Solar Powered Pontoon

biglurr54

My father just put in a large grid tied solar panel array and it has inspired me to harness some of the sun for my self. I looked at adding a grid tie solar array to my house but my energy consumption is so much lower than his house that my pay off period would be a long time. I would rather continue to work towards an off grid solar system. I decided to move my attention to a solar powered party boat. Everyone I talk to in the marine world say it can not be done with out a solar array the size of the entire boat and a battery bank that would sink the boat. I disagree. Lets look at this as just an off grid set up for say a cabin in the woods. I will have a dc motor that at half throttle, the normal cruising speed it will be operated at, draws 8.4 amps at 12 volts. It will be operated 5 hours a day on Saturday and Sunday mostly (2 days a week). A stereo will draw 2.5 amps at 12 volts for 5 hours as well. So the system will draw 10.9 amps for 5 hours meaning I will need 54.9 ah on board each day. Suppose I get confused and try to go out on a bad weekend where there is no sun. I will need 109 ah and a really stiff drink. I know we do not discharge a battery below 50% to save its life. So I would need a deep cycle battery with approximately a 220 ah rating. These can be had for about $500 and only weigh 100 lbs and it is one battery. Expensive but manageable. Then I would need to replace 54.9 amps in a day. I live in the great northeast so lets say 6 hours of sunlight. It will only be used only in the summer so it will have peak sun time for our area which is about 6 hours. A 10 amp charger should replenish the depleted battery in one day. 1 140 watt panel connected to a 10 amp charger for off grid cabins can be had for about $400. This all seems to work out with my math. One solar panel, one large but not sink a boat battery, $900, and a stiff drink and I will be cruising on the water with power from the sun! Please let me know where all my mistakes are as I'm sure there are many.

Photowhit

Re: Solar Powered Pontoon

Most trolling motors don't run at 12 volts, I doubt 12v at 8.5 amps will provide much power pushing around a pontoon boat, if a slight wind comes up I think you'd be lost, so I'd suggest at least a kicker motor to get you home if a wind comes up.

Here's a blog about a solar pontoon boat, there are others out there, this is just from a search here.

Pontoon Boat Blog.

Cariboocoot

Re: Solar Powered Pontoon

Welcome to the forum.

Well let's look at it as an off-grid cabin and say for the sake of argument you want 220 Amp hours @ 12 Volt of battery.
First of all, it's easy to get that as a couple of 6 Volt golf cart batteries in series and would cost less/be more manageable than one big 12 Volt.
Second, you'd want to charge it at more like 20 Amps, remembering that if the motor is running while charging the actual current going to the battery will be what comes out of the charge controller minus what goes in to the motor.
So then you've got a panel calculation that looks like this: 20 Amps * 12 Volts = 240 Watts. If you're using a PWM type charge controller you need to check the Imp rating of the panels. You'd be looking for (20 Amps * 17.5 Vmp) about 350 Watts of panel.

What you'd get from one 140 Watt panel & a 10 Amp controller would be about 8 Amps of current, because that's all the panel can produce. On a 220 Amp hour battery bank it's only a 3.6% charge rate maximum, far below the 'no loads' minimum of 5% recommended for batteries of this type.

Don't fall into the "replace 'X' Amp hours" trap; battery charging is not linear. You need that high peak charge current available to bring it up quickly so that there's enough time to finish charging at the much slower rate during the Absorb stage.

Basic deep cycle battery FAQ'S: http://www.solar-electric.com/decybafaq1.html
Look them over before you go spend a lot of money on equipment.