Just enough knowledge to be dangerous

[energyhunter]

I'm a busy old guy overwhelmed by prepper projects, food needs etc. I need to buy my solar components and wait my turn for delivery, presumably months out, to install an off grid system for our 1600 sq ft home. (Just my wife and I.) The energy audit is problematic because we purchased the property in Jan 2021 but did not occupy it until Aug 2021; All those months the house was empty and the 3 ton heating/cooling ran at bare minimum. The kw PV system we need I estimate is between 12 and 18. I'm hoping to use >400W Q cell (?) panels (12) on my garage roof which will hold that number perfectly. (Because the house roof is partially shaded.) Both roofs face mainly south/SW. I am comparing EG4 Lithium batteries 25.6V (24V) 5.12kWh ( x 2 inverters?) or Bluetti system AC 300 or 500 with 2 inverters for a 240V system to support our heating/cooling system. Quality and longevity of components is a must. I will not be feeding excess power to the grid we are on because here in Tennessee the payback is minimal. My purpose is driven by grid down, not pay back. My son would help me install the system and I will have a qualified electrician inspect it before operation. Can anyone here help me with my shaky assumptions and direct me to the most practical choice of components?

​

 

[SparkyJJO]

Roof angle sounds similar to mine, I have gotten up a little over 50kWh on a nice sunny March day with a 7.9kW panel setup. But, on a cloudy rainy day, I was lucky to get 5kWh. Keep in mind those cloudy days!

I would NOT use a 24V setup to run your house, especially if you're trying to do your central air (big power hog). And you'd need much more than 5 kWh of batteries. I'm building out closer to 20kWh of battery and I'm not planning on running AC from it. If you're trying to run your central air, you'll probably want a soft start unit for your compressor to bring down that huge surge load at startup. And I'm going to assume you'd want to run more than just the AC in a grid down situation anyway.

For a power audit you could start by looking at the nameplate power requirements from everything you want to run. It will be higher than actual, most likely, but will give you a worst case scenario. Then, figure out what you could likely run into running at the same time (examples being fridge and freezer both at the same time, lights, your laptop, and the wife turns on a hair dryer, etc). You can start there at least for inverter sizing.

Then you can look at battery sizing. If you're in a grid down, no solar situation, how much stuff would you be running? How long would you need it to run?

You could use a Kill-a-Watt to find out a 24 hour power usage from typical items (freezer, etc) to get an idea of an average day's load. Then add some percentage for excess usage in case of warmer ambient temps, etc...

Some stuff to think about.

I am NOT an expert. Just trying to help throw some ideas.

 

[Steve_S]

The general basic rule is to NOT exceed pulling 250A from a Battery Bank (Bank being a series of complete batteries configured in either series or parallel).
12V@250A=3000W,
24V@250A=6000W,
48V@250A=12,000W
240VAC@100A = 24,000W
240VAC@200A = 48,000W

Inverters can be set in Parallel which allows going past the 250A to deliver higher wattage.
High Voltage DC Systems are possible BUT there are several rules & requirements once you pass 48VDC and that adds costs as well.

Honestly, I would consider a "Split System" in your case... Set one Circuit Panel for Grid-Supplied power, to power the general stuff you can live without in the event of an outtage. Set 2nd panel as "Essentials" which is powered by your solar & batteries to run all the things that are required for living (and DO make sure you get the right priorites figured out). The Solar Side can operate independently and do it's own thing AND it can be "plugged" into the Grid Side so that in the event the Batteries need charging without Sun/Genset the Inverter/Chargers can pull from gid power to do so.

Many advanced systems can be programmed to do as indicated above and even to schedule for Off-Peak Use Only to charge batteries...
Some will allow to "Prioritize" in several ways... IS If Batt's Low, try Grid IF OFF-HOURS or start Genset, if on Peak-Rate time and so on...

A WORD OF CAUTION !
Many AIO's (All In Ones) can accomplish many of the functions noted above BUT NOT ALL ! Assume Nothing !
Tier-1 Top Quality products will be feature & function rich but at a price that goes with it. See Victron as one example.
Tier-2 QUality products will have several features and in many cases have add-ons to complete function "as needed".
Value products, are just that they work, do the job but may not be very efficient but get the job done cheaply.
AIO's also by their very nature tend to have a higher operating power consumption than component builds BUT this is the "overhead cost" that many fail to factor in, as AIO's are also a set of compromises and so this is the cost of compromise. (It is not that much but some freak out when they realize it).

Hope it helps, Good Luck.

 

[energyhunter]

Roof angle sounds similar to mine, I have gotten up a little over 50kWh on a nice sunny March day with a 7.9kW panel setup. But, on a cloudy rainy day, I was lucky to get 5kWh. Keep in mind those cloudy days!

I would NOT use a 24V setup to run your house, especially if you're trying to do your central air (big power hog). And you'd need much more than 5 kWh of batteries. I'm building out closer to 20kWh of battery and I'm not planning on running AC from it. If you're trying to run your central air, you'll probably want a soft start unit for your compressor to bring down that huge surge load at startup. And I'm going to assume you'd want to run more than just the AC in a grid down situation anyway.

For a power audit you could start by looking at the nameplate power requirements from everything you want to run. It will be higher than actual, most likely, but will give you a worst case scenario. Then, figure out what you could likely run into running at the same time (examples being fridge and freezer both at the same time, lights, your laptop, and the wife turns on a hair dryer, etc). You can start there at least for inverter sizing.

Then you can look at battery sizing. If you're in a grid down, no solar situation, how much stuff would you be running? How long would you need it to run?

You could use a Kill-a-Watt to find out a 24 hour power usage from typical items (freezer, etc) to get an idea of an average day's load. Then add some percentage for excess usage in case of warmer ambient temps, etc...

Some stuff to think about.

I am NOT an expert. Just trying to help throw some ideas.

Thank you SparkyJJO for replying to my first post. Yes, I will factor in those cloudy days to have a bigger margin of error.

I was assuming I would get 48V batteries. Just don't know if I should get rack mounted EGG or Bluetti more portable.

I just heard about a "soft start" 3 days ago to cut down the surge requirement for the 3 ton compressor. You just confirmed it. I replaced the old system when I moved in last August and it cost me $8700!! Had I known about going solar then, I would have purchased 2 or 3 smaller units they have now that are ultra efficient and ideal for solar set ups. Would have been half the price....Kicking myself.

Just bought a Kill-a-watt last month. I need to triage my essential vs luxury usage as you suggest. I'll make a chart. Guessing I would get a sub-panel to manage my essential usage. I need to be sure about the number of solar panels and batteries as I do not want a grid connection at all.

Good advice, thank you.

 

[energyhunter]

The general basic rule is to NOT exceed pulling 250A from a Battery Bank (Bank being a series of complete batteries configured in either series or parallel).
12V@250A=3000W,
24V@250A=6000W,
48V@250A=12,000W
240VAC@100A = 24,000W
240VAC@200A = 48,000W

Inverters can be set in Parallel which allows going past the 250A to deliver higher wattage.
High Voltage DC Systems are possible BUT there are several rules & requirements once you pass 48VDC and that adds costs as well.

Honestly, I would consider a "Split System" in your case... Set one Circuit Panel for Grid-Supplied power, to power the general stuff you can live without in the event of an outtage. Set 2nd panel as "Essentials" which is powered by your solar & batteries to run all the things that are required for living (and DO make sure you get the right priorites figured out). The Solar Side can operate independently and do it's own thing AND it can be "plugged" into the Grid Side so that in the event the Batteries need charging without Sun/Genset the Inverter/Chargers can pull from gid power to do so.

Many advanced systems can be programmed to do as indicated above and even to schedule for Off-Peak Use Only to charge batteries...
Some will allow to "Prioritize" in several ways... IS If Batt's Low, try Grid IF OFF-HOURS or start Genset, if on Peak-Rate time and so on...

A WORD OF CAUTION !
Many AIO's (All In Ones) can accomplish many of the functions noted above BUT NOT ALL ! Assume Nothing !
Tier-1 Top Quality products will be feature & function rich but at a price that goes with it. See Victron as one example.
Tier-2 QUality products will have several features and in many cases have add-ons to complete function "as needed".
Value products, are just that they work, do the job but may not be very efficient but get the job done cheaply.
AIO's also by their very nature tend to have a higher operating power consumption than component builds BUT this is the "overhead cost" that many fail to factor in, as AIO's are also a set of compromises and so this is the cost of compromise. (It is not that much but some freak out when they realize it).

Hope it helps, Good Luck.

Thank you Steve_S for replying to my post. The general rule you mention is something I'm not familiar with. I'll try to wrap my head around it.

The split system you bring up has a part I've not yet heard, from being new at this; If I understand you, even though I'm "off grid", it would automate grid usage if the batteries deplete for lack of solar charging. I may need to re-assess my passion to be fully off grid, but one thing is for sure: I don't want to be feeding extra power back to the grid as I mentioned because it doesn't pencil here in Knox Co Tennessee. Also I assume it will entail more paperwork and inspections to keep linemen safe etc.

Tier one quality components with great BMS is what I'm aiming for. Not sure as yet which system. Victron though might be overkill for my needs. Also I don't want my monitoring or adjusting to be dependent on my cell phone.

When I started my energy hunt a few months ago, I had a solar company come out to work up an estimate including a Generac battery and installation. The quote came in at $34,000!!! My son convinced me to get educated and do it myself. Counting the current US gov tax credit of 26%, I hope to pay not more than $15,000. I need to research more to learn if this is realistic, but remember that "pay back time" is not my concern; prolonged periods of grid down is my motivation.

Thank you for the links and all your input...much appreciated.

 

[Mike 134]

Have you run the PTwatts program yet?

 

[Steve_S]

If you already have grid power connected you can use it as a "backup" for the offgrid system, no different than a generator, except without fuel. Of course they all have connection fees and whatever they can lop on there to keep you connected, so that has to be factored in as well.

With a Split-System as I described, it also let's you scale up on your battery bank over time, t5hat's an advantage with LFP, you can keep adding to it as long as you have the right foundation built to handle it. Pre-planned capacity essentially.

Cell Phone apps for everything is the most common thing today LOL... like a POX really, just can't escape that... BUT Victron for example also has a PC Application and there are some programs that can run off a RaspberryPi to monitor & control everything (if compatible of course).

Soft-Start systems CAN be retrofitted to most equipment and there are many "kits & components" out there to do it. Quite often it's fairly inexpensive and not terribly difficult.

Whatever you do is DO NOT BUY ANYTHING until you have a Good Plan with solid figures all worked out.
A Failure to Plan is a Plan to Fail ! Take your time, ask questions, learn and look at how people have accomplished their own builds & the troubles they resolved. Never be afraid to ask a Question, the only Dumb Question is the One NOT ASKED ! This can be a very tricky subject and quite techy, so ASK !

Hope it helps, Good Luck.

 

[energyhunter]

Have you run the PTwatts program yet?

No...Did you mean PVwatts? (No on that too.)

 

[RV10flyer]

Last years monthly kWh consumption was between 1600-2500 kWh per month. I'm north of you 165 miles. All electric 2800 sq ft. 3- 16-20 SEER HP's. 1 ea Fujitsu 9K 33 SEER mini split. 80 gal wh. I installed 20,640W pv, two Sol-Ark 12K's and 132kWh LFE battery bank. We have barely made it four weeks without needing our 10kw Honeywell LP Gen. I can see already that we will need to install another 3440W of PV (top off the Sol-Arks PV input) and 53kWh of battery. It will be needed in Jan/Feb. Just to give you an idea of what a 4-person off-grid home rquires.

 

[energyhunter]

Last years monthly kWh consumption was between 1600-2500 kWh per month. I'm north of you 165 miles. All electric 2800 sq ft. 3- 16-20 SEER HP's. 1 ea Fujitsu 9K 33 SEER mini split. 80 gal wh. I installed 20,640W pv, two Sol-Ark 12K's and 132kWh LFE battery bank. We have barely made it four weeks without needing our 10kw Honeywell LP Gen. I can see already that we will need to install another 3440W of PV (top off the Sol-Arks) and 53kWh of battery. It will be needed in Jan/Feb. Just to give you an idea of what a 4-person off-grid home rquires.

This is very relevant for a regional comparison. The differences are that our house is 1600 sq ft, 2 level and we are just 2 adults in home. Also have natural gas for the heating but everything else is electric.

4 loads of wash once a week. We both use laptops every day. Very limited tv. Using elec stove everyday. Need to change our old 40g WH for larger but more efficient.

Our Feb usage was 707kw. Aug was 1295kw. (Have no figures before because we first occupied the house last Aug.) Might buy a soft start and just continue to use the new Trane 15 seer 3 ton.

Thank you RV10flyer for providing me with location relevant info about your system and real needs! I can adjust it for our needs and add a hefty margin for error. Much appreciated.

 

[energyhunter]

If you already have grid power connected you can use it as a "backup" for the offgrid system, no different than a generator, except without fuel. Of course they all have connection fees and whatever they can lop on there to keep you connected, so that has to be factored in as well.

With a Split-System as I described, it also let's you scale up on your battery bank over time, t5hat's an advantage with LFP, you can keep adding to it as long as you have the right foundation built to handle it. Pre-planned capacity essentially.

Cell Phone apps for everything is the most common thing today LOL... like a POX really, just can't escape that... BUT Victron for example also has a PC Application and there are some programs that can run off a RaspberryPi to monitor & control everything (if compatible of course).

Soft-Start systems CAN be retrofitted to most equipment and there are many "kits & components" out there to do it. Quite often it's fairly inexpensive and not terribly difficult.

Whatever you do is DO NOT BUY ANYTHING until you have a Good Plan with solid figures all worked out.
A Failure to Plan is a Plan to Fail ! Take your time, ask questions, learn and look at how people have accomplished their own builds & the troubles they resolved. Never be afraid to ask a Question, the only Dumb Question is the One NOT ASKED ! This can be a very tricky subject and quite techy, so ASK !

Hope it helps, Good Luck.

Yes, will use grid as the backup. The split makes perfect sense too. Soft start will be just what I need also.

"Do not buy anything" best advice yet!! I will complete a plan first and run it by the members of Will's forum here.

Thank you again Steve_S for steering me the right direction.

 

[Sirtate]

Thank you Steve_S for replying to my post. The general rule you mention is something I'm not familiar with. I'll try to wrap my head around it.

The split system you bring up has a part I've not yet heard, from being new at this; If I understand you, even though I'm "off grid", it would automate grid usage if the batteries deplete for lack of solar charging. I may need to re-assess my passion to be fully off grid, but one thing is for sure: I don't want to be feeding extra power back to the grid as I mentioned because it doesn't pencil here in Knox Co Tennessee. Also I assume it will entail more paperwork and inspections to keep linemen safe etc.

Tier one quality components with great BMS is what I'm aiming for. Not sure as yet which system. Victron though might be overkill for my needs. Also I don't want my monitoring or adjusting to be dependent on my cell phone.

When I started my energy hunt a few months ago, I had a solar company come out to work up an estimate including a Generac battery and installation. The quote came in at $34,000!!! My son convinced me to get educated and do it myself. Counting the current US gov tax credit of 26%, I hope to pay not more than $15,000. I need to research more to learn if this is realistic, but remember that "pay back time" is not my concern; prolonged periods of grid down is my motivation.

Thank you for the links and all your input...much appreciated.

I'm just spit-balling here.
But, what if you just used the grid to charge your Batt-Bank when solar was weak?
Kinda like turning the whole house into a giant U.P.S.

My understanding is; You've got grid power currently, and you're looking to avoid relying on it as much as possible. (If not 100%)

So, you'd have the setup you're talking about, with the entire house running on your own inverters, with the Batts being charged by solar.
But, you add a 100amp grid powered battery charger (like a Victron Centaur) in addition the rest. It runs independently of the solar system, with lower voltage settings than the solar, so if you have solar, it doesn't attempt to charge. If the bank drops below its setpoint, it'll start propping-up the bank...
It wouldn't be pushing any power back into the grid, and if the grid went down, the battery voltage would only drop if solar wasn't generating enough.
Meanwhile the inverters are supplying all the loads in the house.

 

[bones1]

I'm just spit-balling here.
But, what if you just used the grid to charge your Batt-Bank when solar was weak?
Kinda like turning the whole house into a giant U.P.S.

My understanding is; You've got grid power currently, and you're looking to avoid relying on it as much as possible. (If not 100%)

So, you'd have the setup you're talking about, with the entire house running on your own inverters, with the Batts being charged by solar.
But, you add a 100amp grid powered battery charger (like a Victron Centaur) in addition the rest. It runs independently of the solar system, with lower voltage settings than the solar, so if you have solar, it doesn't attempt to charge. If the bank drops below its setpoint, it'll start propping-up the bank...
It wouldn't be pushing any power back into the grid, and if the grid went down, the battery voltage would only drop if solar wasn't generating enough.
Meanwhile the inverters are supplying all the loads in the house.

I like that idea. Can you give me an idea of what would be good inverters( models etc) to use in this instance?

 

[energyhunter]

I'm just spit-balling here.
But, what if you just used the grid to charge your Batt-Bank when solar was weak?
Kinda like turning the whole house into a giant U.P.S.

My understanding is; You've got grid power currently, and you're looking to avoid relying on it as much as possible. (If not 100%)

So, you'd have the setup you're talking about, with the entire house running on your own inverters, with the Batts being charged by solar.
But, you add a 100amp grid powered battery charger (like a Victron Centaur) in addition the rest. It runs independently of the solar system, with lower voltage settings than the solar, so if you have solar, it doesn't attempt to charge. If the bank drops below its setpoint, it'll start propping-up the bank...
It wouldn't be pushing any power back into the grid, and if the grid went down, the battery voltage would only drop if solar wasn't generating enough.
Meanwhile the inverters are supplying all the loads in the house.

This grid powered battery charger is another new angle for me to explore...seems though that Steve_S was saying the grid would charge my batteries directly,,,hmmm...thank you for this new info.

 

[Steve_S]

There are various ways to configure advanced equipment.
For example I use a Samlex EVO Inverter/Charger with dual AC Input. 1 can be for Grid AC the other for Genset AC. Auto-Transfer is built in and the Samlex (Tier-1) are Very Programmable for various modes of operation.