2200 watts of solar on the roof?

MTVR

Well-known member
If I'm doing the math right, we would be able to fit 22 Renogy Monocrystaline Compact 100-watt solar panels on our roof. Our roof would be 192" long, and 102" wide. We should even have room for a roof vent located between the two panels that are sideways.

I would be inclined to build our battery bank out of AGM batteries- we just can't justify the expense of lithium on this scale. Our MTVR has a 30,000-pound payload capacity, so the concerns about weight aren't as much of a concern for us as they would be for most people.

Our truck has a 150-amp 24-volt large case alternator, and we would probably use a DC to DC charger to harness whatever is available when the truck is running, but we do not plan to run the truck's engine just for the purpose of creating electrons.

I would not be inclined to have one massive pure sine wave inverter- We'd probably have a smaller pure sine wave inverter to run sensitive stuff off of, and then a giant cheap one to run the high-powered stuff off of.

I'm assuming that there would be enough heat from the electrical components, that we'd want to have fan(s) ventilating our electronics cabinet with outside air.

So what would the rest of our solar system look like, in terms of sizing the battery bank, solar charge controller(s), etc.?
 

glennm01

Member
An array that large will be a lot more cost-effective and simple using 24volt panels. You can get single panels in the 300-400 watts range, so you need fewer panels, which means a much simpler mounting solution, much less wiring, the panels are cheaper per watt, charge controller will be a lot cheaper, etc... Once you get over 500 watts or so, I think 24 volt starts to make real sense.
 

Alloy

Well-known member
We run 8x330W@70V (best $ vs. efficiency at the time) Panasonic all in parallel. Splitting the system between portable and roof top has worked for us.

Keep the solar panels in from the edges of the roof/away from tree branches.

Our inverters are 3000W and a 600W. Both pure sine wave.

What benefit do you see in AGM over FLA? Lithium shouldn't be discounted due to initial price.

The size / location (outside wall) of the cabinet will dictate if forced air is needed. Outside air introduces dust/debris.
 

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Joe917

Explorer
Yes it can be done. Don't use 100 watt Renogy 100 Watt, use big residential panels, 300 Watts plus each. We run 2X330 W.
Do you need 2200 W? What are your power requirements? Microwave , induction cook top, Air con? (if yes to these then yes to 2200 Watt)
Budget is an issue go FLA golf cart batteries (they will perform better and cost less than AGM). Go with a quality coulomb counting meter and charge controllers(MorningStar )
You comment that weight is not an issue, just because the truck can carry it does not mean you should load it to the nuts. A lighter vehicle will always perform better than the same heavier vehicle , all those don't matter decisions will add up to tonnes at the end.
 

luthj

Engineer In Residence
The size of system you are building may justify paying a professional to help you flesh out the design, and choose components. There may be good reasons to go with a 24V system. You may need multiple parallel controllers and inverters, etc. This is moving from the typical small system seen in a 4x4, to a boat or even off grid home design.

In addition to cooling the component compartment, there can be unique wiring and fusing requirements for large battery banks. Same goes for solar arrays. A 2kw array may have fault currents large enough to cause fires, so proper fusing and wire types/sizes are a must. For optimal output there is a number of considerations at play, wire gauge, controller efficiency, shading (roof mounted gear, etc).
 

dreadlocks

Well-known member
+1 on house panels, check out Panasonic HIT's if your going to spend alot of time in hot areas, Ive been following your build and im sure your wanting to flat mount the panels w/no room for circulation under em, so getting panels w/great heat coefficient is going to reward you as the hotter panels get the less wattage they output.. if your going to cover roof in panels keep in mind anything extending past roof line will cast shade, even power vents.. best to not have any of that if you can help it, if you can do power vents out the side and leave the roof to just solar only then you'll have an easier time getting all the panels full sun and utilizing that high output your investing in..

+1 on GC2 batteries, build your system so you can go LFP later down the line.. so make sure all charge sources are fully adjustable and customizable.. you also would need far less lithium than lead, espically with a huge solar array.. I've got 650W for 100AH of LFP@12V and its pretty damn sweet, I would think 200AH@24v would be all needed for a 2kw solar, thats alot of energy to get through the night and durring the day you'd be full in a few hours and everything else the solar is producing can go to day time loads.. with a huge solar array you dont need a huge LFP bank since it can take high charge rates in stride.. it just needs to be large enough to buffer energy overnight, maybe a full day if your only getting a few hours of sun a day, not days/weeks.

+1 on high safety factor on a system such as this, well beyond what most of us here are dealing with.. on a portable platform there's lots of room for catastraphic failures.
 
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Peter_n_Margaret

Adventurer
I agree with the AGM choice if weight is not an issue. I have had 5 years use out of AGMs while full time on the road and 9 years with more "normal' use while operating a mostly electric house (diesel for hot water and central heating and gas for cooking only).
Getting rid of gas and going for an induction cook top is the next step and I can do that with 600Ah (@12V) of AGMs (enough to restrict voltage drop) for a fraction of the cost of Lithium.
There is also the benefit of being able to remove an dud AGM from the bank without killing the whole system. Not always possible with Li.
The fact is though, the more solar you have the less batteries you need. The batteries only need to supply power when the sun does not shine and you still have the alternator for emergencies.
As far as solar controllers go, there is good sense in multiple smaller controllers (all feeding the same batteries) to provide some redundancy, just like having multiple inverters.
Cheers,
Peter
OKA196 motorhome
 

Alloy

Well-known member
The size of system you are building may justify paying a professional to help you flesh out the design, and choose components. There may be good reasons to go with a 24V system. You may need multiple parallel controllers and inverters, etc. This is moving from the typical small system seen in a 4x4, to a boat or even off grid home design.

In addition to cooling the component compartment, there can be unique wiring and fusing requirements for large battery banks. Same goes for solar arrays. A 2kw array may have fault currents large enough to cause fires, so proper fusing and wire types/sizes are a must. For optimal output there is a number of considerations at play, wire gauge, controller efficiency, shading (roof mounted gear, etc).
Yes, I forgot about going with a higher voltage....even 48V. It will makes everything more efficent. I would have done it but we already had four 12v motors that draw 70A each.
 

rayra

Expedition Leader
neat. So your shelter is some sort of cab-over arrangement? Real nice part of a full solar array up there is that it will shade your shelter.


I have (5) New Old Stock Prowatt800 24V inverters, if you are interested.
 

MTVR

Well-known member
I was looking at those particular 100-watt panels because using them allowed me to fit the most power on the roof.

What configuration of larger panels would allow us to put that much solar up there?
 
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MTVR

Well-known member
Our electrical needs during the dark would not necessarily be a lot. But if we are somewhere hot, I'd like to see how much we could run the A/C every day.

So we don't necessarily need to store a lot of electricity, but we may need to use a lot of electricity during the hottest part of the day.

If the required size of our battery bank is not massive, then we may be able to afford to do lithium.

Otherwise, we're looking at AGM, with standard lead-acid batteries still up for discussion.
 

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MTVR

Well-known member
I don't object to configuring at 24 volts- after all, our truck is 24 volt, so I'm guessing the DC to DC charging would be simpler.

Are any of the components required to configure at 24 volts, going to be more expensive than if I stuck to 12 volts?
 

dreadlocks

Well-known member
The Panasonic HIT's have a higher efficiency rating, higher efficiency rating == more watts in less space, if your trying to cram the most solar wattage you can.. you will have more wattage on the roof with 20% efficient panels than you will with 16% efficent pannels.. if you buy house panels in bulk you can get more wattage for less money from a higher quality source.

During the day if the sun's shining right on your rig running a "small" aircon may be feasible, you need to minimize all losses and realize only a few hours a day its gonna be doing full output, if even.. get a nice, high efficiency split unit that would be happy to run at 75% output of your solar and you should make it work reasonably well, at least June-Aug with long days and high sun.

Higher the voltage the better w/this system, a 5% loss w/100W solar nothing to sweat.. only 5W, its 100W at your level, thats significant.. 24v would be bare minimum IMO, if anything I'd look at 48v

AGM is lead, really nothing special about it other than it costs more money.. GC2's are cheap, robust, and disposable lead batteries that are likely to last just as long as AGM, perform just as well as AGM, and cost a fraction of AGM.. IMO AGM is a bunch of snake oil, for most people paying more money for AGM is fundamentally the equivalent of running ultra-premium race fuel in a bone stock Geo Metro.. functionally just burning money.

Lithium takes up to 0.4C charge rate (1C = Capacity in AH), so for a 200AH LFP bank @ 24V thats 80A (1920W) of charge current it will take from empty, til its completely full.. no tailing absorb charge or any of that.. that results in a full charge from empty to full in about 2.5-3h at that rate.. so if you drain the battery flat (5%) every night, after ~3h of sunlight it'll be 100% full.. or if you drive your rig or run the engine for a couple hours to completely refill it.. compared this to AGM or FLA and your looking at 6-7h minimum to get from 50% to 100%.. that means you need full days of sun shining, full days of driving, and a huge bank to compensate for the days/weeks that is not achievable.. 2-3h of sunlight a day, or a full day of diffuse light for LFP is much easier to accomplish.

LFP is also nearly 100% efficient at energy IO, if you put 100AH into it you get 100AH back out of it.. with lead chemistries, you'll have to put >120AH in it to get 100AH back out of it.. and its variable on loads, a 100AH for a 10A load will turn into like 60AH with a 150A load, those inefficiencies that make huge lead banks a requirement.
 
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