Re: Soler Panel help how many watts?
In the summer months in Utah, an unshaded solar panel mounted horizontally will generate an average about 5 W-hr per rated watt per day.
In other words, your 30 W panel, will give you about 150 w-hrs of energy. Is that enough to offset the load of the radio and the lights? well that depends on how long you want to run them for.
If the lights are not leds and are 50 W total. You'll get about 3 hours of use of the lights for every day of charging.
In practice, your solar panel is not likely to be totally unshaded all day long and there are some charge/discharge losses associated with battery charging so I'd probably count on about half that much on a typical day.
So if you sail once or twice a week and then leave the boat to charge the other 5 days, I think 30W will probably do it. If you sail more often, or run more loads, you might think about a 50 or 70 W panel instead.
hope that helps,