Houseboat Solar

Ken Floyd
Ken Floyd Registered Users Posts: 6
We recently purchased a 14 x 56 pontoon houseboat and would like to make some enhancements to the solar system. It currently has a small 3 watt panel connected to the starting battery, the house battery is charged via generator. I have a 55 watt panel I'd like to hook up to the house battery to help with charge. Our intentions are to eventually go to an inverter system to minimize or eliminate the generator use. The total max amp hrs for the equipment we have would be 450 amp hrs per day, of course it's highly unlikely we would use that much but could use in the range of 350 or so.....the majority of that usage would be 2 DC refrigerators at 6 amps an hr totalling 288 amp hrs.

My question is I need a controller for the 55 watt panel but want to get one that I can use in the future with a larger system-is there something available that would work? Don't want to spend money on something I'll have to change out in the near future. Also would a charger controller be a better option.

Would appreicate any recommendations on a future proof controller as well as complete system set ups used in similar situations.

Thanks for any help, Ken


  • BB.
    BB. Super Moderators, Administrators Posts: 33,476 admin
    Re: Houseboat Solar

    To be honest--The single 55 watt panel is pretty small for a large battery bank/high power system. And it is very difficult to "future proof" over a large range of array sizes (55 watts today, 550 watts next year).

    Your better bet would be to get an "inexpensive" 4-10 amp PWM battery charger today (assuming this is a Vmp=17.5 volt and Imp=3 amp solar panel) and wait until you build out your final system.

    wind-sun_2167_22239007SunGuard 4.5 amp solar charge controller
    Price: $26.00

    wind-sun_2167_66469399SunSaver 6 amp solar charge controller
    Price: $38.00

    It would be helpful to know the eventual size of your array... There are different choices in charge controllers based on array size and other questions (wire run distance from array to battery room, etc.--but being a house boat, I would not expect a long run).

    To fully support 350 AH per day at 12 volts during summer months could run upwards of a 1,700 watt array--You probably do not have enough room for that.

    Conservation will be helpful--Even down to measuring the Amp*hours per day used by the refrigerators. Would you be able to use propane fridges instead?

    Are you planning on using the boat 9+ months of the year, or more towards summer weekends + 2 weeks full time per year...

    If just summer weekend use--you might be better off sticking with the genset (check its fuel efficiency kWH/Gallon of fuel, etc.).

    A full "Off Grid" solar system with large loads (like refrigerators) is hard to justify for more folks unless the space is occupied for much of the year.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Houseboat Solar

    Welcome to the forum, Ken.

    Now, did you mean you might use 450 Amp hours per day or 450 Watt hours? There's a pretty big difference: 450 Amp hours @ 12 Volts is 5400 Watt hours, whereas 450 Watt hours on 12 Volts is only 37.5 Amp hours. Sorry if this is confusing, but it's important to get the nomenclature right as you can see.

    Your refrigerators are not likely to draw 6 Amps all the time; only when cycling. If they are good refrigerators that will be about 1/3 of the time. If there are bad children opening the doors every two minutes it will be about 1/2 the time. :p

    The key to sizing up your controller for potential future expansion is: what size is the house battery? It should be a true deep cycle (not the RV/Marine type usually used for trolling motors and such) for best results. There should be an Amp hour capacity rating for it. You want to try for a peak potential net charge current that is 5%-13% of that rating. And you want to be able to replace the Amp hours used daily.

    Based on that, here's two bits of information for you to think about:
    Your 55 Watt panel would be able to charge a 30 Amp hour battery. Most likely all you'll get from it is a slight reduction in generator recharge time.
    Your 450 Amp hour prospective demand is huge. It would require 900 Amp hour battery and about 1680 Watts of panel for full recharging from solar. There probably isn't enough room on the boat for all that panel, so you'll still be running the generator.

    Please note these are rough calculations based on a 12 Volt house system; not precise and not a recommendation.

    How are we doing so far?
  • Ken Floyd
    Ken Floyd Registered Users Posts: 6
    Re: Houseboat Solar

    OK, I had the refrigerators wrong, they are propane powered, found they should use approx. 1.5 to 2 amps an hr, so that puts me in a much better situation. So my total amp hrs per day should be approx. 225 amps, this would be a max. use. We just purchased a group 31 house battery as a stop gap to use for this weekend, It is a 105 a/hr battery. I know we will need to add more battery to meet our needs but unsure how to determine how much. Could I just take the amp hr rating of the battery (105 amp hr) and add to meet my 225 amp hrs a day use? And then add panels to meet the demands of the batteries? Sorry for the basic questions but I'm a newbie and unsure.

    BB-thanks for the controller suggestions, I didn't realize they were that inexpensive so thats where I'll start.

    Again thank you guys for your help and the info, I appreciate it all.

    Thanks Ken
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Houseboat Solar

    Basic formula for determining how much battery you need: expected Amp hours used X2 (at least).
    So for 225 Amp hours of use you want at least 450 Amp hours of battery. That's four "golf cart" 6 Volt units. About 865 Watts of panel to fully charge from solar. A much better set of numbers to work with!

    That size battery bank and array would be using a 45 or 60 Amp controller, and probably MPPT type if you're going all the way with this.