On Thu, 10 Apr 2008 11:33:17 +0000 (UTC), Adrian
wrote:

A big problem with a single genny is that it must be large enough to
supply your peak load. A generator that size is very inefficient most
of the day when the load is low.

Yes, but given...

An on-site generator can also be used
to sell surpluss electricity back to the national grid.

...can the over-size generator not be providing income by selling that
surplus capacity back to the grid? I s'pose it would depend on the exact
cost of generating versus the price paid by the grid as to whether it
would be profitable...

You don't have a hope of generating electricity as cheaply as a large
power station, so you'll be losing money, but it *might* reduce the
overhead of an underloaded genny running 24/7. IIUC the cost of the
equipment needed before you will be permitted to connect your genny to
the grid is pretty high.

A better way is to have a large battery bank that powers the house,
with the generator cutting in automatically when the charge gets below
a set amount and runs just long enough to recharge the batteries. An
invertor with sufficient output to power a house is very expensive, so
are large capacity batteries. Maybe best to do it the old-fashioned
way and use the batteries to power a brushless DC motor that drives an
AC generator rather than using an electronic invertor. The diesel or
paraffin generator would be DC and connected to the batteries via a
charging circuit and battery charge monitor.

For standing batteries you might go for a bank of open lead-acid cells
in a small outbuilding. The plates can be removed from the container
of each cell and replaced separately when needed (the old plates sold
for recycling), and the acid can be filtered and the container cleaned
periodically. The plates would probably last 3 to 5 years between
replacements.

You'll not get the cost down below what you pay for on-grid
electricity though, and using home-generated power should only be
contemplated if you don't have access to a grid supply.

DIY electricity only becomes cost-effective in factories that need
*huge* amounts of power.

--
Cynic