combining different panel voltages...ok?

System · August 2009

I currently have the following older vintage system on my sailboat:
2 Unisolar 32watt panels
2 Unisolar 64watt panels
(total 192 watts, at "12 volts")
Prostar 15 amp controller
Batteries: 4x 6V Lifeline GPL-6CT's for 600 A/H at 12V

I'd like to add/upgrade the system, by adding 2 new Kyocera 210 watt panels. I also plan to upgrade the controller to an MPPT model.

I have the following questions:
Will the new controller be able to handle the 6 panels, with their varying voltages (the 210's are rated at 26V) ?
Since the older Unisolars are junction box type, and the new ones will have the MC connectors, any advice on connecting?
I've read that the new panels can be combined in series to raise voltage to the controller. Can I add in the older panels as well?
Any recommendations on MPPT controller? Concerned about reliability as well as RFI interference with onboard radios and other nav equipment.

Thanks for any advice!

Adam
SV Bravo
Seattle

Cariboocoot · August 2009

Re: combining different panel voltages...ok?

All things considered, you should think about removing (and possibly selling) the old panels entirely. It is not likely that they will work with the new panels (2 "12 V" in series = 24, but that's not the "real" voltage). Or at least not work very well.

What's your end goal here? How many Watt/hrs are you going for? If you're adding panels, is it because the existing ones can't keep the batteries charged? You need to look at the bigger picture. Most of the time trying to add very new equipment to very old equipment is more trouble than it's worth.

System2 · August 2009

Re: combining different panel voltages...ok?

Cariboocoot wrote: »

What's your end goal here? How many Watt/hrs are you going for? If you're adding panels, is it because the existing ones can't keep the batteries charged? You need to look at the bigger picture. Most of the time trying to add very new equipment to very old equipment is more trouble than it's worth.

End goal is to minimize/eliminate need for genset or engine charging, so that solar can take care of all needs, especially refrigeration in the tropics. The system as it stands cannot do this. All works fine, though, so I thought I'd use some add'l space for new panels, but keep the old in addition, in order to max the available output. If too big a hassle to combine the panels, I could offload the old ones, but would be losing the 192 watts in the process.

What about keeping the existing system intact, inc. its controller, and adding the 2 new panels and MPPT controller as a completely stand alone add'l charging system to the battery bank? Secondary benefit is the redunancy, which, especially on a cruising sailboat, is always a PLUS!!!

Thanks
Adam
SV Bravo
Seattle

dwh · August 2009

Re: combining different panel voltages...ok?

svbravo wrote: »

What about keeping the existing system intact, inc. its controller, and adding the 2 new panels and MPPT controller as a completely stand alone add'l charging system to the battery bank? Secondary benefit is the redunancy, which, especially on a cruising sailboat, is always a PLUS!!!

Thanks
Adam
SV Bravo
Seattle

I was going to suggest that, but you beat me to it. I might suggest replacing the other charge controller as well, so that both are MPPT.

Cariboocoot · August 2009

Re: combining different panel voltages...ok?

Yes, trying to combine the arrays would be troublesome.

Putting up the two Kyoceras (420 Watts peak) with their own, separate charge controller would work better.
Is 600 Amp/hrs enough battery capacity for your usage? The two new panels would be (just) capable of keeping them up (there's a lot more variables on a boat than on a house, as you know!)

Think about the space those old panels take up. You'll find new ones produce more W per sq. ft. Plus, the old ones probably aren't up to full capacity anymore - panels degrade over time.

It's debatable if MPPT controllers offer any advantage in a boat installation. You might want to save some money and go with a PWM type capable of around 30-40 Amps like this:

http://store.solar-electric.com/ps-30.html

mike95490 · August 2009

Re: combining different panel voltages...ok?

How old are the uni solar panels? More than 5 yrs old, they have likely lost a fair amount of capacity. (20% fade in first 6 months is usual)

As others have said, series, high voltage arrays, are a poor choice on a sailboat, because of shade from stays issues. One shadow can shut down your whole string, or knock a lot of it out of operation, unless you have bypass diodes in each panel.

I doubt there is a good way, with only 500w, to acomplish refrigeration in a sailboat.

Cariboocoot · August 2009

Re: combining different panel voltages...ok?

I don't know, Mike; I do it with 700 Watts at a fixed location and it's a full-sized 'frige. Plus, that has to run everything else. Problem is: those 'compact' refrigerators such as would be fitted to a boat are usually energy hogs - especially per cu. ft.

Now, if there were three of those 210 Watt panels ...

combining different panel voltages...ok?

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