coulomb wrote:I note that the oft-quoted power limit of 3000 W is really a 60 battery amp limit...
So, if there's 3kw load and only 2kw charging will it take 5kw panels? What's the actual mppt limit?
Sorry, perhaps I wasn't clear. The SCC measures its power on the battery side, where the current is higher than on the PV side. Example: 3000 W @ 100 V on the PV side is 30 A plus losses, say 32 A; on the battery side, if the battery is 50 V, it will be 60 A. But if the battery is say 55 V, you'll get 10% extra power from the 10% extra voltage, so 3300 W.
So the real limit is 60 A of SCC charge current on the battery side; that's all the MOSFETs can handle.
So any load on the battery is irrelevant to this limit, as is the total current into or out of the battery. In your example of 3 kW load and 2 kW charging, there will be 1 kW net out of the battery, but you still have the ability to increase that charge current from 2 kW to whatever 60 A times the battery voltage comes to.
The nominal power of the PV panels also doesn't matter. If you have 5 kW of panels, then the SCC won't "work harder" than it takes to make 60 A flow into the battery from the panels (via the "DC transformer" of the buck converter inside the SCC). Likewise, if you have 2 kW of panels in ideal conditions, or 5 kW of panels with shade such that there is only 2 kW available, the SCC will hunt around till it finds the most power it can get, which hopefully will be 2 kW. It will essentially work harder and harder until it finds that the power actually starts dropping, and will wind back to where the maximum power point was. As the sun and shade moves, the panels heat up, and so on, the maximum power point will move about, but the maximum power point tracking software keeps working the panels close to the maximum power point all the time.
The advantage of more than 3 kW of panels is that instead of having 3 kW only for half an hour on ideal days, you'll get 3 kW from say 9am to 3 pm (ignoring daylight saving), and only start falling off either side of those hours. You'll never get more than the 3 kW (or whatever 60 A times the battery comes to), but you'll get more "value" from your panels in non-ideal conditions.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, PIP-4048MS inverter, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.