Swift

Techie Week: Thoughts on Solar Panels

Brace yourselves: gone are the days of fun and frolicking. Instead, we are thinking, staring blankly, researching, thinking some more, and very occasionally enacting thought out plans.

When we bought Independence, she came with 220 watts of solar mounted above the dinghy davits. While nice to have, this really has never been enough to keep us going and we’re always looking for more ways to squeeze in more watts. Added to that, the panels are very old and are not very efficient: they are mounted too low with shadows affecting them most of the day and are connected to a very basic charge controller. We’ve left that situation alone while we pondered our next move. 
In with the new, out with the old? We'll see! (New panels on hardtop, old panels on dinghy davits)
To get us through our first season or two, I bought and mounted three “cheap” flexible 100 watt panels on the hardtop. These I connected to an equally “cheap” PWM solar controller. They worked okay for awhile, but never produced great power. The panels were chipping and flaking in the sun after 6 months, and I have seen one too many references online to panels like these posing a fire hazard should they become damaged. I was anxious to get rid of them. The panels that we had were made by SolarHQ, but similar Chinese panels are available from many different names online. 

Our winter season in the Bahamas really brought to light some electrical deficiencies. We didn’t have enough effective solar watts. Our batteries were suffering because they weren’t getting topped off regularly. And our beastly fridge and equally beastly freezer were struggling and sucking down the amps. In short, we put a lot of hours on our Honda generator this year. Time for some upgrades.
Our new Solar World panels.
So let's start with some of things I have learned about solar power on boats in the last two years of research and experimentation:
  • Shop for solar panels based on the warranty. Good panels provide a linear power output warranty in the neighborhood of 20-25 years! That means that they’ll still be making 90-95% of their rated power in 20 years! The flexible ones on Amazon -- 1 year warranty. I would say, “You get what you pay for”, but the flexible ones on Amazon are $180 for 100 watts and I just paid $207 for 285 watt solid panels with a 25 year warranty. So it’s not necessarily the price!
  • Monocrystalline panels produce more power for a given size than does a polycrystalline panel, and therefore may cost slightly more.
  • MPPT controllers really are worth the extra money. They convert excess voltage (something solar panels make in abundance) into extra power. This means you can use 24 volt (or more!) panels on a 12 volt system.
  • Speaking of controllers: you really can’t mix and match panels/arrays on one controller. More than one type of panel means more than one controller. 
  • You’re never going to get rated power for any length of time on a boat!
  • You must minimize shadows, which is very hard to do on a sailboat! 
  • Many wiring options exist, but use of parallel wiring should be maximized to maintain the best power output from multiple panels. If panels are wired in series and one panel gets shaded, power is lost from all panels in the series.
  • Flexible or even walk-on panels are a great idea for boats, but expect to pay double, triple (or more) the price for good quality panels that will last.
  • Figuring out “How much solar do I need" is one of the toughest questions of all. The question goes hand-in-hand with “How large of a battery bank do I need”. Start with a detailed inventory of your usage in watts. Figure out how many hours per day of potential solar you can expect. http://www.nrel.gov/gis/solar.html Figure out how many days of reserve you want to last for those cloudy days. 
I choose to buy 24 volt panels this time, and here is why. The MPPT controller safely converts the extra voltage. 24 volt panels carry fewer amps to the controller, which means smaller wire to run long distances. The charge controller is going to start charging the batteries as soon as the voltage of the panel is about 5 volts over the battery voltage. On 24 volt panels, that occurs at about 42% of rated output. On 12 volt panels, it would occur somewhere around 90% of rated output. To me, that seems to indicate that the 24 volt panels are going to be charging more often and for longer periods of time. 

When considering installation options I even considered getting two pair of 12 volt panels and wiring them in series to get two 24 volt arrays (so many choices!). Lastly, the larger 24 volt panels make up a majority of the panels used at homes and land-side solar installations…they are readily available and are cheap. We bought our SolarWorld panels, a very highly rated company, from Beyond Oil http://beyondoilsolar.com/ in California, for only $207 per 285 watt panel. That’s only $0.73 per watt! Even with freight costs for the two panels (another $125) we averaged $0.95 per watt.

Which panels you choose really comes down to your boat design. The catamaran gives us two nice options: the hardtop and the dinghy davits. I had originally planned on mounting these two panels over the davits, but quickly realized that the work involved in getting a new frame built to get them closer to the sun and out of the shadows was off putting. I’m also enamored with the idea of getting rid of the panels above the dinghy and opening up our view. Who wants to sit on the terrace and look at solar panels? 

Of course, putting them on the hardtop created more problems with the shadow from the boom, but that’s pretty easy to move around depending on how the sun is hitting the panels. Many folks make the frame over the davits adjustable, so that they may angle the panels more directly into the sun. That’s super cool, but I know myself and I’m either going to not do it or do it so fanatically that it takes over my life.

Victron MPPT controller
Speaking of things that can take over your life, I paired these panels with a very neat Victron BlueSolar MPPT controller with Bluetooth dongle. This contraption connects to an iOS or computer app that allows you to track exactly what’s going on and change any settings you like. How cool is that? Not only does it show you live data (you can see the changes as clouds or shadows cross the panels!!) it logs history so that you can analyze performance over time.
Blue Solar charge controller live stats.
Blue Solar charge controller history
Notice that in that 6 day period, we never topped 463 watts, even though we have 570 watts of panels. Yeah, you never get 100%. The panels aren’t angled directly at the sun. The air quality is bad. The temperature is too high. A bird flew by. Yada yada yada. Life sucks then you die, what can I say.

I just did an experiment. With the boom in between the panels, only a small amount of shadow on one panel from the topping lift and lazy jacks: we were averaging around 360 watts. If I moved the boom directly over one panel, this caused a big shadow and a drop to about 240 watts. With the boom completely clear, no shadows: 390 watts. I’ll try to be good about moving the boom. 

While my battery monitor does show me the system amps, it is nice to have the reading directly from the controller to compare. If the controller is putting 30 amps into the batteries, but only 20 amps is being added, I know I’m using 10 amps in “other stuff” (refrigerator, computer to write blogs, etc)

What about wind and water? 
During our first trip north, we had a Duogen wind and water generator installed. We bought it used (problem #1!) and it had some issues. We got it generally working, but it was a lot of tinkering and parts and emails to the manufacturer. In water mode, you really had to be booking along (6 knots plus) before it made any real power. Slower than that it all it did was add drag and slow you down! The wind mode worked well, but never really made much power. The advantage of wind power is that it makes power 24 hours a day, whereas solar makes it’s power 4-6 hours a day. Still, it was too much tinkering and moving parts to deal with for us. And too much noise. Furthermore, the Duogen concept did not fit well on our Lagoon 380 with the dinghy on the davits. It worked fine in water mode but sat too short in wind mode with the hardtop blocking some air flow. Additionally, the boom did not ALWAYS clear it in wind mode (if the Duogen was off center and the boom crossed, it would impact the air blades). This made wind generation while sailing impossible. The end result: when the bearings failed and I was looking at yet more parts, the whole thing went in the dumpster during our haul-out last August. I haven’t regretted that decision…cut your losses!

We have been on friends boats that have the D400 wind generator. It is absolutely silent and unnoticeable. Other friends have the Rutland 914, which is often compared to the D400, but we found theirs to be very loud. We researched the D400 (and others) heavily, but in the end decided to just get more solar and avoid wind altogether. We are put off by the unsightlyness of the wind genny, the noise and maintenance of moving parts and the very high cost of the installation (remember, not only is the genny expensive, the pole is too!) If I did get a wind genny, it would be a D400. 

Conclusions
I think it should be reiterated that the number one thing you can do to make your solar and electrical system work better is to conserve power. The advantages of lower usage are many:
  • fewer solar panels top off batteries quicker
  • batteries last longer 
  • smaller, cheaper battery bank saves money, space and weight
  • lower depth discharges on the battery bank and quicker recharges
  • lower depth of discharge means longer battery life
Next time I’ll discuss one of the biggest things we’ve done to reduce electrical usage: redesign our factory Lagoon refrigerator.

What electrical items can you not live without? Does the hum of a wind generator during sundowners distract and irritate you or do you hear the wallet soothing sounds of free electricity?
570 watts of new Solar World panels on the hardtop!
Resources
Solar World panels: https://www.solarworld-usa.com/
Victron Blue Solar controllers and accessories: https://www.victronenergy.com/solar-charge-controllers
>TIP: be sure to download their Excel spreadsheet to calculate which controller best suits your system! It was a big help!<
Gone with the Wynns, including their current setup on their Leopard 43 catamaran and why they got away from the flexible panels on their RV: 


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2 comments

  1. We had to use our Honda generator several times for early morning engine starts. Our solar array is fine (which is a good thing after all the hassles dealing with it earlier this year), but our battery bank is on its last legs and doesn't hold a charge very well.

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    1. Batteries are a real problem. We're uncertain of ours, can't have lead acid because our bank is in our living space, can't afford lithium, and fireflies are on 3 month back order. We're hoping the current ones will limp on for another year!

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