On May 28, 10:42*am, Roland Perry wrote:

In message , at 01:09:37 on Thu, 28 May
2009, David A Stocks remarked:

A similar mechanism already exists for off-peak domestic customers
using night storage heaters, who get a contract stating something like
"you get 7 hours of cheap rate electricity between the hours of 2300 and
0800 the following morning", together with a radio controlled switch
for that part of the supply. The switches are used by the local
suppliers to manipulate their overall load in order to buy bulk
electricity at the best market prices from the generators.

What they forget to mention quite as loudly is that you get charged
*more* for the daytime electricity, not just *less* for the night-time.
Unless at least a third of your consumption is overnight, you will end
up paying more overall.

Hence night storage heaters and hot water boilers with timers (a
principle that can extend to other appliances e.g. washing machines
and dishwashers).

Also, this uSwitch webpage suggests that it can make sense if one's
night-time energy consumption is "roughly 20%" as opposed to a third
as you suggested:
http://www.uswitch.com/gas-electricity/economy-7/

Still, you're quite right to say that it could well prove to be a
false economy.

Nonetheless the principle could be utilised for car charging, either
through on-street charge points or fed by the car owner's domestic
electricity supply - of course charging a car from one's domestic
supply entails being able to park the car more or less next to one's
home, and dealing with getting the cable across the pavement as well
(these problems don't apply with a driveway or garage of course).

Nearby-ish to where I live there's someone who has one of these G-Wiz
electric cars - they seem to be able to park it outside their house
most of the time (it's a quiet dead-end street) and the cable they use
across the pavement (which doesn't get a lot of traffic) is one of
those arrangements with a rubbery mat so it lies flat and appears to
largely mitigate the trip factor, but I'm not sure it'd be so workable
if the pavement was a somewhat more popular walking route.