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Old 05-03-2016, 16:18   #1
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12v vs 24v Solar

It seems 12v is the best solution for most boats for Solar. I know 24v is more efficient is homes with long runs, but this shouldn't matter on boats.

Any reason to consider 24v for a 400w to 600w solar system?

There will be 2 of us. Both heavy laptop users, led lights, fridge, nav equipment with autopilot, windlass, bilge, radios. (AC will be AC with a Honda 2000i).
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Old 05-03-2016, 16:55   #2
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Re: 12v vs 24v Solar

"It seems 12v is the best solution for most boats for Solar." may be the cheapest or possibly the simplest but NOT the best. 60 + volts is better.

Higher the panel voltage the lower the current, means less lose in the cabling from panel to controller for a given size cable. There is no such thing as too much power.
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Old 05-03-2016, 18:31   #3
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Re: 12v vs 24v Solar

Quote:
Originally Posted by PaulinOz View Post
"It seems 12v is the best solution for most boats for Solar." may be the cheapest or possibly the simplest but NOT the best. 60 + volts is better.

Higher the panel voltage the lower the current, means less lose in the cabling from panel to controller for a given size cable. There is no such thing as too much power.

With an MPPT charge controller you can have high DC voltage off the panels (my two 250 watt panels will be wired in series for 60v, for under 10 amps through the wires), run that to the MPPT, and the MPPT will charge a 12v battery bank(it will auto sense the voltage if it's any good). Have the MPPT very close to the battery bank so you only need short runs of large cable.

At home with a lot more panels and power, I have 120v going into the controller, and that feeding 48v battery banks, which then feed 48v to a 220v 8kw/24kw pure sine wave inverter (pretty much everything in the house plugs in to 220v sockets).

Despite being a big fan of 48v in optimum systems (all running off mains voltages), for the boat I will put in a 12v to 110v 2500 watt inverter, as most things will be running off 12v anyway (only a steam cleaner and dehumidifier will be run at 110v).

Don't forget to put automatic circuit breakers (resettable fuses which you can manually trip when necessary) in to be able to isolate the panels, charge controller, and the battery bank.

PS Even though you will only have 10 amps max going to the controller, make sure it can handle over 41 amps at 12v to feed the batteries with its output.
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Old 05-03-2016, 19:44   #4
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Re: 12v vs 24v Solar

Would think a 24-volt solar system would be best for a 24-volt boat.

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Old 05-03-2016, 20:43   #5
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Re: 12v vs 24v Solar

"Would think a 24-volt solar system would be best for a 24-volt boat."

The boat Battery voltage is only relevant to the Output of the MPPT controller not the input voltage.

The discussion is on the Solar Panel output voltage that is feed to the MPPT.
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Old 05-03-2016, 21:40   #6
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Re: 12v vs 24v Solar

We have two 49 (open voltage) panels... wired in parallel for minimal shade effect; Outback MPPT handles it very well
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Old 05-03-2016, 22:29   #7
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Re: 12v vs 24v Solar

When I finish my refrigeration refit I will rewire for both 24V and 12V and run the fridges on 24V. When my mains power alternator finally gives up I will be replacing it with a fairly large capacity inverter which I will also run from the 24V.


The 24V on the fridges is because I am converting them to eutectic and the compressors will run for long periods during the day and I am hoping the compressors will run at a lower temperature. The inverter so that I don't have to handle the excessive amperages 12V requires.


I will stay with 12V on lighting and fans etc. because it is more readily available.


It would be nice to go up to 48V if the gear was readily available as the wiring conduits are filling up as I add more gear and luxuries but the gear is not readily available (I am considering switching to ring mains and switching at the appliance using data cable and mosfets in order to simplify excessive cabling and free up some room in the conduits when I do a wiring refit)
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Old 06-03-2016, 01:40   #8
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Re: 12v vs 24v Solar

Just installed 6 X 85 watt panels, 3 panels in series and 2 banks in parallel to give around 54v to the mppt controller. As others have said, lower amps, smaller cables possible and reduced shading impact?
I would go higher voltage, limited by the mppt input.
Good luck.


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Old 06-03-2016, 09:45   #9
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Re: 12v vs 24v Solar

I went with one 40 V panel, at 325 W. I think the higher the panel voltage the better. The controller is very important, get the best you can. Try to install the panel without any shadows at all. I was told a higher voltage panel will provide more output at lower sun angles, I don't know if that is true.
Agree, get as much power as you can, always a way to use it.
good luck, Bob
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Old 06-03-2016, 10:04   #10
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Re: 12v vs 24v Solar

Quote:
Originally Posted by Ribbit View Post
With an MPPT charge controller you can have high DC voltage off the panels (my two 250 watt panels will be wired in series for 60v, for under 10 amps through the wires), run that to the MPPT, and the MPPT will charge a 12v battery bank(it will auto sense the voltage if it's any good). Have the MPPT very close to the battery bank so you only need short runs of large cable.

At home with a lot more panels and power, I have 120v going into the controller, and that feeding 48v battery banks, which then feed 48v to a 220v 8kw/24kw pure sine wave inverter (pretty much everything in the house plugs in to 220v sockets).

Despite being a big fan of 48v in optimum systems (all running off mains voltages), for the boat I will put in a 12v to 110v 2500 watt inverter, as most things will be running off 12v anyway (only a steam cleaner and dehumidifier will be run at 110v).

Don't forget to put automatic circuit breakers (resettable fuses which you can manually trip when necessary) in to be able to isolate the panels, charge controller, and the battery bank.

PS Even though you will only have 10 amps max going to the controller, make sure it can handle over 41 amps at 12v to feed the batteries with its output.
Good info, that. Higher voltage coming off the panels can be transmitted safely and efficiently. I'd like to find an array of household products standardized at 48 volts.
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Old 06-03-2016, 10:17   #11
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Re: 12v vs 24v Solar

24v Panels no questions. Also cheaper to buy.
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Old 06-03-2016, 11:14   #12
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Re: 12v vs 24v Solar

Is there anything wrong with connecting 2 - 12 volt panels in series to create a 24 volt "panel" and then feeding that to the MPPT controller. (of course if the mppt controller can handle the setup)

why did/would I buy a 12 volt panel when the 24v would/would have given me a possible better option.

thanks
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Old 06-03-2016, 11:21   #13
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Re: 12v vs 24v Solar

Just installing solar. I found higher voltage panels seem to be about half the cost of 12v ones, presumably for a much larger market, as well as appearing easier to fit and more efficient.
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Old 06-03-2016, 11:56   #14
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Re: 12v vs 24v Solar

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Originally Posted by roland stockham View Post
Just installing solar. I found higher voltage panels seem to be about half the cost of 12v ones, presumably for a much larger market, as well as appearing easier to fit and more efficient.
Higher voltage = lower current = smaller wiring and breakers =less mass = lower cost to source, build, ship, finance
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Old 06-03-2016, 12:50   #15
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Re: 12v vs 24v Solar

With the limited real estate on a mono hull sailboat efficiency of a solar install is important. I think one large panel will be more efficient than two smaller panels. The two smaller panels will have some electrical differences so the MPPT controller can not optimize the output for both.
You will also have more electrical connections with smaller panels so more to go wrong, more to check when it does.
The larger panels manufactured for use on off grid homes will generally be the lowest cost per watt. Often you can buy one that is slightly out of specification at a great price. I would only use one controller per panel. The Kyocera panels are the only ones that will retain their warranty when used on a boat.
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