12v or 24v

[quadna71]

I see a few threads discussing the merits of each system, but the advantages of 24v over 12v don’t seem to be realized until the you are a large system. Is that true? I’m looking at installing four 200w panels on the roof of my shed and don’t foresee it expanding (due to physical size of roof) so am not sure if I’ll realize enough of an advantage with a 24v system to offset the cost of the panels. I mean they are only $10-$15 more per panel, but would I net a improvement of $40-$60 in the system?

 

[Supervstech]

4 200W panels can produce around 4.8KWh of energy average in a day…

12V is 375 Ah with 24V it’s 183 ish Ah…

12V is fine at this level of storage, it’s also fine at 24V… I guess it really depends on what you are powering in the shed.

 

[quadna71]

Garage door, radio/speakers, indoor lights, outdoor lights, and recharging 60v power tool batteries once or twice a week. Most items on 12v power and the battery chargers off a 2000 inverter. Nothing heavy like heat or a/c and only occasionally as the grass dictates. I know it would likely be fine with 400w or maybe even 200w but I’d rather be over than under.

 

[Rednecktek]

Your charge controller is also a factor. You've got 800w of panel, so for a 12v system you'd need a 70a SCC to utilize all that potential, at 24v you'd need 35a. The 24v system would also allow for larger inverters upwards of 5Kw whereas a 5Kw on a 12v would be 400a fuses and wiring.

If your stuff mostly runs off 12v then the best setup might be a 2s string facing SE for morning sun and a 2s facing SW for afternoon sun. That way you're getting more generating hours through the day and a 12v battery setup would just clip any excess power at noon (if there was any). Throw it on a decent quality 60a MPPT and walk away.

With a 2Kw inverter, that's only 200a fuses and wiring, still totally do-able.

 

[quadna71]

70a controller? I wonder why Renogy and Rich Solar pair their respective 40a MPPT controllers with the 800w kits. I’ll have to dig deeper on that - thanks.

 

[Rednecktek]

I wonder why Renogy and Rich Solar pair their respective 40a MPPT controllers with the 800w kits.

Because if you do a 24v system 800w / 24v = 35a so a 40a would be perfectly fine.

If you're doing a SE/SW setup on 12v, rather than a single 60a you could do a pair of 40a units, one for each string. It's an option, although maybe not as cost effective as a single 60a.

 

[chrisski]

I recommend 24 volts for an inverter sized 2000 watts and up. 12 volts is OK if the 2000 watt inverter will be used at its potential for a couple of minutes (2 real minutes not, “I’ll be there in a couple minutes”) at a time four or five times a day, like to warm a meal up, not cook it. I have Milwaukee tools and they are 18 or 20 volts, I forget, but they charge at 100 watts.

I have a 24 volt 3000 watt system for my RV. I have a 24 volt 300 watt inverter for a portable generator that I also have three USB chargers.

If the large portion of your power is 12 volts, such as 12 volt LEDs, then by all means go for 12 volts. There’s loss either was 12 volt DC to 120 volt AC or 24 volt DC to 12 volt DC. For me 24 volts won for both the big build and the small one.

 

[rmaddy]

I mean they are only $10-$15 more per panel

What do you mean by this? Why is the price of the panels dependent on your battery voltage choice?

 

[quadna71]

I meant the difference in price for 12v panels and 24v panels. I wasn’t sure if it is better to get 24v panels and wire in parallel or get 12v panels and do pairs of series wired panels that end up paralleled together.

 

[Supervstech]

I meant the difference in price for 12v panels and 24v panels. I wasn’t sure if it is better to get 24v panels and wire in parallel or get 12v panels and do pairs of series wired panels that end up paralleled together.

Ahh.
With panels, it all depends on the charge controller.
With a REAL MPPT controller, it won’t make any difference. With a cheapo, they need to be close to battery voltage to function, or they just burn off the extra watts, and fail rapidly.

 

[DerpsyDoodler]

I meant the difference in price for 12v panels and 24v panels. I wasn’t sure if it is better to get 24v panels and wire in parallel or get 12v panels and do pairs of series wired panels that end up paralleled together.

Unless youre using a PWM controller and need to maintain the same voltage on the panels as on your battery bank, the panel voltage is irrelevant except to determine max input voltage to whatever charge controller you plan on using. Don't think of panel voltage as having to be the same as your battery voltage.

 

[rmaddy]

I meant the difference in price for 12v panels and 24v panels. I wasn’t sure if it is better to get 24v panels and wire in parallel or get 12v panels and do pairs of series wired panels that end up paralleled together.

Use a good MPPT controller and completely ignore any reference to "12V" or "24V" panels. Those are meaningless terms at that point. Focus on how much wattage you need. That's all that matters. Then find a good deal on panels that meet your total wattage needs. Then decide how you need to arrange them. This should also factor into how many panels you buy. For example, 5 panels is a terrible number to get. 2, 3, 4, 6, 8, 9, 10 panels are good numbers because they allow for lots of options (series/parallel). Then finally you can determine the best sized MPPT controller to get based on your system voltage, total panel wattage, and panel arrangement. The first two determine charge current and the third determines the max input voltage.

 

[time2roll]

I would consider loads more than the solar to determine 12 or 24 volt battery. 2000w inverter is fine at 12 volts, 3000 watts inverter is better with 24.

If this is just what voltage panels to buy.... I would go 24v panels unless fitment was an issue to need physically smaller 12v.

 

[orangezero]

Use a good MPPT controller and completely ignore any reference to "12V" or "24V" panels. Those are meaningless terms at that point. Focus on how much wattage you need. That's all that matters. Then find a good deal on panels that meet your total wattage needs. Then decide how you need to arrange them. This should also factor into how many panels you buy. For example, 5 panels is a terrible number to get. 2, 3, 4, 6, 8, 9, 10 panels are good numbers because they allow for lots of options (series/parallel). Then finally you can determine the best sized MPPT controller to get based on your system voltage, total panel wattage, and panel arrangement. The first two determine charge current and the third determines the max input voltage.

I bet the reference to 12v and 24v panels is because when you look at prices of used panels, 60 cell solar panels can be 1/4 the price of 36 cell solar panels. I had my heart set on these cool, thin, all-black glass solar panels only to discover the open circuit voltage would require equipment that is 5x more expensive than the electronics I wanted to use. And the mounting hardware was all custom and expensive. So often I could get 80% of the project together only to discover no one does it that way because the last 20% either doesn't exist or is too expensive.

To the original poster, one thing is to consider is if you want to use any 19v DC or 24v DC items at all. Some new televisions and many computers and laptops now run on 19v or similar, and not having to use an inverter to run those things would perhaps be more efficient. If everything you use is 12v DC, and your inverter use is low, 12v battery is certainly fine. But to confuse it more, you could always use a DC-DC boost converter to get 12v to 19v to power those things. I guess another reason to point towards 12v is the bms may be less expensive, not sure though.

Someone correct me on this, but I believe the physics answer to this is that 12v x 200a is 2.4kw. At 24v it would only need to carry 100a through your cables and less likely to heat up. So if you don't use the inverter at capacity much, this is a moot point.

 

[JWLV]

Start with 24V and you'll be glad that you did. Eventually you may want to go 48V, but that's much later down the line. But if you start at 12V, you'll be thinking "man, I should have started with 24V" in a short while.

 

[orangezero]

Start with 24V and you'll be glad that you did. Eventually you may want to go 48V, but that's much later down the line. But if you start at 12V, you'll be thinking "man, I should have started with 24V" in a short while.

Really, though, only if he ever needs more than a 1500-2000watts. What am I saying? I'll show myself out...

 

[pollenface]

24v lets you double the size of your PV array with any 12-24v SCC, so essentially you get more bang for your buck.

 

[quadna71]

Well this is just for the roof of my shed, lights and garage door opener are likely the largest loads it’ll see, and the inverter will only be used occasionally to charge up my 60v lawn equipment batteries. I think I’ll keep it simple and stick with 12v. Man you guys are smarter at this stuff than I’ll ever be!!!

 

[pollenface]

Don't cut yourself short by thinking it's ONLY going to be for a few small things. It will become an obsession and you'll want to add to it and do more with it as time goes on. Think BIG

Personally I have two 12v circuits and one 24v circuit all with separate battery banks, chargers, inverters, arrays, etc, The 24v system is my primary system which runs a 3kw inverter to power my workshop/garage. I started with one battery, one panel and a 500w inverter ... then it became an obsession.

 

[pellicle]

for me its about the Amps ... and I drive an inverter and only really am interested in 240VAC. So 24V is half the amps. This makes less potent cables needed. I feel weird about needing 100Amps flowing just to run a vacuum cleaner.