On Thu, 10 Sep 2009 10:17:20 +0100, The Natural Philosopher wrote:

I've got a 12 KW boiler, so it fires up for just ten minutes a day to
heat the tank.

Small boiler, ours is 38kW and that can struggle to keep this place
warm when the wind is up and the temperature down.

My oil bill is about £2000 a year of which about £1300 is in December
January and February. The rest is in the spring and autumn, and in
summer,(June July and August) it uses almost nothing.

I'm surprised a 12kW boiler can burn that much oil. B-) We get
through 4000l/year, so depending on the price anything from £2000
down to £1200 a year. And yes it is space heating that gobbles the
oil up; more or less 25l/day in the winter and 25/lweek in the
summer.

So get a bigger tank and fit an immersion heater.

A bigger tank in the form a heat store/bank is on the cards to go
with the wood burner and once that is in solar panels may as well be
added.

I had toyed with the idea of a windmill and dumping any excess into
the heatbank before selling to the grid. That was before I plotted
estimated power generation v useage the other day. A fairly windy day
with the 6kW unit producing full output for several hours did produce
a significant surplus (50kWHrs, about 2 1/2 days consumption) but
since then (the 8th) it's been calm... The 2.5kW unit would struggle
to meet our base load most of the time let alone generate a surplus
to be dumped into the heat bank or sold.

--
Cheers
Dave.