On Thu, 23 Apr 2020 09:11:21 +0100, newshound
wrote:

On 22/04/2020 17:20, Martin Brown wrote:

It is a problem with the UK's high latitude and low sun in winter so
probably applies to the entire country. I expect the signs work fine at
lower latitudes that get some decent amount of winter sunshine.

We used to have a "private" speed sign on the approach road to work. It
would have been well designed and maintained, and it worked fine all the
year round. It did have quite a big panel with an unobstructed view of a
lot of sky.

And that's the thing isn't it, it would have to be designed (both it
and it's location) to work with the energy available at that location
and in 'worst case' scenarios (little sun for a time, lots of usage
for a time, battery / panel efficiency reduction over time etc).

Anything less, causing the unit to fail down to lack of energy is
simply down to poor design limitation considerations.

So, if you have the OP's garage 12V supply situation. If you know how
much power the air pump takes (easy to read off the plate or measure
with a DMM), and the longest time you might run it for in a particular
period, you know what the battery will need to supply that energy and
therefore what size panel you might need to be assured you can cover
both that usage and any parasitic drain created by any charge
controller.

Or, that with a big enough battery and a matched panel (that wouldn't
do the battery any harm by overcharging in the 'best' conditions),
just a straight panel battery config (that the OP is not going to
never going to discharge the battery beyond say 50%) then he should be
good to go. ;-)

Cheers, T i m