# Small off grid solar system



## backstay (Feb 3, 2011)

I thought I would post a set of pictures of an off grid system I just finished. Four REC 280 watt panels, DPW pole mount, an Outback FM80 charge controller, Outback VFX3524 inverter, a Midnite Solar 250AL Plus E-panel, and eight six volt sealed storage batteries.


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## backstay (Feb 3, 2011)

More of the system.


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## HackWork (Oct 2, 2009)

For batteries, have you looked into that Tesla wall thing?


I saw something else interesting (don't mind the source): 





Another question I thought of, why not add an interlock to the panel so that they could backfeed a portable generator if necessary? Or do you have another method for alternate power?


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## backstay (Feb 3, 2011)

HackWork said:


> For batteries, have you looked into that Tesla wall thing?
> 
> 
> I saw something else interesting (don't mind the source):
> ...


I have, but the Power Wall 2 is an AC coupled system( inverter inside) so it's more of a grid tie system. It really doesn't need solar. It can be used for time of day billing, to offset high priced power.


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## Moonshot180 (Apr 1, 2012)

Looks good! Thanks for sharing!


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## B-Nabs (Jun 4, 2014)

HackWork said:


> For batteries, have you looked into that Tesla wall thing?
> 
> 
> I saw something else interesting (don't mind the source):
> ...


Ha, the solar engineer's name in the video is Nick Soleil.

Sent from the unmarked van outside HackWork's house.


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## telsa (May 22, 2015)

Backstay...

Have the old Edison batteries ever taken off in your cold climate ?


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## RePhase277 (Feb 5, 2008)

telsa said:


> Backstay...
> 
> Have the old Edison batteries ever taken off in your cold climate ?


There's always talk around the off-grid world about nickel-iron batteries by a small few... but the conclusion is they're just not practical mostly due to cost.


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## splatz (May 23, 2015)

I wouldn't mind hearing a little more about how you designed the whole thing!


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## backstay (Feb 3, 2011)

splatz said:


> I wouldn't mind hearing a little more about how you designed the whole thing!


I start by doing a site survey. Looking for the best place to set the panels. I have a digital camera and software that maps the sun path and looks for shade. After all these years I can stand and look without it and tell you how well it will do. Pictures are nice thou. Then I talk with the owner about usage, time of year, that kind of thing. If you only come on weekends, a small PV system and larger battery stack works. Shade will cause me to increase the number of panels. I also won't go under 4 panels. 

So I go to the mount manufacturer's web site. Put in all the variables(wind load, snow load, hight, ground type, panel model, and number. They give me an engineered drawing with burial depth, pipe size and schedule. If it's a four panel, I series two sets and combine then at the pole. They'll run about 50-75 volts DC and 7-8 amps each set. So I run 10/2UF( 15 amps x 1.56 = 23 amps. 

The white panel (Midnite Solar E panel)you see the equipment mounted to comes with buses for all your wiring, 250 amp inverter breaker, AC disconnect, bypass breakers and spaces for a gfci breaker. Plus the inverter and charge controller mount on that. I usually spec a 3500 watt inverter and a 24 volt system if the panel watts are under 2000, charge controller only put out 80 amps. If the system gets bigger, you either add a charge controller or up the voltage to 48 volts. 

Batteries are vented if they are outside or in an area you can vent. Eight 200 amp hour 6 volt batteries are the smallest I will put in. If you need more storage, then a bigger battery like 225 ah or higher. 




HackWork said:


> Another question I thought of, why not add an interlock to the panel so that they could backfeed a portable generator if necessary? Or do you have another method for alternate power?


The inverter has an input that a generator can be connected to. There is also a bypass breaker in case the inverter fails. Your house wiring is then run right off the inverter. 

If you have specific questions I will answer if I can.


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## Glock23gp (Mar 10, 2014)

So your incoming leads from the panels come in the back of the white box where the 2" bushing is in the lower left corner?

Then just have an 8-3 or something from the white box feeding the panel we can't see?

No meterbase totally off grid?

Sent from my SAMSUNG-SM-N910A using Tapatalk


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## backstay (Feb 3, 2011)

Glock23gp said:


> So your incoming leads from the panels come in the back of the white box where the 2" bushing is in the lower left corner?
> 
> Then just have an 8-3 or something from the white box feeding the panel we can't see?
> 
> ...


Incoming from the solar panels is in the lower left of the white box, its 1-1/2. 

The 120 volt AC is in 3/4 FMC. It's the red wire, #6 you see coming in the bottom of the service panel. 

No utility, just solar. This is a cabin. It is close to the power line, but they can't get an easement through the neighbor's property. 

Here is the combiner at the pole. This where the two strings of two panels are joined to make one.

I could put the gfci breaker out here. Then the burial depth would only have to be 12 inches. But that is getting a little shallow. I would if there was ledge rock. But then it would go in conduit just for protection.


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## Glock23gp (Mar 10, 2014)

Wish we had more sun and no coastal salt air to justify playing with solar here...

Sent from my SAMSUNG-SM-T337A using Tapatalk


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## MechanicalDVR (Dec 29, 2007)

backstay said:


> I thought I would post a set of pictures of an off grid system I just finished. Four REC 280 watt panels, DPW pole mount, an Outback FM80 charge controller, Outback VFX3524 inverter, a Midnite Solar 250AL Plus E-panel, and eight six volt sealed storage batteries.


Thanks, I think that's a good looking job. If I ever get ambitious I'd go for something very similar for myself.


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## emtnut (Mar 1, 2015)

Curious about the tilt on the panel

Would the customer adjust 4 times a year, or just leave it as is ?

What about those suntracker type mounts ... worth the cost/load for what extra you'd get out of it ? Or even manual adjustments .. worth it ??

Or just calculate for december, and size it that way.


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## HackWork (Oct 2, 2009)

What's your opinion on panel mounted micro inverters?


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## backstay (Feb 3, 2011)

emtnut said:


> Curious about the tilt on the panel
> 
> Would the customer adjust 4 times a year, or just leave it as is ?
> 
> ...


Most off grid systems we leave at 45 degrees. These pole mounts are very easy to adjust. Loosen four bolts and move it, calm day of course. 

This far north trackers are not cost effective. You get more for your dollar by adding panels. In some rare cases it's better. 




HackWork said:


> What's your opinion on panel mounted micro inverters?


I'm not sold on them. Have you checked out an optimizer system? SolarEdge has them, they look like the way to go. I installed 96 on one job.


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## splatz (May 23, 2015)

backstay said:


> I start by doing a site survey.
> 
> If you have specific questions I will answer if I can.


I wouldn't even know where to start, I have basically everything to learn about this and this looks like a nice install. I like this kind of thread, gives me a look at what other people are up to, it's not something I've had a look at up close in my travels. So thanks very much for posting this! 

A lot of people here have hunting cabins and shacks with no power, I am sure they'd love a system like this.


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## backstay (Feb 3, 2011)

splatz said:


> I wouldn't even know where to start, I have basically everything to learn about this and this looks like a nice install. I like this kind of thread, gives me a look at what other people are up to, it's not something I've had a look at up close in my travels. So thanks very much for posting this!
> 
> A lot of people here have hunting cabins and shacks with no power, I am sure they'd love a system like this.


$11,600 for that system. Turn key, with batteries and with a plugin for a generator backup. A six panel is $17,400.


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## RePhase277 (Feb 5, 2008)

That's a nice system.... it's nice to have a customer pay for those goodies.... But 2ait until you see what I'm going to do with my three gently used 300 watt panels out at the Super-Secret Off Grid RePhase Remote Property.. None of that solar specific equipment for me.... just wait, I'm about to put together a system that would make Cletis blush.


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## emtnut (Mar 1, 2015)

RePhase277 said:


> That's a nice system.... it's nice to have a customer pay for those goodies.... But 2ait until you see what I'm going to do with my three gently used 300 watt panels out at the Super-Secret Off Grid RePhase Remote Property.. None of that solar specific equipment for me.... just wait, I'm about to put together a system that would make Cletis blush.


Are we going to see pictures ? Or are cameras prohibited according to the Super-Secret of Grid RePhase Remote Property security lock down procedures ?


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## emtnut (Mar 1, 2015)

backstay said:


> Most off grid systems we leave at 45 degrees. These pole mounts are very easy to adjust. Loosen four bolts and move it, calm day of course.
> 
> This far north trackers are not cost effective. You get more for your dollar by adding panels. In some rare cases it's better.


What did you set LVD LVR HVD HVR at ? The systems I've done were all with 8D AGMs, and I had to do quite a bit of research to find optimal settings. One system was with the LiFePo4, I can't remember the settings now, but the manufacturer really helped us out on that one.
Been awhile since I've done one, so curious if the Mfr's give usable presets or recommendations now ? Or did you have to do quite a bit of digging around as well ?


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## RePhase277 (Feb 5, 2008)

emtnut said:


> Are we going to see pictures ? Or are cameras prohibited according to the Super-Secret of Grid RePhase Remote Property security lock down procedures ?


Oh, there will be pictures... but they'll be encrypted with a 256-bit RNA sequenced fractal algorithm.


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## RePhase277 (Feb 5, 2008)

I see that you used eight 200 Ah batteries, series parallel, for 24 volts. That's a total of 200 Ah if you limit DoD to 50%. So 4.8 kW-hrs. It doesn't seem like there's a whole lot of reserve built in unless they just don't use much.

It would take a little more than 4 hours to to bring 4800 watt-hours out of 1120 watts of PV. What kind of numbers did you run to size the system? What's the customer load?


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## backstay (Feb 3, 2011)

RePhase277 said:


> I see that you used eight 200 Ah batteries, series parallel, for 24 volts. That's a total of 200 Ah if you limit DoD to 50%. So 4.8 kW-hrs. It doesn't seem like there's a whole lot of reserve built in unless they just don't use much.
> 
> It would take a little more than 4 hours to to bring 4800 watt-hours out of 1120 watts of PV. What kind of numbers did you run to size the system? What's the customer load?


Wouldn't two strings of four six volt 200 ah batteries be 400 ah?


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## RePhase277 (Feb 5, 2008)

backstay said:


> Wouldn't two strings of four six volt 200 ah batteries be 400 ah?


Not taken at 50% depth of discharge.

It's 400 Ah if you run it flat to 0, but I hear that's bad.


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## emtnut (Mar 1, 2015)

RePhase277 said:


> Not taken at 50% depth of discharge.
> 
> It's 400 Ah if you run it flat to 0, but I hear that's bad.


The AGMs that I've used are 80% DoD ... but in an enclosed space, there aren't many other options !


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## RePhase277 (Feb 5, 2008)

emtnut said:


> The AGMs that I've used are 80% DoD ... but in an enclosed space, there aren't many other options !


I've never contracted a solar job. I want to preface that my on-the-invoice solar experience goes as far as wiring the parts of a kit to a battery in a field station. And a few gate operators. Then there's my own experiments. So anything I say is mostly theoretical. But so far, I'm of the opinion that "If it can go to 80% DoD, imagine how long it will run at 50% DoD!" philosophy.


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## emtnut (Mar 1, 2015)

RePhase277 said:


> I've never contracted a solar job. I want to preface that my on-the-invoice solar experience goes as far as wiring the parts of a kit to a battery in a field station. And a few gate operators. Then there's my own experiments. So anything I say is mostly theoretical. But so far, I'm of the opinion that "If it can go to 80% DoD, imagine how long it will run at 50% DoD!" philosophy.


I don't have experience with the 'vented' batteries, but I'm pretty sure it *IS* 50% DoD .... I was just throwing out the number for AGMs.

If you draw the battery bank down on either battery technology,past the recommended DoD, you are really killing their longevity.

That's why I asked about the LVD setting as well.


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## backstay (Feb 3, 2011)

RePhase277 said:


> I see that you used eight 200 Ah batteries, series parallel, for 24 volts. That's a total of 200 Ah if you limit DoD to 50%. So 4.8 kW-hrs. It doesn't seem like there's a whole lot of reserve built in unless they just don't use much.
> 
> It would take a little more than 4 hours to to bring 4800 watt-hours out of 1120 watts of PV. What kind of numbers did you run to size the system? What's the customer load?


I don't understand the 4 hours to bring 4800 watt-hours out, using the array size. Do you mean 4 hours to replace 4800 watt hours? My system at home is 3000 watts, and sixteen 225 ah batteries. I can harvest around 10-12 kW per day. I use around seven. But this is a full time home with electric freezers, fridge, internet, laundry, septic, well. I don't run any backup from March-October. The cabin owner has no standing electrical load. And as such will at most use 2 kW on average. The usage is lighting, and convenience outlets. So load is very low. I figure they will easily make a 4 day weekend with no sun. 

A off grid home can not be compared to the normal home. If I paid the utility for power, it would be 84 cents a day. As far as reserve, I try to stay above four days.

AGM batteries are discharged to 80% when compared to flooded batteries at 50%. This gives you the same cycles.


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## RePhase277 (Feb 5, 2008)

backstay said:


> I don't understand the 4 hours to bring 4800 watt-hours out, using the array size. Do you mean 4 hours to replace 4800 watt hours?


Yes. My question was basically how many watt-hours of consumption was the system sized around? How many reserve days does 4.8 kW-hrs give this cabin?


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## HackWork (Oct 2, 2009)

RePhase277 said:


> I've never contracted a solar job. I want to preface that my on-the-invoice solar experience goes as far as wiring the parts of a kit to a battery in a field station. And a few gate operators.


Don't worry, I have done lots and lots of solar, yet you still know more than me.


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## backstay (Feb 3, 2011)

emtnut said:


> What did you set LVD LVR HVD HVR at ? The systems I've done were all with 8D AGMs, and I had to do quite a bit of research to find optimal settings. One system was with the LiFePo4, I can't remember the settings now, but the manufacturer really helped us out on that one.
> Been awhile since I've done one, so curious if the Mfr's give usable presets or recommendations now ? Or did you have to do quite a bit of digging around as well ?


I don't have those in front of me, I will get them and post. LVD (LBCO)is dependent on load. Normal load LBCO should be 21 volts(24 volt system). After disconnect, a healthy flooded battery should rise to 24.2 vdc This is your 50% level. Then reconnect should be 25 vdc.

I don't know about the high cutouts, my charge controllers only go to 34 vdc max. I run flooded at 28.8 and AGM at 28.6 I do have less experience with the sealed batteries.



RePhase277 said:


> Yes. My question was basically how many watt-hours of consumption was the system sized around? How many reserve days does 4.8 kW-hrs give this cabin?


AGMs are 80% So 400x .8 = 320 Ah at 24 volts = 7680ah. Then at 2000 per day =3.84 days. That is with no input from the array(unlikely) even when there appears to be no sun, the system is harvesting 10-20%.

This is a good discussion, I do so much of this on what has worked in the past, this makes me think about it and do it by the numbers.

Here's a link to some larger battery stacks. I have this at one customer's place. 
http://www.hupsolar.com/buy-HUP-batteries-prices-pricing

The Hup-21 has something like 20 kWh useable energy for $3000 this is my next battery.


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## backstay (Feb 3, 2011)

I need to make a correction. AGM batteries at 24 volts should be charged at 29.6, not 28.6. This is at a battery temperature of 75 F.


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## emtnut (Mar 1, 2015)

backstay said:


> I need to make a correction. AGM batteries at 24 volts should be charged at 29.6, not 28.6. This is at a battery temperature of 75 F.


Thanks for all the info Backstay :thumbsup:

I think would be a good sticky for the Alternative energy forum


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## backstay (Feb 3, 2011)

Went back today to install the generator connection and program the setpoints for that. Connected the interface device(Mate B) and no data. Screens come up but I can't configure anything! Mate is 6-7 years old, maybe it needs an update. Found this little tidbit on Outback's site: 

*The FXR inverter is not compatible with mate or mate2, only with mate3
Sandra Herrera
Applications Engineering

OutBack Power Technologies
*

So last years inverters don't have the R, in FXR and there is some better stuff in the brains, but really! The Mate B was $200, the new Mate3 is $400. Crap!


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## backstay (Feb 3, 2011)

Drove 3-1/2 hrs to install racks and panels at an offgrid place. HO installed his own pole off of engineered drawings I sent him. Got there and found he had concreted a six inch tube instead of pipe. Sent him to town to buy concrete and rebar to fill the tube. Needless to say there is no warranty on the system staying up. I thought it looked off and snapped a photo of my level on the pole.

I have to shake my head at the work and ability of people to follow simple directions.


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## RePhase277 (Feb 5, 2008)

backstay said:


> Drove 3-1/2 hrs to install racks and panels at an offgrid place. HO installed his own pole off of engineered drawings I sent him. Got there and found he had concreted a six inch tube instead of pipe. Sent him to town to buy concrete and rebar to fill the tube. Needless to say there is no warranty on the system staying up. I thought it looked off and snapped a photo of my level on the pole.
> 
> I have to shake my head at the work and ability of people to follow simple directions.


Your level must be out of whack, obviously.


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## dronai (Apr 11, 2011)

Backstay, being that solar panels are only about 300W a piece, and you are only installing (4) , even with the battery storage, it seems like someone would use up that power pretty fast ?


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## backstay (Feb 3, 2011)

dronai said:


> Backstay, being that solar panels are only about 300W a piece, and you are only installing (4) , even with the battery storage, it seems like someone would use up that power pretty fast ?


It's a cabin, weekend use. This customer has eight 205 ah batteries. I figure he will not need to run his generator again. He should have enough storage for 4 or 5 days, depending on how much water he pumps. It's mostly lights, some well water for domestic use. He'll harvest 4-5 kw on sunny days. Even if he uses more than that, there is more capacity than that in the battery stack. I have many systems that are similar and they work perfectly for weekend use. Some have more panels because of shade issues.


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## dronai (Apr 11, 2011)

Is the storage battery cabinet in a utility room not connected to the main cabin ? Reason I ask, is about the gas released. The city made a friend remove his system because of that problem, and no approved plans.


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## backstay (Feb 3, 2011)

dronai said:


> Is the storage battery cabinet in a utility room not connected to the main cabin ? Reason I ask, is about the gas released. The city made a friend remove his system because of that problem, and no approved plans.


I didn't take any pictures. He had an inverter system already that he replaced the batteries(vented lead acid) with sealed gel cells. They are in a metal cage. When I put batteries in a dwelling, I use a battery enclosure and use sealed AGM batteries.


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## Cow (Jan 16, 2008)

I'm with Splatz on this deal. 

I know nothing about solar, but appreciate you taking the time to walk some of us through how it comes together. 

Makes me want to do a small solar job, just so I can say I've done one!

Thanks Backstay!!


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## dronai (Apr 11, 2011)

Backstay, the grid tied systems I've worked on have about 400V-600V DC going to the invertor, you have how many from the panels ? 60V ?

From the batteries in series, you have how many volts going to what ? A different type of invertor ? 

I guess my question is, what other componants are added that's different from a grid tied system ?


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## backstay (Feb 3, 2011)

dronai said:


> Backstay, the grid tied systems I've worked on have about 400V-600V DC going to the invertor, you have how many from the panels ? 60V ?
> 
> From the batteries in series, you have how many volts going to what ? A different type of invertor ?
> 
> I guess my question is, what other componants are added that's different from a grid tied system ?


Off grid system will have two or three panels in series. That puts the DC at 70-105 volts at 70 degrees. That DC power then goes to a charge controller. They typically are 150 volt max. There are some that are higher, I just haven't needed to go there yet. The charge controller outputs to the battery voltage(24,36,48). They are typically 80 amp outputs regardless of output voltage. 

So the difference is a charge controller, the box that all the bus work lands in and batteries. And of courses the inverters are different. The inverter connects to the batteries, not the solar panels. The solar panels connect to the batteries through the charge controller. 

Here's a picture of the connection box.

And a wiring diagram.



http://www.midnitesolar.com/pdfs/outBackPlusFrontBack_loRes.pdf


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## scotch (Oct 17, 2013)

Do you need an exhaust fan on your battery room/enclosure as well.....we had quite a discussion with one Electrical Inspector who wanted an explosion proof fan assembly .


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## backstay (Feb 3, 2011)

scotch said:


> Do you need an exhaust fan on your battery room/enclosure as well.....we had quite a discussion with one Electrical Inspector who wanted an explosion proof fan assembly .


If they are vent style batteries, yes. They make one just for that.


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## Signal1 (Feb 10, 2016)

The IAEI journal has an article about solar just about every month, and I always read it because I don't know much about solar stuff.

I think I just learned more about solar on this thread than anything I've ever read.

Thanks Backstay.:thumbsup:


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## backstay (Feb 3, 2011)

Here's what's going up today. Not so small, 12 panels. They are older panels, 255 watt. I've been waiting two years for the pole to go in because the owner hired a "contractor" instead of me. 8 inch sch 80 pole, about 11 ft in the ground. Got the center spine(strong back) in by myself, weight is about 150 pounds. That was yesterday, rails and two modules today. Had to quit early, too much rain yesterday and too much wind today.


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## drsparky (Nov 13, 2008)

Did annual PM yesterday, well of the grid.








Nosy neighbor.








Rigging a lift.


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## backstay (Feb 3, 2011)

drsparky said:


> Did annual PM yesterday, well of the grid.
> 
> 
> 
> ...


What were you lifting? A dead moose?

How about pictures of disconnects, inverters, battery stacks!


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## drsparky (Nov 13, 2008)

I need to shoot some new photos from inside the shelter, had lots on photobucket before they went evil. The moose we standing in the road on the way to the LZ, wouldn't get out of the way. We had a contractor replacing the shelter roof so we had to lift a lot of tools and materials in, my test equipment and laptop fly in the cargo bin. Setting external loads I don't have time for shooting photos until after it is in the air, makes for boring shots. 
Basically we use Outback FM 80s and Deka Unigy 2 and 3 batteries. Here is a a picture off the net of the typical battery pack.


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## The_Modifier (Oct 24, 2009)

@backstay , many thanks for the links you sent. You wouldn't believe how much I have watched, taken notes and have been reading more. I can't thank you enough for the information.

:thumbup:


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## backstay (Feb 3, 2011)

drsparky said:


> I need to shoot some new photos from inside the shelter, had lots on photobucket before they went evil. The moose we standing in the road on the way to the LZ, wouldn't get out of the way. We had a contractor replacing the shelter roof so we had to lift a lot of tools and materials in, my test equipment and laptop fly in the cargo bin. Setting external loads I don't have time for shooting photos until after it is in the air, makes for boring shots.
> Basically we use Outback FM 80s and Deka Unigy 2 and 3 batteries. Here is a a picture off the net of the typical battery pack.


I have been transitioning from Outback FMs to MidNite Solar's Classic 150. More features and better voltage spread on the high side.





The_Modifier said:


> @backstay , many thanks for the links you sent. You wouldn't believe how much I have watched, taken notes and have been reading more. I can't thank you enough for the information.
> 
> :thumbup:


You're welcome, glad I could help!


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## dronai (Apr 11, 2011)

Backstay, had a call yesterday from a guy having a problem with the inspector over a grid tied system that had a center fed main breaker. I know about the 120% rule

Question is, if this happens, what allowable kw system can you have ? His main and his busing were 200A


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## backstay (Feb 3, 2011)

dronai said:


> Backstay, had a call yesterday from a guy having a problem with the inspector over a grid tied system that had a center fed main breaker. I know about the 120% rule
> 
> Question is, if this happens, what allowable kw system can you have ? His main and his busing were 200A


So the 120% rule puts his max amps at 40 over the 200. But it 125% of the inverter output. So assuming 240 volt system, 32 amps would be 7.68 kW inverter max on a 200 amp bus. Breakers need to be at the ends away from the main. 7 kW inverters are typically max for a dwelling solar system. They make 175 amp mains for many different panels, this allows you to install 12.48 kW in the same situation. Then you would see two 6kW inverters. The center main might change that. If they treat it like installing the breaker next to the main, you're screwed. Because you can only go to 100%, then the main needs to be smaller.


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## dronai (Apr 11, 2011)

backstay said:


> So the 120% rule puts his max amps at 40 over the 200. But it 125% of the inverter output. So assuming 240 volt system, 32 amps would be 7.68 kW inverter max on a 200 amp bus. *Breakers need to be at the ends away from the main*. 7 kW inverters are typically max for a dwelling solar system. They make 175 amp mains for many different panels, this allows you to install 12.48 kW in the same situation. Then you would see two 6kW inverters. The center main might change that. If they treat it like installing the breaker next to the main, you're screwed. Because you can only go to 100%, then the main needs to be smaller.


Bus rating (A) x 1.2 - Main Breaker rating (A) = pv rating
200Ax1.2-200A = 40A

Ok, so lets say you can only go 100% so at 200A what is the formula, or are you screwed ? (panel change)


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## dronai (Apr 11, 2011)

Also, why use two invertors on your 12.48 kw example ? Do they not make a single invertor in this size ?

By the way I installed (2) invertors for the Solar Contractor on my last installation, but he doesn't want to teach, so I didn't ask why


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## backstay (Feb 3, 2011)

dronai said:


> Bus rating (A) x 1.2 - Main Breaker rating (A) = pv rating
> 200Ax1.2-200A = 40A
> 
> Ok, so lets say you can only go 100% so at 200A what is the formula, or are you screwed ? (panel change)


You have to lower the main breaker size. The bus can't see more than 120% if the main and solar are on opposite ends of the bus. If it's something eles, only 100% total. So you change the main to 175 amp. You now can put 25 amps addition on the bus. But 125% of inverter output is what you size by, so only 20 amps of power or 4.8kW


There is an exception where all breakers installed can add up to 100%. You don't count the main for that. I use that for solar only panels. I got into a debate with someone from California about that and they told me I was wrong. But I posted the section and it was clear. Come to find out they said it was a rule there that you couldn't use that. I don't know, I'm not in that state. 


Here is an article that talks about it. I don't see mention of the 125% of the inverter output, but when I get a chance, I will look that up to make sure I'm not wrong. It's in 705.12 


https://www.civicsolar.com/support/installer/articles/what-panelboard-sizing-120-rule


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## dronai (Apr 11, 2011)

Why two invertors ? For two large strings on seperate parts of the roof ?


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## backstay (Feb 3, 2011)

dronai said:


> Why two invertors ? For two large strings on seperate parts of the roof ?


There are standard sizes to correspond with string sizes. So if you have want to install a 7.2kW-14.4kW system, I use these numbers because they fit nice inside my example. 12 modules in a string, 300 watts each equals 3.6kW. *Most of the inverters allow two strings.* The total would be 7.2kW, so that is just under the max 7.68kW a 200 amp panel can use. Your string size is limited by the lowest temperature in your area. Most inverters can't take more than 600 volts. So the colder it is the less number of modules you can series. If I had a 175 amp main in a 200 amp bus, I'd use two 6kW inverters to stay under the 12.48kW. Now you could buy a 225 amp panel, install the 175 main. Then you could put in 18.24kW

System sizing really starts by looking at the roof size, what's the max number of modules I can get up there. Then it's by service size and if it's a load side tap or line side. Then it's the thickness of the customer's wallet.


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## backstay (Feb 3, 2011)

Modules are up(twelve) plus the one that got hit by the tree. Wind gusts to 20 mph, so it was a challenge.


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## JoeCool612 (May 22, 2016)

backstay said:


> $11,600 for that system. Turn key, with batteries and with a plugin for a generator backup. A six panel is $17,400.


How long does it take to do a system like that? And how many guys?


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## zac (May 11, 2009)

JoeCool612 said:


> How long does it take to do a system like that? And how many guys?


That machine is a racist!









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