Peter,

Maine Sail and many, many others recommend solar for boats on moorings. Size the solar system for however you use your boat. A small panel will give you a system that will replenish your bank during the week. The larger systems do much more.

Your boats, your choice.

You can also start small and grow it as you deem necessary.

Peter,

I keep my boat on a mooring in Maine and have a small solar panel to keep the starting battery fully charged. It works great. The unit has a Controller on it so the battery does not over charged. As I usually sail off and back to my mooring, I seldom us my motor except when cruising and there is no wind.

I also use the Honda 2000 on occasion to get my 2 4D house batteries fully charged prior to a long ( 5-7) cruise or at the end of the season, which was this last week. I also use the Honda at the beginning of the season as well.

It is difficult to ever get your House Batteries to a full charge using a small solar charger but the solar charger will keep the batteries at a level that will extend the life of the battery. After replacing two 4D batteries this past season, I take a reading prior to starting the engine using a Voltmeter to make sure I am keeping the batteries fully charged.

I would not run the engine to charge the batteries.

Ned Black
Black Magic 2222

Ned,

You'd actually be better served to apply that solar to the house bank. Even running a Honda on the mooring you'd need to do it for 10+ hours to get the batteries full. Charging batteries to full is a time/acceptance issue and there is no short cutting it.

Considering the start battery only ever has 1Ah or less draw off it for starting the solar applied to it often goes wasted because the battery is already "full". Unless the panel is really small, and in that case its not doing anything anyway but "maintaining", I would move it to the house bank..

You have more to lose in $$$ in the house bank than you do in the starting battery.

For charging on a mooring a panel of 30W or more can take you from 80% SOC to 100% in the time between weekends. Topping up batteries to 100% is important to longevity. Letting them sit at anything but full for extended periods leads to sulfation and short life.

In Maine the equation looks like this:

Panel max amp output X 4 - 4.5 hours per day

Battery bank Ah capacity at 20 hour rate X 0.2 (80% of capacity) = needed deficit

Plus charge inefficiency of X 1.15

or

A 320Ah bank at 80% SOC = 64Ah deficit

64Ah's X 1.15 (charge inefficiency) = 73.6 Ah that needs to be replace.

A panel with a 3.6A output, roughly 65W panel, gives 16.2Ah per day @ 4.5 hours output so it takes about 4.5 days to get the house bank to full. Panels below 30W on boats of this size do little except to drain the wallet. Going up a few more watts requires little more in outlay than investing in a small panel but the return in extended bank life is greatly increased.

Flooded lead acid batteries survive better than AGM lead acid when left at less than full but still need to be topped up to see the longest cycle life.

Feel free to read this on mooring solar recharging:

[B][URL="http://www.pbase.com/mainecruising/solar_panel"]Installing A Small Marine Solar System[/URL][/B]

I just re-read the article MaineSail posted, as well as this thread (and others) and I still have a question:

You recommend connecting the solar output to the house batteries, for reasons explained. But if I already have a "smart" battery charger (an older model Xantrex that currently charges both banks either from the alternator or shore power), can't I connect the solar system to the charger and get both banks charged as they need? Or does the solar controller need to "hear" directly from the battery(ies) it's charging?

Thanks

nick

Nick,

Your Xantrex charger charges from shore power or possibly a gen set but the alternator will not power it. You may have a Xantrex Echo Charger, which is a battery to battery charger. They take power from the house bank and feed it to the starting bank.

Your alternator is what charges the bank/banks when away from the dock unless you have a generator to power the AC battery charger. Either way all charge sources are usually best led to the house bank and then you control how the start battery gets charged via a B2B, combining relay or manual switch..