On 19/08/2019 21:42, Chris Green wrote:
Andy Burns wrote:
Chris Green wrote:

I can't find a site providing what seem
to be realistic 'ball park' figures for UK regions.

http://www.reuk.co.uk/wordpress/solar/solar-insolation/

What I *actually* want to know is the 'average over the year' *watts*
from a panel. I could work it out backwards from the above but a
simple "you'll get about 20% of the panel rating averaged over the
year" would be more useful. I want to know how much panel I need to
install to run a water pump, or how big a water pump I can reasonably
power from a 260 watt panel.


With or without something to store energy?
The output from a panel will vary from zero to 260W so if you attach a
pump that uses a couple of hundred watts it isn't going to start on a
cloudy day.

So you really need a battery of some sort and then use the average to
size the pump.

Does it need to run on demand or will it be OK running one day in three
in summer and once a fortnight in winter?