Server Rack batteries and solar panels in a (short) skoolie.

[PoppaBlade]

Hello everyone! So I recently watched a video from Will that inspired me. I love the idea of having a 24v system with both a growatt all in one system @ 3000w and an EG4 24v server rack battery. My question is, what are my requirements for solar? Do I just need to be wary of the amps/volts (can't remember which one) and not exceed the amount they are rated for?

My previous understanding was that you needed to have (or at least ideally) double the solar panel wattage to your aH. However I don't think I can achieve that on a short bus. I'm looking at around 800 of solar currently. Will that be alright with a server rack battery at around 5kwh? Maybe I'm missing something? Would the same rules apply for a 24v system at 100ah? (For example, if I have 200ah of battery at 24v, would I just need roughly 400w of solar?)

I apologize for all the random numbers and questions, I'm just trying to get a good understanding of what a server rack battery is going to require for a skoolie type build. If the same rules apply from like a 12v system, then I'll be just fine. I just want to make sure.

Thank you for your time! I can't wait to hear from you all.

 

[Rednecktek]

So a couple quick thoughts in no particular order:

1: I find that when you have a limited anything it pays to start from there and work backwards to see what your limits are. In your case you say about 800w of panels. Can you get higher density larger panels up there or are you stuck with 800? Let's assume you are at 800w max, being flat you're going to take a 30% hit on potential so let's call that 600w best case scenario. Guesstimating a 5 hour day of direct sun you're looking at 600w * 5Hrs = 3000Wh best case scenario. Your AIO is going to need about 50w/hour just to exist so let's subtract 50w * 24Hr = 1200Wh going to the AIO. That leaves you about 2Kwh of charge potential. A 100Ah 24v battery is about 2Kw so if you have more battery than that you'll never be able to fully charge your batteries. The AIO is going to need 50Ah of battery on it's own.

2: A sketch with measurements might be handy here.

3: A 100Ah 24v battery will take half the space of a 100Ah rackmount battery. A DIY battery will take only slightly more space than a regular 24v battery for up to 300% more capacity buying you lousy weather buffer. It'll cost you about $1300 for a 24v 300Ah battery, and some time.

4: I'm assuming that you have multiple 12v devices like lights and diesel heater and the like? You'll need a step-down converter large enough to cover all those loads as converters have zip for surge. So if everything firing up all at once is 54a you'll need a 60a unit.

5: Growatt and MPP both have 24v inverters in that wattage range.

6: You really need to do a power audit to figure out what you have to work with. The form over in Resources will help immensely and tell you what size inverter, battery, and solar you'll need. You'll run through it at least 3 times.

The first pass put everything on there. Mini-split heat pump? Sure. Jacuzzi? Why not. MargaritaMaster-9000? Go for it.

The second pass is the "Absolutely NEED this to survive!" where you put in the minimum light bulbs and internet access (because you can't leave us!) and such that you have to have.

The third pass will be the "Reasonably can do this" pass where you'll figure out how close you can get to your goals and where you'll need to tweak. Somewhere in that Venn Diagram of "What I want", "What I can fit" and "What I can afford" you'll come up with your system.

7: This will be completely independent of your starting battery, rrriiigghhtt? If you want to be able to alternator charge you'll need to factor in a DC-DC converter for that as well.

8: Sadly there's really nothing over 1Kw for 12v AIO's and they don't parallel.

9: What's your heating source? The general consensus for heating is "Anything But Solar!" because it's so hard on systems. Have you looked at Diesel Heaters? They're fantastic for Skoolies, especially when you can run them from the main fuel tank and they're cheap! (I know WAY too much about those, feel free to ask.)

OK, I think that's enough rambling for now. ?

 

[PoppaBlade]

So a couple quick thoughts in no particular order:

1: I find that when you have a limited anything it pays to start from there and work backwards to see what your limits are. In your case you say about 800w of panels. Can you get higher density larger panels up there or are you stuck with 800? Let's assume you are at 800w max, being flat you're going to take a 30% hit on potential so let's call that 600w best case scenario. Guesstimating a 5 hour day of direct sun you're looking at 600w * 5Hrs = 3000Wh best case scenario. Your AIO is going to need about 50w/hour just to exist so let's subtract 50w * 24Hr = 1200Wh going to the AIO. That leaves you about 2Kwh of charge potential. A 100Ah 24v battery is about 2Kw so if you have more battery than that you'll never be able to fully charge your batteries. The AIO is going to need 50Ah of battery on it's own.

2: A sketch with measurements might be handy here.

3: A 100Ah 24v battery will take half the space of a 100Ah rackmount battery. A DIY battery will take only slightly more space than a regular 24v battery for up to 300% more capacity buying you lousy weather buffer. It'll cost you about $1300 for a 24v 300Ah battery, and some time.

4: I'm assuming that you have multiple 12v devices like lights and diesel heater and the like? You'll need a step-down converter large enough to cover all those loads as converters have zip for surge. So if everything firing up all at once is 54a you'll need a 60a unit.

5: Growatt and MPP both have 24v inverters in that wattage range.

6: You really need to do a power audit to figure out what you have to work with. The form over in Resources will help immensely and tell you what size inverter, battery, and solar you'll need. You'll run through it at least 3 times.

The first pass put everything on there. Mini-split heat pump? Sure. Jacuzzi? Why not. MargaritaMaster-9000? Go for it.

The second pass is the "Absolutely NEED this to survive!" where you put in the minimum light bulbs and internet access (because you can't leave us!) and such that you have to have.

The third pass will be the "Reasonably can do this" pass where you'll figure out how close you can get to your goals and where you'll need to tweak. Somewhere in that Venn Diagram of "What I want", "What I can fit" and "What I can afford" you'll come up with your system.

7: This will be completely independent of your starting battery, rrriiigghhtt? If you want to be able to alternator charge you'll need to factor in a DC-DC converter for that as well.

8: Sadly there's really nothing over 1Kw for 12v AIO's and they don't parallel.

9: What's your heating source? The general consensus for heating is "Anything But Solar!" because it's so hard on systems. Have you looked at Diesel Heaters? They're fantastic for Skoolies, especially when you can run them from the main fuel tank and they're cheap! (I know WAY too much about those, feel free to ask.)

OK, I think that's enough rambling for now. ?

Thank you so much! Ok, so a couple of things:

-i was under the impression that a 100ah 24,v was either close to, or at 5kwh. Maybe that's a 200ah 24v? I'm talking EG4 server rack battery

-my original choice in battery was 2x - 200ah SOK batteries bc they are reliable and not super overpriced. I've since changed to this 24v setup bc it's cheaper and maybe better?

-Being that I have a short bus, I think I can only fit 2 MAAAAAYBE 3 400w panels on top.

-heating source will definitely be diesel heater

-i plan on using Growatt (3000w) as my inverter

-as for 12v things, I don't want to step down too much, but if need be then that's what I'll do. I guess overall I'm having a hard time converting myself to 24v lol. Maybe it's not as hard as I'm making it out to be? I just don't wanna screw things up when I go plugging things together. I still haven't bought anything, so I'm good there. Just trying to understand this 24v stuff first.

Thank you again! If you need more details or any more suggestions lmk! Thanks.

 

[Rednecktek]

Thank you so much! Ok, so a couple of things:

-i was under the impression that a 100ah 24,v was either close to, or at 5kwh. Maybe that's a 200ah 24v? I'm talking EG4 server rack battery

200Ah * 24v = 100Ah * 48v = 400Ah * 12v = 5.2Kwh

-my original choice in battery was 2x - 200ah SOK batteries bc they are reliable and not super overpriced. I've since changed to this 24v setup bc it's cheaper and maybe better?

Will has done a LOT of reviews on cheaper batteries and been impressed by some of them. Might save you quite a few bucks over the SOK's. Maybe peruse some of the threads on other batteries.

-Being that I have a short bus, I think I can only fit 2 MAAAAAYBE 3 400w panels on top.

Hope for 3 if you can do it, or 4 if the combined wattage works out on smaller panels (I.E 4x 250w VS 2x 400w) If you go with 3 you'll need fuses for each string or a combiner box, but if you can get 4 you can roll a 2s2p and no fuses needed.

-heating source will definitely be diesel heater

Gods I love those things. ? You want a copy of my cleaning and service guide?

-i plan on using Growatt (3000w) as my inverter

Good plan. It's got that little bit more output than many other brands for 24v.

-as for 12v things, I don't want to step down too much, but if need be then that's what I'll do. I guess overall I'm having a hard time converting myself to 24v lol. Maybe it's not as hard as I'm making it out to be? I just don't wanna screw things up when I go plugging things together. I still haven't bought anything, so I'm good there. Just trying to understand this 24v stuff first.

Totally understandable. Basically you've already (probably) got a 12v bus and fuse block and the like, so you'd just install the converter as another 24v device right off the battery (like the AIO) and connect it's output to the 12v bus block. It's 3 extra screws. The hardest part is figuring out what size you need. I found a uxcell 60a unit online for a good price and 60a of 12v is a lot. Remember that when you're figuring out the sizing, that diesel heater is going to need 15a for start up with the glow plug.

Thank you again! If you need more details or any more suggestions lmk! Thanks.

We're here to help.

Make sure you get a separate shunt to keep an eye on your battery state and charging. The built-in units just go by voltage which is pretty worthless for LFP.

 

[PoppaBlade]

Well the biggest reason I want a server rack battery is because it's cheaper with more to it. I won't have to run a crazy setup with just the growatt and a server rack battery. Bc both of those items have things like a breaker already installed on them. Well I know the server rack battery does. The growatt has something else that's really handy as well, can't remember what though.

Sure I'll have a couple fuse things here, wiring for solar panels, and wiring for lights but beyond that it's such ab affordable and easy setup, that's the route I want to go. Figure I could scale up with 2 server rack batteries later on maybe.

The solar panel dilemma is a bit different. I'll just have to keep my eyes open I suppose.

I'll peruse the forum a bit more and see if I can't find some links/charts/ etc to help me answer my questions more clearly.

I'm still learning a lot, but I know what I want and I am getting close to knowing how I'm going to get it lol.

 

[Rednecktek]

Well the biggest reason I want a server rack battery is because it's cheaper with more to it. I won't have to run a crazy setup with just the growatt and a server rack battery. Bc both of those items have things like a breaker already installed on them. Well I know the server rack battery does. The growatt has something else that's really handy as well, can't remember what though.

A server rack battery, a Growatt, and a set of panels is a good start! It's simple and that's a good thing. The cheapest way (or at least the most cost effective way) is to roll your own battery out of 8 cells and a BMS. It really is simpler than you would think and I freely admit I was nervous my first time, and I've done 5 now. The Growatt lets you turn off the unit but the charge controller still runs so even if it's off it'll charge the batteries.

Sure I'll have a couple fuse things here, wiring for solar panels, and wiring for lights but beyond that it's such ab affordable and easy setup, that's the route I want to go. Figure I could scale up with 2 server rack batteries later on maybe.

Yeah, depending on how insane you want to get with fuses and disconnects and such it can be simple to overly complicated. If you go with 2 panels/strings no fuses needed, but if you go with 3 you'll need fuses or a combiner box (I would recommend that as the inline MC4 fuses are notorious) to bring those together. The battery has a breaker already, so all you need for a 2 panel setup would be one from the battery to the 24v->12v converter, one from the panels to the AIO (for safety and troubleshooting), and the breakers in your AC panel.

The solar panel dilemma is a bit different. I'll just have to keep my eyes open I suppose.

If you get a chance to grab a ladder and a tape measure, put together a drawing showing what the roof looks like and we might be able to find a better option.

I'll peruse the forum a bit more and see if I can't find some links/charts/ etc to help me answer my questions more clearly.

Ask away in here too, don't panic. You're just starting the process so exact questions are up next anyways so feel free to ask.

I'm still learning a lot, but I know what I want and I am getting close to knowing how I'm going to get it lol.

Learning is good! You've got a good start on a medium size system so now it's just a matter of fine tuning the parts list.

 

[PoppaBlade]

A server rack battery, a Growatt, and a set of panels is a good start! It's simple and that's a good thing. The cheapest way (or at least the most cost effective way) is to roll your own battery out of 8 cells and a BMS. It really is simpler than you would think and I freely admit I was nervous my first time, and I've done 5 now. The Growatt lets you turn off the unit but the charge controller still runs so even if it's off it'll charge the batteries.

Yeah, depending on how insane you want to get with fuses and disconnects and such it can be simple to overly complicated. If you go with 2 panels/strings no fuses needed, but if you go with 3 you'll need fuses or a combiner box (I would recommend that as the inline MC4 fuses are notorious) to bring those together. The battery has a breaker already, so all you need for a 2 panel setup would be one from the battery to the 24v->12v converter, one from the panels to the AIO (for safety and troubleshooting), and the breakers in your AC panel.

If you get a chance to grab a ladder and a tape measure, put together a drawing showing what the roof looks like and we might be able to find a better option.

Ask away in here too, don't panic. You're just starting the process so exact questions are up next anyways so feel free to ask.

Learning is good! You've got a good start on a medium size system so now it's just a matter of fine tuning the parts list.

Ok, I just want to understand one thing now that I can't seem to get a good answer on.

That is...do my solar panels still need to be double in wattage vs my AH of batteries? For example: if I have 400ah of battery, I'll want 800w of solar, correct? The reason being, is to keep my battery levels sustainable right? Or maybe it just depends on my usage?

Also... because I have "battery charge anxiety" I fully intend on having a decent (budget friendly) generator as well as a portable power station for emergencies or for cloudy days and such.

I'd love to get maybe 2 server rack batteries if it makes sense, but then I'm not sure what my solar panels should be.

Thanks everyone for your comments!

 

[Tomthumb62]

A 100Ah 24v battery is about 2Kw so if you have more battery than that you'll never be able to fully charge your batteries. The AIO is going to need 50Ah of battery on it's own.

Not sure of OP’s intent, but some people will oversize their battery even though their solar can’t keep up. This gives them some cloudy day storage that will help them get through until they can plug into shore power to fully recharge. On a skoolie that’s intended to be mobile, this could be a good idea.

But I generally agree with your logic and it really helps keep the expectations in line; ie, not expecting your solar array to fully charge a battery bank when the reality is that the bank is too large to be charged to 100% by solar alone