Solar power recommendation help

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WoodyZ
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Re: Solar power recommendation help

Postby WoodyZ » Sat Sep 12, 2015 2:34 pm

One is nominally a 12 volt panel and the other is a nominal 24 volt panel. The different amperage is a product of the different voltages. If you are replacing your existing panel, which one you choose comes down to what solar controller you will be using.

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Re: Solar power recommendation help

Postby Neddy » Sat Sep 12, 2015 3:34 pm

The higher voltage panel has more solar cells, but they are smaller. Output power is measured in
Watts - ie Volts x Amps. Any 160 watt panel therefore puts out more power than any 150 watt panel.
Pros and Cons.
The 30 volt 160 watt panel....
Is probably cheaper.
Puts out a little more power than the 150 watt 18 volt panel.
Because of the lower current, cabling can be a bit lighter.
BUT
The higher the panel/battery voltage gap, the lower the overall efficiency.
A (more expensive) MPPT controller is essential (but gives more power).
Overall, given the choice between these two panels, I would go for the 30 volt one and an MPPT controller.

Grant, you do know that neither of these are big enough to even run your fridge. I presume (hope) that you are therefore looking at buying two. So, you leave your old 80 watt panel on its old controller, buy 2 new 160 watt panels, wire them in parallel to feed a new 30 amp MPPT controller and you have got 400 watts of solar power. From what we know of your wants and needs, this should be regarded as an adequate but minimal installation.

Neville.

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Re: Solar power recommendation help

Postby landlubbers » Sat Sep 12, 2015 3:44 pm

Thanks neville, yes I definitely will be putting two new panels in at this stage, and removing the old 85 watt one. If needed in the future, I will add another new solar panel with the two new panels. Another question I have is if I need to add a third panel in the future, would I be able to add a 150 watt with the two 160 watt panels? Reason being is the room on the roof would not allow a third 160 watt panel without some difficulty. I have to remove the 85 watt panel because the new panels would not fit due to the size of them. I appreciate everyone's input.

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Re: Solar power recommendation help

Postby Neddy » Sat Sep 12, 2015 4:27 pm

"In the future, would I be able to add a 150 watt with the two 160 watt panels?".
Unless you wanted to run it from its own separate dedicated controller, No, you wouldn't.
Having neither a common voltage nor a common current, is would be incompatible with the 160 watt panels.

Grant, 2x 160 watts really isn't enough for your needs. Rather than "plan" to extend these in the future, I would strongly encourage you to "do it once and do it right". Can you fit 3x 150 watt panels? With a 40 amp MPPT controller, that would be quite a good option if you had the room.
What shape/size is the rooftop space that is available to you?

Neville.

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Re: Solar power recommendation help

Postby NeilV » Sat Sep 12, 2015 6:24 pm

Indeed, I'd say 2x250w right now would probably suit you better (space allowable) than the 450w combination you'd need three panels for in some future upgrade?

Perhaps measure the roof area and work out the best combination to fit and suit your future needs now, rather than planning to upgrade and hope to fit them in later?
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Desultory

Re: Solar power recommendation help

Postby Desultory » Sat Sep 12, 2015 7:28 pm

Hey Landlubbers,

there is a 150 watt solar panel, 18 volt, 8.33 amps. A second panel is 160 watt, 30.2 volts and 5.30 amps. They are both mono crystalline solar panels. My question is, why so much difference in the voltages and amps? and which would you recommend and why?


To answer your question, the 150w panel is wired / configured as a 12v panel (yes I know it has a max voltage of 18v but it's still considered to be part of the 12v panel class), while the other panel is wired / configured as a 24v panel (yes again I know the voltage is 30.2v max, but it's still considered to be part of the 24v panel class).

With panels it's horses for courses (so to speak).

There's advantages and disadvantages for both (depending on how you'll be configuring your setup), so I'll outline these below to try and help better explain for you.

1. If you are going to be using a 12v battery storage setup (eg 1 x 12v battery or even 2 x 12v batteries running in parallel) and you are going to be using a cheaper style PWM controller, then you really are stuck with using a 12v style panel (as this is then closely matched to your 12v battery voltage). If you are using a 24v battery setup (eg 2 x 12v batteries wired in series) then you CANNOT use this 12v panel as it wouldn't have enough voltage output to charge your 24v battery setup.

2. If you are going to use a 24v panel with a 12v battery setup then you CANNOT use a PWM controller (as the PWM contoller cannot convert the voltage down like a MPPT controller can). So with the 24v panel you would need to either use a 24v battery strorage setup or else use a MPPT charge controller which takes the 24v and outputs 12v (at double the amperage).

Typically as a general rule an MPPT charge controller gives about 20-30% more performance output (from the same panel) compared with the PWM controller, but they do cost more at time of purchase, but personally I'd never usually recommend people go with the PWM controller option as then you are just throwing away precious output each day from your panel setup.

Lastly you need to think about whether you will only ever be running 1 single panel on your roof top, or whether you will want to eventually have 2 or 3 (or more panels) and whether you actually have space for these on your roof top, or whether other items on the roof such as vents / satellite dishes etc are in the way.

Typically if people are only going to be going for 1 panel on their roof (and never plan on adding more) then I'd usually recommend going as higher wattage as possible from the 1 single panel, so either a 265w 60cell (1.65m x 1m size panel) or a 315-330w 72 cell (2m x 1m size panel).

The last thing your want (in my opinion) is to have filled your roof space up with 1 or 2 low wattage panels, then then have no more roof space left available to generate any more power. If everyone had an RV the size of a school bus then sure I'd have no problems installing a couple of low wattage panels and simply adding on more as you need them, but the reality is that roof space on most people's RV roof tops is precious and hard to come by, so I tend to like to generate as much power as realistically possible from any panel that is installed on the roof top (knowing that I don't have space to install as many as I like for more output).

Also just so you know, as a general rule if you are connecting 2 panels together (in series) it's recommended that they be the same wattage (or as close as possible specs wise, eg voltage / amperage output) so that they work nicely together without one making the other panel loose some of it's output.

I hope that best explains things for you, and WHY you'd want to choose a 12v panel or 24v panel (depending on the setup you end up going for).

PS: What size (physically) were both the 2 panels you were looking at, and how much roof space (length and width) do you have available on your roof top for 1 or more panels ? Also are you planning on using your RV much during winter months, as that's the time when ALL Solar Panels will give their lowest output.

Also, the Mono vs Poly really doesn't make much difference to be honest. The OLD style poly cell panels used to have flecks all through each cell (and look almost like the cells was cracked or smashed) but nowdays the new technology poly cells will usually have the same style AR treatments on the cells and so they usually look a nice uniform / consistent deep blue colour, and aside from poly cells being square and mono cells having their corners cut off (typically) there's almost no real performance difference between them any longer (as long as the panels have the same wattage output). Eg I could get a 265w [edit: brand] Solar Poly and a 265w [edit: brand] Solar Mono and put them side by side and get about the same output per panel YEAR ROUND. This is a good test as both panels are made by the same manufacturer and are the same wattage. I've personally done this test to see these results for myself here (so I can honestly comment on this as being accurate rather than hype or sales jargon).


Regards
Steve

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Re: Solar power recommendation help

Postby landlubbers » Sun Sep 13, 2015 12:00 pm

Neil, I don't have the room to fit two 250 watt panels due to their size.

Steve and Neville, thanks for your suggestions. My roof space, after removing the 85 watt panel, is 2 metres across the roof by 1400 fore and aft. If 85 watt panel was to stay where it is, the space left is 1200 by 1400. I don't think this is an option for me. The way that I look at it, I have room to put two 160 watt panels at the back of the roof, and I do have some room at the front of the motorhome to possibly put one more panel, which would give a total of 480 watts. If I put one big solar panel (330 watt) at the back of the motorhome, I will be struggling to put the same size at the front.

As far as changing my 10 amp PWM regulator to a MPPT regulator, there is no problem.

This damn fridge is becoming a bone of contention :x ;) but thank you all for your help, I am slowly getting there.

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Re: Solar power recommendation help

Postby Neddy » Sun Sep 13, 2015 1:52 pm

Grant, try as I might, I am unable to come up with a better solar panel configuration than the one you propose.
480 watts from 3x 160 watt panels would give you a nicely sized installation for around $600.
What I would like to do now is convince you to fit all 3 panels in your initial install.
In the long run, this would be quicker and easier than adding the third panel later.

Neville.


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