Slightly off topic but you are absolutely right to question the need. Regarding PV, we have never seen such a variety of professional advice, ranging from 3kw to 14kw, battery & no battery, single & three phase. I think it comes down to a) what we believe is going to happen to the price of energy and b) how much we are going to use. If we end up with a house with four busy adults running two electric cars, a three phase system may be worth the investment. If it ends up being just me and the wife, we may have overcooked it!