When sizing a battery on the Storage tab, you may see a warning about the ratio between Power Rating and Energy Capacity — also known as the C-rate. Here's what that means.
What's the limit?
Due to limitations in our storage simulation engine, the maximum C-rate we currently support for hourly consumption files is 0.7.
C-rate is calculated as:
C-rate = Power Rating ÷ Energy Capacity
For example, if your battery has an Energy Capacity of 100 kWh, the Power Rating can't exceed 70 kW (70 ÷ 100 = 0.7).
If you've seen this warning on the Storage tab of Designer, your battery's specs have exceeded this limit:
In this example, an Energy Capacity of 100 kWh and a Power Rating of 500 kW exceeds the maximum supported C-rate, triggering the warning: "For a 100 kWh Energy Capacity, Power Rating must be at most 70 kW."
Another way to think about it: duration
C-rate is the inverse of battery duration — how many hours the battery can discharge at full power. A few examples:
| C-rate | Duration |
|---|---|
| 0.5 | 2 hours |
| 0.25 | 4 hours |
Why does this limit exist?
We know this limitation may prevent you from entering the true specs for certain batteries. We're working on a permanent fix to significantly raise this limit and support all physically realistic C-rates.