Which Size of Panel To Use
Solar panels are rated in Watts. If you wanted to trickle charge a 12V battery which is occasionally used a 10W solar panel can be appropriate as the battery will have time for re-charging between use.
Alternatively where 12V or 230V appliances are in regular use much higher rated solar panels are needed to re-charge batteries to supply the required power. Appliances are also rated in Watts.
Generally battery manufactures recommended not discharging a battery more than 50% to avoid damaging the internal lead plates. Example of available power (Watts) for a 100A battery will be 12V x 100A for 1200W divided by two for 600W therefore important to know the rating of appliances in use as this will give the number of hours an appliance can be used without a battery being charged