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Bret
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# Posted: 3 Jun 2016 08:11am
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Anyone using 24v instead of 12v off grid? Smallish system, about 600 watts of panels. What sort of components, lighting etc do you use. Thoughts on benefits or not would be greatly appreciated.
Bret
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razmichael
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# Posted: 3 Jun 2016 08:40am
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I'm only running 12V so this is an opionion only - Higher voltage has the advantage of less voltage drop and/or smaller gauge wires (especially useful if your panels are a long way away. Disadvantages depend a lot on just how samll the system is and how you intend to wire it. 24V inverters are more expensive (smaller market) if you are using 120AC for the cabin although this is a one time expense. If you are sticking with a DC cabin, 24V "things" are much more limited and generally more expensive. You could drop the 24V down to 12V but, again, more bits and peices needed. I think a lot comes down to a balance between what you mean by a "smallish" system, how you plan to wire it, run distances and cost. 600 watts of panels is starting to get up in size and wiring them for 24V (even 48) might have advantages but may be overkill for everthing else you want to do.
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MtnDon
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# Posted: 3 Jun 2016 09:52am
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If using 24 volts means you eliminate any parallel battery connections go for it. We use 24 volts; most everything runs from the inverter.
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NorthRick
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# Posted: 3 Jun 2016 01:59pm
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Not for an off grid cabin, but I have a small set up to power circulation and ventilation fans in a greenhouse. Two 190W panels, a basic Morningstar charge controller, four 6v golf cart batteries wired in series for 24 volts, and a 300W sine wave inverter.
Works great and the only thing I'd do different would be to get a MPPT charge controller instead of the PWM one I have now. All the loads are 120AC through the inverter. As razmicheal pointed out, if your intention is to run loads straight off the DC battery bank, 12v stuff is easier to find than 24v. I long ago decided that 120ac stuff is way easier to find and cheaper, so my systems run everything through an inverter.
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Bret
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# Posted: 4 Jun 2016 09:03am
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Thanks for all the insight. So. . . I could convert my 24v panels running in parallel to 12v using a dc converter, then I'd only need half the number of batteries running in series, and I could go with a less expensive and smaller inverter to run the ac circuits. Does this sound OK or am I looking at this thing wrong?
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MtnDon
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# Posted: 4 Jun 2016 09:48am - Edited by: MtnDon
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??? wrong, if I interpret what you said...
The DC-DC converter is used to convert 24 VDC from a 24 volt battery bank to 12 VDC to run 12 VDC devices. We have a DC-DC converter to operate a 12 volt pump and a few 12 volt LED strip lights.
The PV panels need to have a Vmp high enough to charge a 24 volt battery bank. For example, panels with a Vmp of around 30 to 36 volts used with an MPPT controller. panels in parallel if close to the charge controller.
Do you already have any equipment? If so, what?
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Bret
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# Posted: 4 Jun 2016 10:15am
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What I have are three of these: https://readymaderesources.com/product/solarpeace-monocrystalline-195w-24v-solar-pane l-m7x-195-call-for-shipping-limited-supply/
Also, a combiner box.
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NorthRick
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# Posted: 4 Jun 2016 11:18am
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Those are almost exactly what I have for my greenhouse setup. Two of them wired in parallel connected to this charge controller:
http://www.solar-electric.com/inverters-controllers-accessories/chco/mochco/stpwmchco /ss-20l.html
The charge controller is attached to four 6v batteries wired for 24 volts. Those in turn power this inverter:
http://www.solar-electric.com/inverters-controllers-accessories/inverters/sasiwain1/s amlex-pst-series-pure-sine-wave-inverters/sa300wa24vos.html
The inverter provides power to timers, fans, and a radio, all regular off the shelf products.
As I said, the only thing I wish I had done different was to go with an MPPT controller instead of the PWM.
Either controller can take the panels you have and charge a 24v or 12v battery bank. An MPPT controller will do it more efficiently than a PWM, particularly if you go with a 12v bank.
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Bret
Member
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# Posted: 4 Jun 2016 02:14pm - Edited by: Bret
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Interesting about the charge controllers. Can all charge controllers do this: take the charge, in this case 24v, from the panels and allow 24v or 12v battery setups to be utilized.
This could mean that I could buy a 12v battery setup and then upgrade to a 24v setup as I expand my needs. I would be starting with some lights and a ceiling fan. Nothing too power hungry.
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MtnDon
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# Posted: 4 Jun 2016 02:53pm
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Not all charge controllers. Check the specs. Another advantage of 24 volts over 12 is a charge controller feeding a 24 volt battery bank can handle twice the wattage of PV panels compared to being used to charge a 12 volt battery.
As for increasing battery capacity from 12 to 24 volts in general that is a bad idea unless done within a few months of the initial installation. That has do do with battery aging. The newer ones will act no better than the older ones.
Always better to plan well and not have to increase the size of a PV system.
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Bret
Member
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# Posted: 4 Jun 2016 04:01pm
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Yeah, I maybe jumped the gun with the solar panels. They were a good price per watt so I bought them. Now I'm trying to find a way not to have to buy the batteries (twice the amount than 12v) and still move forward.
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NorthRick
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# Posted: 4 Jun 2016 04:20pm
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Quoting: Bret Now I'm trying to find a way not to have to buy the batteries
Except for a few specific cases, you have to have batteries for an off-grid solar PV system.
You should really determine what you want to power, peak power in watts, and the total draw in watt hours per day. That will help you determine the appropriate size battery bank and inverter. Then, you can decide on the right amount of panel, system voltage, and charge controller.
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creeky
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# Posted: 4 Jun 2016 05:13pm
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You've got the panels. And they're good panels. If you want to save on battery costs as your loads are light. go with a 12v battery pack. 2 deep cycle batteries. And a 12v inverter.
get a good mppt controller. Expand as necessary.
I have a 2kw system that started as 4 250s at 48v going into 1200 amp hrs of battery at 12v. It's worked well for 5 years. Up for 3 years 4 months without issue.
Year one: The first thing i did was change the pwm solar controller for an mppt one. Got some erroneous advice.
Year two. I bought a better inverter. After the early cheap one died. That was a bit nasty to be fair. Two weeks before I left for xmas holidays.
Year 3: I put in a second mppt controller. and upped to 2 kw.
Year 6: If you look at my lithium post. I'm now replacing the inverter and battery pack. Going to 48v. And lithium batteries.
The reason I describe this process is to show ... it is a process. There is nothing wrong. Or bad. Or even more expensive to building slowly overtime as your needs grow.
I have sold the vast majority of the older equipment for what I paid for it. In fact. My mppt controllers are worth more now than when I bought them. Canadian dollar took a hit.
Now. You have a good size solar array. So MPPT for sure. No doubt. You should build around 600 amp hrs at 12v (300 at 24). But if you don't have the need... yet.
I, as others have recommended, would skip any idea of doing DC power lines unless you have a specific need. It's a waste of money. All my DC equipment has gone to the sales table. I am all AC. Stuff is just cheaper and better selection (lights. appliances. etc)
A 300 watt inverter is a great place to start.
I have a real pricy TBS 1600 at 12v for sale that would do you for the next 10 years ... lol. 
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