New Off-Grid System

[matthewinder]

I have been researching and planning for a few months now. I think I have a plan that will work, but I do have a couple of questions and wanted a quick "system check" to make sure I am not missing anything. Any input you all can give is extremely helpful.

First a description of the project:
This is a completely off-grid garage lodge in northern Missouri. We are not close enough to any existing power to run poles for any reasonable rate, so we plan on building a system for 90% solar and 10% propane generator backup when needed in the Winter. This is a building that will be used mostly on weekends in the Spring/Summer/Fall with mid November (deer hunting) being the last real plan usage each year.

Usage:
- Spring/Fall we expect 100% solar with minisplit heating/cooling as needed.
- Summer we expect 100% solar with the minisplit on but sitting somewhere around 80.
- Mid November we expect to be 90% solar with the minisplit heating/cooling as needed.
- Winter we expect to be 90% solar with the minisplit heating to keep the building above freezing.

Building:
- 30' x 60' all steel building with spray foam insulation
- 28' x 30' will been fully finished living space
- Runs east/west with a single pitch (approx 30 deg) to give a nice south facing roof.
- Pole Barn construction with roof rafters on 4' centers
- Wired with no input to breaker box
- Plumed with no input to manifold

Major Loads (5120W , 13Kwh - 30 Kwh based on season):

Load​	Watts​	Hours​	Watt Hours​
3 head mini split	2500 W	3 - 10 (based on season)	7500 Wh - 25000 Wh
Standard Fridge	300W	4	1200 Wh
Microwave	1000 W	.25	250 Wh
Water Pressure Pump	1000 W	1	1000 Wh
Led lighting and fans	500 W	6	3000 Wh
TOTALS	5120 W	.	12950 Wh - 30450 Wh

Core System:
- 2 x EG4 6000XP Off-Grid Inverter
- 2 x EG4 48V Indoor 280Ah WallMount Battery
- 2 x EG4 wire way
- 30 x Hyperion 395W Bifacial Solar Panel
- Kohler 14kW Home Standby Generator 14RESA

Mounting:
- 2 x IMO DC Disconnect Rooftop Isolator Switch | 4 Pole | 2 String
- Roof mounting on Rails (TBD which solution)
- 3 Strings of 10 in series

Questions:
- Is it worth the extra $1500 to upgrade from Hyperion 400W(12 Year warranty) to Sirius (25 year warranty, US assembled)?
- Do I have a use case for the EG4 LiFePOWER4 Communications Hub?
- Do I need to plan on a Chargeverter (or 2) with that Kohler generator?
- Am I missing any obvious other components such as disconnects or fuses?
- Do I need a combiner box if I am planning to run these in three strings of 10 (in series) directly to the EG4s?
- I am concerned about battery, If I get 2 years down the road and realize I need more, how easy will it be to add?
- Should I be concerned about my 4' on center roof rafters for rooftop mounting?
- Am I bananas for wanting these on the roof vs a ground array (limited space and would need a long run to the building)?

 

[MisterSandals]

Major Loads (6000W all together):
- 3 head mini split (2500W)
- Standard Fridge (1000W)
- Microwave (1000W)
- Water Pressure Pump (1000W)
- Led lighting and fans (500W)

You need to put a usage time on each of these for different times of the year and come up with a daily Wh (watts x hours) number to properly size your array, SCC, battery and inverter.

 

[matthewinder]

You need to put a usage time on each of these for different times of the year and come up with a daily Wh (watts x hours) number to properly size your array, SCC, battery and inverter.

Good call out, I actually have this data figured at a more granular level, but my post already seemed like a novel so I was worried about overdoing it. I hope the new table helps to show what I am planning for. Right now I planned on building a system that could provide about 20kWH a day of power and then supplementing the additional with the Kohler Generator.

Its all estimates at this point, so the thought was run it for a year or two to determine real usage rates and solar gains and then adjust from there.

 

[Mattb4]

...

Questions:
- Is it worth the extra $1500 to upgrade from Hyperion 400W(12 Year warranty) to Sirius (25 year warranty, US assembled)?
- Do I have a use case for the EG4 LiFePOWER4 Communications Hub?
- Do I need to plan on a Chargeverter (or 2) with that Kohler generator?
- Am I missing any obvious other components such as disconnects or fuses?
- Do I need a combiner box if I am planning to run these in three strings of 10 (in series) directly to the EG4s?
- I am concerned about battery, If I get 2 years down the road and realize I need more, how easy will it be to add?
- Should I be concerned about my 4' on center roof rafters for rooftop mounting?
- Am I bananas for wanting these on the roof vs a ground array (limited space and would need a long run to the building)?

Before attempting to answer your questions I will say you look like you have put some thought into it all. Just understand that what might work for one person would not for another.

1. Long term Warranty periods require a company to be around a longtime and for that company to remain reliable. It has been my experience that paying more for better Warranty is a loosing proposition.
2. Don't have a clue. I run my PV without all the communication and remote stuff.
3. Depends if your EG4's will work with the Kohler. Since you are Off grid there is not the concern about preventing inadvertent grid export.
4. Likely you be finding all kinds of things you need when you start putting it all together. Tools and testing equipment for instance.
5. A combiner box is not needed if you are not paralleling the strings into an Array.
6. Adding more battery with liFePO4 is not too difficult especially if you have those tools I mentioned earlier. One big issue maybe communication.
7. So long as you roof meets the loading requirements it should not be an issue about the rafter spacing other than your rail anchor points.
8. Personally I prefer a ground mount setup to allow for panel cleaning and access. But I would not call you bananas because you wanted a roof mount setup. Especially if there was no good place to put a ground mount setup near to your home.

 

[MisterSandals]

system that could provide about 20kWH a day of power

20000Wh / 5h solar charging = 4000W solar panels operating at 100% (figure 5-6k)
4000W / 56V = 71A charger

If power needs are equal around the clock (they aren't but i have no data) and there are 19h outside solar charging:
20000Wh x 19h / 24h = 15833Wh stored in batteries

15833Wh / 51.2V battery nominal = 309Ah battery bank

 

[matthewinder]

20000Wh / 5h solar charging = 4000W solar panels operating at 100% (figure 5-6k)
4000W / 56V = 71A charger

If power needs are equal around the clock (they aren't but i have no data) and there are 19h outside solar charging:
20000Wh x 19h / 24h = 15833Wh stored in batteries

15833Wh / 51.2V battery nominal = 309Ah battery bank

Maybe I am missing a few things here. But my thought process is like this.

Based on PVWatts my solar is between 3.5 - 7 hours a day with the average at 5 (as you stated)

With my 12,000W of panels I will make 60,000 Wh of power take into account 10% loss. I am at 50,000 Wh on average (35 kWh - 65kWh).
This will give me enough to hit my 20,000 Wh a day goal and charge the battery (28500 Wh) from empty to full (if the previous day was cloudy or didn't get any solar).
This will in turn give my Solar system about a 1 day buffer from a completely lost solar day.

I also ran these numbers through the PVWatts and the PVGIS 5.3 calculator (HERE ).
The results say with a system my size and the power requirement on 20,000 Wh a day the batteries will only get completely drained 5% of the days and they will stay above 50% for 12% of the days. To me that sounds like a reasonable amount of time to run the generator.

Another small clarification you mention running the panels at 56V is there a reason for that? I planned on running 10 in series for a Voltage at my charge controller of about 310v @ 13 amp for about 4030 Watts at each MPPT (this setup will have 4, but only 3 utilized).

 

[matthewinder]

Before attempting to answer your questions I will say you look like you have put some thought into it all. Just understand that what might work for one person would not for another.

1. Long term Warranty periods require a company to be around a longtime and for that company to remain reliable. It has been my experience that paying more for better Warranty is a loosing proposition.
2. Don't have a clue. I run my PV without all the communication and remote stuff.
3. Depends if your EG4's will work with the Kohler. Since you are Off grid there is not the concern about preventing inadvertent grid export.
4. Likely you be finding all kinds of things you need when you start putting it all together. Tools and testing equipment for instance.
5. A combiner box is not needed if you are not paralleling the strings into an Array.
6. Adding more battery with liFePO4 is not too difficult especially if you have those tools I mentioned earlier. One big issue maybe communication.
7. So long as you roof meets the loading requirements it should not be an issue about the rafter spacing other than your rail anchor points.
8. Personally I prefer a ground mount setup to allow for panel cleaning and access. But I would not call you bananas because you wanted a roof mount setup. Especially if there was no good place to put a ground mount setup near to your home.

Thanks for your input. I appreciate your input on these questions. Its also always good to hear you're not "bananas"

 

[green mountain boys]

Why do you need such a large (14Kw) generator? Can't you use a much smaller generator to keep the batteries topped off when needed?

 

[MisterSandals]

Another small clarification you mention running the panels at 56V is there a reason for that?

I was figuring you'd charge your 51.2V nominal battery at about 56V.

With newly revealed info:
12000W solar / 56V charging = 214A charging amps available for 3x MPPT SCCs, ~70A per charger.

The panel voltage only needs to be within the SCC range.

I planned on running 10 in series for a Voltage at my charge controller of about 310v @ 13 amp for about 4030 Watts at each MPPT

Assuming Vmp of 31V @ 13A = 403W

12000W array / 403W panels = 30 panels

Why not 4 arrays of 8, 8, 7, 7 panels to go easier on your MPPTs? 57A, 57A, 50A, 50A

 

[matthewinder]

Why do you need such a large (14Kw) generator? Can't you use a much smaller generator to keep the batteries topped off when needed?

Ah good question. There are others invested in this building that REALLY want a way to run the building entirely off the generator. I think in the short term it will be our stop gap until the solar system is installed. But long term there will be a large switch to choose between the building getting power from the Generator or the Solar system.

 

[matthewinder]

Why not 4 arrays of 8, 8, 7, 7 panels to go easier on your MPPTs? 57A, 57A, 50A, 50A

The thought process here was 2 fold, but I fully admit ignorance so tell me if I have something wrong.

The MPPTs state an OPERATING VOLTAGE RANGE 120-385 VDC.

1) It would be much easier to expand this solar system at a later date if all the panels on the roof were wired together and I left 1 mppt free for an auxiliary set of panels if I felt like they were needed at a later date. (vs trying to tie into the roof strings or rewire later)

2) I felt like the more room I left on the lower end would ensure that I have the best chance of making power on cloudy or snowy days. If a string drops below 120v then my understanding is that it wont charge power the system. at 7 panels 50% efficiency already takes me below that threshold.

Thanks again for your input!

 

[MisterSandals]

The thought process here was 2 fold, but I fully admit ignorance so tell me if I have something wrong.

Sounds like you have it figured out right! I like all your reasoning.

 

[Brucey]

Maybe I am missing a few things here. But my thought process is like this.

Based on PVWatts my solar is between 3.5 - 7 hours a day with the average at 5 (as you stated)

With my 12,000W of panels I will make 60,000 Wh of power take into account 10% loss. I am at 50,000 Wh on average (35 kWh - 65kWh).
This will give me enough to hit my 20,000 Wh a day goal and charge the battery (28500 Wh) from empty to full (if the previous day was cloudy or didn't get any solar).
This will in turn give my Solar system about a 1 day buffer from a completely lost solar day.

You will prob get closer to 70% production from nameplate on average, versus your forecast 90%

 

[green mountain boys]

The thought process here was 2 fold, but I fully admit ignorance so tell me if I have something wrong.

The MPPTs state an OPERATING VOLTAGE RANGE 120-385 VDC.

1) It would be much easier to expand this solar system at a later date if all the panels on the roof were wired together and I left 1 mppt free for an auxiliary set of panels if I felt like they were needed at a later date. (vs trying to tie into the roof strings or rewire later)

2) I felt like the more room I left on the lower end would ensure that I have the best chance of making power on cloudy or snowy days. If a string drops below 120v then my understanding is that it wont charge power the system. at 7 panels 50% efficiency already takes me below that threshold.

Thanks again for your input!

10 of those panels in series at a temperature of -10C will yield a voltage of 421 volts. The voltage will be higher if the temperature is lower. Have you calculated the voltage for your record low temperature at your location? Do not exceed the maximum PV input voltage of the MPPT.

 

[MisterSandals]

10 of those panels in series at a temperature of -10C will yield a voltage of 421 volts.

Good catch. Lets run the numbers...

Specs show Voc temp coefficient of -.27%/deg C

Standard temp is 25C so -10C represents -35 deg C change

Voc is 36.98V x -35deg C delta x -.0027 = 3.5V increase so 40.5Voc at -10C

10x 40.5Voc = 405Voc yes, too high!

The MPPTs state an OPERATING VOLTAGE RANGE 120-385 VDC.

Is that the input limit or the MPPT (optimized) operating range? Big difference.

 

[green mountain boys]

Good catch. Lets run the numbers...

Specs show Voc temp coefficient of -.27%/deg C

Standard temp is 25C so -10C represents -35 deg C change

Voc is 36.98V x -35deg C delta x -.0027 = 3.5V increase so 40.5Voc at -10C

10x 40.5Voc = 405Voc yes, too high!


Is that the input limit or the MPPT (optimized) operating range? Big difference.

Whoops! I mistakenly used Pmax -0.35%/deg C in my calculation. Sorry for the confusion. Still higher than the 385V the OP cited.

 

[matthewinder]

DC INPUT VOLTAGE RANGE 100-480 VDC

RECOMMENDED MAXIMUM SOLAR INPUT 10000W (for both so 5000w each mppt)

Based on these two values I think I'm safe at those voltages, but there might be wasted voltage.

 

[MisterSandals]

Based on these two values I think I'm safe at those voltages, but there might be wasted voltage.

No, you're good. Once it starts producing, the voltage will drop to Vmp.

Best to state what voltages you are using and whether the ranges are working range or critical ranges!

 

[NC_hydro]

only thing I would suggest is take the money used on the giant generator and do 2 more batteries. And of course anything but Eg4 on the inverter if it was mine. If budget is important then Growatt, otherwise Victron or couple of midnight Rosie’s or The One.

 

[matthewinder]

only thing I would suggest is take the money used on the giant generator and do 2 more batteries. And of course anything but Eg4 on the inverter if it was mine. If budget is important then Growatt, otherwise Victron or couple of midnight Rosie’s or The One.

The generator is out of my hands as I've stated above. I was able to find it at half price, so that lessons the blow a bit.

But I'm surprised by the negative opinion of the EG4 inverter. My understanding is that it's the go to option for all in one off grid systems right now. I understand it shares much of the same components as the sol ark which is also highly recommended from what I've found.

Care to share more as to the issues you have with the EG4 6000XP?

 

[NC_hydro]

The generator is out of my hands as I've stated above. I was able to find it at half price, so that lessons the blow a bit.

But I'm surprised by the negative opinion of the EG4 inverter. My understanding is that it's the go to option for all in one off grid systems right now. I understand it shares much of the same components as the sol ark which is also highly recommended from what I've found.

Care to share more as to the issues you have with the EG4 6000XP?

It would work don’t get me wrong but it’s not really something designed to last 10-20yrs like a more quality unit like Victron, SMA or Midnite. Sometimes budget means you get what you can afford though.