In a new and updated patent application, Tesla explains how these grid-tied projects are using its Powerpacks and inverters for what the company describes as a scalable “turnkey” solution.
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Tesla first applied for this patent back in September 2015, a few months after it launched ‘Tesla Energy’, and it updated it and applied again a year later when it was working on the second generation of its Powerpack.
It was released publicly yesterday.
In the background of the application, Tesla explains why they focused on making the system “scalable and flexible”:
Various approaches for energy storage have been tried. Some batteries that are designed for large scale energy storage have smaller cells arranged in series and parallel. For example, some cells are arranged in parallel, and then that unit is arranged in parallel with another similar unit, and so on. This can require the system to have a disconnect and fuse, and to apply some management strategy that occurs at the high level. These systems can be configured so that they are paralleled at an electrical interface, which can make them complicated to parallel.
One problem with such approaches can be that when batteries are paralleled, one must match their voltage characteristics precisely because they in parallel electrically. This can significantly limit scalability of the system. For example, one may need to use very similar chemistry, or similar cells, or come up with particularized balancing strategies, to manage the different cells within their ranges of operating characteristics. Also, with regard to the individual cells, the system is in a sense limited by its weakest link. That is, if one cell malfunctions this typically renders the whole array of batteries out of service.
That’s why they came up with turning hundreds of cells into dozens of pods which in turn go into the actual ‘Powerpack”:
The diagram from the patent application shows 6.5 kWh of energy capacity per pod, but that has doubled since Tesla uses the 2170 battery cells manufactured at the Gigafactory.
In the application, Tesla explains that they can even use different types of cells in the same project:
“For example, in a field that includes batteries with a cumulative capacity of one GWh or more, the system can allow use of different cell types, different ages of cells, different cell voltages and/or different physical types of cells.”
The company hasn’t built anything close to 1 GWh in capacity so far, but it’s interesting to know that it’s even a possibility. The biggest project so far is a 20 MW/80 MWh Powerpack station with Southern California Edison.
In order to scale, Tesla combines the packs into larger systems that are in turn scalable in parallel:
It gets very technical, but the application is interesting and goes into many details. You can discuss it in the comment section below.
Here’s the patent application in full: