Looking for help designing an off grid system

[phred3512]

My name is Danny. I'm living in a house that has been off grid for over 30 years. The latest system has been in place since 2015. It was a 12v lead acid battery bank with an inverter/charger and a solar with panels.
The battery bank was 16 250ah 6v golf cart batteries wired seriesD3/parallel. The panels are Siemens 75w Pro 4jf of which there are six. The inverter/charger is a Xantrex freedom sw-12. 815-3012 and the solar charger is a PWM taper charge CC-60E.
This system was in place when I moved here in 2020 so my knowledge of the system is limited. There is a generator that would charge up the batteries when they got low. In 2021 I installed a direct bury #10 wire from a power source 450 feet away. That eliminated the need for the generator for a year.
Our power requirements are lower than most. We cook, dry clothes and refrigerate with gas.
The original batteries are no longer usable. Recently I have acquired 16 280ah 3.2v lifepo4 cells. Unfortunately I feel like a dog whose chased a truck and caught it! What do I do now? Having looked around there appears to a lot of ways to go. I'm hoping to get ideas to aid in this endeavor.
My plan is to make a 48v system and swap the propane refrigerator for an electric one. Any advice on how to complete this project would be greatly appreciated.

 

[50ShadesOfDirt]

Many old(er) or (possibly) failed/tired components in place ... could be time for a clean slate approach?

It costs you nothing to go ahead and run through the design steps now, so you know where you want to go ... a few calculations, power audit, and such will help you know what an "ideal" system is for your home and needs.

From there, you can do what-if's to keep parts of the old (possibly piece-meal?) system components, or choose to go with all new, all mostly trouble-free components.

The generator (is it propane?) is a key backup component to your system, so that part is mostly done. Note: I don't understand the "another power source has replaced the gen for a year" comment, so that's still a question mark. Solar panels are there, but you'll need to poke around with them and get numbers off of each set, and figure out how they were layed out (how many "strings" of what kinds of panels). This feeds into your calcs below.

The design steps:

1. Go here, and enter in each appliance's values (watts, hours/day you want to run it, etc.):
https://unboundsolar.com/solar-information/offgrid-calculator

2. Go here, using numbers from above, and fiddle with various entries/components, and you'll see in real-time what your system component (inverter, mppt, panel) sizing is:
https://www.altestore.com/store/calculators/off_grid_calculator/

There are many similar website pages/calculators, but these two pages should help you get through most of the necessary calculations. This helps you quickly decide if you can do what you want to do, and you can vary component choices for what-if scenarios.

This is off-grid, so a small, standalone system would likely consist of an AIO inverter, a battery-bank (most likely LiFePO4, or LFP for short), and solar panels, along with connecting bit & bobs (cables, fuses, etc.); generator would be a backup to recharge battery-bank if solar not cooperating, or if powering large occasional loads.

Keep in mind that the overall system reference voltage is 12v, 24v, or 48v ... you already know that you want to get to 48v, and key components of your system *all* need to be at 48v.

Once your initial calcs are done, you can see Will's videos & diagrams for example systems, under "DIY Solar ..." drop-down list at top of this forum. It's a journey, and lots of learning (some of which you've already done), but I think a fun one!

Hope this helps ...

 

[timselectric]

Since you are already living off grid. You should have a pretty good handle on what your needs are. This will help immensely in the planning process.

 

[sunshine_eggo]

My name is Danny. I'm living in a house that has been off grid for over 30 years. The latest system has been in place since 2015. It was a 12v lead acid battery bank with an inverter/charger and a solar with panels.
The battery bank was 16 250ah 6v golf cart batteries wired seriesD3/parallel.

Two in series for 12V and then 8 of those in parallel?

That's 250Ah * 8 = 2000Ah

The panels are Siemens 75w Pro 4jf of which there are six.

6 * 75W = 300W

300W/12V = 25A.

Your batteries needed to be charged at at LEAST 100A and preferably closer to 200A. Your lack of solar likely accelerated your battery's demise.

The inverter/charger is a Xantrex freedom sw-12. 815-3012 and the solar charger is a PWM taper charge CC-60E.

12V/3000W inverter?

CC-60 is only capable of 60A, so again, that's likely a big contributor to your battery demise. They were undercharged for their entire lifetime.

This system was in place when I moved here in 2020 so my knowledge of the system is limited. There is a generator that would charge up the batteries when they got low. In 2021 I installed a direct bury #10 wire from a power source 450 feet away.

Hydro?

That eliminated the need for the generator for a year.

Still eliminated?

Our power requirements are lower than most. We cook, dry clothes and refrigerate with gas.
The original batteries are no longer usable.

Yep.

Recently I have acquired 16 280ah 3.2v lifepo4 cells.

From where?
Do all 16 cells measure between 3.25 and 3.30V?
When you're ready: https://diysolarforum.com/resources...ls-using-a-low-cost-benchtop-power-supply.65/

Unfortunately I feel like a dog whose chased a truck and caught it! What do I do now? Having looked around there appears to a lot of ways to go. I'm hoping to get ideas to aid in this endeavor.
My plan is to make a 48v system and swap the propane refrigerator for an electric one. Any advice on how to complete this project would be greatly appreciated.

First, I'm a "run what you brung" kinda guy, so if you go 48V, you replace EVERYTHING. If the charge controller and inverter are still working, I wouldn't replace them. Sticking with 12V may be more appropriate for your needs if they're as low as you say they are.

This would require you to build 4 4S 12V batteries in parallel. This would require 4 BMS, but it would handle whatever loads you may throw at it with the 3000W inverter.

Changing from propane to compressor means you now need another 1-2kWh/day of energy you weren't using before, and that's more than your 300W of solar can provide. You'll need to max out the 60A controller installing 700-800W of solar being careful to not exceed the 60A limit on the PWM controller. On good days, the fridge will gobble half of your daily energy from the sun.

Somethings to keep in mind:

The amount of PV and sun you have determines how much energy you can use per day.
The amount of battery you have determines how long you can go between charging.

In the spirit of @50ShadesOfDirt 's recommendation, link #1 in my signature references resources for determine your available solar and loads for a complete energy audit.

 

[OffGridForGood]

What they said - agreed on all points made.
what they didn't say - budget to work with?

 

[phred3512]

Boy that's a lot to chew on!! I was figuring on replacing the inverter, charger and panels. The direct bury wire I ran from nearby grid power provided enough power to charge the batteries at night. Hence the generator wasn't needed. I wired a transfer switch from a motorhome in case of a prolonged power outage. That way the generator was for emergencies. Saved a bunch on gas.
My thoughts are, using the cells to make a 48v battery, getting a split phase inverter and getting the appropriate panels and inverter to handle everything.

 

[sunshine_eggo]

Boy that's a lot to chew on!! I was figuring on replacing the inverter, charger and panels. The direct bury wire I ran from nearby grid power provided enough power to charge the batteries at night. Hence the generator wasn't needed. I wired a transfer switch from a motorhome in case of a prolonged power outage. That way the generator was for emergencies. Saved a bunch on gas.

Cool.

My thoughts are, using the cells to make a 48v battery, getting a split phase inverter and getting the appropriate panels and inverter to handle everything.

You have about 14kWh of battery capacity. That's enough for half the average U.S. household daily electrical use. You'll need 3000-4000W of solar to pull that in daily.

If you want to "handle everything" it sounds like you are not planning to retain your low power utilization. Remember, more inverters and split phase means more PV to feed it.

If that's the route you want to go, that's fine, and your battery may be fine for it, but you need to have a good handle on absolutely everything you want to run on the system per @50ShadesOfDirt 's recommendation.

You don't need to think about 12, 24 or 48V until AFTER you've completely documented what the system NEEDS to do. Then you figure out the design.

 

[phred3512]

Boy that's a lot to chew on. My thoughts are to replace everything. The idea about running a small power line (#10 wire) from grid power a few years back was to change the role of the generator from backing up the solar panels to an emergency power source to back up the grid power when it goes down. The #10 wire is 240v same as the generator. I suppose my most important question is will the new batteries I have be enough to do the job. I was thinking of a split phase inverter/charger and new panels. Other than lights, a washer, propane dryer, and a tv the only addition to the load would be a refrigerator.

 

[OffGridForGood]

the only addition to the load would be

...And the new inverter stand-by consumption, which depending on what you choose can be significant.
This is also where budget can play a large role, top tier equipment tends to be low stand-by consumption, but higher initial cost. Lower tier equipment is lower initial cost, but higher standby consumption. In small systems, with long periods of poor solar PV potential,(cloudy NW?) this can be major factor.

 

[phred3512]

Sorry for being unclear. My load now is compromised of lights, tv, washer and propane dryer. I would like to add an electric refrigerator if possible. What kind of equipment do I need? A picture is starting to emerge in my mind thanks to all the responses I've received. Unfortunately it also has generated more questions. Is my idea of split phase a healthy thought or a hair brain scheme? Is my battery sufficient? What kind of inverter and panels would work? My assumption is that I need to replace both.

 

[OffGridForGood]

Is my idea of split phase a healthy thought or a hair brain scheme?

What 240 loads do you need to run? Fridge, washer, lights - sound like all 120v AC loads to me. Did I miss something?
If you stick to just 120, the standby consumption may be lower, and cost of equipment will be less.
In a simple plug and play set up you could use one of the entry level 3kW 120volt (single phase) inverters like the Growatt, or MPP or several others that are more or less re-branded Voltronics inverters. But these are also pretty hungry on stand-by current. If you have the budget, a higher tier Victron 3kW will run less standby, but cost up front x3 or x4. Depends what your budget is.

 

[Hedges]

Is 450' 10awg run carrying 120V or 240V? If 240V, does it have L1, L2, N, G? How many amps available? Is it reliable?
You can feed that AC into an inverter/charger, keep battery floating (that's a lead-acid concept, so "charged" for lithium) and it supplies starting surge. You will be limited to the current your battery & BMS can provide.

Given constant power source, I would have considered small AGM battery. But you now have lithium to work with.

How much does electric cost you? How much sunshine do you get?

Some inverters will feed grid through and blend in power from battery and/or solar. Others have to switch back and forth.
I use Sunny Island. It can be programmed to draw anywhere from 0V to 56A per 120V inverter. With two, 120/240V. It could draw up to amount of current line can supply without excess voltage drop.

With Sunny Island, PV can be connected either AC coupled or DC coupled. AC coupled, it will disconnect from grid whenever PV exceeds needed power. DC coupled, I'm less familiar with how it can make use of available PV vs. grid power.

A quality all-in-one might be better for this application. There are some inexpensive models ($700 to $1500) and some higher end ones (SolArk).

The new Midnight Rosie should be a good inverter-charger (they have separate PV charge controllers), but like Sunny Island and SolArk, price is over $4000.

It sounds like you just have lithium cells to make up to 48V battery. You will need a BMS. Select the inverter you want and a BMS that talks to it for closed loop charging. I use Sunny Island, and REC is one model BMS that supports it. Some other inverters will support same or different BMS. Some inverters may not do closed-loop at all - some forum members have systems like that, but (without having actually used lithium), I think closed-loop will be better.

 

[sunshine_eggo]

Sorry for being unclear. My load now is compromised of lights, tv, washer and propane dryer. I would like to add an electric refrigerator if possible. What kind of equipment do I need? A picture is starting to emerge in my mind thanks to all the responses I've received. Unfortunately it also has generated more questions. Is my idea of split phase a healthy thought or a hair brain scheme? Is my battery sufficient? What kind of inverter and panels would work? My assumption is that I need to replace both.

12V systems are practical up to about 2000W - 3000W if you have really good wiring. Higher peak power requires 24V or even 48V.

A fridge is only going to draw maybe 100-200W when running with a surge at start - maybe 1000W.

If you have 240V things you wish to power, split phase makes sense. If everything is 120VAC, you don't need split phase.

If your inverter is the 3000W model, and if you have 4/0 wires between battery and inverter, that should be fine.

Your existing inverter sounds more than capable of handling what you want to do, so does it need to be replaced? Probably not.

The biggest limitation is your charge controller... 60A means you can't use more than about 800-900W, BUT 800-900W should deliver 3.2-4.5kWh/day which is about double what the fridge needs.

 

[phred3512]

From all the responses I've gotten so far, thanks to all by the way, and also from what I've been reading it would appear that the split phase idea is not a good one. So I'm gonna toss it.

 

[Hedges]

From all the responses I've gotten so far, thanks to all by the way, and also from what I've been reading it would appear that the split phase idea is not a good one. So I'm gonna toss it.

Although not necessarily bad either. If it would be useful for your loads you can plan at least for expansion.

Is your 450' run single or split phase?
Will you have large motors you want to run?
Some of the inverters can be configured either 120V or 120/240V split-phase. You could start out with 120V only and later use the split-phase, or maybe later stack two inverters for split phase.

Avoid wiring any circuits in your house so two branches L1 and L2 share a single N wire. Shared would be OK with split phase, but not with L1 and L2 both powered by a single phase because then N would carry twice the current. If each circuit has separate N, you can power it with either single or split phase. RVs plug into both kinds of shore power so also need to support single as well as split phase.


I think the key parameter of your situation is availability of grid power. That is likely 20A maybe 30A 120V.

Consider Midnight DIY line:

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

"Hybrid" charging would use PV to the extent available, supplement with grid as needed. I think that means it operates as an on-line UPS.

I don't find mention of communications with BMS. That probably only provides last-ditch protection, and the inverter manages battery open-loop, only knowing voltage and current.

This inverter may be single phase only.

 

[phred3512]

Although not necessarily bad either. If it would be useful for your loads you can plan at least for expansion.

Is your 450' run single or split phase?
Will you have large motors you want to run?
Some of the inverters can be configured either 120V or 120/240V split-phase. You could start out with 120V only and later use the split-phase, or maybe later stack two inverters for split phase.

Avoid wiring any circuits in your house so two branches L1 and L2 share a single N wire. Shared would be OK with split phase, but not with L1 and L2 both powered by a single phase because then N would carry twice the current. If each circuit has separate N, you can power it with either single or split phase. RVs plug into both kinds of shore power so also need to support single as well as split phase.


I think the key parameter of your situation is availability of grid power. That is likely 20A maybe 30A 120V.

Consider Midnight DIY line:

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

"Hybrid" charging would use PV to the extent available, supplement with grid as needed. I think that means it operates as an on-line UPS.

I don't find mention of communications with BMS. That probably only provides last-ditch protection, and the inverter manages battery open-loop, only knowing voltage and current.

This inverter may be single phase only

Although not necessarily bad either. If it would be useful for your loads you can plan at least for expansion.

Is your 450' run single or split phase?
Will you have large motors you want to run?
Some of the inverters can be configured either 120V or 120/240V split-phase. You could start out with 120V only and later use the split-phase, or maybe later stack two inverters for split phase.

Avoid wiring any circuits in your house so two branches L1 and L2 share a single N wire. Shared would be OK with split phase, but not with L1 and L2 both powered by a single phase because then N would carry twice the current. If each circuit has separate N, you can power it with either single or split phase. RVs plug into both kinds of shore power so also need to support single as well as split phase.


I think the key parameter of your situation is availability of grid power. That is likely 20A maybe 30A 120V.

Consider Midnight DIY line:

Category Products - MidNite Solar's

MidNite Solar Category Products.

www.midnitesolar.com

"Hybrid" charging would use PV to the extent available, supplement with grid as needed. I think that means it operates as an on-line UPS.

I don't find mention of communications with BMS. That probably only provides last-ditch protection, and the inverter manages battery open-loop, only knowing voltage and current.

This inverter may be single phase only.

My power line is #10 two conductor w ground. It is 450' and I have 120v on both conductors and used the ground as the neutral. At the end of the run I'm using the ground rod as the ground. The source is a 30a split phase breaker.

 

[Hedges]

"My power line is #10 two conductor w ground. It is 450' and I have 120v on both conductors and used the ground as the neutral. At the end of the run I'm using the ground rod as the ground. The source is a 30a split phase breaker."

Do you mean L1 and L2 to the two conductors, 240V? I think so from "split phase breaker"

If Neutral and Ground are already bonded at the source, I don't like using a single wire to carry both. Would have preferred 3 wire + ground.
I would prefer to have L1, L2, and ground for 240V, then maybe put through that an isolation transformer to derive a neutral that can be grounded.

You've got 6kW you can draw continuously. Not sure how much starting surge, would have to consider voltage drop vs. current. You might not need inverter at all. Using inverter and battery, that can provide more surge.

To use 240V I think you should get a 5kVA or larger isolation transformer (program inverter to limit draw to what breaker or transformer can handle), and get a split-phase inverter. There are some inexpensive ones like MPP, more expensive like SolArk, Schneider, SMA. And others to choose from.

Alternatively, reconnect the wire to L1, N, G and have 120V 3kW continuous available to a single phase system. No transformer needed.

 

[phred3512]

"My power line is #10 two conductor w ground. It is 450' and I have 120v on both conductors and used the ground as the neutral. At the end of the run I'm using the ground rod as the ground. The source is a 30a split phase breaker."

Do you mean L1 and L2 to the two conductors, 240V? I think so from "split phase breaker"

If Neutral and Ground are already bonded at the source, I don't like using a single wire to carry both. Would have preferred 3 wire + ground.
I would prefer to have L1, L2, and ground for 240V, then maybe put through that an isolation transformer to derive a neutral that can be grounded.

You've got 6kW you can draw continuously. Not sure how much starting surge, would have to consider voltage drop vs. current. You might not need inverter at all. Using inverter and battery, that can provide more surge.

To use 240V I think you should get a 5kVA or larger isolation transformer (program inverter to limit draw to what breaker or transformer can handle), and get a split-phase inverter. There are some inexpensive ones like MPP, more expensive like SolArk, Schneider, SMA. And others to choose from.

Alternatively, reconnect the wire to L1, N, G and have 120V 3kW continuous available to a single phase system. No transformer

The suggestion to revert to 120v to me is sound advice. That is the direction I think I'll go. What size inverter would you suggest?

 

[Hedges]

Inverter needs to supply .continuous wattage of load, and surge to start any motors.
Just add those things up.

Back to your wire run: 450' of 10 awg is almost 1000' round trip, 1.0 ohm

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To limit voltage drop to 5%, 120V x 5% = 6V, 6V / 1 ohm = 6A for 720W. 240V x 5% = 12V, 12V / 1 ohm = 12A for 2880W.
If you put a 240V to 120V step-down transformer at the far end, 12A @ 240V could deliver 24A @ 120V, the same 2.88kW

That is a viable alternative to using an inverter. Here's 5kVA 240/480 step down to 120/240 for $250 delivered (not to a residential address, so go pick up at freight terminal or ask about residential delivery probably $120 more.)

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That's a fraction the price of an inverter and will deliver 3kW day in and day out for decades.

If you do use an inverter, you can connect the wire from utility with or without transformer. I think with isolation transformer is the best way to provide higher wattage. Without transformer, probably 120V so neutral and ground are separate.

 

[phred3512]

What size inverter would you suggest? Really the purpose of the wire is to help charge the batteries when the days are short (winter). It would be best to not have to depend on either the wire or the generator.