1. Size of the system = 12.24KW - is that DC power? Because I notice that the inverter has input power and out power of different numbers, output would be lower than input due to losses.
12.24kW is DC power. A number of inverters do allow more DC input than AC output, primarily because you are unlikely to get the full amount of DC input due to shading and panel orientation and such. If you have so much DC input at a given time that it exceeds the AC output capacity then there will be clipping.
The advantage of an inverter that allows more DC input than AC output is that it allows for a less expensive inverter and a bigger DC system. Clipping, if it happens, would only happen for a short time in the afternoon, but during the rest of the day you would be able to take advantage of that larger DC system and generate more power overall.
2. How does 12.24KW translate to 11605KWh est. annual production? Is it related to efficiency?
It doesn’t directly translate. A 12.24kW system that is oriented north will have a much lower annual production rate than a 12.24kW system oriented south. The angle of the panels will also affect the annual production numbers as well as any shading, not to mention weather. Annual production is simply an educated guess based on panel orientation, panel angle, your location and weather patterns, etc.
3. How accurate is PVWatts? There I get an est. annual production of 13000KWh
As I said above, annual production numbers are little more than an educated guess. Different calculators weight things differently, so they will all come up with slightly different numbers. In my experience Tesla tends to estimate on the conservative side, it I wouldn’t be surprised if your numbers are closer to the PVWatts numbers, but there’s really no way to know for sure until you’ve had your system for a year.
2. Does having two inverters make the system inherently less efficient in its overall output?
As long as the two smaller inverters have the same efficiency as the one larger one, then no. Efficiency would be the same. Two smaller inverters are likely to be more expensive than one larger one, not only because of the cost of the inverters, but there would also need to be additional electrical connections, breakers, and possibly even an additional panel.
3. Considering the PVWatts number above, would that make a difference in the clipping?
Clipping will really be minimal. Say that your system could generate a full 12.24kW at peak times, but your inverter is limited to 11.4kW. In the real world there’s no way that your system would generate the full 12.24kW, but we’ll use that for the sake of argument. That peek time might be for an hour a day, so you would lose .84kWh a day (12.24kW - 11.4kW = .84kW over one hour = .84kWh). If that happened every day of the year (Which, again, it won’t, because of weather) the most you would lose over an entire year would be 306kWh. (.84kWh times 365 days a year = 306kWh). That’s less than 3% of Tesla’s annual production number. And like I said, that 306kWh number would be in absolute perfect conditions. In real world conditions, you will likely lose much less than 100kWh over a year due to clipping.
