diy solar

diy solar

Shipping container design

Torkrench

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Joined
Oct 30, 2019
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7
I am planning an installation in a shipping container used as a small office. The unit is going to be completely off-grid, with a 2kw generator as a backup.

What I need the system to do:
Power an 8000 BTU A/C during the day in the sun (1000W roughly)
Power a small microwave occasionally (We can turn off A/C to run microwave if needed)
Power 3-4 IP cameras, NVR, POE Switch for 2 outdoor wireless point-to-point devices
Power a 32" LED TV for camera monitoring during the day
Provide power for charging of phones and tablets

Equipment I'm thinking of using:
4 3.5KWh 24V LifePo4 battery packs in series-parallel for 14KWh at 48V
3kw/9KW 48V hybrid inverter/MPPT charger
12 245W solar panels in 4 parallel banks of 3 panels in series


Obviously I'll need some BMS setup. I'm thinking of using 2 seperate 16-cell BMS's set up so that either pair of 24v batteries can shut down if there is a cell problem leaving the other pair connected. Any recommendation on a BMS setup that would handle this?

I'll also need a way to connect the panels to the system. Amazon sells some interesting solar combiner boxes with distribution and circuit breakers installed. Has anyone had any experience with these? I figure each bank of panels will produce an open voltage of 112.5V and figuring 245W panels, that should put the load on each bank at 6.5A with a total theoretical load through the PV cables being about 26A. I know my numbers are all assuming 100% efficiency which won't happen, but it makes the math easier. The cable run between panels and inverter won't be longer than 15 feet. With all of this being the case, I'm thinking wire gauge should be 10AWG between panels and 6AWG or 8AWG between the combiner and inverter.


Any feedback anyone here might be able to provide would be greatly appreciated. Let me know if I've made any mistakes in my planning so far. If there are better options for any of this I'm open to that as well. Nothing has been purchased yet, so nothing is set in stone.

Thanks everyone.
 
The air conditioner would appear to be well over 80 percent of the load.
This is the thing to optimise if possible.
What is the make and model of the AC unit?
Is a swamp cooler an option?
How bout passive cooling
It's a metal container in the middle of a field in central California. During the summer, there's no way the anything short of running an air conditioner all day is going to make it habitable for someone. It'll be insulated which will help a little bit, as well as sitting under the shade of it's in solar panels, but we're taking about ambient 3 digit temps with direct sun beating down on a big metal box.

I just double checked and the air conditioner is only 5000btu which may even be too small to keep it cool, but that's why I am over-planning the system.

I figure as long as the solar can top off the batteries in the morning before the AC gets turned on, then a 3KW solar system should be able to handle the 1KW of average usage most of the day. In the afternoon as the panels start to lose sun, the batteries might have to step in and provide power to finish the day. Fortunately we are in an area that cools in the evening for most of the summer, so the AC will probably be off before the panels stop producing. There are no trees anywhere on the property, so the panels will get unobstructed sunlight the entire day.
 
3 digit temps with direct sun beating down on a big metal box.
You can make a shade canopy for a couple hundred bucks using Aluminet. Easiest is to drape it over your container, put some foam swim noodles between Aluminet and container for a little air space.
I understand you want your panels on top too to provide shade and capture sun. Running a Aluminet around the sunny sides and exposed roof (if any) will help a lot.


Otherwise, i really like swamp coolers. You shouldn't have any moisture issues if your locale description is accurate.

Or can you partially bury the container or stack hay bales around it?
 
The location it is in gets regular sustained winds of 20-30mph with gusts much higher occasionally. I'm pretty sure Aluminet wouldn't last very long being battered by the winds. A swamp cooler would probably make it cool enough not to die inside, but it still wouldn't be comfortable enough for 1 or 2 people to be in all day. They would also have to get water from the water truck regularly in order to feed the swamp cooler. It's just not worth the hassle.

They are ready to spend about 10k on the whole system since getting power out to the site would be much more expensive and the generator they are running right now takes about 10 gallons of diesel a day and they run it 6 days a week. At almost $4.00 per gallon, thats $240 a week. Doesn't take long to justify the cost of the solar system. Also, the generator is off at night, so no cameras or lights when no one is there.
 
If we want to get a little 'out there' Earth tubes might be an interesting alternative as well.
 
I am well acquainted with the central valley.
My thoughts are The AC will be used primarily in the day so even if you need 5 more panels, so what that would power the AC during the day and the other panels can run everything else and charge the batteries.. the problem will be at night where it doesn't cool much but with 14Kw of storage you could get quite a bit of Ac going but maybe not 24/7 however with good insulation you may be able to cut night time usage in half and get by.

Im not too far away and am glad to help if necessary.
 
Well if the AC uses about 1kw and the solar produces 3kw peak(I know they will produce more like 2-2.5kw peak and only for a small part of the day) then that leaves 2kw(1-1.5kw) for other items inside. All of the other devices total will probably draw 400-500w. Plenty of overhead I think. We could add more panels if needed like you said. It's at the base of the Altamont, so winds are a very real concern. I'm even a little worried about the solar panels becoming sails if mounted at an angle. At night, no one is there, so no AC needed. At night, the only draw on the system would be the internet equipment(2 Ubiquiti wireless devices), cameras, and motion led lights.

I've had decent luck with swamp coolers out here. I've got one in my shop and it keeps it very comfortable during the summer when it's over 100 outside. It does have a water feed from the cool well water though, so that helps a little bit. I just know in the container, it just wouldn't be enough. It's also nice to have a cool place to come in out of the heat for breaks/lunch.

I feel I'm being pretty realistic with my numbers, but I've not done a system like this before, so if I'm over-estimating things, feel free to let me know.
 
The altamont pass was one of the early large wind farm areas...... Dare I say it....... Put up a windmill?:LOL:
 
At some point, as a business, it costs more to worry about it than to just put in a large system.
 
Well if the AC uses about 1kw and the solar produces 3kw peak(I know they will produce more like 2-2.5kw peak and only for a small part of the day) then that leaves 2kw(1-1.5kw) for other items inside. All of the other devices total will probably draw 400-500w. Plenty of overhead I think. We could add more panels if needed like you said. It's at the base of the Altamont, so winds are a very real concern. I'm even a little worried about the solar panels becoming sails if mounted at an angle. At night, no one is there, so no AC needed. At night, the only draw on the system would be the internet equipment(2 Ubiquiti wireless devices), cameras, and motion led lights.

I've had decent luck with swamp coolers out here. I've got one in my shop and it keeps it very comfortable during the summer when it's over 100 outside. It does have a water feed from the cool well water though, so that helps a little bit. I just know in the container, it just wouldn't be enough. It's also nice to have a cool place to come in out of the heat for breaks/lunch.

I feel I'm being pretty realistic with my numbers, but I've not done a system like this before, so if I'm over-estimating things, feel free to let me know.
So you are in Tracy or Mountain House?
 
It's at the base of the Altamont, so winds are a very real concern. I'm even a little worried about the solar panels becoming sails if mounted at an angle.

I researched this when my sister was investigating solar for her place in St John Virgin Islands where they get hurricanes. Most commercial solar racking systems will withstand any wind you will see near Altamont. (As long as they are properly installed). I guess the bigger concern would be tipping over the container but that should be easily prevented if it is anchored to a decent concrete pad.
 
It's a metal container in the middle of a field in central California. During the summer, there's no way the anything short of running an air conditioner all day is going to make it habitable for someone. It'll be insulated which will help a little bit, as well as sitting under the shade of it's in solar panels, but we're taking about ambient 3 digit temps with direct sun beating down on a big metal box.

I just double checked and the air conditioner is only 5000btu which may even be too small to keep it cool, but that's why I am over-planning the system.

I figure as long as the solar can top off the batteries in the morning before the AC gets turned on, then a 3KW solar system should be able to handle the 1KW of average usage most of the day. In the afternoon as the panels start to lose sun, the batteries might have to step in and provide power to finish the day. Fortunately we are in an area that cools in the evening for most of the summer, so the AC will probably be off before the panels stop producing. There are no trees anywhere on the property, so the panels will get unobstructed sunlight the entire day.

Not sure if you have a 20 or 40 foot container BUT either way 5000 BTU "may" not work for you ... IF it is well insulated on the OUTSIDE then maybe but here in S. Texas we have several of those 40 foot container offices and it get around 105 here in the summer by 1100 and the 5000's just can't keep up ... At best it will get it down to maybe 85 or so ... so we use allot of 12-15000 units ... NOW here's the "gotcha" ... IF you are insulating them really well on the outside - anything to keep the sun from hitting it directly on the side and roof then a 12-15000 is an overkill and although it will make the container damn comfortable - the A/C will not be running enough to draw out the humidity ... so its really a flip ... anyway .. put the A/C on the narrowest part of the container and as high up as possible -- warm air rises -- cool sinks ... for the real senior folks out here with the fancy container offices the guys mount 15000 BTU Coleman A/Cs on the roof -- the same ones the R/Vs use .. and they work great ... and much easier to mount then a window unit .. and easier to work on if needed ...
 
They are ready to spend about 10k on the whole system since getting power out to the site would be much more expensive and the generator they are running right now takes about 10 gallons of diesel a day and they run it 6 days a week. At almost $4.00 per gallon, thats $240 a week. Doesn't take long to justify the cost of the solar system. Also, the generator is off at night, so no cameras or lights when no one is there.

If you are already powering the load off of a generator then you should have good numbers.
5000 btu seems small for a 40 foot container.
It is 40 foot?
 
So you are in Tracy or Mountain House?
Tracy, out near 580.

I researched this when my sister was investigating solar for her place in St John Virgin Islands where they get hurricanes. Most commercial solar racking systems will withstand any wind you will see near Altamont. (As long as they are properly installed). I guess the bigger concern would be tipping over the container but that should be easily prevented if it is anchored to a decent concrete pad.
I don't think there will be enough surface area to tip the container. The bigger problem may actually be people messing with the panels at night. We might do a skirt around the top to make it look less like there is something up there.

Not sure if you have a 20 or 40 foot container BUT either way 5000 BTU "may" not work for you ... IF it is well insulated on the OUTSIDE then maybe but here in S. Texas we have several of those 40 foot container offices and it get around 105 here in the summer by 1100 and the 5000's just can't keep up ... At best it will get it down to maybe 85 or so ... so we use allot of 12-15000 units ... NOW here's the "gotcha" ... IF you are insulating them really well on the outside - anything to keep the sun from hitting it directly on the side and roof then a 12-15000 is an overkill and although it will make the container damn comfortable - the A/C will not be running enough to draw out the humidity ... so its really a flip ... anyway .. put the A/C on the narrowest part of the container and as high up as possible -- warm air rises -- cool sinks ... for the real senior folks out here with the fancy container offices the guys mount 15000 BTU Coleman A/Cs on the roof -- the same ones the R/Vs use .. and they work great ... and much easier to mount then a window unit .. and easier to work on if needed ...
They are planning on installing foam panels inside the container. Pretty much the entire top will be covered in solar panels, so no direct sunlight on the roof. They just installed an overhang on the north side of the container, so that will shade the entire north wall from sun. That only leaves three walls with direct sunlight. Hopefully the foam will be enough so the AC can handle it.

It's a 20ft container, with a window and door, on the north side in the shade, so we'll see how it works out. I think the cutout for the AC is big enough they could probably squeeze an 8000btu unit in there if we had to. It just had a 5000 in it when they bought it.
 
Tracy, out near 580.


I don't think there will be enough surface area to tip the container. The bigger problem may actually be people messing with the panels at night. We might do a skirt around the top to make it look less like there is something up there.


They are planning on installing foam panels inside the container. Pretty much the entire top will be covered in solar panels, so no direct sunlight on the roof. They just installed an overhang on the north side of the container, so that will shade the entire north wall from sun. That only leaves three walls with direct sunlight. Hopefully the foam will be enough so the AC can handle it.

It's a 20ft container, with a window and door, on the north side in the shade, so we'll see how it works out. I think the cutout for the AC is big enough they could probably squeeze an 8000btu unit in there if we had to. It just had a 5000 in it when they bought it.

If you can have them install the insulation on the OUTSIDE ... we have found that that will dramatically work better then insulation on the inside ... if you insulate inside the metal outside heats up .. and the inside of the container is cold .. and the inner wall starts to sweat like crazy -- and mold ... and mildew ... IF you insulate the outside the metal on the container does not heat up thus the coolness inside causes very little sweat ....
 
If you can have them install the insulation on the OUTSIDE ... we have found that that will dramatically work better then insulation on the inside ... if you insulate inside the metal outside heats up .. and the inside of the container is cold .. and the inner wall starts to sweat like crazy -- and mold ... and mildew ... IF you insulate the outside the metal on the container does not heat up thus the coolness inside causes very little sweat ....
That explains a picture I saw a while back! A guy was spraying insulating foam all over the outside of a container.
 
That explains a picture I saw a while back! A guy was spraying insulating foam all over the outside of a container.

Seriously ... we have found that protecting the outside of the container vs the inside of the container SIGNIFICANTLY lowers our cooling requirement and cuts dramatically down on mold and mildew .. even if you just take sheets of plywood and lay it in front of the container sides it helps .. anything to block direct sunlight ...
 
Have a look at Rapid Wall skirting material. It comes in 12' X 4' pieces. It is 2" foam bonded to a tough plastic layer. I have whaled on it with a carpenters hammer and hardly made a mark on it. It cuts easily with a saw.


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It interlocks on the long edges. You will have to fasten it at intervals to the building to protect against the wind. In my case I screwed it under the cap. I used it against my concrete foundation so it was shorter pieces.

Check with mobile home dealers.
 
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