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December 22, 2014


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Do you know (and/or can you say) whether the type of storage will be chemical batteries or something mechanical?

Sure! Most of 'em are lithium-ion batteries. (RES, for example, delivers systems that can supply 19.8 MW and store 7.8 MW-hours.)

But there are also the Ice Bears! These things basically use energy to freeze giant ice cubes on rooftops. The ice is then used to chill interior spaces the next day. How cool is that? :-)

Professor Maurer,

A 95% output drop does not pass the sniff test for the 40 MW solar facility ET Solar and EDF are building. See Figures 5 and 6 of this paper by Sandia National Labs:


A 40 MW facility in Puerto Rico would almost never have output drops of more than 40% within minutes. In San Diego, the result would have an even lower probability of occurrence. My guess is that the Negev is not so different.

A 95% drop is more reasonable for a small residential solar array, but the output drop from a small array is unlikely to cause voltage problems on the grid. In contrast, multi-MW solar facilities exhibit significant benefits from geographic diversity. This is all the more true as as central inverters get replaced by string inverters and microinverters for utility-scale solar.

Lest you think this is propaganda from the pro-solar lobby, I speak representing an energy storage company that benefits from solar's problems. My company, http://www.greensmithenergy.com , builds software controls for energy storage, including storage devices designed for solar ramp rate control. We are also the technology partner for one of the winners of the SCE storage procurement. The energy storage hype cycle continues to pick up speed!

David Miller
The Energy Business and Geopolitics, Fall 2012

Thank you, David! I wish I got more comments like this.

The 95% figure, not surprisingly, was passed to me by an official of the Israel Electric Corporation. I need to do more due diligence ...

I hope it's not a storage hype cycle! As you know, good cheap storage really does change everything. Your company looks fascinating, by the way. Congratulations!

Thank you! And I should not be so flippant in my comments. I too am excited for the wide-scale deployment of energy storage!

Here in Germany, some interesting options for storing windpower are being explored. One is using windpower to pump water. This is site-specific, so it has limited applications, but it lets windpower be stored indefinitely as potential energy.

Another is useing windpower to crack hydrogen out of water. The hydrogen can then be used to turn turbines at off-peak, or it can be injected directly into natural gas lines. It turns out that spiking natural gas with a few percent by volume of H2 works great -- and some natural gas is saved, thereby slightly but noticeably reducing reliance on expensive (and mostly Russian) gas imports, and you also cut your greenhouse emissions by a little.

The good news: There are already several hydrogen-producing windmills, including a 2 MW pilot project that's putting H2 into natural gas lines in the former East Germany. And it looks like this will be a money-making proposition.

The less good news: efficiency is not high; we're talking maybe 25% on a good day. Also, scaling up will be a challenge. Burning H2 directly requires expensive specialized equipment. Putting it into the gas lines is much cheaper and simpler, but it only works up to a point. That's because once the proportion of H2 exceeds 10% or so, normal equipment can no longer handle the mix -- hydrogen starts to leak out of the system, ignition and combustion temperatures change, and so forth.

Doug M.

Yes, very cool. (groan.)

Doug, I can see that there's no point in re-plumbing domestic gas appliances to handle pure H2, or more than 10% 'spiked'. Are there many industrial users of gas who could invest in an alternative H2 system to sit alongside their natural gas system?

Chris, that's a good question and I don't know the answer. My tentative guess, though, would be that H2 from windpower is never going to be that big -- when you convert windpower to hydrogen, you're throwing away ~3/4 of the energy. That only makes sense if it was waste energy to begin with.

Which can certainly happen! For instance, if the wind is blowing hard all over the country, the sun is shining brightly at the same time, and/or you're at an off-peak time when demand is low. But it shouldn't happen *too* often, or you're not going to make much money off that particular windpower site.

So, since the hydrogen thing is going to be a relatively minor by-product, building industrial infrastructure around it is probably not in the cards. But using it to reduce natural gas consumption by a few percent? Hey, that's money you're not mailing to Vladimir Putin. Win-win.

Doug M.

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