Planning a Home Standby System - Input Welcome!

smdl

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Jan 8, 2022
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Hi, folks.

First post, as I am new to the forum and the world of residential backup power systems. I have been watching videos, reading posts, and working to formulate a plan to meet my needs. However, before starting to purchase components, I wanted to document what I am thinking of at a high level, and hopefully tap into the expertise of the group in order to minimize dumb mistakes. First of all, I'd like to acknowledge what a great resource this forum is, and thank everyone in advance for any assistance you can provide. A quick bit of background:

I live on a rural property fairly close to town, but without water, sewer or natural gas services. Obviously, this means that we have a well pump (1hp), and we also have a 1hp sewage grinder, plus two 1/3hp sump pumps. Until recently, we had a functioning Generac 7kW standby generator, which had been fairly trouble free for the 6 years it has been in service. However, on December 26th, it grenaded, leaving us operating on our backup portable generator and extension cords (until we get a better solution in place). Unfortunately, Generac has no parts available for the unit, so repair is impractical, and we need to come up with a better solution. While the current emergency power setup is not ideal, it is workable for the short term, so I am taking this opportunity to carefully consider our needs, and build a cohesive plan for a more resilient standby power system.

After a fair amount of research and careful consideration, I believe that the best solution for us is to install a 48v all-in-one system of sufficient capacity to support the critical loads, plus a few additional comforts (a few lights and a couple of outlets). Fortunately, our climate tends to be relatively moderate (at both extremes), so we don't need to be overly concerned about either heat or AC, and we're less concerned about comforts than just keeping the basics running. In addition to this, I'm planning on having an auto start generator that we can use for recharging batteries during extended power outages. Most outages in our area are <4 hours, but they can sometimes extend (Christmas Eve was more than 14 hours). As a further layer of redundancy, I am planning to maintain the existing transfer switch to allow the generator to be manually redirected to support the critical loads directly if the inverter ever fails. We're not immediately planning on solar, but like having the option, and will probably explore that further in the near future. For now, the priority is to get a reliable, automated, backup power solution in place, with normal replenishment through the grid, and generator backup as needed. Minimizing cost is important, but simplicity and reliability are the primary objective.

In the current setup, only the sump pumps, grinder, a few lights, and a couple of plugs have emergency power, but we would like to add refrigerator, freezer and well pump, at minimum. So, our emergency power needs look like something this:

1642020122685.png

With the assumption that not everything will running at the same time, and based upon the surge capacity of the unit, I'm leaning towards the following components, and would appreciate any feedback on my thinking:

- Growatt 6000T.
- Fortune LiFePO4 100AH cells. I'd be interested in hearing about recommended capacity and configuration.
- Overkill BMS (model appropriate for final battery configuration)
- Standalone charger to be powered by generator on demand from the 6000T.

The reason I am planning for a separate charger is that the generator is an 8000w (10,000w surge) unit that doesn't have the capacity to support the various loads (especially with startup) and the recharging load. Also, this is not an inverter generator, so the power isn't clean, and it probably isn't fantastic for the pumps over time. Configured this way, everything operates on inverter, taking advantage of clean power and 18,000w surge capacity, and the generator will just kick in as necessary to charge the batteries independently of the power situation. I'm also suspecting that a consistent charging load on the generator might be healthier for it over a constantly-changing load, not to mention that it will have to run much less than if it were supporting the loads directly.

Hoping to get input on a few questions:

1. Am I understanding things correctly? I'm still very much in learning mode, so please feel free to poke holes in my logic, or fill on obvious gaps.
2. Am I sizing the all-in-one unit correctly? I have read that it should be sized at about 70% of the anticipated combined run load, and I have gone larger than that, but should I go larger?
3. Based upon my obectives (reliability first, but minimizing costs where it make sense), are these components recommended, or should I be looking at others?
4. Does anyone know if the Growatt unit will immediately turn off the generator dry contact if grid power returns?
5. If the answer is no, are there any issues with running a separate charger in tandem with the inverter charger when grid power returns?
6. Based upon generator capacity, what standalone chargers might be recommended to recharge batteries during an extended outage?
7. If I understand correctly, the Growatt 6000T is an off-grid unit, so it should not be capable of feeding power back to the grid, correct?

Apologies for the long first post, but I wanted to try to provide as much info as possible up front. Looking forward to any input.

Cheers,
Shaun
 
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Bud Martin

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Right now the 7240W figure does not really mean much, it is the Watt-Hour/day that you need to know.
You need to figure out Watt-Hour you typical use in one day, you may actually want to measure in for 3 ~ 4 days period to see what the average will be.
That info then will be used to figure out the system size and run time.
Do you have Kill-A-Watt meter? That is one of the tool you should have.
 

GLC

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Bud is correct, you need a daily total of energy used. You will also need to have a possible max wattage draw that you may try to use all at one time to think about your inverter size.
 

OffGridInTheCity

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My goal is to power my home. Over the course of working on this, I have some stats I can share that can get you some ballpark understandings. I'm off-grid - meaning I don't feed back to the grid but I use the grid as backup. Things are sized to 100% of the PV I produce.

Goals:
I can power my home 75% for 8 months of the year - but in winter 4 months I depend on supplemental power. To power things in the winter I'd have to go to at least a 39kw PV array and would be wasting a LOT of power the other 8 months. I'd do it but I don't physically have room for 120 panels!! So you have to think about winter if you have one.

Panels:
I have a 13kw PV array that generates 18,000kwh/year (2000kwh/month hi/summer and 400kwh/month low/winter). You can use PVWatts https://pvwatts.nrel.gov/pvwatts.php for your location and type in various PV numbers and see what you're monthly production is likely to be.

Consumption:
My home consumes an overall yearly average of 2679w/hour. A low of 2217w/hour in winter and Aug spike of 4517w/hour for AC.

Off-grid ratio of Panels to Battery:
To consume all I produce with a 2600w/hour average consumption I need 40kwh of battery to go with 13kwh of PV. I believe this ratio can be used for guidance. So let's say.... you average 1100w/hour - e.g. 50% of what my house uses. Then you could approximate my experience with 6.5kw PV and 20kwh of battery. But you'd need supplemental power for 4 months of winter.

So maybe you have room for 13kw PV - you'd likely need at least 40kwh battery bank but would do much better in winter.

Best Advice:
Start of modestly but leave room for a 2 and 3rd GroWatt. Start of with 6kw of PV but leave room for 13 or 20kw of PV. Start of with 20kwh battery but leave room for 40 or 60 or 80kwh of battery. *Get a viable system up/running and then you'll gather info / learn a BUNCH - but leave room to grow.
 

smdl

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Joined
Jan 8, 2022
Messages
21
Right now the 7240W figure does not really mean much, it is the Watt-Hour/day that you need to know.
You need to figure out Watt-Hour you typical use in one day, you may actually want to measure in for 3 ~ 4 days period to see what the average will be.
That info then will be used to figure out the system size and run time.
Do you have Kill-A-Watt meter? That is one of the tool you should have.
Thanks, Bud. I don't have a Kill-a-Watt yet, but have ordered one, and should have it soon. I suppose that it would be fairly easy to connect each device (with the exception of the 240v well pump), but there is a lot of variability there. Friday and freezer should be no problem, but sump pump draw will vary greatly depending upon time of year and current weather conditions. I'll see what I can do and will share the results..

Cheers,
Shaun
 

smdl

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Jan 8, 2022
Messages
21
Bud is correct, you need a daily total of energy used. You will also need to have a possible max wattage draw that you may try to use all at one time to think about your inverter size.
I think the max potential draw should be as simple as adding up the surge specs listed above, or am I missing something?

Thanks for helping me to learn!

Cheers,
Shaun
 

smdl

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How old are the appliances? You can get big payback with new appliances.
Appliances are mostly as old as the house, which is 6 years. That said, they are steadily failing (Samsung), so are being replaced at a fairly rapid rate with new appliances.
 

smdl

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Joined
Jan 8, 2022
Messages
21
My goal is to power my home. Over the course of working on this, I have some stats I can share that can get you some ballpark understandings. I'm off-grid - meaning I don't feed back to the grid but I use the grid as backup. Things are sized to 100% of the PV I produce.

Goals:
I can power my home 75% for 8 months of the year - but in winter 4 months I depend on supplemental power. To power things in the winter I'd have to go to at least a 39kw PV array and would be wasting a LOT of power the other 8 months. I'd do it but I don't physically have room for 120 panels!! So you have to think about winter if you have one.

Panels:
I have a 13kw PV array that generates 18,000kwh/year (2000kwh/month hi/summer and 400kwh/month low/winter). You can use PVWatts https://pvwatts.nrel.gov/pvwatts.php for your location and type in various PV numbers and see what you're monthly production is likely to be.

Consumption:
My home consumes an overall yearly average of 2679w/hour. A low of 2217w/hour in winter and Aug spike of 4517w/hour for AC.

Off-grid ratio of Panels to Battery:
To consume all I produce with a 2600w/hour average consumption I need 40kwh of battery to go with 13kwh of PV. I believe this ratio can be used for guidance. So let's say.... you average 1100w/hour - e.g. 50% of what my house uses. Then you could approximate my experience with 6.5kw PV and 20kwh of battery. But you'd need supplemental power for 4 months of winter.

So maybe you have room for 13kw PV - you'd likely need at least 40kwh battery bank but would do much better in winter.

Best Advice:
Start of modestly but leave room for a 2 and 3rd GroWatt. Start of with 6kw of PV but leave room for 13 or 20kw of PV. Start of with 20kwh battery but leave room for 40 or 60 or 80kwh of battery. *Get a viable system up/running and then you'll gather info / learn a BUNCH - but leave room to grow.
Good advice to leave room to grow. Thanks for that.

Shaun
 

WYtreasure

It's not happy hour, I'm just like this.
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Thunder Basin Wyoming
Appliances are mostly as old as the house, which is 6 years. That said, they are steadily failing (Samsung), so are being replaced at a fairly rapid rate with new appliances.
The last time I bought an appliance it was used and that was about 6 years ago. There may be an issue with the way they were being powered, or those 6 children helping.
 

Bud Martin

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I think the max potential draw should be as simple as adding up the surge specs listed above, or am I missing something?

Thanks for helping me to learn!

Cheers,
Shaun
The power usage is rated in KW-Hr per day, see your utility bill as an example it will show what your average KW-hr you are using per day.
Lets say for simplicity, you have 100W lamp running for 24Hr, that means you consume 100W x 24Hr = 2.4KW-hr/Day, now if you leave the lamp on for only 10 Hours per day then your consumption will be 100W x 10Hr = 1KW-hr/Day, so if you have 1KW-hr battery, it will run for 10 hours.
The fridges and the pumps are not on 24/7 so that why you need to measure the actual power you use per day so you can calculate the correct system size to meet your needs.
I hope you understand my writing, English is my second language so my explanation may not make sense to you, may be some one can explain it better.
The surge spec is what you will need so you can get the inverter that can handle the surge when they start up, I.E. fridge compressor can have surge 5 ~ 7 times the running power. How did you measure the surge to come up with those numbers?
 
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smdl

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The power usage is rated in KW-Hr per day, see your utility bill as an example it will show what your average KW-hr you are using per day.
Lets say for simplicity, you have 100W lamp running for 24Hr, that means you consume 100W x 24Hr = 2.4KW-hr/Day, now if you leave the lamp on for only 10 Hours per day then your consumption will be 100W x 10Hr = 1KW-hr/Day, so if you have 1KW-hr battery, it will run for 10 hours.
The fridges and the pumps are not on 24/7 so that why you need to measure the actual power you use per day so you can calculate the correct system size to meet your needs.
I hope you understand my writing, English is my second language so my explanation may not make sense to you, may be some one can explain it better.
The surge spec is what you will need so you can get the inverter that can handle the surge when they start up, I.E. fridge compressor can have surge 5 ~ 7 times the running power. How did you measure the surge to come up with those numbers?
Thanks, Bud. Your explanation was excellent, and makes perfect sense from the perspective of calculating battery requirement. All of the numbers that I have listed are theoretical and were obtained from one of online load calculators available. They do not reflect actual usage at my home. Sorry, I should have mentioned that previously.

So, the numbers listed reflect a worst possible case scenario, where all of the appliances are running all of the time. My assumption was that this formed a 'safe' approach where the worst case would be more than covered, with lots of available capacity to add other things, as well.

Then, as you say, I'll need to understand how long I want everything to run, which will dictate the battery capacity required.

Thanks,
Shaun
 

Bud Martin

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About the fridge power consumption.
My fridge (1991 25 cu-ft Whirlpool) shows about 250W (ice maker is not on) of power using Kill-A-Watt meter, after 24 Hours it uses about 2.2KW-hr/day (that is included the 700W power for about 1/2 hour for defrosting function), it is 2.2KW-Hr because the compressor cycle on and off, if it does not cycle on/off then the power consumption will be huge! 700W x 24Hr = 16.8KW-hr/day. You must have a big fridge, 700W running Watt is a lot.
 

smdl

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Makes sense, thanks. I'm sure the numbers used in the online calculator are also 'safe'. I'm this case, maybe REALLY safe.
 

Wellbuilt

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you’re going to have a problem with the pumps, they can surge to 4 times running watts plus the frig /freezers
that’s a big system to just sit there in case the power gos out .
You may be better off with a small battery / inverter system for lites radio tv charging and run the generator for the pumps and frig
 

smdl

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you’re going to have a problem with the pumps, they can surge to 4 times running watts plus the frig /freezers
that’s a big system to just sit there in case the power gos out .
You may be better off with a small battery / inverter system for lites radio tv charging and run the generator for the pumps and frig
Fair point, and I haven't done a great job in explaining *why* I'm doing this. What I'm looking for, is peace of mind. The thought of being away, and my wife having to try to figure out why the generator isn't starting, or what to do because it just blew up (real world scenario!) makes it difficult for either of us to relax. With an inverter in place, I know that I've at least got X hours of standby without having to worry about water (in our out). I'm also pretty comfortable that the majority of power outages in my area are likely to be resolved before the batteries are depleted. Finally, having the ability to charge the batteries with the generator extends this window even further. Still, you're right. These larger surge loads are definitely the elephant in the room.

Thanks again.

Shaun
 

Wellbuilt

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Hmmmmmm , if you want piece of mind just get a Honda ?
Dam things just run , no fuss no muss just power .
You could get a switch that would only allow one device at a time to come on .
You could get a diesel unit for a fraction of what a 3 inverter with a pile of battery’s system would cost .
 

Brett V

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I installed a Growatt 6000T for the exact purpose you describe. Since I already had the majority of the house on a sub panel for generator operation, it was an easy install. Like you, I'm in the country with no public utilities other than electricity and my biggest challenge was getting water without the generator. So far the Growatt has been flawless and easily runs everything in the house except a few obvious power hogs like an electric range, washer and dryer, dish washer, and electric baseboard heat. I had installed a heat pump type water heater so I could run it on the generator and it's on the sub panel fed by the Growatt. My current battery is a 16s pack using EVE 230 amp cells and a Overkill 100 amp BMS. I'm in the process of upgrading to a second battery of identical specs for extended run time. With the single battery I run the whole house for 8-12 hours depending on loads but we have tested it to absurd levels and the Growatt had no problems. The wife and I both took showers, she had the tv on all day, including a sound bar. I worked all day in my home office with 2 computers and 3 monitors going. There were lights on, she heated her lunch in the microwave, and even vacuumed the carpets in the downstairs of the house. The whole time we were doing this, an 18,000 btu mini split heat pump was in AC mode and cooling the house. There was literally no way to tell the house was running off grid!

I installed a manual transfer switch in the AC input lead to the Growatt so I can run and charge on generator. I have a Smarter Tools 9500 watt peak 7500 watt continuous generator and although this generator is known to be dirty, the Growatt handled it. Going by the numbers on the BMS, the charging in the Growatt at 40 amps DC is around 3000 watts AC load. She was using a hair dryer when the well pump kicked in and there was a significant voltage sag which threw an under voltage alarm which made me nervous but the Growatt recovered. This again was an absurd test to see how far we could push it before things got wonky. Although I believe the generator would have been sufficient if I wanted to be careful about loads, I got a good deal on a used Harbor Freight 9500 watt inverter generator so we'll be running with that in the future.

Overall the Growatt 6000T has exceeded my expectations and I plan to but up a moderate size ground mount solar panel array maybe next summer just for a SHTF scenario.
 

smdl

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Hmmmmmm , if you want piece of mind just get a Honda ?
Dam things just run , no fuss no muss just power .
You could get a switch that would only allow one device at a time to come on .
You could get a diesel unit for a fraction of what a 3 inverter with a pile of battery’s system would cost .
Very good point, and I'm intending to purchase a Honda generator, at some point, for backup charging. The only reason I didn't go that way last time was that I wanted propane, which Honda doesn't offer. I know that this can be added, but that then messes with warranty. Regardless, as I say, I'll likely go with a Honda, at some point.

Cheers,
Shaun
 

smdl

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I installed a Growatt 6000T for the exact purpose you describe. Since I already had the majority of the house on a sub panel for generator operation, it was an easy install. Like you, I'm in the country with no public utilities other than electricity and my biggest challenge was getting water without the generator. So far the Growatt has been flawless and easily runs everything in the house except a few obvious power hogs like an electric range, washer and dryer, dish washer, and electric baseboard heat. I had installed a heat pump type water heater so I could run it on the generator and it's on the sub panel fed by the Growatt. My current battery is a 16s pack using EVE 230 amp cells and a Overkill 100 amp BMS. I'm in the process of upgrading to a second battery of identical specs for extended run time. With the single battery I run the whole house for 8-12 hours depending on loads but we have tested it to absurd levels and the Growatt had no problems. The wife and I both took showers, she had the tv on all day, including a sound bar. I worked all day in my home office with 2 computers and 3 monitors going. There were lights on, she heated her lunch in the microwave, and even vacuumed the carpets in the downstairs of the house. The whole time we were doing this, an 18,000 btu mini split heat pump was in AC mode and cooling the house. There was literally no way to tell the house was running off grid!

I installed a manual transfer switch in the AC input lead to the Growatt so I can run and charge on generator. I have a Smarter Tools 9500 watt peak 7500 watt continuous generator and although this generator is known to be dirty, the Growatt handled it. Going by the numbers on the BMS, the charging in the Growatt at 40 amps DC is around 3000 watts AC load. She was using a hair dryer when the well pump kicked in and there was a significant voltage sag which threw an under voltage alarm which made me nervous but the Growatt recovered. This again was an absurd test to see how far we could push it before things got wonky. Although I believe the generator would have been sufficient if I wanted to be careful about loads, I got a good deal on a used Harbor Freight 9500 watt inverter generator so we'll be running with that in the future.

Overall the Growatt 6000T has exceeded my expectations and I plan to but up a moderate size ground mount solar panel array maybe next summer just for a SHTF scenario.

This is very relevant and helpful, thanks. I'll take some time to review digest it tonight, and will undoubtedly have a few questions, if you don't mind?

Cheers,
Shaun
 
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