Tag Archives: batteries

On the Tesla home battery

During Tesla Motors’ Q4 2014 earnings call on February 12th, Chariman and CEO Elon Musk and CTO JB Straubel talked a bit about upcoming plans for a battery pack for use in homes and business. Musk said that the design was complete, that production was probably 6 months or so away, and that a formal announcement was probably a month or two out.

This isn’t a surprise. Stationary storage is an obvious use for expensive vehicle packs once their capacity and current-handling characteristics are no longer suitable for transportation use. In such applications, they are an obvious compliment to solar panels, like those installed by Solar City where Musk serves as chairman of the board, and which already has a pilot project using Tesla supplied packs. Oh, and Musk has talked about it during another earnings call last spring.

“We are trying to figure out what would be a cool stationary (battery) pack,” Musk said. “Some will be like the Model S pack: something flat, 5 inches off the wall, wall mounted, with a beautiful cover, an integrated bi-directional inverter, and plug and play.”

To read some of the coverage, this is a major threat to the utility industry.  The Verge thinks that “[…]Tesla’s battery for your home should terrify utilities,” though the article appearing under that headline is more tempered in its assessment.

For Tesla’s part, they seem to see utilities as an ally rather than an adversary at this point. Musk and Straubel’s comments during the latest earnings call were prompted by a question from Ben Kallo, from Robert W. Baird (a financial firm). Kallo asked about developments on the storage side of the business, specifically about Tesla’s position on a number of big RFPs for energy storage from utilities.  Musk’s reply was that they were bidding on a lot of RFPs already, and CTO JB Straubel said they were talking to almost all of the utilities. He went on to caution that the time-frames are very long, but that utility storage was getting an increasing amount of Tesla’s attention.

Tesla has other reasons for closer ties to the electrical utility industry too. Tesla’s current cars have a range competitive with a typical gasoline car. To achieve that range, they need a huge battery pack, and the cost of that pack is major contributor to the purchase price of the car.  For longer trips, the Tesla is at a disadvantage. Filling up a gasoline vehicle takes ~5 minutes. Recharging a Tesla to full range takes over an hour at a Tesla Supercharging station, and ~10 hours with a beefy home charging station. If Tesla is going to achieve their ambitions, they’ll have to lower the cost of their cars and broaden access to rapid charging infrastructure. The utilities are an obvious partner on the infrastructure front, and broader access to rapid charging infrastructure can help lower the cost of cars, by making smaller, cheaper batteries more practical.

Of course, if you look for other commentary on this, you’ll find plenty of other articles and blog posts that go at least as far as the Verge’s headline in proclaiming the death of the grid.  Let’s just say, I think those people are wrong.

Inside look at HP’s approach to laptop batteries (circa 2012)

While trying to find details of what’s inside HPs extended runtime batteries, I came across video shot by Tom’s hardware of a press junket / meet-and-greet with Dr. John Wozniak from HP talking about what goes into designing and HP’s battery packs.

It’s from spring of 2012, which makes it a bit dated in some regards, but I still found it informative, particularly since most of the battery packs I’m getting are of a similar vintage.

Some things I found interesting:

  • Relative to 18650 cells, prismatic LiIon are ~1.4x more expensive, and pouch packs are 2x more expensive for the same capacity.
  • At the time, 18650 cells were clearly HPs focus for price/capacity. They were, however, using prismatic cells and pouch-packs for thinner form factors.
  • Pouch cells are relatively easy to get 1000 charge cycles from because they can expand and contract as needed when being charged and discharged, reducing the pressure that degrades the electrodes. The downside is that cells can also expand due to gas generation, which can damage the pack and/or other components.
  • At least for the products being discussed, HP seemed to be transitioning from prismatics to pouch packs.
  • Safety regulations limit companies from stuffing more than 100Wh into a single battery pack. This, combined with improved capacities, have lead to the demise of 12-cell extended runtime packs.
  • At the time, HP was using LG 3000 mAh cells for their high-capacity 18650 packs.
  • Apple shouldered the growing-pains of getting pouch-cell pack design and manufacturing right.
  • Because the cells are a commodity, HP tries to distinguish its packs on quality, reliability and manufacturability. This has led them to use conformal coatings on circuit boards to protect against shorts and corrosion. They’ve also switched from wires to flex circuits within the packs for improved reliability and their pouch-cell packs have moved to welding the cell contacts directly to a PCB.
  • Their primary suppliers are Panasonic, LG, Samsung.
  • Among Chinese cell manufacturers, they’ve tried to work with a few, but the economics haven’t worked out. B&K is a qualified supplier for some of their packs, but HP doesn’t ship many of their cells.