We use Sun ware solar panel which are manufactured in Germany for over 20 years. They are specifically for use in salt water and other marine environments.The sun ware range are extremely flat, only 5mm deep, have no sharp edges, robust and can be fitted to a surface with a curve of up to 3%.  The smaller panels can be used for maintenance charging for boats on mooring, where as a large panel can be used to help run electrical equipment on your boat.

Solar panels will product energy even if they are not placed in direct sunlight. It is to be noted, however, that the power output is proportional to the amount of light that reachers its surface. For example a solar panel can generate  100-80% under full midday sun but only 50-70% of max output on bright overcast days, and only 10-20% on dark overcast days. So your power  with a 100 watt solar panel output /week based on 5 hours per day over a week of charging in full sunligth  would be 3500watt hours but with the same panel on a cloudy dark day  8 hour day this figure would drop to about 1000 watt hours.

This is a example of the requirments for a liveaboard boat just to give you a

 

WEEKLY REQUIREMENTS	WATT HOURS REQUIRED
12V Bilge pump(36watt) for 3 hours	108
19" colour TV (80 watt) for 14 hours	1120
Laptop (30 watt) 4 hours	120
Washing machine(260watt) 2 hours	520
12V Larder fridge(28 watt) 168 hour	4704
10 Lights(10 watt) 14 hours	140
Total	6712 watt per week

On a sunny week you would need 2x100 watt panels, on a dark cloudy day you would have to run your engine to top up your power needs.

Conclution

So although solar panel can be an ideal way of maintaning you batteries whilst your boat is on a mooring, to run all your electrical requirment soley all year round on a liveaboard  is genally not possible.

Note: These are average rating and will vary from appliance to appliance and the effectiveness of your panel will vary depending on which part of the country your boat is moored in and its average sunlight hour for that area.