The Battery Thread (Solar / Inverter)

[johnjm]

Question for those with solar panels installed... what peak solar are you getting out of your array? I'm maxing out at around 75% of rated power on the roof, which I dont think is too bad.

I've got 8 x 535w JA solar panels on 2 strings of 4 panels each. It quickly ramps up to around 3.25kw of power and can pretty much stay there from 8h30 till around 15h00 if the load is sufficient or batteries are charging. My panels are NE-facing with a 30 degree angle bracket with a slight east tilt as well because of the roof leaning that way. Not ideal but not bad.

On the battery side, I think anyone buying lead acid is making a HUGE mistake. Yes, LiFePO4 is a huge investment, but cycling them overnight is where I'm starting to claw back money from my investment. I have 2 of the PylonTech 3.5kwh batteries which are rated at 6000 cycles at 95% DoD. I run them down to 15% each night and that seems to work well. I've had two sets of lead acids on a purely backup system before and they just dont work well and are VERY hard to monitor. With the Pylons sorting themselves out, life is much easier.

I have a 650w rated PV setup and have hit 700w actually, but that was only on one day where factors aligned.

On average I get 90% of rated power (590w).

In terms of batteries, my system is for loadshedding and I have no intention of going off grid. The system is only used to keep the batteries on float, and when lodshedding hits I then only turn on the inverter system. Lead acid is fine for my needs and have no requirement to invest in something where I have no intended ROI.

Edit
I’ve also got JA solar, mono 325w, two in series. Vocc 80v.

What MPPT are you using and have you measured the open voltage?

 

[gimpex]

Question for those with solar panels installed... what peak solar are you getting out of your array? I'm maxing out at around 75% of rated power on the roof, which I dont think is too bad.

I've got 8 x 535w JA solar panels on 2 strings of 4 panels each. It quickly ramps up to around 3.25kw of power and can pretty much stay there from 8h30 till around 15h00 if the load is sufficient or batteries are charging. My panels are NE-facing with a 30 degree angle bracket with a slight east tilt as well because of the roof leaning that way. Not ideal but not bad.

On the battery side, I think anyone buying lead acid is making a HUGE mistake. Yes, LiFePO4 is a huge investment, but cycling them overnight is where I'm starting to claw back money from my investment. I have 2 of the PylonTech 3.5kwh batteries which are rated at 6000 cycles at 95% DoD. I run them down to 15% each night and that seems to work well. I've had two sets of lead acids on a purely backup system before and they just dont work well and are VERY hard to monitor. With the Pylons sorting themselves out, life is much easier.

I get about 85% but not as early as you. I’ve got 5800w of panels , approx 5 degree slope , facing north.

On a good day I get 1kw by 9am , then quickly goes up to about 4kw by 10am , and it can be there past 4pm ( on the odd day that my batteries aren’t full).

Normally my pool pump kicks in at 9 till 3. Geyser 1 , from 10 to 12 , geyser 2 from just after 12 to 2 ( from experience each takes just under 2 hours to get fully hot and switch off). Most days when the sun goes down I start the evening with a full set of batteries . The next morning I have anything from 60% down to about 20% left depends on the activities . The 20% is extreme if the dishwasher and washing machine and oven and stove were all going , normally the washing machine and dish washer are on during the day , dishwasher before first geyser and washing machine after second geyser

 

[Crush]

I get about 85% but not as early as you. I’ve got 5800w of panels , approx 5 degree slope , facing north.

On a good day I get 1kw by 9am , then quickly goes up to about 4kw by 10am , and it can be there past 4pm ( on the odd day that my batteries aren’t full).

Normally my pool pump kicks in at 9 till 3. Geyser 1 , from 10 to 12 , geyser 2 from just after 12 to 2 ( from experience each takes just under 2 hours to get fully hot and switch off). Most days when the sun goes down I start the evening with a full set of batteries . The next morning I have anything from 60% down to about 20% left depends on the activities . The 20% is extreme if the dishwasher and washing machine and oven and stove were all going , normally the washing machine and dish washer are on during the day , dishwasher before first geyser and washing machine after second geyser

That's fantastic yield! How many batteries do you have?

A buddy of mine is getting the same 8 panels installed tomorrow, so that will be a good test to see what he maxes out in terms of generation as we have the exact same panel setup, but with different inverters. His orientation will be fairly similar to mine - NE.

My geyser timers are only going in this week, so once that's done, I should be 80-90% off grid for spring / summer / autumn. Will need 1 more battery to get to 100% I reckon. For winter I'm hoping for a 50% reduction.

 

[wingnut771]

@Crush

You don't mention what solar charger you have, MPPT is more efficient than PWM. Also, how long is the run and how thick is the solar cable? Maybe you've got losses because of the cable?

 

[Crush]

@Crush

You don't mention what solar charger you have, MPPT is more efficient than PWM. Also, how long is the run and how thick is the solar cable? Maybe you've got losses because of the cable?

I'm actually not sure what gauge wire the installer used. Will have to check and see.

Wire runs about 9m inside the garage to my inverter and probably another 15-20m up the wall to the roof and to the panels.

It's a Deye 5kw dual MPPT inverter, running 4 panels on each string.

 

[The_Traveller]

Question for those with solar panels installed... what peak solar are you getting out of your array? I'm maxing out at around 75% of rated power on the roof, which I dont think is too bad.

27 x 410w JA mono ... I’ve seen it touch 11k one day (not that I monitor it daily )

 

[wingnut771]

I'm actually not sure what gauge wire the installer used. Will have to check and see.

Wire runs about 9m inside the garage to my inverter and probably another 15-20m up the wall to the roof and to the panels.

It's a Deye 5kw dual MPPT inverter, running 4 panels on each string.

Nice inverter so the problem isn't there. I'm no expert but to me that cable run seems on the long side. What are the specs of the panels and MPPT range of inverter? Are you able to run just 1 string of 8? That way you have higher voltage which is better for underspecced cable (less current) and easier/cheaper than running new cable if it turns out to be underspecced. I think solar cable comes in 4mm and 6mm.

Can someone check my work?

 

[Crush]

Hmmm... that's very interesting. So it seems that I should maybe be seeing a bit more coming through.

Around 10-11am is when orientation should be absolutely spot on for my setup.

Since it's running two identical strings, its unlikely that just a single panel is not working optimally both strings are running equally.

For now I guess I'm happy with the results as I'm still making more than I can store or use. It's only that my north-east facing arrays with east tilt means that I lose out in the late afternoon, so it's a long stretch for the batteries.

 

[wingnut771]

Hmmm... that's very interesting. So it seems that I should maybe be seeing a bit more coming through.

Around 10-11am is when orientation should be absolutely spot on for my setup.

Since it's running two identical strings, its unlikely that just a single panel is not working optimally both strings are running equally.

For now I guess I'm happy with the results as I'm still making more than I can store or use. It's only that my north-east facing arrays with east tilt means that I lose out in the late afternoon, so it's a long stretch for the batteries.

I suspect it's the 30m distance to the inverter.

 

[Crush]

27 x 410w JA mono ... I’ve seen it touch 11k one day (not that I monitor it daily )

Nice inverter so the problem isn't there. I'm no expert but to me that cable run seems on the long side. What are the specs of the panels and MPPT range of inverter? Are you able to run just 1 string of 8? That way you have higher voltage which is better for underspecced cable (less current) and easier/cheaper than running new cable if it turns out to be underspecced. I think solar cable comes in 4mm and 6mm.

Can someone check my work?

Inverter specs:



Panel specs:



I could run it as a single string if needed. Will have to read up a bit to understand any efficiency gains by going that route. I'm a bit rusty and left the calcs up to the installer.

 

[wingnut771]

Inverter specs:



Panel specs:



I could run it as a single string if needed. Will have to read up a bit to understand any efficiency gains by going that route. I'm a bit rusty and left the calcs up to the installer.

I think the issue is the voltage of the string is in the low end of the 125V-425V MPPT range as Vmp of 41.47 x 4 = 165.88V. Then you have to consider voltage drop over a long distance with DC, so if I had to guess, it's low voltage causing your issues. Making one string will bring 331.76V so voltage drop won't have as much effect. You just have to be careful of not going to close to the max MPPT voltage, that's when smoke happens. Amps is less of an issue as the MPPT will clip the output to 11A.

Are you able to measure the output voltage of the strings either manually or through the inverter?

 

[TheChamp]

Would someone be kind enough to explain the 11+11A of the MPPT? Is it because of the high voltage? How is the inverter able to charge batteries with a measly 22A? Or can it up the current when it lower to the battery voltage?

 

[wingnut771]

Would someone be kind enough to explain the 11+11A of the MPPT? Is it because of the high voltage? How is the inverter able to charge batteries with a measly 22A? Or can it up the current when it lower to the battery voltage?

I'm guessing it's more the watts than the amps.

 

[Crush]

Thanks @wingnut771...

I see what you're saying! I think you're quite right... running 8 panels in a single string will be safely under the max voltage.

Each string is currently running around 170v.

And the theoretical max with 8 panels is just under 400v for the string. So still well within the range for the inverter.

How does wiring work? More panels means thicker wiring needed?

 

[wingnut771]

Thanks @wingnut771...

I see what you're saying! I think you're quite right... running 8 panels in a single string will be safely under the max voltage.

Each string is currently running around 170v.

And the theoretical max with 8 panels is just under 400v for the string. So still well within the range for the inverter.

How does wiring work? More panels means thicker wiring needed?

Amps (current) dictates wire thickness. You don't need thicker wire to up voltage. Thicker wiring also has less resistance so less voltage drop over distance. Running high voltage negates this to a degree. For example, assume over 30m you lose 10V so your 170V becomes 160V. If you were now running 330V, it now becomes 320V. Less of an impact.

Looking at your numbers, maybe upping the voltage may increase your amp rating, as you only getting 7amps.

Can someone check my work?

 

[wingnut771]

@Crush

If you feel the solar cables coming into the inverter with your hand, are they warm?

EDIT: keep us updated on the progress after making 1 string.

 

[TheChamp]

Amps (current) dictates wire thickness. You don't need thicker wire to up voltage. Thicker wiring also has less resistance so less voltage drop over distance. Running high voltage negates this to a degree. For example, assume over 30m you lose 10V so your 170V becomes 160V. If you were now running 330V, it now becomes 320V. Less of an impact.

Looking at your numbers, maybe upping the voltage may increase your amp rating, as you only getting 7amps.

Can someone check my work?

I doubt his issues have much to do with the wires and voltage drop, to me it looks like too low mppt voltage as you said, the voltage drop will be minimal at 30m on a 6mm wire, just assuming since it's mostly what's used to install the panels.

I had a nice formula for voltage drop but now all I find is in AWGs and feet, I hate those.

 

[Crush]

@Crush

If you feel the solar cables coming into the inverter with your hand, are they warm?

Nope, not warm at all.

It's also 6mm2 cabling (according to the quote) and looks about right.

So maybe will try a single string setup in the near future and see how that compares.

 

[TheChamp]

Thanks @wingnut771...

I see what you're saying! I think you're quite right... running 8 panels in a single string will be safely under the max voltage.

Each string is currently running around 170v.

And the theoretical max with 8 panels is just under 400v for the string. So still well within the range for the inverter.

How does wiring work? More panels means thicker wiring needed?

With MPPT you don't want to be at the low end or the high end of the range, you want to be in the middle, so to me a 6panel string would be my choice.

Remember that the higher you go with the series strings you will have to start to worry about the voltage rating, I am sure your installer chose stuff that are rated up to a certain voltage and current, your cables, fuses and switches.

You want to modify the installation without having to install new cables and stuff, 8 panels take you over the 300V mark, I am not sure what everything is rated for but I wouldn't want to go too close.

 

[wingnut771]

Nope, not warm at all.

It's also 6mm2 cabling (according to the quote) and looks about right.

So maybe will try a single string setup in the near future and see how that compares.

Great, that's a good sign. Yeah, just looked up the voltage drop calculator (thanks @TheChamp) and it looks like only 3V on 4mm and 2V on 6mm about over 30m.

Keep us updated on the results.