I have an installation that has three potentially high-power aspects to it:
a water pump that can technically draw 8A but that I have never seen draw more than 1.5A. This will be on for perhaps a half hour every day between April and September. Typically during hours where the solar cells will be active.
some LED arrays that consume between them about 3W @12V. These are attached to motion sensors so usage is difficult to assess. Perhaps 15 mins every 24 hours
a SIM900 module. Technically this can draw up to 3A. I have never seen it take more than 200mA. Usage is dependent, but possibly 1 minute per day.
The rest of the circuitry is at the microAmp level.
So it seems that the possible energy usage is about 1Ah.
the installation will be powered by an old 12V 60Ah car battery (sealed)
to save costs (this is largely an upcycling project) I'd like to avoid a charge controller.
the solar install will be in the South of France (the Gers). So between 6 and 9 sun-hours per day between April and September.
This suggests that I should be able to "get away with" a solar panel of 5W. is that correct? I can't help feeling I've screwed up my maths somewhere ....