Houseboat solar system

mdwells · October 2015

Well...been following several discussions on this forum for some time now and have learned a lot. Thanks to all for the immense volume of knowledge posted here. Now that I have a little better understanding of solar systems I have decided to tackle a solar setup for my house boat.

Came across a set of 4 Powersafe 12v 190 A/H batteries from 1 yr service in a cell tower backup system at a reasonable price, so I thought I could build a system from there. Don't plan to run the whole boat on the batteries or solar array at any one time. We only spend 2 to 3 days out and I am actually only looking for nighttime use of a led tv, fan and some lighting.

A 12v fridge, few toilet flushes, water pump and occasional bilge pump cycle should take care of daytime consumption. Onboard a/c, water heater, microwave etc I will run from my gen set. So I figure I should be at about 1600 to 1800 wh per day load for the batteries, which should be nominal for the 760 ah battery bank.

I have access to 3 solar panels - 2- 175w, and 1-280w. All are 36 vmp, 5.3 and 7.9 amp respectively. I am limited to panel size and these fit within my limits. These will give me 630w of panels. Might can get one more 175w in there, but gonna be close. In central Florida, I get my share of daily sun.

There is much discussion regarding charge controllers, mppt and pwm, as well as the efficiency of 24 and 48v systems vs 12v. My train of thought is to series 2 batteries in each of 2 banks, then parallel the 2 banks to give me 24v, using a 40 amp mppt controller, then an inverter to power my 120v appliances.

My question is, how to operate the 12v system on the boat since my batteries will be banked at 24v. I realize I can tie on to one battery to get the 12v, but think that might create an unbalanced load on the battery bank. Might there be a way to draw 12v from the whole battery bank thru a modulator or regulator? I'm sure this is not the first setup with a 12v requirement on a 24v system.

Anyway these are just starting points for me. I would like to have more panel capacity, but unless I cover the upper deck with panels, this is all I get. Thanks again for the wealth of information here and any thoughts you may have regarding my installation.

Mountain Don · October 2015

Just a friendly well meant suggestion. I have trouble reading and comprehending large paragraphs like the above. It helps a lot to separate the background info and the questions into smaller word groups. Don't take this as a personal attack, others may not have the same issues I do.

mike95490 · October 2015

> set of 4 Powersafe 12v 190 A/H batteries from 1 yr service in a cell tower backup system

Well, they will get you started, but they are not designed for many deep cycles, they sell them off to avoid disposal fees.

You are a bit short on solar, to be running air conditioning, so be careful.

There is no good way to have a 12V starting system and 24V house battery running off the same bank, as you suspect, it will be unbalanced.

mdwells · October 2015

Appreciate the reply. My bad, didnt mean to imply I would be using the solar or battery bank for a/c. I have a gen set onboard for a/c and hotwater.
Also have a separate 12v starting battery. I just wanted to run my 12v appliances off the 24v bank. I may just have to parallel the batteries at 12v. Just thought the 24v setup be more efficient.
Just read an article regarding positioning of the panels and the effect on the charge controller output. The mounting surfaces on my houseboat are at 3 different angles. This will put each of the 3 panels at a different angles to the sun by approx 15 deg each.
Apparently, it is not efficient to run all three panels thru the same mppt controller unless the panels are on the same plane. This would mean I need 3 controllers. If so, how should they be wired to each other?
I feel the output would be affected if I just tie all the outputs together, then to the battery bank, but that may be my only option.
It is possible this boat is not a prime candidate for solar due to it's configuration, but if I can get the components at a fair price, it would be worth the convienence to me.

tabbycat · October 2015

A Samlex 24 volt to 12 volt converter will not unbalance the 24 volt battery bank.

BB. · October 2015

mdwells said:

Came across a set of 4 Powersafe 12v 190 A/H batteries from 1 yr service in a cell tower backup system at a reasonable price, so I thought I could build a system from there. Don't plan to run the whole boat on the batteries or solar array at any one time. We only spend 2 to 3 days out and I am actually only looking for nighttime use of a led tv, fan and some lighting.

As always, knowing your exact power needs (Watts*Hours or Amps*Hours @ xx volts, peak power used, etc.) are really helpful to design your system.

1,000 Watt*Hours per day can be enough to run LEDs, small TV/laptop, and possibly some other stuff (cell charger, water pressurization pump, etc.). But, in the end, power usage is highly personal set of choices. Need to meet your needs, not what I think you "should" use.

1,000 Watts (AC assumed) * 1/0.85 inverter eff * 1/12 volts battery = 98 Amp*Hours @ 12 volt battery bank per day

Assume 2 days of back up power (no sun), and 50% maximum discharge:

98 Amp*Hour * 2 days * 1/0.50 max discharge = 392 AH @ 12 volt "optimum" battery bank (i.e., 4 x 6 volt @ 200 AH golf cart batteries)

A 12v fridge--That can really add to the size of the battery bank--Do you know how much energy per day that uses?

If you want to run 1,800 WH per day for battery power--Then you are close to the 760 AH@12 volt battery bank you are looking at (but know that the Telecom batteries are not going to last at all for deep cycling--They are designed to float and be replaced if deep cycled--after a few emergency power situations).

The 12 volt batteries wired as 24 volts to power a 12 volt system--Not usually the best choice. You cannot (or should not) draw 12 volts from a 24 volt bank. You can use a down converter (24 to 12 DC to DC converter), or a "balancing" converter that can charge discharge the "high 12 volt batteries" with the "low 12 volt batteries" (common on 24 Volt Bus/RV conversions).

If this is your first Off Grid power experience--I would suggest that you look at 6 volt @ ~200 AH golf cart batteries. They will make a good 12 volt bank (series parallel connected). I do not really like paralleling 12 volt batteries into 12 volt battery banks--hard to monitor batteries to make sure all is going well (hydrometer and DC current clamp DMM help).

-Bill

Houseboat solar system

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