My knowledge is limited, but how long do your PV panels last? I read at one point you need to replace them after about 15 years, maybe sooner, because they go down to about 40% efficiency, or something like that, after that time.
Actually they don't know how long PVs will last. Most warranties are 20 years. There are panels that are 30 years old and still producing good amounts of electricity. I have some 15 years old panels that I bought and when I installed them they were still producing 90% of their rated value.
To do it piece meal, the Enphase micro-inverter will let you buy a panel and their micro inverter and install them one at a time. It just plugs into your power panel. You just have to install a kill switch in case the grid goes out so you don't put juice on the grid and fry some line worker. http://www.solar-electric.com/enmigrsy.html
Nice setup Deano. 5.4 kw is huge. I was wondering why you still had to buy from the grid, and then I read you had children. Nuff said.
Very impressive, though 12 - 6 vdc batteries isn't that much amp hours. Maybe 7 kwh worth of backup. Glad you made the plung.