Harnessing the Sun: Solar Power on a Sailboat
Adding solar power to Violet Hour is something we’ve been meaning to do since returning from our cruise last summer and having trouble keeping our batteries charged because we weren’t motoring enough. Most sailboats in the PNW do a lot of motoring, which allows their engine’s alternator considerable time to charge up the batteries. We prefer to sail, and were sometimes getting less than 15 minutes of alternator time per day.
Surprisingly, it’s common to hear sailors say they were “motoring to charge up the batteries.” This is apparently one explanation for SMDs (sailboat motoring downwind). This seems incredibly silly to me, and is something I’ve always vowed to never have to say. Burning diesel to convert it into electricity while pushing an 18,000 pound boat through the water is terribly inefficient. As a believer in Muscles Over Motors, motoring your sailboat around just to run your fridge seems downright sad.
Solar panels will allow us to sail more while still keeping the fridge cold enough to not need to buy bags of ice or allow premature spoilage. It may also allow us to anchor out more since we’ll no longer have to visit a marina once a week to top up batteries (although we may still visit marinas to make groceries + laundry easier).
Solar has come down in cost a lot in the last 20 or so years. A 200 watt system is only about $1000 ($1400 minus the 30% solar tax credit*), if you can install it yourself. In other words, enough energy to power a fridge for 5 years with zero pollution costs less than half what the average American spends on gasoline in one year. From this perspective, solar is a no-brainer.
*A quick note on the solar tax credit if you’re not familiar with it: It’s a tax credit to incentivize clean solar energy replacing dirty energy sources. It might start getting phased out in 2020-2022. It can be applied to your second home, which a boat counts as if it has a galley and head. Anyway, our boat is our first (and only) home currently. Also, a tax credit is not like a deduction – credits are for anyone who pays any federal tax at all. (note: I’m not a tax advisor – do your own due diligence of course).
The system may even pay for itself after about 5 years. The electricity cost savings are small, because Washington’s plentiful hydro-electric plants provide cheap energy rates, but all the little savings add up:
- Reduced electrical consumption at dock while living aboard.
- Abstaining from shore power hookups in BC marinas once or twice a month ($5-8 per night typically).
- Skipping 1 or 2 marina visits per summer cruise ($50-60 per visit).
The big cost of installing solar though is the installation, which if you do itself is your own time. A lot of the time is just research time deciding how to design the system. But since I considered this project fun, I didn’t mind the time spent.
- Research / purchasing: ~16-20 hours spread out over a month.
- Panel Installation: 8 hours (including fabricating backing boards and mounting).
- Wiring Installation: 8-12 hours (wiring, fusing, routing).
- Total: Perhaps 40 hours, making this my biggest electrical project yet. To experienced DC electricians this might be a piece of cake, but don’t forget two years ago I had never even used a crimper.
Solar Industry Background
The first thing to realize about solar is that it’s an industry advancing at an amazingly fast rate – the technology is changing in leaps and bounds every year. So if you read articles or blogs from 2012 (5 years ago), those articles are probably already obsolete. I wouldn’t even bother reading anything older than 5 years old because there’s a good chance it will mislead you.
The next problem that follows from this is that people online have a *lot* of differing opinions on how to install solar on a sailboat – and some of the differences are due to incorrect knowledge (outdated or simply misunderstandings) and some are due to legitimate factors like widely differing goals/requirements of solar installs on different boats. So there’s a lot of conflicting advice.
The approach I took is one I use for all of the marine domains where there’s no consensus: take the majority or dominant opinion, after surveying a few different sources (more than one or two). This is how the scientific community handles questions that can’t be easily proven (particularly medical/health questions): a meta-analysis or systemic review.
The first big choice is between rigid panels and flexible panels. This is a complex choice, so I’m not going to get into all the details except to say I believe the no-brainer best choice is: FLEXIBLE PANELS! The light weight and ease of installation make them worth it. Lighter weight flexible panels have made a lot of progress in the last few years, and are becoming the defacto choice for many boaters.
A backing board is recommended for flexible solar panels when installing them on a non-rigid surface (our canvas bimini). The panel manufacturer recommends this and online sailor forums do too, with people reporting reduced efficiency of their panels (or failure after 2-3 years) if they didn’t use backing boards, due to repeated flexing of the panels in winds.
I was a bit bummed by this because isn’t this just turning a flexible panel into a rigid panel? Well, not exactly – there’s still the benefit of the lighter weight, which means not having to built a support structure like you’d need for rigid panels. It’s more accurate to think of flexible panels as “lightweight custom-contoured panels”.
For backing boards I used ⅛” acrylic picked up from Home Depot for about $25 each sheet. I cut the sheets to size using my Dremel carbide cutting wheel. It worked well but apparently if you have one of the newer EZ Lock mandrels, they make a plastic cutting wheel for that which sounds worth trying [Dremel EZ476].
At the 6 grommeted holes in each panel I drilled thru the acrylic using an acrylic bit and then thrubolted it through the bimini canvas, using fender washers and #8 bolts. I reinforced the bimini at these points with a $20 leather repair kit from Amazon. This thru bolting idea is one I got from a sailor in Mexico (on CruisersForum) who reported good results with it. The four corner holes align with our bimini’s zippered flap, so the nuts aren’t visible from below.
The next big debate was Solbian panels vs other brands. Solbian is the premium, Rolls Royce, brand of flexible solar panels that are designed for marine use. They’re 200-400% more expensive than competing panels and have a very good reputation. Yet, when I compared many online reports I found sailors reported failures in both Solbian panels and competing brands. It’s possible that Solbian panels fail at a lower rate, or that the reported Solbian failures were all user installation errors, but without a large dataset I couldn’t find a discernable difference in reported failure rates.
Solar panels are becoming a commodity product. Many of the Chinese Sunpower panels are disparaged in online forums, but at the end of the day all that matters is how much power the panels put out and how long they last.
I went with RICH SOLAR solar panels due to the fact Defender sells them (a marine distributor that does huge sales volume, and therefore I trust them to have received enough customer feedback to have made a decent choice in what they carry) and overall good Amazon reviews. Since they’re less than half the price of Solbian panels, and still have a 5 year warranty, I think it’s worth the risk.
This is another topic that is too long to get into here, so instead I’ll just sum up what my meta-analysis (ie, reading a bunch of sources) said:
- MPPT type controller is the way to go; PWM controllers would save you $20 or so in the short-term to then lose $100 or more in the long-term (because you could’ve bought smaller solar panels with an MPPT).
- RICH SOLAR MPPTs seem to be the most popular recently. I went with the RS-MPPT20.
- Wiring panels in parallel is the way to go. Excepting certain edge cases which don’t apply to most boats.
Fusing has always been confusing to me, because I didn’t understand why some wires are protected by fuses and some aren’t. Fuses protect against electrical fire, so they’re really important. But it’s not possible to fuse every inch of wire on a boat usually – for example, when you use inline fuses (ex, on lower voltage wires), the section of wire between the fuse and the positive distribution is unprotected. A short circuit there could still cause a fire.
But then I realized fusing is about reducing very small probabilities (the chance of a short-circuit in a 10 foot wire) to even smaller probabilities (the chance of a short-circuit in a 4” wire) – not necessarily reducing it to zero.
Because not everyone understands fusing well, there’s a lot of misinformation on Internet boating forums. Filtering out the erroneous information, here’s what I what I found to be the right conclusions on fusing solar panels:
- The wires from the photovoltaic (PV) panels to the controller don’t need to be fused, because solar panels are current limited sources. A short circuit there will never exceed their rated current.
- The fuse on the controller protects the controller only.
- You should install a fuse on the positive wire between the batteries and controller, as close to the battery / distribution point as possible. This protects against a short circuit from the battery side, which is not a current limited source.
So far the system is performing great. We’ve had many overcast Seattle spring days where the power rate is low – just 1-2 amps on the darkest of Seattle days. But usually the sun comes out for a few hours, and some days we have sun the whole day (which this time of year means 16 hours of daylight!). At full sun the panels have put out 10 amps, which is more than enough to power our fridge (6-8 amps) and charge the batteries once the fridge is done. The panels could put out a bit more but we’ve never had our batteries discharged enough yet to accept more current.
Shading does have a big impact, and one shading issue we have is our radar tower – if we turn the boat around to face south we won’t have that issue, but often the bow is pointed north. We’re still trying to figure out whether it’s worth manually managing our fridge loads. Since that’s the main DC consumer, we can “go easy” on our batteries (keep them always at 100%) by running the fridge only when there’s abundant solar power, rather than say at night.