Sanity Check ~13kw System Build, Storage Requirements, Growatt 12kw?

jasonjsimon

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Joined
Nov 2, 2021
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5
Hi.

New member here that's been studying up on building out a solar system for my 3k sq ft home on acreage. First off this forum and it's members are awesome and thanks to Will for all his great DIY videos.

I have grid power, but want to go off it entirely - right away if possible, but gradually is fine if necessary if costs become a constraint. I've run through several energy audits and calculators, but I'm not clear on a few product specific questions.

My average daily usage over the 10 months in my home is around 43kwh per day. Typical household appliances, AC/Heat pump (propane), electric water heater and just added propane tankless water heater, washer/dryer, dishwasher, 2x desktop PC's, 5 laptops, lots of small electronics, security cams, etc.

I have a large shop with gobs of south-facing rooftop next to my home, so I'm thinking I can go with less efficient panels and gain some cost savings from that.

Here's what I'm thinking I can start my system with:
I know I have lots more to learn, but here's where I'm getting stuck.
  1. Can the 12kW inverter handle 56x 48v 240watt panels? I'm thinking 4 rows of panels splitting the full system into 4 3360watt segments. Am I reading correctly that this inverter can only accept a max of 250volts and/or 7000 watts - or is that per string/array? Am I going too big with my plan for 56 panels?
  2. I'm reading the 12kW inverter cannot stack. Is there any way to expand it if needed in the future? I'm honestly not even clear if the 12kw is sufficient for my usage.
  3. Am I better off going with 3 (or 4) of the stackable 5kw inverters? If so, is the midpoint transformer needed for all inverters or is 1 sufficient?
  4. With an average daily use of 43kwh, is 30kwh battery storage enough? Will this get me through a cloudy day or two given the solar input I'm planning? Could I get away with 4 of these initially with a capacity of 20kwh?
I apologize if some or all of the questions are obvious or stupid, but appreciate any help I can get as I get started.

Jason
 

mopat

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Joined
Jun 22, 2020
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510
You can place 6 of these panels in series and parallel 5 more for a total of 30 panels.
Open circuit voltage and wattage should be appropriate for your "1x 12kW 48V 250VDC 120A Inverter by Growatt" .
Cannot figure out your climate, sun index, but maybe figure 4 days of no sun.
 

jasonjsimon

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Joined
Nov 2, 2021
Messages
5
You can place 6 of these panels in series and parallel 5 more for a total of 30 panels.
Open circuit voltage and wattage should be appropriate for your "1x 12kW 48V 250VDC 120A Inverter by Growatt" .
Cannot figure out your climate, sun index, but maybe figure 4 days of no sun.
Thanks so much for your response. I guess that would only utilize a smaller count of panels than I was planning to buy... I'm in NW Missouri, so I'm not sure if that would give me enough juice to supply 43kwh per day. If I'm doing the math right, the 30 panels would provide 7000watts (at best) and assuming 4.7 hours per day I'd get about 33kwh per day from the array. I'm not sure if I'm calculating that correctly.
If that's the case, can anyone recommend a different all-in-one inverter that might accept a higher input?
 

740GLE

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Apr 30, 2021
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525
How are you possibly using that much energy each day? 43kwhr is huge! Do you have a hot tub or two you don’t know about?

What can be done to reduce your consumption?
 

Diysolar123

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Feb 28, 2021
Messages
645
How are you possibly using that much energy each day? 43kwhr is huge! Do you have a hot tub or two you don’t know about?

What can be done to reduce your consumption?
well, in florida with AC running in a well insulated house I run about 40KWh a day hehe
and no it is not set at "server room" temperatures ;-)
 

Diysolar123

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Feb 28, 2021
Messages
645
Thanks so much for your response. I guess that would only utilize a smaller count of panels than I was planning to buy... I'm in NW Missouri, so I'm not sure if that would give me enough juice to supply 43kwh per day. If I'm doing the math right, the 30 panels would provide 7000watts (at best) and assuming 4.7 hours per day I'd get about 33kwh per day from the array. I'm not sure if I'm calculating that correctly.
If that's the case, can anyone recommend a different all-in-one inverter that might accept a higher input?
well, you have hit the reality point in your calculations...people often use a LOT of power, much more than they think...

while solar math seems tricky it really is not, X amount comes in, Y amount goes out.
You seem to have a handle on what you "on average" use, which was your 43KWh a day; that is a serious amount of power.
This can be done with solar but it will be a challege...

first get a handle on your local sun conditions by looking here and put in your items in an online calculator to get to your 43KWh:

this is just a ball park of course
you really need to get a handle on what your specific area sun hours are per day, so your real zip code will get that.
In addition you want to design for WINTER sun hours..

I suspect your current solar panels and battery bank are probably half of what you would actually need...

complete a full audit of what you are using and study that to shrink your power footprint.
If you have really really deep pockets to spend on this trying to go full modern comforts all on solar in a reasonably large house means a rather large system.

Think about these things:

1) your battery storage size is what you need for cloudy days AND nights; its not just about a single day...Have you ever had 4 cloudy days in a row??
2)your solar array needs to provide energy to your house AND charge your batteries..at the same time!
3)solar power needs a lot of space unless you willing to seriously change your power demands. you must NOT HAVE ANY SHADOWS on your panels; this can be a challenge even for people that have space.
 

jasonjsimon

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Joined
Nov 2, 2021
Messages
5
How are you possibly using that much energy each day? 43kwhr is huge! Do you have a hot tub or two you don’t know about?

What can be done to reduce your consumption?
Yes, I'm sure it's a lot. As of now we aren't too conservative and there's some things we can work on, but I also want to build it with the max usage in mind. And yes, we do have an inflatable hot tub we use outside for a couple months in the winter time but I'm not too sure how much power it draws by itself. :)
 

jasonjsimon

New Member
Joined
Nov 2, 2021
Messages
5
well, you have hit the reality point in your calculations...people often use a LOT of power, much more than they think...

while solar math seems tricky it really is not, X amount comes in, Y amount goes out.
You seem to have a handle on what you "on average" use, which was your 43KWh a day; that is a serious amount of power.
This can be done with solar but it will be a challege...

first get a handle on your local sun conditions by looking here and put in your items in an online calculator to get to your 43KWh:

this is just a ball park of course
you really need to get a handle on what your specific area sun hours are per day, so your real zip code will get that.
In addition you want to design for WINTER sun hours..

I suspect your current solar panels and battery bank are probably half of what you would actually need...

complete a full audit of what you are using and study that to shrink your power footprint.
If you have really really deep pockets to spend on this trying to go full modern comforts all on solar in a reasonably large house means a rather large system.

Think about these things:

1) your battery storage size is what you need for cloudy days AND nights; its not just about a single day...Have you ever had 4 cloudy days in a row??
2)your solar array needs to provide energy to your house AND charge your batteries..at the same time!
3)solar power needs a lot of space unless you willing to seriously change your power demands. you must NOT HAVE ANY SHADOWS on your panels; this can be a challenge even for people that have space.
Thanks so much for your input. I really appreciate it.

I'm starting to understand how big of an undertaking it will be to go off-grid with our current usage. I put my zip and monthly kwh into the calculator and it's advising I need a 23.5kw array!

Funny how my initial guesses of what I needed already had to be doubled when I first started calculating it all out. Now we're looking at doubling it all again. :)

Fortunately I do have a large south facing roof with no shade - roughly an 80'x28' area. I calculate that I could easily fit 92 panels in landscape orientation with room to spare. Coincidentally, 92 of these 240watt panels equates to 23kw. That's still a lot bigger than what I was planning/hoping. :)

I definitely understand the battery storage needs to account for a number of low solar days... I do like the idea that I can add more and more battery over time to build bigger as needed to ease the upfront cost a bit.
 

jasonjsimon

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Nov 2, 2021
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The 12kW 48V 250VDC 120A Inverter by Growatt is NOT stack-able; so maybe consider (2) MPP Solar LV6548, they are stack-able.
The LV6548 will take up to 250Vdc PV input and 8000 watts.
Two of these will handle all 56 panels.
Thanks for pointing me in the direction of the LV6548. I love that it is a split phase and stackable up to 6. Looks like a great unit. Do you know where the best place to get these would be? I haven't been able to find much more than a seller in China with them on eBay. Several other stores show they carry them, but are out of stock.
 

NaughtGeek

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Oct 7, 2021
Messages
7
The LV6548 stays on backorder. If that's the route you go, be sure to leave yourself 45-60 days lead time provided the supply chain doesn't deteriorate any further.
 

duunoit

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Apr 28, 2021
Messages
15
Thanks for pointing me in the direction of the LV6548. I love that it is a split phase and stackable up to 6. Looks like a great unit. Do you know where the best place to get these would be?

Shows out of stock right now. I would get on the email list to be notified when they come back in.
 

Quattrohead

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Joined
Oct 13, 2021
Messages
19
Hi Jason,
You are doing similar to what I hope to do next year, except I am building a new house with ICF and spray foam insulation on the roof deck.
Walls will be R22 but equivalent to R50 and roof around the same R50, high quality doors and windows etc.
I also have plenty of land so can save on cheaper smaller used panels if I need to save costs. However, Mrs QH insists on 100% reliability like/better than grid. I am thinking of using a critical circuits and general circuits panels, both 240v. Also I want to wire the house exactly 100% to code so that any possible future buyer (after I am dead !!!) could hook up to FPL with no issues at all.

So power saving thoughts for you.
HWT, use a hybrid unit in the garage. Plenty of heat available and you get a cooler dryer garage.
HVAC use a variable speed compressor system like Mr Cool/ Gree/ Daikin split units. They soft start and run according to actual load.
Clothes dryer. I am doing to try and run it at half heater power, either with a big (6KW) power controller or simply running a different heater coil of around 3KW. Might have to built this.
Cooking, use an air fryer. Great food from these.
LED lighting obvious savings and better light.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,397
I have grid power, but want to go off it entirely - right away if possible, but gradually is fine if necessary if costs become a constraint. I've run through several energy audits and calculators, but I'm not clear on a few product specific questions.

Why would you want to do that? Batteries cost more per kWh (purchase price divide by all the kWh cycled through them until they're dead or at end of useful life) than buying power from the grid. With a few exceptions it recycled or DIY batteries actually last as long as hoped.

With grid available, I would only use batteries to ride through power outages.

I put my zip and monthly kwh into the calculator and it's advising I need a 23.5kw array!

Coincidentally, 92 of these 240watt panels equates to 23kw. That's still a lot bigger than what I was planning/hoping. :)

24kW isn't entirely unreasonable, and might cost $8k for the panels. I put hardware (no labor) for grid tie at $1/watt, so could reach $24k with inverters, mounting, electrical. But if grid-tie net metering, probably doesn't need to be so big because you build for average year round, not for the month with least sun.

The 240W SanTan panels may not be your best choice. More recent panels with 20% or higher efficiency put out 1.5x the power for a given area.

You have some motors to power. Find their Locked Rotor Amps, or multiply nameplate running amps x5 to get surge current. That's what your inverter (and battery) need to produce for maybe one second. This may influence which inverter you buy, assuming you do want off-grid or grid-backup.
 

markansas

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Joined
Nov 23, 2021
Messages
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Why would you want to do that? Batteries cost more per kWh (purchase price divide by all the kWh cycled through them until they're dead or at end of useful life) than buying power from the grid. With a few exceptions it recycled or DIY batteries actually last as long as hoped.

With grid available, I would only use batteries to ride through power outages.



24kW isn't entirely unreasonable, and might cost $8k for the panels. I put hardware (no labor) for grid tie at $1/watt, so could reach $24k with inverters, mounting, electrical. But if grid-tie net metering, probably doesn't need to be so big because you build for average year round, not for the month with least sun.

The 240W SanTan panels may not be your best choice. More recent panels with 20% or higher efficiency put out 1.5x the power for a given area.

You have some motors to power. Find their Locked Rotor Amps, or multiply nameplate running amps x5 to get surge current. That's what your inverter (and battery) need to produce for maybe one second. This may influence which inverter you buy, assuming you do want off-grid or grid-backup.
panels are cheap .. used i bought 30 trienas at 240watts for 1800.. free shipping and that is over 7k watts . good time to buy
 

Zwy

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Joined
Jan 3, 2021
Messages
835
Thanks so much for your response. I guess that would only utilize a smaller count of panels than I was planning to buy... I'm in NW Missouri, so I'm not sure if that would give me enough juice to supply 43kwh per day. If I'm doing the math right, the 30 panels would provide 7000watts (at best) and assuming 4.7 hours per day I'd get about 33kwh per day from the array. I'm not sure if I'm calculating that correctly.
If that's the case, can anyone recommend a different all-in-one inverter that might accept a higher input?
The way around overpaneling an All In One like the GW 12Kw unit over 7000w is to add a second charge controller. Do not run over 7000w into the inverter, regardless of what sellers might tell you. One member here overpaneled and let the magic smoke out. Split your array so you only have less than 7000w into the GW 12Kw unit and the rest to the second SCC.

Several choices out there, Watts247 has a SCC in GW like this one https://watts247.com/product/sc48120/ and some use a Midnite for extra SCC capacity.

I went with the LV6548 in parallel, maybe it doesn't work out. I had thought about the GW 12Kw unit but decided in the end to go with the LV6548 in parallel.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,397
If you can do multiple PV orientations, one string facing SE and one facing SW with 90 degree angle between them should let you over-panel to 140% of wattage (rating) without exceeding 100% of current and instantaneous wattage. With 60 degree acute angle, 200% of wattage without exceeding 100% of current (but diminishing Wh of harvest per W of panel rating, because more of the off-angle sun exposure gets clipped by horizon.)

Do this even with additional SCC. Instead of running GW at 100% (one orientation) and SCC at 100% (one orientation), you can use 90 degree angle to run each at 70% for less stress. Charging over more hours of the day also means less DoD from battery at night.
 
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