A Guide: Choosing a Solar System for your Yacht

[Sailor_Rob]

I've been reading sailnet for years, gleaning little bits of information here and there. One thing that I have done an extensive bit of reading on is solar power. I've learned quite a bit, and since buying my own cruising yacht I installed my own system and am now using it to cross the Pacific Ocean. I wrote up a guide on how to choose a solar system, and thought it would probably be of interest to sailnet users. I cover choosing batteries, panels, and a charge controller.

I've posted the guide here on my blog. I welcome any comments or suggestions if you have them.

I'll been keeping the blog up on my trip across the Pacific, and my other posts may also be of interest to you guys on sailnet as well. Thanks for all the info over the years, hopefully my guide will prove to be a good resource to some of you, it's my way of giving a little back!

Cheers,
Rob
www.SailorRob.com

[Maine Sail]

Rob,


Some quick thoughts..

You really ought to get a battery monitor.. For example just because the AP draws a "rated current" of 4A it is not burning 4A constantly over 20 hours. It is very likely you could cut that 80A in half by balancing your sails and trim and then the AP would only need to "correct" occasionally. This drastically cuts down on AP consumption unless in rough weather.

[Sailor_Rob]

Maine Sail,

I completely agree, and I mentioned that in the post. The autopilot is never a constant draw on the battery. The guide is just for people trying to gauge the size of the system they will need to install. I have a battery meter on my system, which is something I should mention in the post, but when I was purchasing and installing the equipment I just used 4amps as a rough estimate for the current draw of the autopilot.

[lajimo]

Very useful write up - thanks!

[rbrasi]

Excellent read. I'm marking this for future reference.
Thanks for posting your results.

[Sailor_Rob]

Thanks guys! As an addition I've wrote another article on how to wire the system up. I hope that some of this info is useful to you all! Have a look at my guide to wiring up your solar system.

[Maine Sail]

Originally Posted by Sailor_Rob

Thanks guys! As an addition I've wrote another article on how to wire the system up. I hope that some of this info is useful to you all! Have a look at my guide to wiring up your solar system.

Rob,

A couple of thoughts as one who installs lots of solar systems on boats.

1- Not all 12V systems need to use 12V panels. 24V and higher panels are very often used with an MPPT controller or two 12V panels in series for a higher voltage. You need the right controller but often times using a 24V nominal panel vs. 12V can have some advantages.

2- Depending upon the particular situation a series wiring may make more sense than parallel but each installation is different so it is impossible to say what each boater needs because the installation is "mission critical" on boats. For example a series panel may begin charging earlier in the day and stop later in the day because the voltage will begin to flow into 12V easier if the panel voltage is 36v, 48v vs. 17v...

3- I generally do not recommend wiring the charge controller output to anything but the battery bank or as close as you can get it. When you move the controller away from the battery is it more easily influenced by house loads, voltage drop and is more susceptible to voltage transients than can damage the controller. Solenoids, motor loads etc. call all throw spikes & dips into the DC system. Having the controller close to the battery or on the battery posts as opposed to further away limits voltage drop and the risk of transients because the batteries act as an excellent filter of spikes.. It allows the controller to properly charge the batteries based on their voltage rather than the voltage of the system wiring which may already have some serious voltage drop or other issues..

4- Fusing is always advised within 7" of a source of power or in this case the battery bank.

5- Voltage drop in panel wiring is quite critical and can really damage the performance of the system if the wire is too small. You made no mention that I can see as to how to properly size the wire. If using an MPPT controller to maximize performance then a 1.5% or less VD is an excellent target.

6- In a perfect world an SSB ground should ideally not be shared with any other devices. On most boats the engine is your ship ground unless an immersed copper plate is installed. Keels can be used but this use should be avoided if the hull has been barrier coated, for obvious reasons. The charge controller + and - leads should complete the circuit at the + & - battery posts and the pos feed should have a fuse within 7" of the + post.

7- The preferred and accepted diagram for 4 6V batteries by just about every battery manufacturer is this:


8- I your previous article this:

4 hours @ 5.7 amps = 22.8
2 hours @ 4.0 amps = 8
2 hours @ 2.0 amps = 4
3 hours @ 1.0 amps = 3

Is extremely optimistic. If you'd stopped at 22.8Ah/day I'd agree... I've been monitoring solar on boats for a long time with battery monitors and specialized solar controllers and find that here in Maine 4 hours a day at full rated output is about "average" for an entire days capture. Some say 5 hours but these calcs work well for land based systems where the panels can be oriented at the sun. On a sail boat they are usually left flat, are subject to shading and in general do not put out anywhere near what the average land based system can. Shading KILLS performance...

9- Deep cycle batteries are rated in how many amp hours they can store not how many amps. Minor semantics but might worth addressing. In a short circuit your battery is capable of delivering 3000+ amps but that is not what it stores in terms of Ah capacity just raw instantaneous short circuit amps. For cranking amps, at 70F, you probably 1000 amps per battery but only 130 amp hours at the 20 hour rate.... Your stored energy is calculated in amp hours not in amps.

10- AGM, Wet Cell and GEL batteries are all lead acid. Wet cells are wet lead acid, AGM are valve regulated lead acid as are GEL... They are all "lead acid" batteries. Absorbed Glass Mat means AGM. AGM are of the VRLA or valve regulated lead acid type. GEL batteries are a gel electrolyte and are also considered a VRLA battery.

Just my thoughts....

I wrote a solar article a while ago and it may give you some more ideas..

Installing A Small Marine Solar System

[Sailor_Rob]

Wow Maine Sail, you have really shed some light on it! I'll get to updating my blog post (as much for MY future reference as for everyone else's). You make some great points and I appreciate your input!

[Don0190]

Originally Posted by Maine Sail

A couple of thoughts as one who installs lots of solar systems on boats.

1- Not all 12V systems need to use 12V panels. 24V and higher panels are very often used with an MPPT controller or two 12V panels in series for a higher voltage. You need the right controller but often times using a 24V nominal panel vs. 12V can have some advantages.

]

I had not thought about this and was figuring the "big" decision other than size was the series/parallel thing. So what advantages are there for using 24V panels on a 12V system? Is there a disadvantage to offset it?