Suppose you have a 100W solar panel。The panelwill generate approximately 3,500 watts hours of energy per week (100 watts x 7days x 5 hours), which can be used to run a number of appliances and electricaldevices. To get an idea as to what a 50-watt panel will run, simply divide thenumbers below by 2, or multiply by 3 for a 300-watt system. To estimate howmuch energy you need, just add up all the electrical drains (lights, pumps,electronics, appliances, etc.) that you typically use in a day. To do this,multiply the nominal power rating of each device (ex: 60-watt light bulb) bythe amount of time you expect to use it in a day (ex: three hours). Add up allthese and divide by 5 (the number of hours per day you have to recharge yourbatteries using solar panels). This should give you a good idea as to the sizeof the solar system you need to keep your batteries from draining.
Be sure to match the right solar controller to the solar panel so it doesn't burn out.