What's the best solar panel? OK, daft question. The ideal one would be powerful, cheap, and compact, but of course these requirements are incompatible. As ever I like to read and read and think and plan before making the wrong choice. Here are my deliberations. Feel free to put me right if you know better. In my experience, people usually do:-)
Why get a solar panel at all?
1. To save running the engine on non cruising days, cutting diesel costs and saving on engine wear and tear.
2. To keep the batteries charged up more which prolongs their life and frees us up to use more power if we need it.
3. To save having to charge the batteries up to protect them when we return to our berth to leave the boat. We can just let the panel get on with it over the next day or two and keep them topped up indefinitely.
4. To reduce our carbon footprint
Wouldn't it be nice to just go out and pick a panel off a shop shelf and be happy ever after. Pigs might fly! The ideal one doesn't exist and as ever there are awkward compromises to be made. Power is what you want, but more power is more money of course and anyway who wants their boat roof covered in black glass panels? We don't. They just don't come small, cheap and powerful.
I decided I would like a minimum of 80 watts peak which equates to about a couple of hours engine running on a sunny day. In winter an 80 watt panel would generate much less, and we do like to spend time on the boat in winter, often without moving. Ideally I'd like rather more than 80 watts. This rules out most of the thin or flexible panels which stick to the roof use amorphous technology and are generally of a lower wattage. Anyway they tend to have about twice the surface area of the crystalline ones for the same power and need space.
So you decide what is the biggest panel you can bear to see (and afford) and get that one. No you don't. A boat roof is not a blank canvass. It has mushroom vents and chimneys, gangplanks and poles, and you need working space to handle ropes without catching on fixtures at critical times. You need to fit the panel in amongst all this, and on Herbie, that's quite limiting.
I'm drawn towards a 95 watt panel by Kyocera which is not too huge and should fit just in front of the aft mushroom vent and won't tangle with the chimney if I mount it a little off centre. It's about four feet by two feet three inches in old money. First I have to remeasure the roof to check I'm right and present my findings to the board (Kath) for approval.
One thing I will spend extra on is the regulator by getting an MPPT one. They cost more, but put about 20% more power into the batteries so worth it.
Will we ever get our money back in savings? You're kidding. No, we will save a bit on diesel and wear and tear on engine and batteries, but that isn't what it's about. Mostly its about not having to run the engine for so long when we're stationary. It's noisy, it makes the boat vibrate and uses diesel. Although running the engine makes hot water, it does that in far less time than it takes to charge the batteries.
One more thing will help. I'm also planning to move to LED lighting. In winter, four lights on for four hours might equate to about an hour of engine running. LED lights would save over 80% of that.