New system - new to solar - panel efficiency? What am I doing wrong?

[Habious]

Hello all.

Very new to the site (account is about 4 minutes old) and new to solar.

Have been an electronics technician for decades so I at least know what end of the soldering iron gets hot. Not exactly a "newbie" with electronics, but definitely newbie on solar...so not sure what I'm doing wrong here with a new system.

Four 100-watt Renogy panels, wired in parallel, on the roof of my house
About 70-feet of 10GA wire running from panels to 30A Renogy Wanderer controller (with BT adapter, for monitoring)
Two 12 30Ah LiFePo4 batteries, also wired in parallel

I have other crap as well (2K inverter, wired to panel, etc.) but I'm good with that stuff

My question is panel efficiency.

I have a "tree" problem - this I know. We've got big-a$$ pine trees in the front yard (south facing). So, I know I'm not really getting much *direct* sunlight right now.

The "tree guys" have been called, and we're getting about a dozen of these 200+' trees knocked down, soonish.

I'm also not sure about the wiring from the panels to the controller. I've got connectivity. Started out with two 100-watt panels, wasn't getting much, added two more (all in parallel). But, I'm still getting practically nothing for output.

This has all been an experiment - will it work for my specific application. So, I've started out small. But, something just isn't right.

I expected the not-so-direct sunlight to effect efficiency quite a bit - hence the call to the "tree guy". I also expect some loss with the longish run of wire from the panels to the controller - but that can't really be helped right now. Not ready to commit to drilling holes in my roof until I'm sure this is gonna work (and right now, it isn't). So, wires run down the roofline, into a hastily-made hole in my gable vent, into the crawlspace, and down to the controller. I have a 20' wire, connected to a 30' wire (wasn't sure what I'd need until I got up there), connected, to the wires that came with the Renogy starter kit (controller and one 100-watt panel). I think it's about another 20'.

Again, I know it's not the best as far as length, or length-versus-wire-gauge - I expected some loss.

I expected my array to give me "only 20%" for now. Or, with both loss from the length-of-wire and the lack of good direct sunlight..."only 10%" for now.

But, I'm getting practically NOTHING. I've got the Renogy app that ties to the BT interface on the controller, plus I've wired a DC-shunted meter on the panel output. Both meters are giving me similar numbers, so I don't think they're wrong.

I'm not getting 20%...which would be about 80-watts.
I'm not getting 10%...which would be about 40-watts.

I'm getting like 0.7-watts, sometimes up to 1.4-watts.

That's it.

What am I doing wrong?

I'm getting SOME power (18-20 volts DC) out of the panels, so I've got conductivity/connectivity.

Am I really getting THAT much loss from 70' of 10GA wire? Or, do the panels absolutely need full-on, put-your-shades-on-because-it's-so-damn-bright-out-here *direct* sunlight to put out ANY power at all?

Any help or suggestions would be most appreciated.

Habious

 

[Hedges]

IR drop in wire is not your problem.
Charge controller - is that MPPT?
What is its maximum Voc?
With four, 100W panels, if all connected in series probably about 100Voc, bit higher on a cold January morning.
After temperature adjustments, if not too high, that would be the best setup.
Otherwise, 2s2p

It is possible those 12V panels aren't high enough Vmp to work with an MPPT charge controller into your 12V battery.
With little voltage headroom, a PWM charge controller is often used.
So first question is, "MPPT or PWM?"

 

[Habious]

IR drop in wire is not your problem.
Charge controller - is that MPPT?
What is its maximum Voc?
With four, 100W panels, if all connected in series probably about 100Voc, bit higher on a cold January morning.
After temperature adjustments, if not too high, that would be the best setup.
Otherwise, 2s2p

It is possible those 12V panels aren't high enough Vmp to work with an MPPT charge controller into your 12V battery.
With little voltage headroom, a PWM charge controller is often used.
So first question is, "MPPT or PWM?"

Thanks for replying!

The Wanderer is a PWM controller

Specs tell me:
Nominal System Voltage - 12 VDC
Rated Charge Current - 30A
Max PV Input Voltage -25 VDC

With four 100-watt panels in parallel, I'm getting 14-18 VDC (but basically no current to write home about). With a 25 VDC max PV input voltage, I can't so series, or 2s2p, right? Based on this, I'm assuming parallel is my only option.

 

[Habious]

OK, found a diagram on the Renogy site that almost-perfectly shows my setup...other than much longer wires from the panels to the controller (all of the summing is done up on the roof, with just the pigtails from the panels. Long wire run is just a single pos/neg set of wires)

 

[Hedges]

Correct. 25V because it is PWM, panels can't be put in series.
What specs on the panels? (should be OK)

Try taking one PV panel, bypass the charge controller, just connect to battery. Observe voltage before, new voltage, see how it rises over time.
If you have a suitable ammeter, use that in series.
Don't exceed maximum allowed battery voltage, of course.

Since a PWM just closes a transistor between PV panel and battery, almost no voltage drop.
It sounds like either you have no sun on the panel, or controller isn't working, or open/high resistance.

Uhh, any chance your batteries are fully charged, therefore no current is the correct result?
Or, charge controller setting thinks batteries are full because set for a different voltage/chemistry?

 

[Habious]

What specs on the panels? (should be OK)

SPECIFICATIONS
Maximum Power at STC: 100W	Cell Efficiency: 21.00%
Optimum Operating Voltage (Vmp): 17.9V	Open-Circuit Voltage (Voc): 21.6V
Optimum Operating Current (Imp): 5.72A	Short-Circuit Current (Isc): 6.24A
Operating Temperature: -40°F to 176°F	Maximum Series Fuse Rating: 15A
Solar Cells: 33 Cells	Maximum System Voltage: 600V DC (UL)

Uhh, any chance your batteries are fully charged, therefore no current is the correct result?
Or, charge controller setting thinks batteries are full because set for a different voltage/chemistry?

Holy poop - I never even considered the possibility that the batteries are just...full...and the controller is making the decision not to pull any amps from the array. It's entirely possible that I'm an idiot!

I haven't really run much of anything on batteries, because I didn't want to run them down and need 3 weeks (at 1.4-watts) to recharge them.

The whole system is new...*new* new. So, I guess it's possible the batteries were sitting at 95% SoC when they arrived.

 

[Hedges]

Don't worry. You're not the first idiot here. I learned that one from somebody else, so I can sound "learned."

Throw a load on it and see if voltage drops, charge current responds.
Happen to have a "state of charge" status from any equipment?

I'm using AGM lead-acid and my inverters seem to know how to manage them.
But I set charge current and voltage for various phases based on battery's technical documentation.
The voltages differed just slightly, but default charge current was 0.55C and I knocked that down to 0.2C
(one of their other recommendations for battery bank capacity vs. PV capacity would have brought that down, but I was deliberately not following it, instead drastically under sizing battery.)

 

[Habious]

Don't worry. You're not the first idiot here. I learned that one from somebody else, so I can sound "learned."

Happen to have a "state of charge" status from any equipment?

Have a battery meter connected (also via DC shunt). So, right now, I'm drawing about 200 watts (2 fans, and a medium-sized TV, playing some Star Trek: TNG...in the garage). I'll let all of that run for a couple of hours, and keep an eye on the battery's SoC. 400 Wh drawn from my 720 Wh battery pack should mean that the controller (I would *think*) realizes that the batteries need some juice, and ups the current.

Of course, Zeta is about to cloud us over for a couple of days. Perfect time to test solar array efficiency!!

 

[Habious]

So, to follow up on this...

Yup, stupidity verified.

We ran our batteries down the other night (got 849 Wh out of our "rated at 720 Wh" batteries...so that's pretty cool.)

The next day (yesterday), Zeta blew through...and it was VERY overcast all day. But, even with that, we got a peak of 52-watts, and a total energy collection of 149 Wh of solar go-juice.

Those numbers make a whole lot more sense. Again, with my tree situation as it currently is, I wasn't expecting much more than 10-20% of my rated panel output. And, thanks to @Hedges brilliant insight, that's right where we're at!

Now I just need a lumberjack.

 

[Hedges]

We ran our batteries down the other night (got 849 Wh out of our "rated at 720 Wh" batteries...so that's pretty cool.)

The next day (yesterday), Zeta blew through...and it was VERY overcast all day. But, even with that, we got a peak of 52-watts, and a total energy collection of 149 Wh of solar go-juice.

Lithium batteries shouldn't be over-discharged or over-charged.
Make sure you have set a conservative low voltage disconnect, and maximum charge voltage, so you don't drastically shorten their life.

Was some of the 849 watts drawn while PV was putting in Wh too?

Tree is directly South ... would tilting some panels toward the East, some toward the West let them directly face the sun during hours when they aren't shaded? You've got up to 12 hours daylight in the summer, but only 6 hours when the sun is within +/- 45 degrees of straight at the panel.

"The "tree guys" have been called, and we're getting about a dozen of these 200+' trees knocked down, soonish."

Sounds like releasing more evil carbon than your panels will offset in their lifetime. Three trees per 100W panel?
Hope you put them to good use.

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[Habious]

Lithium batteries shouldn't be over-discharged or over-charged.
Make sure you have set a conservative low voltage disconnect, and maximum charge voltage, so you don't drastically shorten their life.

The controller and inverter I've got are super-uber basic. I don't see ANY settings on them (the only "setting" the controller has is "battery type", which is set it LiFePo4).

The inverter specs say low-voltage cutoff is 10V (and that's when it stopped outputting juice)

Was some of the 849 watts drawn while PV was putting in Wh too?

Nope. I intentionally tripped the panel circuit breaker I have installed, so that I would run the batteries down and get a true test of battery-only capacity.

Tree is directly South ... would tilting some panels toward the East, some toward the West let them directly face the sun during hours when they aren't shaded? You've got up to 12 hours daylight in the summer, but only 6 hours when the sun is within +/- 45 degrees of straight at the panel.

At the moment, the panels are installed on a basic knocked-together frame (not drilling any holes in the roof until I know this is gonna work). So, all four of them are just...laying on the roof. Westerly morning sun is a possibility. Easterly is ALL trees. That direction is a total no-go, solar-wise.

If you want, I can take a pic from the roof, so you can see the extent of the "tree problem" I'm talking about. When I say I got trees, I got *trees*! Angling the panels 15 or 20° is not going to make nearly as much of a difference at getting rid of at least a few of the 100+ trees (my girlfriend once counted them) in my front yard alone.

Sounds like releasing more evil carbon than your panels will offset in their lifetime. Three trees per 100W panel?
Hope you put them to good use.

The "tree guy" is giving me a discount for him taking the lumber away (and selling it later on). Much as I'd like to keep it all, and have a 5-year supply of firewood (house has an awesome ca. 1970's wood-burning stove in it), I needed a deal that would allow me to knock down the maximum amount of trees for the minimum amount of money.

As sacrilegious as I'm sure this sounds on this forum, I'm not all that concerned with the environment. That's not why I'm doing this. I'm worried about having power available in a long-term power outage situation. I know I'm never going to have a "whole home" solar system but, having *some* power available in perpetuity is very attractive.

Probably an odd thing for a guy with a burgeoning solar array, and a prior Tesla (Roadster) owner, to say but, whatdayagonnado?

 

[Hedges]

Something like this would give you steady power for decades. Works for space probes.

Radioisotope thermoelectric generator - Wikipedia

en.wikipedia.org

You need to set up a low voltage shutdown/disconnect of the inverter or you'll kill the batteries.
BMS do that, but your batteries may have the cell balancing function inside, so you're not using a separate one.
Is there an on/off control you could tap into?
Maybe get an additional voltage monitor or charge controller that has a "load" output with adjustable disconnect, and wire that to a relay (car starter solenoid for high power? and high drain?)
You could build a circuit with resistor-divider compared to resistor-zener, feed into an op-amp or comparator, control a relay.
Or buy a different inverter.

At 10V disconnect, your batteries won't be long for this world.

 

[Habious]

Something like this would give you steady power for decades. Works for space probes.


You need to set up a low voltage shutdown/disconnect of the inverter or you'll kill the batteries.


At 10V disconnect, your batteries won't be long for this world.

I think the RTG is not a realistic solution to my power problems.

I've found a simple low-voltage disconnect, and should be able to wire it into the power switch on the inverter.

Recommended voltage to disconnect?

The disconnect I found has the following options:

12.1 VDC
11.4 VDC
10.7 VDC
10.0 VDC

 

[Hedges]

I haven't worked with any Lithium batteries, but quick search here I found:

Recharging LiFePo from BMS low volt shutdown

What would be considered a safe time limit between the time your BMS shuts your LiFePo battery down with BMS set at 11.2v low volt disconnect at night after using to the time the sunrise begins recharging the battery back up? I know it’s not a wise practice and can damage a LiFePo sitting at...

diysolarforum.com

That mentioned 11.2V as safe to disconnect and sit at for a while, so I'd go with your 11.4V option.
But check your battery's documentation, discharge curves, other recommendations.

I use radioisotope for illumination but not for electric generation. No bothersome paperwork needed.

 

[Habious]

I haven't worked with any Lithium batteries, but quick search here I found:

Recharging LiFePo from BMS low volt shutdown

What would be considered a safe time limit between the time your BMS shuts your LiFePo battery down with BMS set at 11.2v low volt disconnect at night after using to the time the sunrise begins recharging the battery back up? I know it’s not a wise practice and can damage a LiFePo sitting at...

diysolarforum.com

That mentioned 11.2V as safe to disconnect and sit at for a while, so I'd go with your 11.4V option.
But check your battery's documentation, discharge curves, other recommendations.

Again, many thanks.

I did some searching (both on Google and on here) and couldn't find a good number. Must've been searching the wrong term. I did find one low-voltage disconnect that mentioned that it cuts off when the battery reaches 2.9 VDC per cell. A quick bit of math gave me 11.6 VDC. So, I also figured the 11.4 VDC option would be the best.

Sadly, the batteries I have don't have a whole lot of documentation (either included with them or online).

The battery documentation says that the batteries have:
Maximum Charge Voltage：14.5V
Discharge Cut-Off Voltage：10V

I looked at the Battle Born batteries and, while they seem very nice, I could not justify the price-per-Wh for my experiment.

Even spending $4K on tree-knocking-down isn't going to guarantee that I'm going to get enough sunlight to make my system reasonably efficient. But, it certainly can't make it worse.

I know that spending more money gets your better equipment, and that spending more usually winds up being cheaper in the long run. Even knowing that, I bought the cheapest panels, that came with a cheap-a$$ controller, and the cheapest Wh-per-$$ batteries I could find.

The idea was that, if this works for the house - awesome. We'll expand and upgrade it over time. If it doesn't, we can put it on the roof of our shed (which doesn't have a problem with shade...but is far from the house) and use it to power some motion-sensitive security lights, so we didn't completely waste our money.

As it is, this "cheap-a$$ experiment" has cost me about $2K so far (not counting the tree guy).

 

[BiduleOhm]

I use radioisotope for illumination but not for electric generation. No bothersome paperwork needed.

Now I'm curious...

 

[Hedges]

Now I'm curious...

Only small incidental applications, based on radium or tritium

Radioluminescence - Wikipedia

en.wikipedia.org

Ever read 'The Radioactive Boy Scout'?

(Not recommended you paint your teeth with the stuff for a Halloween costume.)

 

[BiduleOhm]

Oh ok, I was thinking bigger stuff.

No but I know the story...