I'm curious about why you discounted solar thermal water heating... I've been following some end users on a forum where they've installed evacuated tube collectors and it seems to be worthwhile. More so that my PV system in terms of power saved by not using gas or electric for water heating.
On a November sunny day it can heat up 200+ litres of water from 15'C to 60'C by the end of the afternoon, according to the guy who's installed 60 tubes on his roof.
See the install here:
www.navitron.org.uk/forum/index.php/topic,8465.120.html
I burn about 4kW a day in electric heating a 100L tank of water (about 30% of all my electricity usage) so am thinking of getting a similar (if smaller) hot water solar system.
My off grid PV system is about 1.2kW now and I've experimented with using a tool transformer to convert the 3kW water heater into a 640W dump load in the summer (by running the 230V heater element at 115V). When the batteries get full I run the inverter to deliver power to the water heater upstairs and get some warm (35'C) water for free. This then saves grid electric in the evening to get it up to 60'C.
I was wondering if it really was worth sticking with off-grid but then last month we had a 90 minute power cut a a few "brown-outs" as well.
This autumn, I've been making an average of 2kWh solar a day (up to 18% of daily consumption).
Maybe the most cost effective thing we've done though is get insulation put in the outer wall cavity just before the weather turned cold... Should save enough gas to pay for itself in under two years (especially as we got it cheap by way of a government grant).