24v system suggestions please

[Ironbull]

Ok I've seem to have gone down a rabbit hole. My wife ran across a YouTube video on how to build a solar generator and asked my if I could build it, I said sure so she ordered all the stuff per the video instructions.

Well I got to researching this stuff before I proceeded and figured out the setup was all wrong, mainly from lurking here. So anyway I sent what I could back and starting over.

What I'm trying to accomplish is a system for 1.4 kwh per day but rounded up to 1.5. I first began with 12v but now want to go 24v. I currently have 4 x 100w 12v renogy panels. From my very confusing calculations I will need roughly 600w of panels. From my limited understanding, I will also need 450ah battery bank. As for a converter, I'm looking at a Samlex 2000w 24v pure sine wave. Not sure what size CC I need but I'm looking at the Outback 60amp.

My solar insolation numbers are 3.1 for a winter low and average 4.9. I would appreciate if anyone could fill in the blanks or correct any mistakes.

Just for clarity, this will be to power 2 chest freezers, one will be modified for refrigeration use. I pulled the energy data from the manufacturer's for a combined 520kwh per year.

[Sunking]

1.5 Kwh per day with 3.1 Sun Hours requires.

12 volt battery = 1500 x 5 / 12 volts = 625 AH
24 volt battery = 1500 wh x 5 / 12 volts = 312.5 AH

Panel Wattage = 1500 x 1.5 / 3 Sun hours = 750 watts

MPPT Charge Controller @ 12 volt battery = 750 watts / 12 volts = 62.5 amps. 60 amp controller
MPPT CC @ 24 volts = 750 watts / 24 volts = 31.25 amps, 30 amp controller.

Anything else? FWIW ditch the 2 KVA Inverter and make your wife pay for it and build it.

[Ironbull]

Well she actually is paying for it. We know it's an expensive endeavor for such little output, but it's what she wants for peace of mind. Happy wife, happy life so they say....

I do have another question about the panels, since they are 12v panels vs 24v, can they be wired in series and then paralleled to provide the volts needed?

And why do you say ditch the 2k inverter? I realize the freezers combined wont utilize that much power, but thought I might need a little headroom for startup. And possibly use something else during peak hours.

[thastinger]

As a guy who has 2 freezers and a converted freezer (serving as a fridge) all running on an off-grid system, I can tell you that your appliances will draw significantly more power in the summer than they do in the winter.
You'll need to size your inverter to be able to start both units as the same time, probably will only happen once or twice a year but statistically there will be a moment where both units start at the same time, may not be a big deal if you can monitor the system but my system is unattended the majority of the time and I only see it once every couple of weeks.
Your power assumptions are about right assuming you don't plan to run anything else but the 2 units. My converted fridge consumes .5Kwh/day and the freezer is .6 in the winter and as much as 1 in the summer (located in an enclosed garage with is uninsulated).
PSW inverter is correct since you'll be running electric motors with it.
Pay attention to cable sizes, some inverters don't have terminals large enough for big battery cables.
get yourself a kill-a-watt meter and test those appliances out before you start designing the system.
I think that once you consider everything, you may end up with a 48V system, mostly because you'll likely end up at a 2 or 2.5Kwh system once you decide you want to be able to charge a few batteries, maybe run a couple of smaller power tools, couple of lights etc.

[SunEagle]

Well she actually is paying for it. We know it's an expensive endeavor for such little output, but it's what she wants for peace of mind. Happy wife, happy life so they say....

I do have another question about the panels, since they are 12v panels vs 24v, can they be wired in series and then paralleled to provide the volts needed?

And why do you say ditch the 2k inverter? I realize the freezers combined wont utilize that much power, but thought I might need a little headroom for startup. And possibly use something else during peak hours.

The answer to your first question is yes. Wiring 2 12V panels in series is the way to get them to charge a 24v battery system.

The reason to not use a 2k inverter is because:
1) it can draw more than 80 amps at 24v which requires some big wires between the battery and it.
2) the big inverters tend to be very inefficient and will draw up to 5% of it's rating (2000w x 5% = 100 watts) just being turned on.

[Sunking]

The reason to not use a 2k inverter is because:
1) it can draw more than 80 amps at 24v which requires some big wires between the battery and it.
2) the big inverters tend to be very inefficient and will draw up to 5% of it's rating (2000w x 5% = 100 watts) just being turned on.

Both good reasons, but the major reason

3) It would take a 24 volt 800 AH, 1100 pound, $2000 battery to deliver 2000 watts for any meaningful period of time. That would require even more panel wattage and larger controller. So in the end you spend $5000 to generate 20-cents of electricity per day. Then in a few short years you get to replace the 1000 pound $2000 white elephant in the room.

I suspect you want this for emergency power when power is out? If so you have absolutely no need for solar and your wifey wasted a lot of money. All you needed to do that is a Battery Charger > Battery > Inverter.

[Matrix]

Well she actually is paying for it. We know it's an expensive endeavor ... but it's ... .

What's Your budget?

[Ironbull]

How should I wire my panels up? I have 8 12v 100w panels?

Panel specs:
vmp= 18.9
voc= 22.5
imp= 5.29
isc= 5.75

[Sunking]

How should I wire my panels up? I have 8 12v 100w panels?

Panel specs:
vmp= 18.9
voc= 22.5
imp= 5.29
isc= 5.75

Depends on Controller. But here is your answer based on the info you provide.

With 8 panels you only have two options of 2S4P or 4S2P. If you go with 2S4P will require an expensive combiner and fuses By a cheap controller and you will have to wire them 2S4P. Take your pick

Why on earth are you using expensive 12 volt battery panels? Al you did is make more headaches and expense you need not incur. 3 x 250 or 3 x 275 watt panels would have saved you a lot of money on panels, hardware, and trouble.

[thastinger]

Depends on Controller. But here is your answer based on the info you provide.

With 8 panels you only have two options of 2S4P or 4S2P. If you go with 2S4P will require an expensive combiner and fuses By a cheap controller and you will have to wire them 2S4P. Take your pick

Why on earth are you using expensive 12 volt battery panels? Al you did is make more headaches and expense you need not incur. 3 x 250 or 3 x 275 watt panels would have saved you a lot of money on panels, hardware, and trouble.

Why not all in series with a MN200?

[Ironbull]

I already have the panels and I'm trying to make lemonade out of lemons. I forgot to mention, I picked up a Outback flexmax 80 CC.

[Ironbull]

I'm thinking of adding one more panel and doing 3 strings of 3?

[Sunking]

Why not all in series with a MN200?

Because Voc = 22.5 x 8 panels x 1.25 = 225 volts. Now that would work great with a 600 volt controller if there are no shade issues, but a bit pricey considering 600 volt controllers are targeted at larger systems. They would be quite a bit of overkill with lots of room to grow. Works if you can afford it.

[Sunking]

I'm thinking of adding one more panel and doing 3 strings of 3?

That would work pretty good. Just be aware once you put more than 2 parallel string together requires fusing and combiner. Other than that would work out pretty good.

Remember 1-tihng. NO PRIME NUMBER of Panels except 1 and 3, and sometimes 5 on higher voltage controllers. With a Prime number only leaves you 2 configurations and one of them is unacceptable (all in parallel). Otherwise all in series which can work if the controller can handle the voltage.

[Ironbull]

Sinking, how would I achieve that? Something like the midnite combiner with breakers? I had already planned on that so I could have an easy disconnect? Or do you mean something different? Thanks for your patience and help.