Dave Liquorice wrote:
On Fri, 21 Dec 2007 11:09:11 +0000, Owain wrote:

I quite like the idea of using E7 to charge a battery bank then use
that for the rest of the day. But in an all electric house you'll need
a 10kW+ invertor assuming you want to have a shower
Why woulndn't you just store the E7 heated water?

My telly doesn't run on hot water... but yes splitting the E7 across a
water based heat bank and a battery bank probably does drop the required
invertor size to sub 10kW. How ever add up the breakfast routine, kettle
(3kW), toaster (1 or 2kW), hob (1kW) for porridge plus lights and
fridges/freezers, breakfast/kids telly. The peak demand of a single house
can be surprisingly high, if short lived, even if 24hr average is less
than 1kW.

Yep. I reckoned 15KW was about right for peak, and 30KWH for a 24 hour
usage.


Actually this got me thinking when I was taking the dogs for a walk..

Tow massive lumps of concrete with holes in, and water pipes (or a
working fluid anyway) buried in the ground under the house in loads of
insulation..and a third under the lwan..heatpump from one to the other
or to teh third..so you have one hot block for heating, one cold block
for cooling..and source or sink the difference into the soil..


Because ultimately - if we take overall domestic power., about 80% is
used to heat things, about 15% to cool things (reverse in hot summers)
and the rest ends up as heat anwyay after doing whatever else it does,
like running a computer...

So if you are talkinng nuclear electric, it makes sense to store tehheat
rather than the electricity through times of peak demand.


Now how big a block of concrete represents 30KWh over say a 40C
temperature span? I found a reference of 0.2BTU per lb per degree F..who
is USING such units..ah well..anyway I get 9995 BTU per ton over a 40 C
change from that..that's 2.91768532 kWh per ton..so to get 30KWh is
about ten tons.

Cripes. That is NOT a lot of masonry at all.The storage heater to end
all storage heaters..

Oh..dunno if I did the calcs right, but WATER is the ultimate store. I
get around 400KWh per metric ton for a 40C change in temperature.

So there's your thermal store then. Bloody great insulated tank of hot
(or cold) water under the house ...

Won't do cooking, but it sure would do house heating or cooling, and
cool room stuff.