On Tue, 20 Aug 2019 11:18:12 +0100, Chris Green wrote:

snip

I *think* it's reducing the rate at which the batteries get discharged
but when adding the panel I also swapped batteries (from 22Ah to the
smaller one).

Yes (OP here),

waves

I can see very little use for small panels except maybe
for maintaining very low consumption devices like simple phones.

It was handy to take one when cycle camping. We left it strapped to
the top of the trailer and it would charge batteries for the GPS or
torches whist we were on the road and again with the panel outside the
tent when pitched up. 'Luckily' we had a reasonably sunny week and
enough batteries to ensure we had some stock should it become overcast
too long. Not having power hookup for the week paid for the panel and
would have been overkill in a small tent in any case. ;-)

We have three 'full sized' (i.e. 260 watt) panels on our boat which is
only a small (10 metre) boat and they are OK in the summer, in France,
to run a domestic fridge plus lights etc.

We see plenty of big panels on the narrow boats near here but they are
often in the shade for at least one half of the day and dirty and not
optimally aligned etc. I question what use they are above maybe
keeping an alarm online?

Through the winter they
maintain the batteries (which is handy since I can remove the shore
power connection and thus reduce the corrosion risk).

When I took battery 'A' off the rabbit hutch electric fence solar
panel and put it on a smart charger indoors you could actually hear it
sigh from the pleasure of a real charge. ;-)

I'm coming to the conclusion that even a similar sized panel (i.e. 250
watt or so) panel isn't going to run much of a pump all the year
round. Since just the panel will cost about £100 that's not a sensible
economic proposition.

I think you can get these things doing what you want but you really do
need to go OTT on both the panels and batteries to *guarantee* enough
power when you want / need it.

It's like when you see places in the back of beyond living off grid
when there may be several pretty large solar arrays, wind turbines,
water wheel *and* a 'battery room' full of pretty big batteries
(sometimes Milk Float / Submarines sized setups).

Again, it's one of those things that if money was no object (and
assuming you had the space etc) I would probably have a large solar
setup, just because. What I wouldn't do though is expect other people
to pay for it ... ;-(

Cheers, T i m