Small setup advice.

[Danjwilko]

So after our original plan for the house and complete off grid living has gone out the window.

We’ve opted for a smaller off grid setup for the garage/workshop.

Now due to constraints on available space, workshop side we have had to opt for smaller panels.

Current battery setup is 24v 460ah. (8 12v 115ah batteries wired in parallel series).
It will be running the led lights, beer fridge and freezer small radio and the odd power tool battery charging point.

We’ve calculated usage to be 1.3-4kw per day so rounded up to 1.5kw for extra sake.

Ideally I’d like to use the victron 24/1200 inverter paired with a pair of victron 100/20 mppt to run everything.

However I have been offered a EPEVER 40amp mppt for half the cost of the two victron units so tempting.

So really main questions are:

What wattage of solar panels would be enough to keep these batteries maintained? The fridge and freezer are the biggest draw being quite old.

With the 100/20 mppt could I put 600w of pv through each providing I don’t go above the 100v ceiling?

Would you use the pair of victron units of save a chunk for extra panels with the EPEVER 40 (100v/40a) mppt?

Cheers all in advance.

 

[Rednecktek]

Just a couple thoughts...

Rule of thumb for 800ah of battery would be at least 1600w of panel, divided by 24v would be about 70a of charge controller.

It looks like with that kind of amperage you'll want a pair of 40a chargers, preferably with higher voltages as many larger panels are pushing 50v-ish of VoC which limits you to 2p arrays so fuses and/or combiner boxes.

I've never found Victron to be worth the money, especially when you get nickled and dimed for things like terminal covers and dongles and such. A pair of cheaper 40a MPPT controllers will be cheaper than anything Victron and still turn solar DC into battery DC.

Multiple SCC's gives redundancy.

You'll need to look into how much solar radiance you get, you may need more panels to make up for it.

Just my initial thoughts.

 

[sunshine_eggo]

So after our original plan for the house and complete off grid living has gone out the window.

We’ve opted for a smaller off grid setup for the garage/workshop.

Now due to constraints on available space, workshop side we have had to opt for smaller panels.

Current battery setup is 24v 200ah. (8 12v 100ah batteries wired in parallel series).

8 * 12V * 100ah = 9600Wh

9600Wh / 24V = 400Ah

If lead acid, cut in half.

It will be running the led lights, beer fridge and freezer small radio and the odd power tool battery charging point.

We’ve calculated usage to be 1.3-4kw per day so rounded up to 1.5kw for extra sake.

Sounds reasonable for the battery size.

Ideally I’d like to use the victron 24/1200 inverter paired with a pair of victron 100/20 mppt to run everything.

However I have been offered a EPEVER 40amp mppt for half the cost of the two victron units so tempting.

So really main questions are:

What wattage of solar panels would be enough to keep these batteries maintained? The fridge and freezer are the biggest draw being quite old.

1.5kWh / 5h of perfect solar (proper orientation, no shade from sunrise to sunset) = 300W minimum. Would go higher for times of year that you won't get optimal solar.

300W/24V = 12.5A of charging. A single 20A would be fine.

With the 100/20 mppt could I put 600w of pv through each providing I don’t go above the 100v ceiling?

600W/24V = 25A You'd leave a little on the table, but you're not often going to generate more than 20A. As long as the PV doesn't exceed 80Voc and 20A isc, you're good.

HOWEVER, 400Ah of 24V lead acid needs to be charged at about 40A, so you want 40A * 24V = 960W.

If LFP, 600W is fine.

This would require 2X 20A controllers.

Would you use the pair of victron units of save a chunk for extra panels with the EPEVER 40 (100v/40a) mppt?

I love Victron with all my heard and soul. I have a wall full of blue that makes me randy, but I'd probably take the single 40A to save the $.

 

[Danjwilko]

Just a couple thoughts...

Rule of thumb for 800ah of battery would be at least 1600w of panel, divided by 24v would be about 70a of charge controller.

It looks like with that kind of amperage you'll want a pair of 40a chargers, preferably with higher voltages as many larger panels are pushing 50v-ish of VoC which limits you to 2p arrays so fuses and/or combiner boxes.

I've never found Victron to be worth the money, especially when you get nickled and dimed for things like terminal covers and dongles and such. A pair of cheaper 40a MPPT controllers will be cheaper than anything Victron and still turn solar DC into battery DC.

Multiple SCC's gives redundancy.

You'll need to look into how much solar radiance you get, you may need more panels to make up for it.

Just my initial thoughts.

Appreciate the info.
I think I got slightly confused converting from 12v-24v and the amp hours.
So just to clarify wiring two 12v 115ah batteries into series would give 24v but the same amp hour rating?
So with 8 batteries I thought It would end up with 4 lots of 24v/115ah.

I was told the array size for a 100ah battery was 300w of panels so I figured 600w for the first 200ah paired with the victron 100/20 and then a second victron 100/20 to cover the the other 200ah.

Side note due to the area we were going to cover size wise being the limiting factor on panel size were limited to 175-200w panels.

How reliable are EPEVER Tracer seres AN units? I keep seeing posts regarding the older series BN units being better and the newe gens have some quirks.

I’m Uk based and iirc we average 4 hours of solar radiance per day Il have to have a double check on that one.

 

[Danjwilko]

8 * 12V * 100ah = 9600Wh

9600Wh / 24V = 400Ah

If lead acid, cut in half.



Sounds reasonable for the battery size.



1.5kWh / 5h of perfect solar (proper orientation, no shade from sunrise to sunset) = 300W minimum. Would go higher for times of year that you won't get optimal solar.

300W/24V = 12.5A of charging. A single 20A would be fine.



600W/24V = 25A You'd leave a little on the table, but you're not often going to generate more than 20A. As long as the PV doesn't exceed 80Voc and 20A isc, you're good.

HOWEVER, 400Ah of 24V lead acid needs to be charged at about 40A, so you want 40A * 24V = 960W.

If LFP, 600W is fine.

This would require 2X 20A controllers.



I love Victron with all my heard and soul. I have a wall full of blue that makes me randy, but I'd probably take the single 40A to save the $.

Thank you for your comment I thought I’d worked the amp hours out right lol was doubting myself.

Unfortunately lead acid so usable will be only 200ah. I can’t grumble they were all practically brand new and free.

Hmmm decisions decisions lol, I’ve got the 24/1200 inverter due to reliability being the biggest consideration for the fridge/freezer. Looking at the reviews and build quality will probably outlast the setup.

I’m still on the fence with the mppts but I’m leaning toward the dual victron but all blue is going to be pricey especially if decide to upgrade later on.

I’ve asked the previous commenter aswell but how reliable are the EPEVER units?

Again thanks for the info it is appreciated.

 

[sunshine_eggo]

Thank you for your comment I thought I’d worked the amp hours out right lol was doubting myself.

Unfortunately lead acid so usable will be only 200ah. I can’t grumble they were all practically brand new and free.

Win!

I’ve asked the previous commenter aswell but how reliable are the EPEVER units?

Less reliable than Victron. You hear about plenty of problems on the forum with EPEVER, but there are likely 10X+ that never post about how they've been trouble free for them.

If you have the $, then Victron all the way. If you want to take the sting out of the startup costs with an eye to upgrade in a few years, 40A Epever.

 

[Pi Curio]

@Danjwilko

How much available space do you have for solar panels? Is there a particular panel you're planning to buy?

 

[Danjwilko]

@Danjwilko

How much available space do you have for solar panels? Is there a particular panel you're planning to buy?

First option:

We have a patch of land at the back of a gravel drive to the side of our garage that is unused, which is circa 1m-1.25m in depth and around 8m in length iirc. During the summer it is a sun trap with sun and zero shadow from around 8am well into the evening. Winter wise different kettle of fish but clear day and no cloud cover probably from 10am until around 3pm ish. (Would be great with a sun tracking system).

Ideally I’d like ground mounted due to the strong winds that come off the open fields north of us. But I could build a small frame for mounting if needs be.

We were looking at some 380w Ja solar panels when we were planning the original full off grid scenario, which were £180 plus £150 shipping costs, but the company ran out of them and haven’t had any back in since.
The only ones we can get locally easily are the old amazon specials 100W-200w panels. 175w being the best value at 77p per watt (zero shipping fees). We have 2 100W panels on loan from a friend who uses them for camping for testing purposes (positioning etc).

 

[Pi Curio]

First option:

We have a patch of land at the back of a gravel drive to the side of our garage that is unused, which is circa 1m-1.25m in depth and around 8m in length iirc. During the summer it is a sun trap with sun and zero shadow from around 8am well into the evening. Winter wise different kettle of fish but clear day and no cloud cover probably from 10am until around 3pm ish. (Would be great with a sun tracking system).

Ideally I’d like ground mounted due to the strong winds that come off the open fields north of us. But I could build a small frame for mounting if needs be.

We were looking at some 380w Ja solar panels when we were planning the original full off grid scenario, which were £180 plus £150 shipping costs, but the company ran out of them and haven’t had any back in since.
The only ones we can get locally easily are the old amazon specials 100W-200w panels. 175w being the best value at 77p per watt (zero shipping fees). We have 2 100W panels on loan from a friend who uses them for camping for testing purposes (positioning etc).

1x8 meters is plenty for a small system. What's the orientation of that area, South?

Best,
D.

 

[Danjwilko]

1x8 meters is plenty for a small system. What's the orientation of that area, South?

Best,
D.

Yeah it’s completely south facing. Doing the maths for the plot and panel angle it works out for bigger panels up to around 2m height.

Just didn’t look that big an area.

 

[Danjwilko]

Win!



Less reliable than Victron. You hear about plenty of problems on the forum with EPEVER, but there are likely 10X+ that never post about how they've been trouble free for them.

If you have the $, then Victron all the way. If you want to take the sting out of the startup costs with an eye to upgrade in a few years, 40A Epever.

Appreciate your input.

I’ve had the test panels hooked up to both scc’s without any issue, however on turning off the dc load (not using the terminals so thought no point having them live) for the EPEVER it gave off a lovely high pitched whine whereas the victron didn’t. I can’t stand the noise usually have to turn plugs off round the house as I seem to be able to hear it where my partner cannot.

It’s a weird one I preferred the built in display of the EPEVER the percentage battery charging infographic is a plus, rather than having to grab the phone to see the inputs but I must admit the victron app is quite seamless.

 

[Pi Curio]

Yeah it’s completely south facing. Doing the maths for the plot and panel angle it works out for bigger panels up to around 2m height.

Just didn’t look that big an area.

Panel efficiency of 20%, 1.6kW solar. That's a decent amount of solar in my humble opinion.

We have a patch of land at the back of a gravel drive to the side of our garage that is unused, which is circa 1m-1.25m in depth and around 8m in length iirc. During the summer it is a sun trap with sun and zero shadow from around 8am well into the evening. Winter wise different kettle of fish but clear day and no cloud cover probably from 10am until around 3pm ish. (Would be great with a sun tracking system).

If I understand correctly, you can get about 5h of Sun during the winter with no shading?

That's not bad at all.

One more thing, you've mentioned you have lead-acid batteries. What is the recommended charge rate for these, 0.1C?

Best,
D.

 

[Danjwilko]

Panel efficiency of 20%, 8m2*0.2 = 1.6kW solar. That's a decent amount of solar production in my humble opinion.


If I understand correctly, you can get about 5h of Sun during the winter with no shading?

That's really not bad at all.

One more thing, you've mentioned you have lead-acid batteries. What is the recommended charge rate for these, 0.1C?

Best,
D.

I do apologise, I could have Sworn I replied to your comment.

Anyway UK based and location iirc we get an average of 4.1 peak hours of solar irradiance.

As say some days will be overcast all day for days on end, others we could have clear blue skies and sun all day just the typical English weather.

The batteries are recommended to be charged at 0.3c just your regular leisure batteries.

On a bit of a side note we had another pretty clear day next to zero clouds in the sky so I set the system up. (Still need to make a frame for everything).

I noticed the wattage from the two 100W panels peak at switch on around 155w. This tailed off in a curve down to 57 watts over just 30 mins even in bright sunshine and zero shade would this be considered normal? The two spikes are myself double checking connections and realigning with the sun and checking for cloud cover which again at this point we had zero.




(Quite like the old victron for data logging.
I run Linux on all my laptops/desktops and the EPEVER software is windows based so stuck in a rut on that front.)

 

[Pi Curio]

I do apologise, I could have Sworn I replied to your comment.

No worries

On a bit of a side note we had another pretty clear day next to zero clouds in the sky so I set the system up. (Still need to make a frame for everything).

I noticed the wattage from the two 100W panels peak at switch on around 155w. This tailed off in a curve down to 57 watts over just 30 mins even in bright sunshine and zero shade would this be considered normal? The two spikes are myself double checking connections and realigning with the sun and checking for cloud cover which again at this point we had zero.


View attachment 134192

(Quite like the old victron for data logging.
I run Linux on all my laptops/desktops and the EPEVER software is windows based so stuck in a rut on that front.)

From the graph, to me it looks like maybe the battery got nearly full and the charger went into absorption?

Anyway UK based and location iirc we get an average of 4.1 peak hours of solar irradiance.

As say some days will be overcast all day for days on end, others we could have clear blue skies and sun all day just the typical English weather.

The batteries are recommended to be charged at 0.3c just your regular leisure batteries.

Are you willing to build the system up as you go, or are you looking to build it now as close to what can be built for the given installation conditions?

Hope it helps a bit.

Best,
D.

 

[Danjwilko]

No worries


From the graph, to me it looks like maybe the battery got nearly full and the charger went into absorption?


I don't know much about the lead-acid battery, but I'll take the 0.3C and work with it.

Summary;

System voltage 24V, capacity 400Ah
400Ah*0.3C(recommended charge)=120A range
Lead-acid 50%, 200Ah usable range. Winter sun 4hours, 200/4=50A
Victron 100/20 @24V system voltage - 580W Solar / 20A@24V

Installation solar potential, 1.6kW
Optimized for the most economical solar panel selection, 4x380-400W panels.
4x400W/ 1.6kW rated II 1.28kW Actual at 80%
1.28kW/24V = 53.3A / 1280W/28V =45,7A / rounded 50A


A twin set of 100/20 with 2x400W panels in series could work just fine. (It's important to make sure the combined Voc of the panels at the expected lowest temperatures does not exceed the SCCs 100V limit).

As long you understand that at a peak you'll be getting near 40A max charging, no more. About, 1.16kW solar at peak.

That translates to, for the 200Ah of usable capacity, it will take about 5 hours for a full recharge.

So, ideally IMO you would need a Victron 100/50 with 4x400W panels in a 2s2p configuration(It's important to make sure the combined Voc of the panels at the expected lowest temperatures does not exceed the SCCs 100V limit).

With this, you would have sufficient power to charge the 200Ah in around 4 hours in winter in good weather.

Yet again, twin 100/20-2x400W is very nice. Merely wanted to point out what could be the ideal SCC selection in my opinion.


Anyhow. It really depends on what you already have, and where you want to go from there.

Are you willing to build the system up as you go, or are you looking to build it now as close to what can be built for the given installation conditions?

Hope it helps a bit.

Best,
D.

You would be correct on the absorption phase, double checked and yes it finished the bulk charge a couple of days ago.

Originally I had only intended to have a small setup maybe powering just a fridge and a couple of mains powered chargers etc but with adding in the freezer at well it bumped up the number of batteries needed, especially with the reserve period and to reduce the amperage going through said cables I opted for the 24v battery bank rather than the 12v.

The 100/20 Victron unit fitted the bill quite well as it will do12/24/36/48v where as the 100/50 was limited to 12/24v so I could alter the battery config if I needed/chose to down the line.
The Epever 40amp MPPT I was offered, will also only do 12/24v so was dubious on that front but the higher average was quite tempting.

However mulling it over the 48v route has got me thinking wether to just go that way from the get go, which I do have the batteries and enough cables to do 48v, but I wouldn't have a clue on the inverter for 48v system, as all my research thus far has been for a inverter based on a 12//24system. Which the phoenix 24/1200 was looking like the ideal candidate (gets some stellar reviews).

So far I have the batteries (8 total here and 2 more on the way).
All the cabling for the batteries (2awg).
Cabling for inverter attachment (need to decide what inverter - 2awg cable)
mega fuses various 100, 150, 200amp.
Battery disconnect switch for inverter.
Battery disconnect switch for mppt battery side.
Solar panel cables from designated site to the proposed install location (30m total).
Solar panel y cables for parallel.
Array shut off switch.
One Victron 100/20 mppt cables and fuses to the battery bank.
2 temporary 100w solar panels (borrowed for testing purposes).
Numerous ancillaries for installation ie conduit, mounts, etc.

If I've missed anything parts wise that I will need do let me know.

So ideally need to decide whether to go 24/36/48v, what inverter to go with and wether to upgrade mppt or stick with the twin 100/20 one.
I'm happy to build a system that will allow expandability if that makes sense, I'm sure there will come a point where I go damn need more solar lol.

Hope that helps clarify a few points.

 

[MichaelK]

The batteries are recommended to be charged at 0.3c just your regular leisure batteries.

That does not sound right? Can you cut and paste a snip of the manufacturer's recommendations? The usual recomendations from the big companies like Trojan and Rolls is 0.125C for flooded lead-acid, and 0.2C for AGM. I have never before ever seen a lead-acid recommendation of 0.3C before.

Sticking with the usual .125C value, you'd need 400Ah X 0.125C X 25Vcharging X 1.175 fudgefactor = 1470W. Call that 1500W of panels.

Problem though is that is for 50A output, and the Tracer 4210AN only handles up to 40A. So, you have two choices. Either get a different controller with at least a 50A limit, or utilize the 4210 and limit your solar input to 1000-1175W.

 

[sunshine_eggo]

That does not sound right? Can you cut and paste a snip of the manufacturer's recommendations? The usual recomendations from the big companies like Trojan and Rolls is 0.125C for flooded lead-acid, and 0.2C for AGM. I have never before ever seen a lead-acid recommendation of 0.3C before.

I have seen some batteries permit 0.3C charges, but they limit absorption/float to 13.8V where high current will not cause gassing, but those are not deep cycle batteries intended for regular cycling but are for standby, UPS-type applications. The vast majority of batteries can handle 0.3C at 13.8V or lower, and I've punished some Rolls at about that level (300A+ into 936Ah @ 12V), but it's not the healthiest for them.

Sticking with the usual .125C value, you'd need 400Ah X 0.125C X 25Vcharging X 1.175 fudgefactor = 1470W. Call that 1500W of panels.

Agreed. I find it's often permissible to overshoot on PV due to the typical charge patterns... batteries are in absorption before peak solar, so a little extra juice doesn't hurt; however, intermittent sun where batteries may not get fully charged every day means the batteries might see > peak current on the day after a cloudy day. For FLA, I like to see 0.15-0.2C from rated PV knowing that they'll typically never exceed 80-90% rated and .2-.25C for AGM/GEL. I figure that's about the same as your fudge factor.

 

[Danjwilko]

That does not sound right? Can you cut and paste a snip of the manufacturer's recommendations? The usual recomendations from the big companies like Trojan and Rolls is 0.125C for flooded lead-acid, and 0.2C for AGM. I have never before ever seen a lead-acid recommendation of 0.3C before.

Sticking with the usual .125C value, you'd need 400Ah X 0.125C X 25Vcharging X 1.175 fudgefactor = 1470W. Call that 1500W of panels.

Problem though is that is for 50A output, and the Tracer 4210AN only handles up to 40A. So, you have two choices. Either get a different controller with at least a 50A limit, or utilize the 4210 and limit your solar input to 1000-1175W.

I may well be completely wrong as that was the info I got given ringing up the supplier not the manufacturer as their specs didn’t have a typical c rating.
Looking at the data sheet:

https://www.yuasa.co.uk/yuasa/datasheet/index/sku/L35-115/

(had to go hunting for it as they are made for a company by Yuasa and are non branded) , they are rated at 115ah with a discharge time of 20hrs.
Ah think I found it bottom right of the data sheet, a recommended charge rate of 6 amps.

Found a calculator plugged in the info and it came back as 0.05c bit of a difference.

Other than that no further info.
Does that sound more plausible?

 

[Pi Curio]

You would be correct on the absorption phase, double checked and yes it finished the bulk charge a couple of days ago.

Originally I had only intended to have a small setup maybe powering just a fridge and a couple of mains powered chargers etc but with adding in the freezer at well it bumped up the number of batteries needed, especially with the reserve period and to reduce the amperage going through said cables I opted for the 24v battery bank rather than the 12v.

The 100/20 Victron unit fitted the bill quite well as it will do12/24/36/48v where as the 100/50 was limited to 12/24v so I could alter the battery config if I needed/chose to down the line.
The Epever 40amp MPPT I was offered, will also only do 12/24v so was dubious on that front but the higher average was quite tempting.

However mulling it over the 48v route has got me thinking wether to just go that way from the get go, which I do have the batteries and enough cables to do 48v, but I wouldn't have a clue on the inverter for 48v system, as all my research thus far has been for a inverter based on a 12//24system. Which the phoenix 24/1200 was looking like the ideal candidate (gets some stellar reviews).

So far I have the batteries (8 total here and 2 more on the way).
All the cabling for the batteries (2awg).
Cabling for inverter attachment (need to decide what inverter - 2awg cable)
mega fuses various 100, 150, 200amp.
Battery disconnect switch for inverter.
Battery disconnect switch for mppt battery side.
Solar panel cables from designated site to the proposed install location (30m total).
Solar panel y cables for parallel.
Array shut off switch.
One Victron 100/20 mppt cables and fuses to the battery bank.
2 temporary 100w solar panels (borrowed for testing purposes).
Numerous ancillaries for installation ie conduit, mounts, etc.

If I've missed anything parts wise that I will need do let me know.

So ideally need to decide whether to go 24/36/48v, what inverter to go with and wether to upgrade mppt or stick with the twin 100/20 one.
I'm happy to build a system that will allow expandability if that makes sense, I'm sure there will come a point where I go damn need more solar lol.

Hope that helps clarify a few points.

As long you understand that for 100/20 SCC to work at 48V, you'll need more investment in solar panels as you need higher Array voltage but you are limited by SCCs 100V 20A limits.

It's far simpler to use an SCC with higher limits, to begin with. In your case, use a bigger SCC at 24V. The 100/50.

Best,
D.

 

[Danjwilko]

As long you understand that for 100/20 SCC to work at 48V, you'll need more investment in solar panels as you need higher Array voltage but you are limited by SCCs 100V 20A limits.

It's far simpler to use an SCC with higher limits, to begin with. In your case, use a bigger SCC at 24V. The 100/50.

Best,
D.

Appreciate the info as always (I read your original reply).

Considering returning the 100/20, it’s great that it covers the whole voltage range but I think I’d be shooting myself in the foot pv capacity wise at 24v.
I’m planning on at least a 1200watt array to start with which would have been suitable for split the 100/20 units just limited at max output.

If I’m sticking with the 24v system, I’d be looking at circa £245 for the 100/50 which is about the price I would pay for two 100/20 units.

Alternatively I did see the 150/45 for circa £340 which is again 12-48v compatible. If i did utilise it it would keep options open for later on.

Just not sure wether to stick with the 24v system components for now and upgrade to 48v later on.