We are going to install a PV in our offices. Our actual needs would be satisfied by an installation of about 4kW, so that ~16 panels of 250W. It's going to be a central-inverter, grid-connected installation.
Now, we would probably need more power in a few years. So I'm asking the contractors to quote me a bigger inverter, say, one for 6kW, thinking that if I already have a bigger inverter, then I can just buy more panels when needed, without having to change the inverter itself. I had the idea that I could put a bigger inverter, say, maybe even a 8kW or so, and it will produce what my panels would produce even if it's just half the capacity of the inverter.
But one of the contractors just told me that it wasn't the case. That the inverters "just work" under specific loads, for instance, the 4kW "doesn't start" if it's not feed 3.2kW (or so) from the solar panels. That doesn't make sense to me, specially since for what I have read the inverters just need a certain voltage to start, and that voltage, for instance, is the same for the inverters (in this case, Fronius) from 3kW to 7.5kW, specifically, 260V. This means (I'm no electrical engineer, but I'm no complete layman either) to me that the same power from the panels array is needed to start any of those inverters, so even if the maximum capacity is different, they can start producing as long as the Voltage from the array is 260V.
I'm not talking about putting 4kW worth of panels and an inverter for 20kW or something like that. I'm talking at most of a 10kW inverter, that it's the max amount I could put of solar panels in our roof, and the max one can generate for oneself here in México (or so I understand).
I understand if they are not at their maximum efficiency if not feed under their expected output range, but that they "don't start" doesn't make sense to me.
Am I missing something?