Dave Liquorice wrote:
On Sun, 16 Dec 2007 14:04:35 +0000, The Natural Philosopher wrote:

30 of them would give you enough to power a house for a day, including
things like the odd heater, shower and electric kettle, and be about the
same size as a fridge. About the same (output) energy as a car tankful
of fuel.

But it's not that simple. Your battery bank couldn't realistically operate
at 12v. The current demand would be so high that it becomes impractical.

I never said it should. Actually it could and can. 15KW is only 1200
amps or so.

Quite doable on an inverter. Not efficient tho.




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 and have other things on at
the same time. 10kW @ 12v is 833A, it comes down to a more manageable 83A
with a 120v battery bank or about 60 wet lead acid cells in series.


Yes. I actually went for about that.

Assuming an average load of 1kW/hr you need capacity of 24kWhr for each
day, which, (if my maths is right) roughly 200A/Hr per cell. Cells of that
capacity are available. Of course you'd need a proper Battery Room (acid
proof floor walls, fittings, ventilated etc) for the cells and a fairly
rigourous electrolyte testing routine to ensure that all the cells are
preforming equally.

Yup. Within a few percent we are talking the same numbers.

Lithium cells would technically be a better solution - no electrolyte to
speak of - but those sorts of capacities are about 10 times the price of
lead acid currently.




Then of course can you thump in enough charge in the available 7 hours to
last 24hrs? (You'll still be wanting to draw power during the charging
period...). I guess so, assuming 50% effciency raw mains to invertor
output and the 1kW average load that comes out at a 7kW charger, small fry
for E7.

charger should be 90% efficient or better.

As would be the inverter. 120VDC is just about perfect for modern
switching MOSFETS. Now there will be a lot of RF interference, but the
thing - the inverter/charge - could be in a shielded grounded box.

I think that an installation like this is on the cards in the next 20
years actually.

If we do go nuclear - and I think we must - the ability to use off peak
cheap electricity to power cars and houses is very great.