Setting up 4kw homestead solar

[sparrs]

Setting up a solar system from scratch, I've found some great, concise information on here and realized the time has come to quit lurking and post for some specific answers.

Batteries:
Looks like a Gen2 Tesla 24v battery pack offers the best value used from a low mileage vehicle. Not sure if I'll be pulling the existing circuit boards off and wiring direct to my charging arrangement? Link here:

TESTED w WARRANTY 5.3 kWh Tesla Model S 85 90 EV Battery Module 24V Gen 2 Cells | eBay

They are backward compatible and will fit 2012 to 2020 Tesla Model S and X with proper knowledge. Beware of Gen 1 modules as they are aging out at 10 to 12 years of age and failing. Total energy storage is 5.3 kWh.

www.ebay.com

Cables: Sized to current. No problem if I'm pulling four pairs of 2AWG.

Panels: Qcells Q.peak Duo ML-G9+ 375-395 Watt, 10 available. Not interested in undersizing any part of this. 42V open circuit, 35V MPP.

System voltage: It seems 24v is adequate, but 48v drops the wire size needed and overall cost into conductors. 24V components seem more common, given that 48v is younger. Open to thoughts, I could go either way. I'm thinking 4 or 5 parallel, 2 series on the panels if 48 volts. Any special considerations for the series panel arrangement, or wire and go?

Charging: This is where it gets complicated. MPPT charge controllers are an apparent choice, with Victron and some other brands mentioned.
If I can do it all with direct feeds from the panels into an inverter/charger, this would be ideal for seamless voltage control, all handled by one unit and power sharing on demand from panels and batteries. I saw the Outback Radian charger/inverter series mentioned, curious if this fits the bill or if there's a better manufacturer for a reasonable price.
Another source mentioned a charge controller still being needed in addition to an inverter/charger - why would both be needed? It's not like the charge controller can step up the voltage. Anything I'm missing, good manufacturer recommendations and some clarity on this design would be welcome.

 

[sunsurfer]

After your done with all the pieces, you may be better off just getting a 24v LFP server battery. You will get WAY more cycles in the long run and MUCH safer if those are colbolt based lithium-ion.

 

[sparrs]

After your done with all the pieces, you may be better off just getting a 24v LFP server battery. You will get WAY more cycles in the long run and MUCH safer if those are colbolt based lithium-ion.

Great point; I'd love to go LFP for the stable chemistry. I'll hash some costs on that. Do server batteries offer any charge management or are they a brick of cells?
Is there a well priced source for these, maybe 1 or 2 year used swapouts?

 

[timselectric]

I would avoid lithium ion, unless you are putting them far away from the house.

 

[littleharbor2]

Building your own lifepo4 battery is literally cheaper than lead acid these days.

 

[OffGridForGood]

Why 4kW?
Running a homestead (I do too) there is always more on the horizon.

I can't recommend 24V (and know that I have 12, 24 and 48 volt systems running right now, just in different places with different load requiremts, and different levels of portability.)
Always start with a power audit. you can do multiple audits, like Present loads, Future loads, options to future loads. What about a future EV, or Freeze Dryer, ...think it through, what can you do now so the system you build can grow with you, expand in the future.
If the budget is there, you can build your future load supplying system right now, if the budget is more modest, then plan a system in stages, and build it a bit at a time over a few years or so.
As @timselectric says LiFePO4 is the current safe and affordable option, good cycles expected, ie 10-20 year life expectancy on the batteries.
As @littleharbor2 says, DIY LiFePO4 packs are very cost effective. Got me to 53kWh without busting the budget. ( I have two factory and three DIY 48v packs, plus 12v and 24v packs for the smaller systems.)

 

[sunsurfer]

Great point; I'd love to go LFP for the stable chemistry. I'll hash some costs on that. Do server batteries offer any charge management or are they a brick of cells?
Is there a well priced source for these, maybe 1 or 2 year used swapouts?

The EG4 are popular, good price per KWH for middle grade but there have been a few BMS issues I have seen. Could be nothing, could be a quality issue. SOK is the best middle grade as far as quality a bit higher price per KWH. SOK's BMS is pretty good. Trophy is an interesting option, good support and suppose to be good BMS but they only offer 48v.

My next batts will likely again be SOK but I may also pickup up some Trophys and give them a go.

They all come with BMS with charge, discharge, balancing and low temp management.

 

[Rednecktek]

Just a couple quick thoughts:

Go 48v right out the gate if you can. 24v tops out at 3kw or so which leaves you replacing everything but the panels if you find you need more power.

If cold is a concern, go with Trophy batteries. Last thing you want to do is destroy your expensive batteries on a cold morning.

Stay away from the used car packs.

 

[sunsurfer]

Just a couple quick thoughts:

Go 48v right out the gate if you can. 24v tops out at 3kw or so which leaves you replacing everything but the panels if you find you need more power.

If cold is a concern, go with Trophy batteries. Last thing you want to do is destroy your expensive batteries on a cold morning.

Stay away from the used car packs.

Hey Rednecktek, I'm not sure what you mean by 24v topping out at 3KW. I'm assuming you are referring to the output of the inverter and the high currents on the DC side?

One of my setups is 12v. It has a 2.8KW Magna-sine, 20kwh LFP battery bank and 5.2KW of panels. I got 2 of the Magna-sine inverters in trade for a car I only had $400 into so it was a great deal. I love the inverter so it was what caused me to go 12v. I probably should of just sold the pair looking back and gone 48v. My 12v setup has a secondary 5KW MSW inverter for diverting to water heating in the winter when the batts get topped off (2400watts of elements). In the summer, I'm moving about 150 amps through the main inverter during most of the day running A/C but I have ran it at a bit over 3KW many times with no issues (my inverter will do 3.5KW for 30 minutes). I'm very happy with this setup and it gets used pretty hard. I keep thinking I will kill the inverter and have to swap in the spare but it keeps going. This system may stay 12v for years

I also have a 24v system with a 4KW inverter(also got super cheap) and similar batt/solar capacity. It runs a well and AC most of the day. I had it at 2.5kw for about 8 hours yesterday. I've ran it to max continues of 4KW also using a compressor with no issues. This system also has a 1.2KW Victron Phoenix inverer running a couple of chest freezers.

Next system I am building will be 48v - 5KW (Victron inverter). Thats still 100 amps @ rated power for the inverter.

I would of gone 48v on my first system but I had allot of good 12v and some 24v inverters I keep getting really cheap.

 

[LydMekk]

In todays modern world going for anything else than 48V is really not viable contemplating getting new parts etc. in the future.
Everything has become 48V based now.

 

[sparrs]

To summarize so far:
48v sounds like the choice for higher kilowatts, and yes this definitely has the potential to grow into a future house build. Currently powering a camper and 18k BTU AC unit, but I may step up the inverter sizing to 8kw. Starting with my needs and working up.
LFP battery chemistry preferred - EG4, SOK, Trophy. Are these all server batteries or individual cell manufacturers? Given the quantity I plan to use, I don't anticipate a bottleneck with charge/discharge rates.

Still hung up on the charging - does a charge controller/programmable charging inverter replace the BMS if I can set up charge/discharge current protection and control cell temps within range?
And for the charging inverter - is a charge controller needed/does it provide a necessary function in addition, and are there other quality brands to consider besides Outback for a charging inverter?

Is there a charge controller/separate inverter combination I should consider?

Any more necessary devices I might have overlooked?

Thank you each for your bits of wisdom.

 

[timselectric]

EG4, SOK, Trophy. Are these all server batteries or individual cell manufacturers?

Pre made batteries.

 

[timselectric]

does a charge controller/programmable charging inverter replace the BMS

No

 

[sunsurfer]

To summarize so far:
48v sounds like the choice for higher kilowatts, and yes this definitely has the potential to grow into a future house build. Currently powering a camper and 18k BTU AC unit, but I may step up the inverter sizing to 8kw. Starting with my needs and working up.
LFP battery chemistry preferred - EG4, SOK, Trophy. Are these all server batteries or individual cell manufacturers? Given the quantity I plan to use, I don't anticipate a bottleneck with charge/discharge rates.

Still hung up on the charging - does a charge controller/programmable charging inverter replace the BMS if I can set up charge/discharge current protection and control cell temps within range?
And for the charging inverter - is a charge controller needed/does it provide a necessary function in addition, and are there other quality brands to consider besides Outback for a charging inverter?

Is there a charge controller/separate inverter combination I should consider?

Any more necessary devices I might have overlooked?

Thank you each for your bits of wisdom.

If you don't go the AIO route, I recommend Victron gear for SCC and inverters. Support of Victron isn't the best but they are solid and have decent software with active development. There are other good brands though.

The main reason I like Victron for SCC is they are super fast and a good price for what you get. I like the multiple SCC method vs one large SCC or AIO. That keeps power density low and provides tons of redundancy.

Most people go the AIO(all in one)route for simplicity.

 

[sunsurfer]

In todays modern world going for anything else than 48V is really not viable contemplating getting new parts etc. in the future.
Everything has become 48V based now.

Its unfortunate vehicles have not gone 48v.

 

[sparrs]

Thanks to each for your input. I've moved to purchasing and plan to update once the system is running a while.
The Trophy batteries with integrated BMS and EVE cells offered a great value for the price.
Manual disconnects for the PV and batteries, the 48V system cuts the current rating needed for those.
I went around the bush on all in one inverters with the EG4 8kw, the MPP Solar 6048LVX and decided to go up one pricing bracket to the Outback/Victron/Sol Ark. The Sol Ark AIO 12kw looked great, but the transformerless design seems to struggle with demanding inductive 120v loads. Running a 120v camper setup as 60% of the load, I opted to order the Outback 8048 for the load sharing to grid/generator instead of a simple switch(similar to Sol-Ark) and the robust functionality with a transformer design handling shock and inrush current better. This is hoped to be more seamless than adding a Victron autotransformer to the Sol Ark output. The Mate3s is needed as a separate purchase to configure the Outback inverter, I thought it should have been included.
Initially I planned to use the Victron 250/100 Smartsolar/bluesolar MPPT charge controller($800-950 vs 1400 for the Outback Flexmax FM100) to avoid syncing voltages on two charge controllers, but realized the system will expand past a single MPPT's capabilities and decided to work the economics of two FM80s.
We'll see how it all works together.

I'm looking now at the details of the electrical side - it doesn't sound like DC breakers on the PV will do much to protect the panels in a single panel failure or charge controller failure? I'm leaning towards terminal block/blade disconnect. The Trophy battery comes with an on/off breaker, so the only other thing I'm thinking I need is a small distribution panel on the inverter output.

 

[schmism]

decided to go up one pricing bracket to the Outback/Victron/Sol Ark. The Sol Ark AIO 12kw looked great, but the transformerless design seems to struggle with demanding inductive 120v loads.

I'm confused how you got to a 12kw Solark from a "4kw offgrid" setup

If we assume thats 4kw of pannels, thats 4kw*5hrs of sun... 20kwh of energy. /24hrs = 800w/hr. I get having a little overhead on the inverter to cover startup loads but a 3kw 48V AIO covers everything you could hope a 4kw array is going to power.

 

[Rocketman]

Make a good plan (with wire sizes and fuses) and post it here. There are many smart experienced people that can spot the errors in the plan. (And yes there will be errors in the plan…)

After the plan is done - then start buying… I have seen many people start buying- then regret that purchase after finding the plan is not the best for that equipment.

You have only been looking at premade batteries- spend some time figuring out if you want to assemble the batteries yourself. (Pros and Cons both ways).

Good Luck on the project.

 

[sparrs]

Schmism, the homestead's power demands will grow as I build and 12kw will be needed before too many years. The inverters can be stacked, but I'm hoping to avoid the runaround getting two inverters to play nicely for a few years. The 12kw Sol Ark was in the budgeted range and I was hoping the larger size might help with oomph for starting the 120v 18k BTU AC unit. 60 idle watts wasn't bad either. I think this 8KW Outback will be durable if nothing else. And yes, looking from the outset I'll need to push the array up to ~8KW, maxing both FM80s soon and eventually a third string. Another Trophy 10.5kwh battery is on the forecast too - nice that it comes with a 200 amp BMS and disconnect.

Rocketman, I'm thinking two strings of 2S3P each. 3S2P would still be within the 150v max on the FM80s, but my understanding is the charge controllers stay cooler and have better efficiency at voltages closer to pass through(~54V for a 48V system, depending on charge voltage settings and battery type) Measuring the OCV on the panels at 36 on a cloudy sundown vs 42 max rated, it seems the voltage will stay above the charging threshold with 2S during changing weather conditions.
Bringing 6 runs 30 ft max of #14 MC cable(rodent protection) into the control house, 2 panels series on each. Simple 1 gang boxes and watertight crimp connectors to connect the panels, then a single MC run home each. Keeping conduit and boxes watertight is a pipe dream in my experience, so I'll make the connections outside watertight - seal and shield. Six Eaton PLS6 series 2 pole 16 amp DC breakers($12 each NOS on eBay) for protection. #10 wire from each of the six breakers, three to each FM80. #8 wire to the battery terminals from each of the FM80s(double up conductors for a 5 ft run of 69 amps DC?)
2/0 welding cable between the battery and Outback 8048(has to be bussed to both sets of terminals on the inverter) and #8 wiring inverter output to the 6 circuit distribution breaker panel per the Outback manual.

 

[sparrs]

Rocketman, my biggest hurdle with the DIY packs is selecting a reliable BMS manufacturer. Any thought on this and the best supplier for genuine EVE cells? They seem to be leading the value range of the LFP sector. I'm comfortable with the technical aspect of it.