Outfitting - Hillbilly Solar Panels

A lot of Northwest sailors don't worry much about auxiliary power sources. As long as you are in one of the great Sounds formed by the Olympic Peninsula or Vancouver Island, you are almost assuredly within a day's sail of moorage with shorepower available, and due to the fickle winds and currents in these parts, you are very, very likely to be spending part of any given day motoring out of necessity, which will charge up your batteries at the same time. And, of course, when you're talking about solar power, the high latitudes mean high angles, and, well, pretty much everyone is aware of the local propensity toward cloud cover.

Be that as it may, I did some figuring for our energy budget and realized that we couldn't go much more than a day without recharging given the expected usage patterns. As we intend to be more aggressive about sailing versus motoring, and waiting for the wind, not to mention spending a lot of time at anchor versus in a marina, I decided we needed some other option to at least take the edge off our reliance on the engine for electrical power.

Although there is a lot of information available on marine solar power and solar power in general, for the most part it is oriented at the high end--people who are primarily relying on it and have massive arrays to work with. Although we are in a position to need some auxiliary energy source, we actually have a pretty low daily power requirement... on the order of 45 amp hours with a fairly generous set of assumptions. So, with the addition of only around 10AH a day of solar power, I can stave off having to charge with the engine for another two days or so, which is acceptable.

Running the numbers (A*V=W) I figured I needed about a 20W panel. The solar pros can get into an all-day-long discussion about the actual versus advertised wattage of panels, and all sorts of detail about different types of silicon and such, but while I appreciate the math, what I really needed was a practical lesson. So to start with, I bought a cheap 2W panel, advertised as being able to keep your battery "topped up" when you were away.

I unpacked it, threw it up in a portlight on a sunny day, and got out my trusty multi-meter. The charging light was on and I measured it as pumping out a whopping 20V, which according to all the theory I had read, should have been plenty. I measured the voltage on the unloaded house battery bank (two Group 21 batteries) and then hooked the thing up and left it for a day.

Imagine my surprise when I measured again around sundown and found that the bank was lower in unloaded voltage than when I started! It was as if the panel had been sucking juice out, not putting it in! Supposedly it has a diode inside to prevent that from happening, so I checked the output voltage again. Still in the high teens, despite the sun being low in the sky. So I hooked it back up to the battery and measured again. A-ha! When connected, the output dropped to the same background voltage as the battery bank had itself. Although I wasn't sure why, I knew this didn't seem right, since other chargers elevate the voltage of the whole system to around 13.5V, which is necessary to impart a charge.

After some asking around on Sailnet, I finally got a somewhat straight answer about the phenomena from the gurus. Turns out, although I hadn't ever heard this mentioned before, that the amperage also affects the charging ability. If the force (the common metaphor for amps) of the power source isn't sufficient to overcome that available in the battery, all the voltage in the world won't help. This makes me wonder about the concept of 'trickle-charging' at all... it seems like it couldn't ever possibly work, although a lot of people seem to buy into it. I still haven't heard a reasonable explanation for that... but from a practical standpoint it meant I needed to experiment with a larger panel.

So, I found a decent price on an 18W panel and bought it. It came with a charge controller, although most of what I have read suggests I don't much need one for this size panel and battery bank.

I installed the charge controller in the engine compartment directly over our Protech AC charger. Neither of them are particularly conveniently located, but they are out of the way and close to the batteries.

I didn't hardwire the controller to the batteries yet; I'm going to use the alligator clips until I am sure that the whole thing works, then I'll wire directly to the battery terminals from the controller.

For the internal wiring I just used some 16 gauge tinned wire I had around, and ran it along the existing conduit path from the electrical panels to the cabintop (a lot of the wiring is out of spec, technically--at some point I needed black and couldn't get it, nor the new ABYC negative standard of yellow, but they had white and so I ended up with a bunch that is used for the negative path on a lot of my DC runs).

The cheap panel I got had things configured a little oddly; it came with alligator clips and a male cigarette lighter adapter, but the plugs on these and on the cord from the panel don't match the charge controller. I didn't mind much--none of the included cabling was sufficiently long to make the run I needed anyway, so I cut the connector from the alligator clips and spliced it to the 16 gauge wire coming out on the cabintop. This will match the plug on the cable coming from the panel, so it can be put in place and removed as necessary for weather, positioning, etc.

It's definitely a hillbilly setup. I don't have the room or wherewithal to permanently mount the 18W panel, and I wouldn't want to anyway without having some solid proof that it works well, so I just rig it with cords and strap it to the cabin-top on sunny days (and put it away when things are rough or dark--it's all-weather, but still, things last longer inside). This has the virtue of being easily removable, and easy to reposition at better angles to the sun as it moves or the position of the boat changes. It looks pretty ghetto, but it has been working quite well keeping the batteries topped up. We've had a lot of sunshine and wind so far, and so we've been relying on it almost exclusively, and it's done well. This week as the clouds roll in I'm likely to find more challenges keeping things charged (although happily, the bad weather will coincide with a part of the trip I would have had to motor through most of anyway).