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2000 Watt, 24v Off-Grid Solar Power

NickinSac

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Joined
Jan 24, 2022
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I am looking to build something like the https://www.mobile-solarpower.com/2000-watt-24v-solar-system.html
I don't have a need for a 24 to 12 volt appliances.
I plan to build this for off-grid, in case power goes down and to use it occasionally for fair weather outside use.

Are my numbers correct for four panels to this MPPT? It seems close.

I am just planning to change the panels to
Panasonic Evervolt EVPV360K 360 Watt panels. It seems like I can use four of these.
With the remaining components as described on the website above (except the DC converter).

Rated Power (Pmax)¹ 360W
Maximum Power Voltage (Vpm) 36.7V
Maximum Power Current (lpm) 9.82A
Open Circuit Voltage (Voc) 43.9V
Short Circuit Current (lsc) 10.49A
Temperature Coefficient (Pmax) -0.26 %/°C
Temperature Coefficient (Voc) -0.24 %/°C
  • 40 amp MPPT charge controller with over-current protection
    • EPEVER 40 Amp MPPT Solar Charge Controller 150V PV Input Negative Ground
  • 2x or 4x 12v,100 ah LiFePO4 Batteries (wire these 4x batteries in series/parallel to create a large 24v battery bank)
    • Initially, I was thinking to not use batteries, but I think I would need a different MPPT, correct?
  • 1000-3000 watt, 24 volt inverter

  • Battery Protect by victron energy, 100 amp
  • 4 gauge copper wire and lugs/heatshrink
  • 50 amp circuit breaker for the MPPT, 25 amp fuse for the converter
  • Wooden board to mount the components
Thanks in advance
Nick
 
4 360W panels is 1440W. On a 24V system that would mean up to 60A of charge current. So a 40A charge controller is a bit small. With a 60 charge controller you will need 6AWG wire and a 75A fuse/breaker.

4 of those panels wired in 2S2P would have a Voc of 87.8V. But depending on the lowest temperature you may ever encounter, a 100V SCC may not quite be enough so you might need one that supports a bit more such as 150V. It looks like anything below -25ºC/-13ºF would put you over 100V.

What is the 4AWG wire for? If you choose a 3000W inverter you will need 1AWG, preferably 1/0AWG, and a 200A fuse. If you choose a 2000W inverter you will need 4AWG, preferably 2AWG, and a 125A fuse.

Are you going to have any pure DC loads? You state you won't need a 24V->12V DC converter but later you mention a 25A fuse for a converter. And you have a battery protect listed which should only be used for the DC loads.
 
Thank you for the reply.

TEMPS
I am in Northern California, I don't think we ever get below -2C (hardly ever below 30F) where I am. We have gone to 48C (118 F) though.

MPPT
The Epever shows it is 150v at 40 amps.

There is this (cheap$99) one on amazon - https://www.amazon.com/PowMr-Controller-Backlight-Battery【Software-Version】/dp/B0719PGGBS/ref=sr_1_19?crid=31OEUP4X5MKS8&keywords=Victron|SmartSolar+MPPT+mppt+60+amp+charge+controller&qid=1643159438&sprefix=victron+smartsolar+mppt+mppt+60+amp+charge+controller,aps,131&sr=8-19
Claiming to do 60 amp at 12V or 24V or 48 at 160VDC max input.

I think I would go for something more like this ($188):
60Amp 24V Max 150V input - 1700 Watt

INVERTER
I was thinking of going with 2000W inverter. I just would hate to kick myself in the rear if this isn't enough some day. I don't have specific plans for AC equipment.
I would like to power my pool pump, but that probably won't happen by me (it's 220V AC - 1100W - and a spinup).
I definetely want to power my pellet grill (700Watt). I presume it will jump to 1400 or 1200 when it ignites the pellets.
Maybe a projector, some LED lights at night.

I will change it to 2AWG, and a 125A fuse 2000 W inverter.

DC to DC
I do not plan to have any DC to DC loads. I thought I would need the battery protect from themselves?!? I guess not. :)
I would remove the 25A fuse and battery protect.

Thank you for your feedback!
I appreciate it
Nick
 
The battery protect is normally used to protect the battery from being over-drained by DC loads. Since you won't have any you don't need it.

When you look at inverters make sure the one you choose lets you set a low voltage disconnect. This would allow the inverter to shut itself off if the battery gets too low.

Keep in mind that it's a bad idea to let LiFePO₄ batteries be charged below freezing. So on the rare days you get that cold make sure the charge controller is turned off or get one that will stop itself when it gets too cold.
 
With the 40A SCC:
If you go 2S2P as suggested and angle your panels with one array SSE and the other pair SW you will spread harvest over a longer portion of the day. This will give you more charging closer to sunset potentially giving you more overnight available power from the batteries being that batteries will be ‘full’ an hour or two later in the day.
When you arrange panels like that you do reduce midday harvest, though probably more watt-hours daily. Since your panels will likely produce enough to exceed the 40A SCC output midday (if facing the same direction) this “loss” will not be as dramatic with the panels facing different compass points.
On the other hand, a 60A SCC may result in slightly more midday charge regardless of whether or not you face strings different directions. Wildhat guessing it won’t be a very big difference.

However: if you buy the 60A Epever it will give you headroom to add two or four more panels should you find you need them.
I would probably get the 60A 150V controller to plan ahead, and cable everything as if you had an 80A SCC and 3000W of panels. Then any upgrades don’t mean new cables: just plug in! (80A wasn’t an oversight; I like to oversize high-amp low-voltage cables)
 
When you arrange panels like that you do reduce midday harvest, though probably more watt-hours daily. Since your panels will likely produce enough to exceed the 40A SCC output midday (if facing the same direction) this “loss” will not be as dramatic with the panels facing different compass points.
On the other hand, a 60A SCC may result in slightly more midday charge regardless of whether or not you face strings different directions. Wildhat guessing it won’t be a very big difference.
I am not sure what batteries I would get. At this time, most likely some cheap 12 volts for now. I had big ideas for two 100Ah LIFePos. But, until I have better idea of my draw and how often we use it, I think I will wait for this costly upgrade (relative).

I was wondering if the 40A SCC get's over it's rating will it fry the SCC?
Or is it just a case of me not getting the (potentially) full PV or Amps from the panels?
It sounds like the latter.
 
Why not use an all-in-one inverter? Would make mounting everything much easier.


Seperately, I am looking at $540 for Inverter and MPPT. This doesn't include the all the little copper and connectors that I would need for the separate components.
The first one, seems to only allow 25A at 24 volt. For $642.

Oh boy that Growatt looks REALLY interesting at $769 online.
3KW it looks like it has a split phase 220. :O That could drive my pool pump. I wonder how big batteries will need to be to drive my pool pump 4 hours. oh boy... lots to consider. Dang it...
here goes the snowball and rabbit hole.
Well dang, I didn't look at the fine print, I would need two of the Growatt to get my 220. Darn. I thought that price might be too good to be true.
 
Last edited:
That's very nice, but much bigger than I am willing to do (or need right now).
I am even beginning to wonder if I should pursue 4 panels and just get two (700W).
I will have to do some battery calculations.
 
I was wondering if the 40A SCC get's over it's rating will it fry the SCC?
Or is it just a case of me not getting the (potentially) full PV or Amps from the panels?
It sounds like the latter.
It’s the latter. If your panels can produce more than the rated charge current then the extra potential will go to waste.

What you must never exceed is the max PV input voltage. This is the panel Voc adjusted for the coldest temperature.
 
Some more stuff to look at.

Talking this over with my GF, it looks like the GROWATT is the way to go. She suggested this can go in the shed. The shed is already wired for multiple outlets in the backyard. Seems pretty simple now.

Now, to find a great deal and/or decide to go 24volt or 48 volt. :)

Is there anything significant to consider regarding GFIs?

We have had the GFIs trip in heavy rain. We also have a fountain on these GFIs.

I haven't looked all the way through the manual, on the GROWATT or other inverters, but since, they are not "really" grounded (literally there is not a copper sunk in the ground), is this a concern?
Or do I simply tie in the ground on the inverter to the grid ground (hence really grounded).
 
OK, so it looks like I do indeed need to ground the inverter as seen here:
 
4 panels and just get two
If your panels can produce more than the rated charge current then the extra potential will go to waste will not be able to be used
No disrespect to rmaddy :) but unused watts aren’t ‘wasted’ as much as you didn’t get them stored. Just another way of looking at it (in summer I have a lot of wasted watts!)

I would stick with four panels. Nobody has ever said, “I could really use less solar!”

Since trying the following myself with very, very good results I would suggest 2S2P configuration. For me it was dramatic because it took me from almost not enough overnight to more than enough for overnight (in summer). Same batteries but “not using the batteries” until several hours later towards sunset.

Face one of the 2S series strings SE and the other SW. This ‘reduces’ noontime harvest somewhat but will give you more watts total harvest in one day. And the batteries should remain fully charged a couple hours closer to sunset.
The results will be more daily watts but not leaving as many (or any) watts on the table.
At this time, most likely some cheap 12 volts for now. I had big ideas for two 100Ah LIFePos. But, until I have better idea of my draw and how often we use it, I think I will wait for this costly upgrade (relative).
I use cheap walmartha grp27 flooded marine batteries with good results. 8 of them. If they didn’t perform ok they wouldn’t be worth it. Are there better lead acid batteries? Yes. But at current ~$90/each and treated well they last ok while not going and selling a kidney and they’re easy to get.

3000W inverter is about the max for a 12V battery bank. Unless you have need to power/charge 12V stuff like wifi routers, lights, pumps, etc. 24V makes more sense. If the convenience of 12V is needed or attractive you can do 3000W but the battery cables will be pretty big.

Or do I simply tie in the ground on the inverter to the grid ground (hence really grounded).

The manual should detail that. You can download and read it ahead of time.
Doing this right is a critical safety issue
 
No disrespect to rmaddy :) but unused watts aren’t ‘wasted’ as much as you didn’t get them stored. Just another way of looking at it (in summer I have a lot of wasted watts!)
I'm hurt. ;)

Yeah, "go to waste" isn't the best term. "go unused" is better.
 
If you think you are going to grow the size of the array, I would go with 48v.

Will cost more up-front, but will allow you to expland quite a bit compared to 24v.
 
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