A typical solar PV panel is 320 watts and the smallest system I would
recommit is about a 3000-watt system, so that is 9-10 panels. In reality
we can build the system any size, but the infrastructure cost to install a
PV system is fairly consistent up through 40 panels so with a very small
system the cost per watt (or per panel) is higher and with less than 9 the
economics alone may not be enough of a reason to make the investment.
However, other factors may come into play that would make the
economics of a small system more desirable: an unreliable grid power
supply, or no grid power available; a desire to be green; or build it small
at first but expandable for future needs.