Barn (Off Grid) Where to Start (to grow)

[Farmerbob]

Central Florida (hot) Duke-land. Okay so I built myself a 4000sqft pole barn that’s 500’ from house. Right now it’s got a roof, walls, slab. Next phase is SPF, doors, power. Then HVAC within five years. And ultimately I’d like to potentially run my house off grid, say within the next ten years.



clearly my power demand is going from a few hundred watts now (lights, door operators, fans) really daytime only to a 100,000btu HvAC just for the barn/shop to (hopefully) a house run. Is there a system that I can reasonably add on to over time? My budget to go 100% off grid is $100k (including all downstream wiring which I can DIY with some beer consulting from a electrician friend. Main panel and up, will be the reverse, I will lay conduit and pull wire but I won’t hook it up. Just saw a house down the road from me burn badly due to some PV install screw up.



Back to money, I can’t spend all $100k now and would prefer a lot less. I’m all about efficiency. Ideally I’d like to get the barn set up by the end of the year for under $25k including ability to handle what I assume will be an 8ton minimum HVAC but (using 2020 dollars) I don’t want to waste money so if I spend $25k now I’d like to assume that I can do the rest for $75k (or less) but just hate wasting money on throwing away a partial system.



I’ve talked myself out of a grid tie system as to me it seems a complete waste of money to run a separate meter or upgrade my 200amp house service to the barn. I’ve got plenty of land to put panels and at least until I hook up to the house, I don’t really need to worry about permits since it’s agricultural. Now the need for MEP permits is debatable but let’s assume I can avoid it for this conversation. That said, I want to meet or exceed code. About six years ago I worked for a company that among other things was financing 10MW solar farms and people being electrocuted during construction absolutely happened so electricity definitely has earned my respect.



Questions:

Is there a system that makes sense for all of the above? Should I just separate the house and barn systems forever? Is there a more logical way to phase in this project?

If you made it this far, thank you.

 

[SolarQueen]

Do you have an estimate of how many kWh you will need a day? That's really what will determine if you can do it for that budget.

 

[Jmac786]

500’ is a long way! My driveway is 590’, so it’s a close reference for your barn. I think I would lean to doing two separate systems. This also makes maintenance easier because one system can stay live while the other is worked on.

 

[Farmerbob]

Do you have an estimate of how many kWh you will need a day? That's really what will determine if you can do it for that budget.

Just for the barn. HVAC. In the summer should be ~80,000-100,000btu for ten hours a day. I know that’s not exactly your question but I don’t know and that’s sort of the dilemma. I’m willing to WAG it a bit as long as I can expand. Other than that I’ve got lights and standard tools but nothing crazy. If I want to run a welder I’be already assumed i’ll do that with the HVAC off or in the winter. I’m going to do PV, but trying to nail down the how. I just put a budget number as a ballpark. Would love for it to be less. If it’s more then I’ll just have to plan on sweating more.

 

[Farmerbob]

500’ is a long way! My driveway is 590’, so it’s a close reference for your barn. I think I would lean to doing two separate systems. This also makes maintenance easier because one system can stay live while the other is worked on.

Is maintenance really a big deal? Seems like two systems at 50% of generated power will be tremendously more. I’ve got a 1400’ driveway but I know how to trench so unless the losses are that big that’s not what scares me. Main house panel to closest corner of barn is more like 400’

 

[Dzl]

Is maintenance really a big deal? Seems like two systems at 50% of generated power will be tremendously more. I’ve got a 1400’ driveway but I know how to trench so unless the losses are that big that’s not what scares me. Main house panel to closest corner of barn is more like 400’

Once you get some numbers you can calculate your voltage drop using a calculator like this one and power loss could be calculated using the formula Ploss = I² x R

Also a basic question, why do you want to go off grid? It sounds like you are currently grid connected and 100k is a hell of a lot of money to shell out.

 

[schmism]

Im still not clear on your intent.

It sounds like the house already exists and is on grid.
It sounds like the barn is a shell, and has no power, and you want to get power to it.
Your asking about solar.

For what? Just the barn/shop? For both the barn and the house?

Your asking about expendability. As in just the barn now? With no wire between the house and barn, and then add to the system in the barn to power the house?

I see several options
1) off grid system at the barn for the barn
2) off grid system at the barn for the barn AND that supplies some 120v AC to the house (crtical loads for power outage)
3) off grid system at the barn. second off grid system at the house (at a later point) the 2 never touch.
4) off grid system at the barn for the barn that is expanded to supply the house also.

1) Id probably start with a sunny island/SMA products. They build LARGE stuff and it can be paralleled for VERY large systems.

A single SUNNY ISLAND 4548-US is 4500w and $4100
6kw of panels is ~$3000 (and up)
540ahr of LFP from the group buy in the forum is ~$3200
racking, wiring, misc - $1500
Napkin math says about $12k for that^^

Times 2 if you want 9Kw and thats your $25 budget.

If your serious about the project I would highly recommend consulting a solar expert in your area that is able to walk you through the various options for hardware. Im not saying its not DIY doable, its just there is a lot more to consider on a 10kw expanding to 20kw build than there is with some kid and his 1000w inverter for the beach.

 

[Steve_S]

I'm going to throw a twist into this and it's the right timing for it... well almost.

Rule One ! Energy Conservation is far cheaper than Generation & Storage.

There are a few ways to do that such as the efficiency of equipment, lighting etc. There are things that you can do to any building to cut costs for cooling / heating just by the structure & material choices even. Thermal Breaks between the cladding & structure benefit both hot & cold climates exceptionally well, for example. Structure orientation, shading (coniferous and/or deciduous). Often folks forget that Trees or other natural Sun Blockers in Hot Climates can save money due to reduced cooling requirements if the home does not heat up from solar gain. Even offset Trellises with Vines work wonders. Many of these techniques can be applied not only to homes but to most structures to varying degrees with different methods.
Such things like using Light Colours for roof, walls.
Rain screening siding system which provides a thermal break from the shell & the outside.
Cool Roof systems which provide a passive convective airflow venting between the roof surface and the roof's sheathing structure again creating that thermal break. This vents the heat away from the structure without any energy use preventing the inside from gaining that heat.

Thermal Breaks are the best way for preventing heat from entering the building during the summer and preventing heat from escaping by being "drawn out" in the cold. Using these methods & thermal breaks for finishing structures does really enhance their performance and to be honest, the ROI (Return on investment) is quick (starting with increasing livability) and with immediate reduced heating/cooling effort.

 

[Hedges]

There are a bunch of trailers from DC Solar bankruptcy on the market. Multiple auctions, then resellers offering them.
An example:

Mobile Solar Generator SCT20 Hybrid | eBay

Find many great new & used options and get the best deals for Mobile Solar Generator SCT20 Hybrid at the best online prices at eBay! Free shipping for many products!

www.ebay.com

Some include a diesel generator. Some have batteries still good, some not. Prices have been all over the map.
The amount of PV panels is minimal, would get you started but you would want to add on later.
What I like about them is they have two 6 kW Sunny Island (my picture), and you can add on AC coupled as well.
One Sunny Island cluster can have up to 4 battery inverters for 24 kW and work with 48 kW of GT inverters. Or, 3 for 18 kW 3-phase and 36 kW GT.
A setup like that will turn over just about any shop equipment or well pump you might have (say up to 5 hp)

$100k is a lot. Pretty hard to spend that on solar these days unless there is a middleman.
I could give myself 100 kW of grid-tied PV (generate half a megawatt hour per day), or 48 kW of PV inverter + 24 kW of battery inverter system, not even looking for used/surplus bargains.

Batteries I try to keep small. That's the most expensive part. I prefer to have PV generation I don't use rather than spending several times as much for batteries to store it.

 

[SolarQueen]

Just for the barn. HVAC. In the summer should be ~80,000-100,000btu for ten hours a day. I know that’s not exactly your question but I don’t know and that’s sort of the dilemma. I’m willing to WAG it a bit as long as I can expand. Other than that I’ve got lights and standard tools but nothing crazy. If I want to run a welder I’ve already assumed i’ll do that with the HVAC off or in the winter. I’m going to do PV, but trying to nail down the how. I just put a budget number as a ballpark. Would love for it to be less. If it’s more then I’ll just have to plan on sweating more.

OK, here's your reality check. 1BTU/hr = 0.29307107 W. So a 100kBTU/hr AC is roughly 30kW. 30kW x 10 hours running = 300kWh used a day (that's assuming it is always on during those 10 hours). Let's say 5.5 sun hours (total time sun equals brightness of noon). 300,000Wh / 5.5 sun hours / .7 losses = 80kW system. If you get the solar panels at $0.50/watt, that's $40k in panels alone.

If you went with lithium batteries, for a 80kW system, you'd need at least 160kWh of batteries to handle that much current (1666A @48V @C/2 charge rate). Lead acid would need much more, as it cannot handle that high of a charge rate. That's probably your whole $100k budget there.

Probably $15k in inverters for 30kW load, $20k in charge controllers. Plus racking, wiring, conduit, etc. My guess is this system is twice your budget.

 

[Hedges]

OK, so A/C is the killer. But it doesn't exist yet. Can you tell us what percentage of the time it runs? Could it be smaller but run closer to 100%?
Some A/C are more efficient than others. Is there anything cooler (e.g. pond, stream, ground water) it can dump heat to instead of air?

100k BTU = 30 kW?
That may be a direct energy unit conversion, but perhaps not the way A/C are rated. Which probably makes some assumption of air temperature differences and transfer of heat.

60,000 BTU A/C draws 208/230V, 35A = 8 kW or less. So 100 k BTU would be 13.5 kW not 30 kW.

https://www.grainger.com/product/GOODMAN-Air-Conditioner-Condenser-38GM36

13.5 kW would be much more manageable.
But trying to achieve the 30 kW figure (enough for the rest of the house & barn?) ...

If it only runs while the sun shines, doesn't need so much battery given a system that limits charge current.
With 3-phase, I think starting surge is less, but not sure.

Consider 3-phase Sunny Island, 18 kW, with Sunny Boy 36 kW. Put about 72 kW (STC) of PV panels on them, 50% oriented at 10:00 AM sun ands 50% at 4:00 PM. That is over-paneled but levels production over the day. Panels would be about 50 kW (STC), something around 42 kW actual STC. Inverters would limit production to 36 kW.

SMA says to use 100 Ah per kW of PV inverter, so 3600 Ah at 48V. That's 180 kWh for lead-acid. I think you can go much smaller, and you program the system for lower charge current. Something like 3 forklift batteries totalling $24k. Maybe even smaller, limit is something to do with the SMA inverter maintaining stable electric grid when load starts/stops. A much smaller 400 Ah battery like I have ($5000) can power the battery inverters for a short time.

https://gb-battery.com/products/ols/products/new-24-85-27-battery-48-volt-1160ah

MSRP $5000 x 3 + $3000 x 6 + $0.50 x 72,000 + $8000 x 3 = $93,000.
That's battery inverters, PV inverters, PV panels, batteries. Mounting hardware and electrical hookup not included.

Hey SolarQueen, bet you could hook him up with everything he needs! What commission do I get??

Multiple smaller A/C would be easier to power than one large motor. Reflective roof, insulation, vented "attic" space, awnings to keep sun off walls, anything to avoid extra heat load.

It would be difficult to run a 30 kW motor with an SMA Sunny Island system due to motor starting surge. The systems can be intertied for 100 kW total battery inverter and 200 kW PV inverter distributed across a village/farm, but not sure limit is for a single load can be increased much.

Other products presently offered in Europe are larger, like 75 kW 3-phase battery inverter.

Sunny Tripower Storage 60 (Successor: SMA Commercial Storage Solution) | SMA Solar

Information on the Sunny Tripower Storage 60 (no longer sold by SMA) ► discover the successor here!

www.sma.de

The products offered today in US are either 6 kW per inverter, or 2 MW and up.

 

[chrisski]

I hope you can make this work for the price you want. When I started to design my system for my RV, I came quickly to the conclusion that there's no cheaper energy out there than connecting to a 50 amp outlet at an RV park and paying their daily rates. I decided for a solar build, but am not including AC in the build.

I've seen the mobile generators pop up for sale on craigslist locally, but they all seem underpaneled with 10 X 235 watt solar panels to power my two rooftop units off solar alone in Arizona heat where I can expect it to be running 24 hours off and on to include after sundown, if its an 11000 watt generator that is attached to it, that certainly would power my two ACs.

I feel confident with a little more time, I could put together a decent system out of that trailer by adding more panels to run the two ACs on my RV, but I would not want to attempt a 100,000 BTU build for a 4000 sq ft structure. To get enough power for my RV to run two ACs, I'd end up with at least another trailer that would need to be towed to the site.

I think SolarQueen who does PV build for a living is probably really close with her $200k quote. I also remember from living in the panhandle in FLorida, A/C was needed at night also in the summer.

 

[SolarQueen]

OK, so A/C is the killer. But it doesn't exist yet. Can you tell us what percentage of the time it runs? Could it be smaller but run closer to 100%?
Some A/C are more efficient than others. Is there anything cooler (e.g. pond, stream, ground water) it can dump heat to instead of air?

100k BTU = 30 kW?
That may be a direct energy unit conversion, but perhaps not the way A/C are rated. Which probably makes some assumption of air temperature differences and transfer of heat.

60,000 BTU A/C draws 208/230V, 35A = 8 kW or less. So 100 k BTU would be 13.5 kW not 30 kW.

https://www.grainger.com/product/GOODMAN-Air-Conditioner-Condenser-38GM36

13.5 kW would be much more manageable.
But trying to achieve the 30 kW figure (enough for the rest of the house & barn?) ...

Figuring out an uninstalled A/C unit power requirements is so hard. Thanks on the correction with the current draw. I'm guessing that's just the compressor, so you have to include the wall unit power as well. Plus other loads, let's say my estimate was 2x reality. Cut everything I said in half, so if you don't run the A/C at night, you may be able to do it for the high end of your budget.

 

[Jmac786]

Is maintenance really a big deal? Seems like two systems at 50% of generated power will be tremendously more. I’ve got a 1400’ driveway but I know how to trench so unless the losses are that big that’s not what scares me. Main house panel to closest corner of barn is more like 400’

I honestly haven’t built one yet, so I’m not sure about maintenance. I do like the idea of some built in redundancy. It is more equipment to do two systems. If I went with one system of this size, I would keep some spare parts on hand from day 1.

I’m planning a 15kw build with the expectation of being forced to add on later. Two things that I can potentially see requiring expansion would be our aging parents losing independence and/or the addition of electric vehicle(s) during the life of the system.

 

[Hedges]

I have four Sunny Island connected 2S2P, sharing one battery. Multiple Sunny Boy.
Some of the battery inverters could be shut down and removed, same for the PV inverters and strings of panels.
Having the battery inverters at one location, you can run AC 400' or 1400' between house and barn, have grid tie PV inverters at both locations.
AC panels can have interlocked breakers as a transfer switch, so a generator can be an alternate source.
Lots of ways to support maintenance on portions of the system.
SMA also has "multi-cluster" where (off grid 3-phase) systems tie together.

 

[Farmerbob]

Figuring out an uninstalled A/C unit power requirements is so hard. Thanks on the correction with the current draw. I'm guessing that's just the compressor, so you have to include the wall unit power as well. Plus other loads, let's say my estimate was 2x reality. Cut everything I said in half, so if you don't run the A/C at night, you may be able to do it for the high end of your

There are a bunch of trailers from DC Solar bankruptcy on the market. Multiple auctions, then resellers offering them.
An example:

Mobile Solar Generator SCT20 Hybrid | eBay

Find many great new & used options and get the best deals for Mobile Solar Generator SCT20 Hybrid at the best online prices at eBay! Free shipping for many products!

www.ebay.com

Some include a diesel generator. Some have batteries still good, some not. Prices have been all over the map.
The amount of PV panels is minimal, would get you started but you would want to add on later.
What I like about them is they have two 6 kW Sunny Island (my picture), and you can add on AC coupled as well.
One Sunny Island cluster can have up to 4 battery inverters for 24 kW and work with 48 kW of GT inverters. Or, 3 for 18 kW 3-phase and 36 kW GT.
A setup like that will turn over just about any shop equipment or well pump you might have (say up to 5 hp)

$100k is a lot. Pretty hard to spend that on solar these days unless there is a middleman.
I could give myself 100 kW of grid-tied PV (generate half a megawatt hour per day), or 48 kW of PV inverter + 24 kW of battery inverter system, not even looking for used/surplus bargains.

Batteries I try to keep small. That's the most expensive part. I prefer to have PV generation I don't use rather than spending several times as much for batteries to store it.

Thanks. I’ve been tracking some RichieBros auctions but figured the way tech moves and unknown conditions it makes no sense to bother. I’m happy to spend less. What sucks about Florida is in the summer I’ll be running probably 10hrs a day but obviously in times like now in October probably half that and won’t even bother with heat come winter so I’d expect my needs to be 20% in Jan vs July. Speaking of auctions, I’m even looking at a small chiller system which makes no sense unless it’s close to free but that’s getting way off topic.

 

[Farmerbob]

OK, so A/C is the killer. But it doesn't exist yet. Can you tell us what percentage of the time it runs? Could it be smaller but run closer to 100%?
Some A/C are more efficient than others. Is there anything cooler (e.g. pond, stream, ground water) it can dump heat to instead of air?

100k BTU = 30 kW?
That may be a direct energy unit conversion, but perhaps not the way A/C are rated. Which probably makes some assumption of air temperature differences and transfer of heat.

60,000 BTU A/C draws 208/230V, 35A = 8 kW or less. So 100 k BTU would be 13.5 kW not 30 kW.

https://www.grainger.com/product/GOODMAN-Air-Conditioner-Condenser-38GM36

13.5 kW would be much more manageable.
But trying to achieve the 30 kW figure (enough for the rest of the house & barn?) ...

If it only runs while the sun shines, doesn't need so much battery given a system that limits charge current.
With 3-phase, I think starting surge is less, but not sure.

Consider 3-phase Sunny Island, 18 kW, with Sunny Boy 36 kW. Put about 72 kW (STC) of PV panels on them, 50% oriented at 10:00 AM sun ands 50% at 4:00 PM. That is over-paneled but levels production over the day. Panels would be about 50 kW (STC), something around 42 kW actual STC. Inverters would limit production to 36 kW.

SMA says to use 100 Ah per kW of PV inverter, so 3600 Ah at 48V. That's 180 kWh for lead-acid. I think you can go much smaller, and you program the system for lower charge current. Something like 3 forklift batteries totalling $24k. Maybe even smaller, limit is something to do with the SMA inverter maintaining stable electric grid when load starts/stops. A much smaller 400 Ah battery like I have ($5000) can power the battery inverters for a short time.

https://gb-battery.com/products/ols/products/new-24-85-27-battery-48-volt-1160ah

MSRP $5000 x 3 + $3000 x 6 + $0.50 x 72,000 + $8000 x 3 = $93,000.
That's battery inverters, PV inverters, PV panels, batteries. Mounting hardware and electrical hookup not included.

Hey SolarQueen, bet you could hook him up with everything he needs! What commission do I get??

Multiple smaller A/C would be easier to power than one large motor. Reflective roof, insulation, vented "attic" space, awnings to keep sun off walls, anything to avoid extra heat load.

It would be difficult to run a 30 kW motor with an SMA Sunny Island system due to motor starting surge. The systems can be intertied for 100 kW total battery inverter and 200 kW PV inverter distributed across a village/farm, but not sure limit is for a single load can be increased much.

Other products presently offered in Europe are larger, like 75 kW 3-phase battery inverter.

Sunny Tripower Storage 60 (Successor: SMA Commercial Storage Solution) | SMA Solar

Information on the Sunny Tripower Storage 60 (no longer sold by SMA) ► discover the successor here!

www.sma.de

The products offered today in US are either 6 kW per inverter, or 2 MW and up.

Worst case for the barn I was coming up with 18kw. Two even three units are fine if it comes down to it.

 

[Farmerbob]

I'm going to throw a twist into this and it's the right timing for it... well almost.

Rule One ! Energy Conservation is far cheaper than Generation & Storage.

There are a few ways to do that such as the efficiency of equipment, lighting etc. There are things that you can do to any building to cut costs for cooling / heating just by the structure & material choices even. Thermal Breaks between the cladding & structure benefit both hot & cold climates exceptionally well, for example. Structure orientation, shading (coniferous and/or deciduous). Often folks forget that Trees or other natural Sun Blockers in Hot Climates can save money due to reduced cooling requirements if the home does not heat up from solar gain. Even offset Trellises with Vines work wonders. Many of these techniques can be applied not only to homes but to most structures to varying degrees with different methods.
Such things like using Light Colours for roof, walls.
Rain screening siding system which provides a thermal break from the shell & the outside.
Cool Roof systems which provide a passive convective airflow venting between the roof surface and the roof's sheathing structure again creating that thermal break. This vents the heat away from the structure without any energy use preventing the inside from gaining that heat.

Thermal Breaks are the best way for preventing heat from entering the building during the summer and preventing heat from escaping by being "drawn out" in the cold. Using these methods & thermal breaks for finishing structures does really enhance their performance and to be honest, the ROI (Return on investment) is quick (starting with increasing livability) and with immediate reduced heating/cooling effort.

Totally agreed. I’ve already got a Polar White 26ga roof and will closed cell foam it completely as soon as I can get a little closer to rough penetrations (easier now than after foam). Going ground mount for PV due to cost and simplicity. Will also work in some room partitions when bay doors are opened. No vines though, that becomes an ant/insect highway into the building but already have some bamboo screens growing.

 

[Farmerbob]

Once you get some numbers you can calculate your voltage drop using a calculator like this one and power loss could be calculated using the formula Ploss = I² x R

Also a basic question, why do you want to go off grid? It sounds like you are currently grid connected and 100k is a hell of a lot of money to shell out.

House is on grid. It’s a happy goal to take house off. I have a long-standing dislike for the monopoly providers due to lobbying force and unreliability come hurricane season (lots of above ground lines and lots of clearly unmaintained ROW trees) so while I don’t want to throw money away I don’t mind an extended payback.

I don’t have a generator now but if I don’t go PV I’ll get a whole house. The barn has no electricity at present. Between upgrading the 200amp service to house or separate meter and permitting I’m guessing $10k to hook up the barn most of which I will throw down the drain if I end up converting down the road.

 

[Steve_S]

Totally agreed. I’ve already got a Polar White 26ga roof and will closed cell foam it completely as soon as I can get a little closer to rough penetrations (easier now than after foam). Going ground mount for PV due to cost and simplicity. Will also work in some room partitions when bay doors are opened. No vines though, that becomes an ant/insect highway into the building but already have some bamboo screens growing.

The reasons I mention this, is because I designed & build my home to be Net Positive.
FPSF Slab Foundation using 4" of HD-XPS under & up the sides of the slab foundation, with 3/4" Pex for Radiant Heat in it.
Walls are 2x6 "Advanced Framed 24 OC" with 5-1/2" of High Density closed cell EPS-II no space between sheathing & interior wall material.
(Cement truck rolled over a piece of it and only left 1/4" deep tread marks in this foam.... (High Density R6 per inch)
Roof (Cathedral ceilings) is 2x8 with 7-1/2" of PolyISO between the rafters, two layers, 1 with 4" thick ISO, 1 with 3.5" thick ISO.

Cool Roof System installed, with 2x4's battens laying on their flats above the rafters with 1x6 cross battens for the metal roof, this provides for the convective airflow from the eaves up through to the Ridge Vent.

Siding in my case is Live Edge White Cedar, installed in a Rainscreen fashion. I also have battens running up along the studs with cross batten that have the 8" Cedar Back Planks nailed to with 4" separation between planks and then the Live Edge Face Planks covering that gap. This allows air to move freely with no cold / hot spots or anywhere for moisture to collect.

All exterior walls are "solid" meaning there is no electrical or plumbing running within... Electrical is all surface mounted on exterior walls where needed. Interior walls have wiring within of course. All plumbing is also "surface mounted" and installed without messing up the envelope.

Doors & Windows are installed within Bailey Boxes passing through the walls and as such extend my widow sill to 6" as it places the windows where they belong. The catch is my walls from Inside drywall face to outside cedar face is 9-1/2" thick, so Bailey Boxes were needed anyways.

WHERE DID I GET INSULATION LIKE THAT ?
It is NOT sold in Retail Land, you wil never see 3.5" or 4.0" thick 4'x8' sheets of ISO in a retail store, nor will you ever see 5-1/2" HD-EPSII Insulation either in retail. I sourced it all from Commercial Roofers (think Office towers, shopping malls.) and WAY CHeaper than Retail Hell !