Andy Bennet wrote:
On 19/08/2019 19:59, Chris Green wrote:
I know only too well that a (for example) 250 watt solar panel doesn't
produce a continuous 250 watts for 24 hours a day every day of the
year. There's those things call nights, not to mention dull winter
days, and even dull summer days.

I've searched diligently but I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions. I suspect there's
a special word for this percentage which I haven't found.

So, can someone either provide a figure for the average output of
(say) a 250 watt panel over the year in eastern England or point me at
a site that will tell me this. (I seem to remember the figure is
something like 20 to 25 percent, so I'll get an average of 60 watts or
so from a 250 watt panel).


Rule of thumb in Eastern England is average of 10% rated power over 1 year.
For example a 250W panel will yield an average output of 25W over the
year, giving a total yield of 220kWh.

Yes, that seems to be about it. The additional problem/downside being
that the average through the winter is going to be much less so,
unless you have *huge* batteries, you need to size your system to
provide your required average power through the middle of winter.

Thus a 250W panel will probably, just about, run a 10 watt pump (or
whatever) through the winter if you have battery capacity for several
days. Assuming 12 volts that means you need something in the hundreds
of amp-hours capacity to keep your 10 watt pump going.

(We have 3 x 100Ah batteries on the boat with 3 x 260 watt panels, as
I said, in France, that can handle a domestic fridge plus some lamps
while we're away from mains power)

--
Chris Green
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