However, ambient temperatures will be the major thermal issue – cooling during hot days to ensure long lifetime, and heating to prevent the cells from freezing in the winter. Thermal regulation may be a hidden performance costĪnother benefit of operating at such low current densities is that there will hardly be any waste heat during charge and discharge (as a result of the lower resistive losses). Customers will just need to be aware that they will need multiple units to serve high power.ģ. This isn’t a show-stopper – the achievement of $350/kWh (DC) is still significant.

Alternately, if you did want to run high power, you would need more cells to supply the 5 hours of energy. In essence, you’re paying for a lot of power you can’t use. (In a car, those two modules would be pushed to deliver about 30 kW of power) In other words, the PowerWall was designed for energy output, not power output.īy the way, this is the traditional argument of flow battery proponents – if you want to store lots of energy in regular batteries, you wind up being massively oversized for your desired power output the faster you discharge electrons, the bigger your losses become, and the bigger energy your battery has to become, to deliver the same kWh to the outside world. The tradeoff is that they are putting in many, many cells to supply the 10 kWh – far more than would be necessary for the rated 2 kW of power, or even the peak 3.3 kW. (Our Catalytic battery model suggests this is as low as 0.6A per cell) For example, a normal Tesla car battery probably has a DC-DC round-trip efficiency of less than 80% because people charge quickly (one round of resistance losses), and output high power when driving (a second round of resistance losses). The two packs are one-eighth of a Tesla Model S 85 kWh.ĩ2% efficiency can only be achieved by running the battery at extremely low current, to minimize resistance losses. This makes a total of almost 900 cells, with an operating voltage of about 48 VDC which makes certain safety aspects easier to design. Each module has 6 groups, and 74 cells in parallel per group. It’s likely that the battery packs are two modules identical to (or very similar to) the Tesla Model S design, in order to achieve production synergies. The battery architecture is designed for long durations, which means low power. Amortizing the capital cost of your system, by ensuring long lifetime for the batteries, is far more important.Ģ. This is lower, but it doesn’t matter, because losing 13% of your low cost electricity is insignificant in the economics. You have to add a AC-DC inverter (with 97% efficiency each direction), so your real-world AC-AC round trip efficiency drops to 87%. The huge difference in voltages means a significant efficiency hit – one-way efficiencies are probably about 94% to 97%. This is to match the DC input of typical inverters. The PowerWall batteries themselves likely run at about 48VDC, and are boosted by an internal DC-DC converter up to 350V-450V. The “92% efficiency” figure quoted by Tesla isn’t as good as it sounds, but it doesn’t matter. Here are our top ten conclusions, with plenty of links to reference information.ġ. 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. In the few days since the Tesla energy storage announcement, we’ve had a half-dozen people ask what we think about it. Today, it’s “What’s your Tesla strategy?” $350/kWh (DC) retail really is that significant. There’s an MBA joke about scaring your clients by asking them “What’s your China strategy?”. Special post by Bruce Lin and Matthew Klippenstein

17000 watt 12 volt magic battery