the money and went back to his laboratory. Month after month, there was no news from him. So the businessmen who’d put up the money went to see him. He said he didn’t have the battery, and in fact he didn’t even have the battery design.

Naturally, they accused him of having taken their money and done nothing. No, he assured them, that wasn’t right at all.

He said there had actually been significant progress, because he now knew of more than fifty ways NOT to make a battery for an electric automobile …

Curiously, Edison ended up inventing a nickel-iron-peroxide battery, which was a commercial failure … so even he couldn’t get past lead-acid.

Similarly, we now know hundreds and hundreds of ways not to make a battery for a city. So I suppose that’s progress in Edison’s terms, but after a century the wait’s getting long. I suspect we’ll solve the puzzle eventually, perhaps with something like a vanadium flow battery or whatever, but dang … it’s a slow one.