Top Ten Facts about Tesla’s $350/kWh (DC) PowerWall battery

Special post by Bruce Lin and Matthew Klippenstein

[Edit May 11 – corrected PG&E peak price to $0.36 not $0.40/kWh – $0.36 was used in the calculation]

There’s an MBA joke about scaring your clients by asking them “What’s your China strategy?”.

Today, it’s “What’s your Tesla strategy?” $350/kWh (DC) retail really is that significant. In the few days since the Tesla energy storage announcement, we’ve had a half-dozen people ask what we think about it. As energy systems developers with experience in several different chemistries and system scales, we can make some well-grounded educated guesses on the design and economics.

Here are our top ten conclusions, with plenty of links to reference information.

1. The 92% efficiency figure is misleading

The “92% efficiency” figure quoted by Tesla isn’t as good as it sounds, but it doesn’t matter.
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Why charging your phone in 1 minute isn’t enough – analysis of Stanford’s aluminum-ion battery

This week’s hot battery news is an aluminum-ion cell out of Stanford Professor Hongjie Dai’s lab, that can charge in less than a minute. Many online articles have claimed this will revolutionize our mobile phones and Tesla cars, but this will be a closer look at the numbers, based on their recent Nature paper (doi:10.1038/nature14340) (and some help from a former battery scientist friend who would like to remain anonymous). Additional comments are welcome, especially on the ionic liquid electrolyte.

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NASA’s Helios HP-03 high-altitude drone and its fuel cell

The NASA ERAST program was a 1990-2000s effort to develop an unmanned (but remotely-piloted) drone. It used solar panels and batteries to fly for a day at a time, and several generations of prototypes were developed by Monrovia, CA company AeroVironment. In an effort to get continuous flight, the batteries of one of the last prototypes, Helios Prototype 03, were supplemented by a fuel cell system with high system energy density.

The original design concept was to use a paired electrolyzer / fuel cell system that could generate hydrogen and oxygen during the day and store it, and then feed the gases into a fuel cell to supply electric power at night. These are almost certainly the Giner stacks mentioned in a 2001 press release.

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Energy at Stanford with Peter Thiel, Steven Chu, and others

There were some interesting talks at the Net Energy Analysis workshop at #GCEP #Stanford.

“The bandwidth for communications with policymakers is astonishingly low. For example, my father worked on communications with nuclear submarines. The bandwidth is very low, basically an antenna the size of Wisconsin is used to transmit 20 characters to the sub commander, who says ‘Yep, I guess I’m supposed to destroy the world’ “. – Howard Gruenspecht, deputy administrator of the EIA

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Stanford and Steven Chu endorse Catalytic Engineering (not really)

I’m in Stanford at a workshop on Net Energy Analysis. Quite an interesting discussion of energy inputs and payback. And check out the middle clip art – clearly an endorsement of Catalytic Engineering!

Below is former Secretary of Energy Steven Chu who gave the keynote. He’s very quotable. (These were paraphrases – some of them I didn’t catch exactly)

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SunEdison and Imergy to install anywhere from 0 to 1,000 flow batteries in India

Imergy announced this week that SunEdison agreed to purchase up to 1,000 flow batteries from Imergy for rural India applications.

Total energy of the deal was reported as up to 100 MWh, so this is 100 kWh per flow battery. Imergy makes a 30 kW and a 5 kW unit. A 30 kW ESP30 running for 3.3 hours is an awfully short runtime, so it’s more likely that these are small ESP5 5 kW units that can run for 20 hours to back up India’s notoriously unreliable grid. [Edit: see below for clarification from Imergy]

(Flow batteries make sense for long runtime applications, since increasing energy is simply a matter of adding more liquid electrolyte, rather than more cells. A 5 kW system has much cheaper cells, power electronics, and overall capital cost than a 30 kW unit)

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Dude, where’s my fuel cell car?

It’s 1994 and a new breakthrough in fuel cells has taken the world by storm. “We could be manufacturing and selling clean hydrogen-powered cars any day now! How soon? Let’s say … 2000.” A newspaper article just like that is how I got into fuel cell engineering almost 20 years ago.

Well, it’s now 20 years later, and Toyota has just announced the sale of its fuel cell Mirai car. It can actually be purchased by consumers – not just leased. Quantities are in the hundreds, and it’s obviously restricted to the areas where hydrogen refueling is available, but it’s a huge milestone.

After these decades of hard work in the chemistry labs and engineering workshops, machine shops and test tracks, , it’s interesting to look back on the hype and overblown ambitions that led here. The interactive timeline below shows how long various people thought it would be before fuel cell cars became commercial. Hover over each bar for a full quotation, or click for a link to the original article where available. Continue reading