I was going through some old papers on my boat, and it's been over 15 years since I installed my solar panels. One of the downsides of solar panels is that the output supposedly declines after about eight years, but this has not been the case. I checked the amperage with a fairly accurate ammeter, and my array puts out 13 amps in overhead sun, exactly what it put out during the first few years. These panels haven't had any vacations: They've been sitting there, right where I installed them, for 15 years and roughly 60,000 miles.
In the terrestrial solar world, people lament the 20-30 year lifespan of a solar panel, but how many pieces of boat gear last 20-30 years? I think I can count them on one or two hands, and they include items such as hull, mast, and engine…if we're lucky.
I've always favored solar over wind power because there are no moving parts. The idea of whirling blades overhead has always made me nervous, and a certain popular brand of wind generator, to remain nameless, sounds like a bloody helicopter taking off if you're anchored anywhere within 1000 yards. If you're on a boat that happens to have one, the vibration seems to resonate throughout the entire boat. I've seen some much slicker, nearly silent wind generators, but they all have moving parts and bearings that must wear out at some point. Solar panels just sit there and do their thing.
It can be difficult to find a good location for solar panels on many boats, and I'm particularly lucky in that my hard dodger is the perfect place. While cruising I always kept them clean, because even a thin coating of salty grime reduces output. Also, output decreases as they heat up, so leaving space for air to circulate underneath the panels also helps the output.
My boat has spent most of the last four years sitting in a marina, and I've never plugged into shore power. The solar panels keep the batteries topped up and ready to go, and this lets me go on procrastinating about replacing my 45-year-old AC system and ancient battery charger, and saves me any worries about shore power-based galvanic corrosion.
My 240-watt array and regulator cost me just over $1100 in 1997. I don't know what they've put out in amp hours over the years, but it adds up to a lot of water making, refrigerator chilling, music listening, instrument energizing, and lighting. The solar system is one of the few pieces of boat gear that feels cheap.