Off Grid Solar System, opinions and advice welcomed

[JamesHird]

Long story short, my wife and I have bought 6.5 acres in South Western Oklahoma. We are going to be starting an off grid homestead, I'm going down at the end of this month (January) to start the ground works. She will be following down later in the spring with our 3 month old son.

I have done a fair bit of research but am not an expert in any way.

The system we have gone for is:

1x 5kW Stackable 48V 240VAC 100A 450VDC Off-Grid Inverter by Growatt (with transformer)​

1x 48V 100AH LiFePower4 Battery by EG4​

8x SanTan Solar T Series 250W solar panels​

This is the first solar system I have ever built so am a little intimedated so would like feed back on the set up.

I'm planning on having all 8 panels in series. Each panel has a VOC of 37.6 therfore the string should produce 300.8VOC. The charge controller/inverter from growatt has a max input of 450v so this should be ok. Right?

The reasoning behind this set up is:

• We need something big enough to power our 5th wheel trailer (major appliances: small fridge freezer, washing machine, propane dryer (winter only), fans, charging battery power tools, small economical window AC unit for a couple of hours a day in the summer, lighting and device charging)
• We dont have a massive budget. It would be nice to have more batterys and solar panels but we cant afford it at the moment
• We can add to this set up as and when we need it. If we need more solar panels then add 4/6/8 more put them in parallel through a combiner box and were good. when we can afford more batterys then add 1 or 2 more. And eventually when we need more watts of power add another charge controller/inverter
• for a complete novice this seems like a straight forward set up. all I need to worry about is wiring up the solar panels and the battery correctly.
• If we dont have enough juice from the solar panels then we can charge the batterys with our generator through the growatt all in one system.

My main questions are:

• is our system big enough for our needs?
• does anyone see any problems with our set up?
• have i missed anything?
• is it possible to charge our batterys with our generator through the growatt all in one system? It has AC input so I think it should be fine. When we bought the growatt inverter through signature solar the guy tried to sell us the battery charger they had on sale at the same time. when I told him I could charge the battery directly through the all in one system he forwarded me to the tech team. I was on hold for a while then the line dropped. So was he just doing his job, selling things or do I indeed need a seperate battery charger.

Thanks in advance, please be nice, i'm new to this. if there is any more infomation i should provide please let me know.

 

[Hedges]

The Voc does sound OK.
If you wired instead as 4s2p, would the Vmp be high enough for the inverter?

You have 2000W of PV panels, 4800W of panels. 2.4 hours of production to recharge 100%.
What I'm thinking is, you might fully recharge battery, then waste PV production, then draw some power, then have a lower state of charge beginning the night.

With 4s aimed South East and 4s aimed South West, you get about 0.7 as high a peak power, 1.4kW. But more hours to (almost) make up for it.
That might keep battery somewhere between empty and full during the day.

2000W/4800W = ~ 0.4C charge rate, typically acceptable for lithium.
Determine what colder temperature is OK at 0.4C (it isn't 0 degrees C, should be greatly reduced current near freezing), and set low voltage charge disconnect accordingly.
If 4s2p as I suggested, then 1400W/4800W = 0.29C, so a bit lower temperature is OK.

Sometimes people have trouble with a generator feeding an inverter/charger because it is picky on frequency. In such case a separate charger can be a solution.

You may or may not need a precharge resistor to avoid 1000's of amps surge when connecting battery, so have some suitable resistor available (I think a 100' or 250' roll of Romex can serve, but most people use a power resistor.)

Use a DMM to double-check things before connecting and before closing switches. Make sure of voltages, polarity, and no voltage before touching terminals.

A DC disconnect if not built in is handy to isolate wires before work. At least, shut off inverter, confirm PV terminals have gone to Voc (no current), then unplug MC connectors for both positive and negative. Then confirm voltage has dropped to zero.

 

[sunshine_eggo]

The system we have gone for is:

1x 5kW Stackable 48V 240VAC 100A 450VDC Off-Grid Inverter by Growatt (with transformer)​

This will be pretty power hungry even when it's not providing any loads. They have a pretty high idle burn - about 90W. This will use 2160Wh/day. This is almost 42% of your battery capacity - just being on and providing no loads.

1x 48V 100AH LiFePower4 Battery by EG4​

Inadequate. See above.

8x SanTan Solar T Series 250W solar panels​

These probably work at about 80% rated, so you have about 1600W of panels. This should get you about 8kwh/day on good days.

This is the first solar system I have ever built so am a little intimedated so would like feed back on the set up.

I'm planning on having all 8 panels in series. Each panel has a VOC of 37.6 therfore the string should produce 300.8VOC. The charge controller/inverter from growatt has a max input of 450v so this should be ok. Right?

Yes.

Note that series panels can suffer from shading. Hopefully, your mounting scheme can insure that all panels remain unshaded from sunrise to sunset.

The reasoning behind this set up is:

• We need something big enough to power our 5th wheel trailer (major appliances: small fridge freezer, washing machine, propane dryer (winter only), fans, charging battery power tools, small economical window AC unit for a couple of hours a day in the summer, lighting and device charging)

That's a big ask for the system you've selected. You really need to use the energy audit spreadsheet in Resources and calculate your needs.

If you have an absorption fridge (ammonia based, propane or AC powered), do not run it on AC. Run only on propane. On AC, they'll destroy you.

• We dont have a massive budget. It would be nice to have more batterys and solar panels but we cant afford it at the moment

Last thing you want is to buy a bunch of stuff and then realize it's no good for you. You've selected an inverter that consumes 40% of your battery capacity before you even get to use it.

Do some more planning with an energy audit.

My main questions are:

• is our system big enough for our needs?

No.

• does anyone see any problems with our set up?

Yes. Mentioned above.

• have i missed anything?

Yes. You have no defined goal that says, "I need to use X Wh of energy per day." Right now, you're limited to about 8kWh/day total with only about 3kWh/day available when solar is unavailable. Since you don't know your needs, you don't know if that will work for you.

• is it possible to charge our batterys with our generator through the growatt all in one system? It has AC input so I think it should be fine. When we bought the growatt inverter through signature solar the guy tried to sell us the battery charger they had on sale at the same time. when I told him I could charge the battery directly through the all in one system he forwarded me to the tech team. I was on hold for a while then the line dropped. So was he just doing his job, selling things or do I indeed need a seperate battery charger.

The growatt AC charger is not typical. It will not act as a battery charger like the solar does - no bulk, absorption, float. It simply turns off below a voltage and stops immediately once the upper voltage is reached, so fully charging is not easy, but you can easily get > 80% charged.

You will need to set the OFF voltage to 58V and the ON voltage to as high as it will go, but under 58V. If your battery is between the on and off values, it won't charge.

 

[Rednecktek]

Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:

1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.

1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the Uber-Sun-Hours calculator site to help figure out how much you'll have to work with. That will be a box in the Power Audit form.

2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that.

3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger. Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.

4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.

5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round ) and help figure out which parts and pieces you're going to want to get.

 

[12VoltInstalls]

The energy audit will tell the truth

My wildhat, however, says you need at least 50% more solar and maybe double but probably triple the battery capacity for 24/7 use that doesn’t require a mental health therapist especially when the wifey arrives. Storage overall is your weakest link even at 1600W effective of panels.

 

[GLC]

This will be pretty power hungry even when it's not providing any loads. They have a pretty high idle burn - about 90W. This will use 2160Wh/day. This is almost 42% of your battery capacity - just being on and providing no loads.



Inadequate. See above.



These probably work at about 80% rated, so you have about 1600W of panels. This should get you about 8kwh/day on good days.



Yes.

Note that series panels can suffer from shading. Hopefully, your mounting scheme can insure that all panels remain unshaded from sunrise to sunset.



That's a big ask for the system you've selected. You really need to use the energy audit spreadsheet in Resources and calculate your needs.

If you have an absorption fridge (ammonia based, propane or AC powered), do not run it on AC. Run only on propane. On AC, they'll destroy you.



Last thing you want is to buy a bunch of stuff and then realize it's no good for you. You've selected an inverter that consumes 40% of your battery capacity before you even get to use it.

Do some more planning with an energy audit.



No.



Yes. Mentioned above.



Yes. You have no defined goal that says, "I need to use X Wh of energy per day." Right now, you're limited to about 8kWh/day total with only about 3kWh/day available when solar is unavailable. Since you don't know your needs, you don't know if that will work for you.



The growatt AC charger is not typical. It will not act as a battery charger like the solar does - no bulk, absorption, float. It simply turns off below a voltage and stops immediately once the upper voltage is reached, so fully charging is not easy, but you can easily get > 80% charged.

You will need to set the OFF voltage to 58V and the ON voltage to as high as it will go, but under 58V. If your battery is between the on and off values, it won't charge.

Excellent reply, just the inverter idling will eat up a big portion of your collected energy.

 

[Quattrohead]

2 reply's above don't even bother to read the request, how can he energy audit land ???
Anyway yes try to get some idea of what you will power and possible loads.
That inverter is not a USA model, slapping a transformer half arsed onto it does not make it right. Look at a pair of SPF3000 for the correct 120/240 split phase IF YOU EVEN NEED IT. It could be OK to just run all 120V appliances off a single 120V inverter of 3KW.
You will probably need 2x batteries and more panels but you can add those easy later on.

 

[sunshine_eggo]

2 reply's above don't even bother to read the request, how can he energy audit land ???

If you had read it, he wants to power a 5th wheel and listed several items. Those are audit-able.

Anyway yes try to get some idea of what you will power and possible loads.
That inverter is not a USA model, slapping a transformer half arsed onto it does not make it right.

Use of an autotransformer is a viable solution. Done routinely to get split phase out of Victron equipment.

Look at a pair of SPF3000 for the correct 120/240 split phase IF YOU EVEN NEED IT. It could be OK to just run all 120V appliances off a single 120V inverter of 3KW.
You will probably need 2x batteries and more panels but you can add those easy later on.

He likely wants split phase because his 5th wheel is a 50A unit and works best with split phase.

 

[Quattrohead]

I will leave my pre coffee reply up for prosperity LOL
Still don't like using wrong equipment with a hack though.

 

[12VoltInstalls]

prosperity

Make the coffee already. For posterity.

 

[sunshine_eggo]

I will leave my pre coffee reply up for prosperity LOL
Still don't like using wrong equipment with a hack though.

How is it wrong equipment? How is this a hack? It's done by professionals. Common to do with EU spec Multis/Quattros in North America or in Marine applications.

Victron literally has schematics for this exactly:

https://www.victronenergy.com/uploa...-phase-240V-to-120-240V-with-Quattro-240V.pdf (240 inverter to 120/240 split phase)

https://www.victronenergy.com/uploa...hase-240V-to-120-240V-with-Generator-240V.pdf (240 generator to 120/240 split phase)

and to step up a 120V unit to split phase:

https://www.victronenergy.com/upload/documents/AT-3-split-phase-120V-to-120-240V-with-Quattro-120V.pdf

Do you regard Victron as stupid or promoting "hacks?"

 

[Quattrohead]

Factory tested to UL specifications, not a hack job.

 

[Hedges]

A 240V inverter with floating output could be used with a 120/240V auto transformer (center tap grounded) to provide split-phase.

If the inverter puts out 240V single phase with one leg as "Neutral" bonded to chassis, a different type of transformer would be required.

If the inverter has floating output, and an AC input disconnected by SPST relay (only disconnecting hot, not neutral), then with autotransformer on the output the "neutral" input would be driven to 120V, a problem for either AC grid or generator input (if not floating). An input wire with plug (not hot wired) would become a "suicide cord" because it would have hot exposed pins.

Victron may not be stupid or offering hacks, with their inverter and their transformer paired together (they include a ground bonding relay in their transformer if I recall correctly.)

A retailer bundling a transformer with a different inverter may not think of issues we clever EEs come up with.

 

[sunshine_eggo]

Factory tested to UL specifications, not a hack job.

What are you talking about?

You recommend a pair of SPF3000. Are those UL?

How many Victrons are UL listed? Very few.

 

[JamesHird]

The Voc does sound OK.
If you wired instead as 4s2p, would the Vmp be high enough for the inverter?

You have 2000W of PV panels, 4800W of panels. 2.4 hours of production to recharge 100%.
What I'm thinking is, you might fully recharge battery, then waste PV production, then draw some power, then have a lower state of charge beginning the night.

With 4s aimed South East and 4s aimed South West, you get about 0.7 as high a peak power, 1.4kW. But more hours to (almost) make up for it.
That might keep battery somewhere between empty and full during the day.

2000W/4800W = ~ 0.4C charge rate, typically acceptable for lithium.
Determine what colder temperature is OK at 0.4C (it isn't 0 degrees C, should be greatly reduced current near freezing), and set low voltage charge disconnect accordingly.
If 4s2p as I suggested, then 1400W/4800W = 0.29C, so a bit lower temperature is OK.

Sometimes people have trouble with a generator feeding an inverter/charger because it is picky on frequency. In such case a separate charger can be a solution.

You may or may not need a precharge resistor to avoid 1000's of amps surge when connecting battery, so have some suitable resistor available (I think a 100' or 250' roll of Romex can serve, but most people use a power resistor.)

Use a DMM to double-check things before connecting and before closing switches. Make sure of voltages, polarity, and no voltage before touching terminals.

A DC disconnect if not built in is handy to isolate wires before work. At least, shut off inverter, confirm PV terminals have gone to Voc (no current), then unplug MC connectors for both positive and negative. Then confirm voltage has dropped to zero.

Setting up the panels in 4s2p configuration for the reasons stated does make sense to me, especially with the high draw of the inverter/charge controler. Maybe because of our battery limitations simplicity isn't the key. haha

I was thinking one way of negating the waste of PV production during optimal sunlight hours is to run all our higher draw appliances during this period. such as doing the laundry, charging all the power tool batterys and running the window AC for a couple of hours to keep the 5th wheel cool. This might not be enough though, I may have to rethink the panel set up. Thank you for the input

I belive the battery has a built in precharge resistor. Will did a tear down video on one

 

[JamesHird]

This will be pretty power hungry even when it's not providing any loads. They have a pretty high idle burn - about 90W. This will use 2160Wh/day. This is almost 42% of your battery capacity - just being on and providing no loads.



Inadequate. See above.



These probably work at about 80% rated, so you have about 1600W of panels. This should get you about 8kwh/day on good days.



Yes.

Note that series panels can suffer from shading. Hopefully, your mounting scheme can insure that all panels remain unshaded from sunrise to sunset.



That's a big ask for the system you've selected. You really need to use the energy audit spreadsheet in Resources and calculate your needs.

If you have an absorption fridge (ammonia based, propane or AC powered), do not run it on AC. Run only on propane. On AC, they'll destroy you.



Last thing you want is to buy a bunch of stuff and then realize it's no good for you. You've selected an inverter that consumes 40% of your battery capacity before you even get to use it.

Do some more planning with an energy audit.



No.



Yes. Mentioned above.



Yes. You have no defined goal that says, "I need to use X Wh of energy per day." Right now, you're limited to about 8kWh/day total with only about 3kWh/day available when solar is unavailable. Since you don't know your needs, you don't know if that will work for you.



The growatt AC charger is not typical. It will not act as a battery charger like the solar does - no bulk, absorption, float. It simply turns off below a voltage and stops immediately once the upper voltage is reached, so fully charging is not easy, but you can easily get > 80% charged.

You will need to set the OFF voltage to 58V and the ON voltage to as high as it will go, but under 58V. If your battery is between the on and off values, it won't charge.

Thank you for your detailed response. As a few people have touched on the same concerns I'll create a new post that tries to address all of the advice.

 

[sunshine_eggo]

Setting up the panels in 4s2p configuration for the reasons stated does make sense to me, especially with the high draw of the inverter/charge controler. Maybe because of our battery limitations simplicity isn't the key. haha

I was thinking one way of negating the waste of PV production during optimal sunlight hours is to run all our higher draw appliances during this period. such as doing the laundry, charging all the power tool batterys and running the window AC for a couple of hours to keep the 5th wheel cool. This might not be enough though, I may have to rethink the panel set up. Thank you for the input

Opportunistic usage is definitely viable for maximizing solar and minimizing battery.

I doubt a couple of hours of a window AC unit will do much besides keep you comfortable while you're sitting in the draft of its output...

We have about 3kW of solar and great sun in AZ. We can run the rooftop AC for about 7-8 hours when we need it, and that thing gobbles 1500W or so. Given that panels are cheap, I'd get more panels to make that happen. Double your array to 8S2P. Split it with one half facing SE and the other half facing SW for more uniform harvest for longer.

 

[12VoltInstalls]

How many Victrons are UL listed

In practice UL isn’t necessarily a “specification” anyway: from my understanding it’s an approval that certain conditions do not exist; that nothing violates NEC/NFPA; and that any legislative or jurisdictional requirements for X class of device are met. NEC references “UL-1234” but UL requires nothing of NEC.

I’ve bought things that advertised “manufactured to conform with UL1234” that don’t have any UL approval.

Things don’t get sent for UL approval because of cost, or sometimes a manufacturer doesn’t want liability and leaves ‘off-label’ applications as the responsibility of the end user.

That doesn’t necessarily make things unsafe imho

 

[JamesHird]

Opportunistic usage is definitely viable for maximizing solar and minimizing battery.

I doubt a couple of hours of a window AC unit will do much besides keep you comfortable while you're sitting in the draft of its output...

We have about 3kW of solar and great sun in AZ. We can run the rooftop AC for about 7-8 hours when we need it, and that thing gobbles 1500W or so. Given that panels are cheap, I'd get more panels to make that happen.

I'm building a roundwood timber framed structure with an earth roof over the 5th wheel with a 16' porch on the front. this should provide full shade from the sun and great insulation. Runing the AC for a couple of hours during the day wont make it a fridge but should take the edge off slightly. Where we are in Oklahoma it only really gets hot for a couple of months (July and August)

 

[sunshine_eggo]

I'm building a roundwood timber framed structure with an earth roof over the 5th wheel with a 16' porch on the front. this should provide full shade from the sun and great insulation. Runing the AC for a couple of hours during the day wont make it a fridge but should take the edge off slightly. Where we are in Oklahoma it only really gets hot for a couple of months (July and August)

I grew up in central and NW OK, and now that I'm in AZ, all I can remember is how miserable 95°F was in that humidity...

"dry heat" at 115°F is less uncomfortable.