Author Topic: 12v or 24 v solar  (Read 3001 times)

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Offline roty

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12v or 24 v solar
« on: July 20, 2014, 12:51:44 AM »
I have recently purchased and installed an off grid system. 3x100 watt panels 12 V system. they work great my issue is that I was not aware of the benefits of having a 24v system.
I am using this in our cottage for several light bulbs as well as a small fridge that will be only used on weekends and on a timer so it pulses on for only about 20 minutes per hour to conserve battery power.
I currently have 2 12v marine batteries that I will swap out in a few years (after the marine batteries die) for 6v golf cart batteries.
I am new to solar and would like to know if I should look at adding another panel so I can get a 24 v system ? if I do go for the 24 system can I add a 225 watt panel to my set of 3 100 watt panels? not sure if I can mix and match different wattages?

Thanks in advance for any assistance.
yes I am new so patience with me please :) :o

Offline MadScientist267

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Re: 12v or 24 v solar
« Reply #1 on: July 20, 2014, 08:21:40 PM »
Roty -

Welcome to the board, first things first. ;)

In a nutshell, yes and no. Can it be connected that way? Yes. Should it? No.

The 100W panels will only pass what they are rated. A larger panel in series with a smaller one will derate to the capabilities of the smaller panel. The "extra" 125W will simply be lost.

It's always best to match panels as closely as possible. *To a point*, no damage will occur to the smaller panel, it will simply go to waste. Someone else may be able to chime in with an experience that draws that line, but they'll all say the same thing beyond that - match.

If you haven't bought the panel yet, don't waste your money. Go for another 100W to complete the second 200W 24V pair (to give you a total of 400W), then add any additional pairs in parallel with the existing panels.

Hope this helped,

Steve

 
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Offline Wolvenar

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Re: 12v or 24 v solar
« Reply #2 on: July 23, 2014, 07:35:06 PM »
At this point unless your going for a large increase of power use, or generation capacity it is maybe not worth the change to 24 volt.

Many things are available in 12 volt for vehicles that can be used, and the added benefit that in a pinch your car could act as a generator.  The car stuff may not be the most efficient but they are sure plentiful.

I miss the ability and options of a 12 volt system, but we outgrew what 12volt systems can supply with reasonable wire sizes or loss.
Trying to make power from alternative energy any which way I can.
Just to abuse what I make. (and run this site)

Offline Rover

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Re: 12v or 24 v solar
« Reply #3 on: August 01, 2014, 01:20:12 PM »
I have recently purchased and installed an off grid system. 3x100 watt panels 12 V system. they work great my issue is that I was not aware of the benefits of having a 24v system.
I am using this in our cottage for several light bulbs as well as a small fridge that will be only used on weekends and on a timer so it pulses on for only about 20 minutes per hour to conserve battery power.
I currently have 2 12v marine batteries that I will swap out in a few years (after the marine batteries die) for 6v golf cart batteries.
I am new to solar and would like to know if I should look at adding another panel so I can get a 24 v system ? if I do go for the 24 system can I add a 225 watt panel to my set of 3 100 watt panels? not sure if I can mix and match different wattages?

Thanks in advance for any assistance.
yes I am new so patience with me please :) :o

Hi Roty,

Now is the time to plan out future growth, actually you are a little late on the planning stage, but none the less. A lot of us started out the same way you are, adding panels, one at time, getting excited, wanting to grow the system, etc. It is the most expensive way to do it, you end up replacing stuff that is working simply because it can't handle the growth or change in voltage etc.

I was 12V and went 24V last year, it was not a cheap endeavor. In your case, I would not think of combining the current 100W panels with 24V (yes it can be done, best way is probably to series the 100s and parallel to the 24V and use an MPPT controller, however, it will be inefficient). I would probably create 2 arrays with 2 separate controllers (Actually how my system is, I have 3 100W  12V panels, and 5 235W 24V panels) you would still series the 3 100s into an MPPT controller, then let the new 24V panel be the first panel on your new array with its own controller. You can use the output from both controllers to charge your batteries. Either case you would need controllers that can charge at 24V, most good controllers have models or the capability to do so, they will cost you as much as a panel, and if MPPT, a couple times more (each).

As far as running 12V stuff off the bank, there are (and I use them) lots of 24 to 12V converters , I use some that are in the 240W range, which is usually more than needed for 12V stuff. But you need to work out your usage. Consider the possible inverter down the road and what it requires, etc.

Rover
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Offline A of J

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Re: 12v or 24 v solar
« Reply #4 on: January 16, 2015, 03:30:36 PM »
Solar panels are DC beasts and as such it is voltage that takes precedent.

You can use different wattage panels, maybe at the loss of some efficiency as opposed to using banks of the same panels through a MPPT.

You could use 2 x 12v x 100W panels in series (12+12=24V) and parallel that with 1 x 24v x 275w panel, it will work just fine. Both strings will work at the same voltage and output amps consistent with their rating at that voltage. Theoretically the 12v string would give 4.1A @ 24v (100 /24) and the single 24v panel 11.4 A (275/24).

Allan

Offline gww

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Re: 12v or 24 v solar
« Reply #5 on: January 16, 2015, 09:14:03 PM »
There might be one other option depending on the voltage of the 24 watt panel and the batteries you use.  If the 24 volt panel had a voltage of 28.6 or something, you might be able to hook it strait to the battery with no charge controller and it would probly be in the voltage range where it wouldn't hurt some batteries.  If you faced it a bit east you would lose some production but it would still be a big help in bulking the batterys.  This is only if you ended up with a 24 volt battery bank which you probly don't need.  Are you wanting to add loads that you don't run now?
gww

Offline rclark

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Re: 12v or 24 v solar
« Reply #6 on: June 05, 2015, 01:58:03 PM »
As others have said, there may not necessarily be harm from doing it otherwise, but it's generally best to match your panels to your voltage. Frankly, in my experience I've found that putting in the extra leg work (or money) to make it right the first time pays off in the long term because I have less maintenance issues and other hassles to worry about.

Offline MadScientist267

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Re: 12v or 24 v solar
« Reply #7 on: July 26, 2015, 12:28:24 AM »
Solar panels are DC beasts and as such it is voltage that takes precedent.

I realize this really isn't an active thread now, but I was reading back thru some of the older stuff under leisure and saw this...

A of J, you're correct with this provided the context you used later in the post is present.

However - PV is a current source, not a voltage source. A single solar cell is really nothing more than an oversize diode that is optimized to catch light. The current that any given cell passes is proportional to the amount of light caught.

I wanted to clarify for future readers of this thread that if a single cell of any given size is placed in series with a larger cell, and exposed to equal quality and quantity of incident light, the current will be limited to the Isc rating of the smaller cell, absolute best case.

You can also think of this another way: Take two identical cells and place them in series, equal quality/quantity light, just as above, and partially shade one of the cells. The current that will pass thru the shaded cell will roughly approximate that of a completely exposed cell the same size as the unshaded area. This of course then scales right up, as the typical panel is a single string of identical cells (not always, but that's another story and really has no bearing as far as this goes).

One other related point... Being a "diode", a cell is also subject to similar rules as their tiny counterparts... The primary difference is that light causes forward conduction. Shaded or "missing", doesn't matter, because the shaded area is effectively reverse biased, and therefore "open". This is why shading only a single cell in a panel will render it "powerless" (bypass diodes are used to address this issue).

I apologize if I took this way out on a tangent, but I think the thread demanded it for completeness... and maybe I'm a little bored LOL

Steve
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