Energy 24 volt solar panels

Discussion in 'Off Grid Living' started by Gafarmboy, Oct 26, 2020.

  1. Gafarmboy

    Gafarmboy Monkey+++

    I was recently given four 265 watt 24 volt Solar World panels. Is there any way to use them with a 12 volt system? In short , use them to charge batteries for a 12 volt system. Do not want to use them in a 24 volt system as all my systems are 12 volt.
    BenP, duane and sec_monkey like this.
  2. sourdough145

    sourdough145 Holder of the M1 thumb award...

    Sure they can be used! Look up MPPT charge controllers. They can take a wide range of voltages and use it with great efficiency. Just make sure the controller can take the voltage (about 36 volts for a 24 volt panels) and the current (4 X 265 = 1045 watts, 1045 / 12 volts = 87amps). In reality you could just get a 60 amp charge controller and do very well. The caveat is can your battery handle that level of charge current? Good charge rates for batteries vary by chemistry. I think a charge rate of .25C is great for lead acid batteries, tapering off as it reaches 80%. So a 200AH battery would take a 50 amp charge rate... YMMV. I'm sure there will be other good opinions on what to buy. Lots of knowledge on the monkey tree, most of it useful... Always take what you get and verify it yourself. You are your best resource, we are just people with opinions...
    BenP, Tully Mars, duane and 2 others like this.
  3. oil pan 4

    oil pan 4 Monkey+++

    Yeah you need a real MPPT charger. Not one of the cheap ones.
    Oh and 12v systems suck. They're really only good for backup power and intermittently used electricity, such as 12v RV pumps for domestic water.
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  4. TnAndy

    TnAndy Senior Member Founding Member

    As already stated, you need an MPPT charge controller. Those panels are around 7amp output at 30-35volts. Wire two of panels in series, that will give you around 70v @ 7amp, then same for the other two, then combine the pairs in parallel, giving you around 70v @ 14amp total.

    The output of the controller will be 17-18v or so, at around (4x 14amp) in full you're looking for a 60amp controller. Also look at the max panel specs on the controller....they will often give you the MAX number of watts you should connect for your system voltage.

    You can expect to pay in the $400+ range for a controller that will do what you want. The more expensive controllers ( I run Outback) allow for a lot more amperage, and are programmable at to system voltage (12,24,36,48,60) and a few other features.
    Last edited: Oct 27, 2020
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  5. techsar

    techsar Monkey+++

    But your math shows @ 14 vdc, nearly 70 amps output..which is what most mppt charge controlers are rated on...
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  6. TnAndy

    TnAndy Senior Member Founding Member

    The real problem with 12v is the amperage. Stepping down the voltage means stepping UP the amperage, so you have to use equipment designed to handle it.

    For example, that charge controller Outback FM 60 (60amp output) would seem like it would handle it....but if you read the specs Outback Power Flexmax 60 MPPT Solar Charge Controllre you'd see Outback says a MAX panel connection of 750w (STC) when using it at 12v output. Step up to 24v, and that doubles the amount of panel watts you can connect to 1500. Go to 48v and it increases to 3000 panels watts. Higher the system voltage, the cheaper it gets to handle.

    SO, according to Outback, you'd have to step up to their 80amp controller for just 4 of those panels.

    Side note.....I've been running 1800 panels watts on two FM 60 (max rating of 1500 on my 24v system) for ten years now with no ill effect my guess is they have a lot of 'fudge' factor built into them. My guess is you could run your 4 panels on an FM 60, but don't take that to the bank.
  7. TnAndy

    TnAndy Senior Member Founding Member

    Yeah, my math was edited. It's early...what can I say......:D
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  8. Merkun

    Merkun furious dreamer

    I would NOT count on that level of fudge now, ten years on. I strongly suspect that the margins are lower now then back then.
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  9. Big Ron

    Big Ron Monkey++

    Make sure you look up the VOC the panels can put out and consider that cold weather increases this. Buy an MPPT controller that can handle it or pfft! up in smoke! I prefer a 48 v system. Read up more about solar.
    techsar likes this.
  10. oil pan 4

    oil pan 4 Monkey+++

    The hell that 12v systems go through to charge and discharge the total through put of each system should only be a few kwh per day at the most.
    Yeah you can build them bigger, parallel more batteries, add more arrays, more charge controllers, bigger wires, more inverters, then you realize a 24 or 48v system would have been way better.
    sourdough145 and techsar like this.
  11. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Can you please post a picture of the sticker on the rear of the panels , all the same ? then just one !
    FM60 /80 are old and dated , go classic , BUT i need a sticker first to post real info
    techsar likes this.
  12. Gafarmboy

    Gafarmboy Monkey+++

    Thanks for all the various levels of information. Sloth, I will get back to you on those specs.
  13. Cruisin Sloth

    Cruisin Sloth Special & Slow

    Thanks , It is very important on the build .
    Also the inverter voltage you plan ??
    12Vdc is toy/crap , 48Vdc is great , 96Vdc is in my would only with HVDC ticket ..
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