High quality high performance solar cells will produce more power at various sun angles than lower quality solar cells; up to 30% more power. An important consideration in determining how much solar power you need is how many watt hours or amp hours of power you can expect to generate in a day. Let's say you cruise in an area that receives an average of 5 hours of full sun a day. The average is computed based on the seasonal sun angle and the sun angle from morning through evening. A 100 watt solar panel with average efficiency solar cells may produce 100 watts x 5 hours or 500 watt hours of power in a day. At 13 volts that's about 38 amp hours in a day. A 100 watt panel with high efficiency solar cells will produce up to 30% more power in a 24 hour period or 100 watts x 6.5 effective hours or 650 watt hours of power in a day. At 13 volts, that's about 50 amp hours in a day. 38 amp hours vs. 50 amp hours in a day is significant on a boat. Add more panels in the mix, say 300 watts and we see 114 amp hours vs.150 amp hours, a difference of 36 amp hours. This simple analysis does not take into consideration the impact of clouds or shading both of which will make the disparity even greater. Clearly, the higher the quality of the solar cells the more power produced over time.
Thomas Trimmer has been cruising with his Ericson 38 sailboat on the Great Lakes for over 20 years. He has pioneered the use of solar energy for wilderness cruising. He is continually designing and building equipment to simplify and enhance the cruising experience.