Power boat, sailboat and yacht builders and dealers

 Bulletin: RollerTrol™ Automation Systems is Launched!  
  • We have been busy making and selling 12v marine roller blinds for some time, and we have decided to start selling the components at RollerTrol.com so others can do the same.
  • Take a look at our online store for tubular motors and other associated products - make your own custom blinds that fit your boat perfectly!
  • While you're at it, check out our tubular motors with built-in radio controllers. When used with our multi-channel remotes, you can control all your blinds with a single remote!
  End Bulletin: RollerTrol™ Automation Systems  
Design a solar panel charging system with deep cycle batteries on your sailboat
Installing a solar panel system with PWM charge controller on your boat
and keep your deep cycle batteries charged at all times.
by Adrian Biffen

Serenade has plenty of electrical and electronic devices on board, and I wanted to ensure that we always had plenty of electrical power available to keep things functioning properly, without depending on shore power or a generator. We have device loads such as onboard computers, 110V inverters, electric actuators, winches, lights, pumps, fans, communications radios, cellphones, a 500 watt stereo sound system, GPS, refrigeration, depth sounder, LORAN and an electric start outboard.
Shell Solar Powermax 80P with Sunsaver charge controller
I had choices to make between some of the alternate energy sources such as solar panels, wind power, prop generation, etc. I chose to start with solar power as I have worked with it for more than 30 years, and I was interested to see how things have advanced since I bought my last panel for our motorhome about 5 years ago. I also like the idea of no moving parts and zero noise.

So I picked up a Shell Solar Powermax Ultra 80-P (they bought out Siemens Solar) for about $400 US. It puts out 80 watts (4.75 amps), which is a relatively high output, considering the size of the panel. It also has a form factor that works with my bimini roof structure that I had designed purposely to carry the panel. You can see it at the rear center of the roof in this picture.
This location is fairly good because it doesn't get too much of a shadow from anything when the sun is shining. Shell Solar PowerMax solar 80 watt panel In the above picture, you can see the shadows of the backstay and boom topping lift running at oblique angles across the roof, just missing the panel. There are latches underneath that allow me to release the panel and tilt it in four directions for additional sun power, or remove it altogether and put it out on the stern seats somewhere.

It's important to remember that the power output of the panel is NOT proportional to the amount of unshaded area. The individual solar cells are arranged in a series configuration, and a shadow cast in the right place acts like a short circuit and can reduce the overall output to near zero. I could have put the panel out on the davit structure and avoided shadowing altogether, but I didn't want the added weight out there, or the panel to be visible.

This Shell panel mitigates the shading problem somewhat, as it is split into two separate halves in a series/parallel arrangement, each having a blocking diode for isolation, so that if one side is cut off by shadow, the other side is still running at full output.

While researching the panel marketplace, I had become aware of the new generation of PWM (Pulse Width Modulation) charge controllers, and I decided to spend the extra $100 to get the Morningstar Sunsaver SS-10L unit. 
SunSaver PWM charge controller from Morningstar
I'll state right now that I'm very glad I did, because the Sunsaver works so well that it is probably going to save me from having to add any additional panels for quite a while. I'm hoping to be able to hold out for the new Quantum Dot solar technology to become available, before I add any additional capacity.

PWM refers to the DC waveform that the charge controller supplies to the battery, and it is a superior new approach that really does work. Here is an excerpt from a Morningstar technical bulletin:

"Charging a battery with a solar system is a unique and difficult challenge. In the "old days", simple on-off regulators were used to limit battery outgassing when a solar panel produced excess energy. However, as solar systems matured it became clear how much these simple devices interfered with the charging process.

The history for on-off regulators has been early battery failures, increasing load disconnects, and growing user dissatisfaction. PWM has recently surfaced as the first significant advance in solar battery charging.

PWM solar chargers use technology similar to other modern high quality battery chargers. When a battery voltage reaches the regulation setpoint, the PWM algorithm slowly reduces the charging current to avoid heating and gassing of the battery, yet the charging continues to return the maximum amount of energy to the battery in the shortest time. The result is a higher charging efficiency, rapid recharging, and a healthy battery at full capacity.

In addition, this new method of solar battery charging promises some very interesting and unique benefits from the PWM pulsing. These include:

1. Ability to recover lost battery capacity and desulfate a battery.
2. Dramatically increase the charge acceptance of the battery.
3. Maintain high average battery capacities (90% to 95%) compared to on-off regulated state-of-charge levels that are typically 55% to 60%.
4. Equalize drifting battery cells.
5. Reduce battery heating and gassing.
6. Automatically adjust for battery aging.
7. Self-regulate for voltage drops and temperature effects in solar systems."

My main deep cycle batteries were pretty old, heavily sulphated and running at maybe a quarter of their original capacity. As per the above statement, the Morningstar people claim that their PWM charge controller technology will actually desulphate and restore aging batteries, and I am happy to report that it is indeed true! I had been using a fairly sophisticated microprocessor controlled charger with 'float' circuitry that theoretically detects and maintains a full charge, running off shore power, and when I started using the Sunsaver/solar panel combo, my disconnected battery voltage was much higher and I had many more amp-hours of capacity than I had before.

When I first installed the system, I monitored the battery condition very closely to see how it was holding up, but I soon stopped bothering about it because I realized I had plenty of capacity. I made several 10 day trips with Serenade, with days of rain and cloud, and never even came close to flattening the batteries, and I have never hooked up to shore power again.

I have since replaced the old deep cycle batteries and added two more deep cycle golf cart batteries for an extra measure of capacity (about 450 amp-hours total), and even under heavy use the system seems to stay well up from the discharged zone. (400 amp-hours means I can theoretically discharge the batteries at a rate of 10 amps for 45 hours. At night, with no charging source, so even with fireplace fans and lights running part of the time, 12 hours of darkness still leaves me with plenty of capacity in the morning before the system starts charging again). 

At times I switch my outboard into the circuit, so that the little 6 amp alternator will help boost the system, but I don't use it very often because I'm sailing whenever I can. Since the engine is very quiet and fuel efficient, I think of it as an emergency generator should the solar system ever fail (unlikely).  

We have initiated a number of improvement projects for Serenade since she was purchased, and we have created a series of articles detailing the work that has been done. Here are the relevant pages in this series:

Wireless remote control autopilot
 (2) Diesel removal & 4 stroke outboard engine mount
 (3) Cockpit Bimini (this page)
 (4) Tender davits on stern
 (5) Waste management holding tank system
 (6) Solar panel, PWM charge controller and deep cycle battery system
 (7) Propane Fireplace