On Fri, 19 Jul 2013 02:50:25 +0000, Bt
wrote:

They wired our electric cooker so that permanently works on mains. That
again was not mentioned on the sales visit

You didn't seriously expect a battery bank to power your cooker,
immersion, or anything else that relies on an electric heating
element?
This is old bull**** - ten, fifteen years ago, it was simply solar,
off-grid, battery banks, inverter (if used) and grid-tie (if needed).
Cost? Thousands. Only worthwhile for a cabin in the woods and if you
were absolutely determined.
Anyone in an urban setting with one of these setups is perhaps hoping
for a bit of a tide-over when the main grid starts falling apart, but
unless you actually have a cabin in the woods, you're kidding yourself
on.