Why don't we get more from 800 watts of solar panels?

[Weldingunltd]

We have 8 100 watt solar panels mount on top of our travel trailer. We have an e-pever mppt solar controller and a Victron BMV 712, and 2 Battleborn 100 ah batteries ( we just upgraded to these from 4 100ah lead acid). We installed 8 panels with the expectation of being able to take in between 400 - 800 watts. We have never seen above 400 watts, and we usually only see around 150 watts on a sunny day, and much lower on slightly cloudy days. We are currently wired in parallel, but we have previously tried wiring in series. Neither offered the results we expected.

 

[snoobler]

Welcome to the forum.

Panels produce their rated power when:

It is high noon.
The skies are completely clear.
The sun is perfectly perpendicular to the panel.
The solar power shining on the panel is 1000W/m^2.
The temperature is 25°C.

Panels flat on a roof in the northern hemisphere while the sun is in the southern hemisphere are getting FAR LESS than 1000W/m^2 of sun on them.

Shading, even partial, can severely impact the production of the shaded panel. Since you have your panels in parallel, that should limit the effect to one panel. If the panels are in series, a single shaded panel can impact the production of the entire series of panels. Roof protrusions on an RV have a tendency to shade panels.

Your charge controller must be rated for 800W/12V = 67A to ensure you can actually collect the peak solar. Anything over 60A should suffice. If you have a lower current charge controller, you can't harvest your solar.

Lastly, if your batteries are in absorption mode, where they've reached peak voltage and a tapering current to maintain voltage, it doesn't matter how much power the array can produce, the SCC will only use as much as the battery can take. A way to test this is to apply 1000W of loads at your peak solar period to see what the array can produce.

 

[Hedges]

You can remove most things from the equation by using an ammeter to measure short-circuit output of a single PV panel.
Compare that to Isc rating of the panel and you'll have a good idea about what percentage of rated wattage is available.

 

[Generis]

The 60amp version of the ePever charge controller is what you want for this much panel. If you have the 20 or 30 or 40 that could be your problem, because the controller will throttle back the panels to your controller's rated limits.

 

[martyfarkle]

Is there a calculator that would figure out total power at the charge controller by entering in panel configuration with mixed parallel and series? For example: I have 8x100 watt panels and I am going to configure them in 4 sets paired in series and then the whole lot in parallel. Is that 4s2p? I never can figure this out.

 

[Generis]

Sure. Here's the math. Works on any config.

Total watts of panels / (divided by) storage voltage = amps of charge controller.

So... 800w of panels divided by 13v battery bank = 60amp charge controller.

Panels Configuration options---
For mppt controller use higher voltage panels or series connection. (Ex: 40v or more panel nominal, 13v battery)
For PWM controller, use panel voltage connect to match battery bank voltage. (Ex: 19v panel nominal, 13v battery)

My experience and my opinions:
If your mppt controller is rated at 105v max input, then aim at a panel voltage LESS than that. Like max it at 80v for instance. This gives the controller components some air to breathe so it's not running at limit all day.
Most panels will operate less than rated. Likely your 800w of panel rating will bring in maybe 650 or 700 most of the time in great conditions. If they hit 800 ever that will be a surprise. My experience.
Run wires that will support your max current according to the math. Watt / voltage = current. Then check a wire gauge chart for the length of wire and gauge you need to use..... At EVERY connection. Panel to controller. Controller to battery. Battery to loads. Etc.
Use a serious duty crimp tool for really legitimate cold crimp joints on your ends. I can't say this any louder. This is the one tool most people seem to cheap out on and it's a top level requirement to get all this power moving around properly. Bad crimps make horrible solar systems. It's rarely the equipment, mostly connection problems I've found.

 

[Forbisher]

We have an e-pever mppt solar controller and a Victron BMV 712, and 2 Battleborn 100 ah batteries ( we just upgraded to these from 4 100ah lead acid). We installed 8 panels with the expectation of being able to take in between 400 - 800 watts. We have never seen above 400 watts, and we usually only see around 150 watts on a sunny day, and much lower on slightly cloudy days. We are currently wired in parallel, but we have previously tried wiring in series. Neither offered the results we expected.

What model and amps is your Epever SCC?
12V battery or 24V?
8 panels in parallel is a lot.

 

[martyfarkle]

I have two MPPT's, Epever 30a and Epever 60a.

Configuration now is 4x100 watt panels set up as 2s2p (is that right symbol?), using 30a CC with a 12v Battery pack consisting of 8 120ah cells. Has been working great

but....

I will eventually use 16 120ah cells configured to be a 24v battery pack and using the 60a Epever CC with 8x100 watt panels set up as a 4s2p (?) configuration. 4 pairs of panels, each pair a series connection, then those 4 in parallel to the CC (or is that 4s4p?). I am currently capacity testing remaining 8 120ah cells (which I overcharged!) to see what damage was done (diminished capacity).

So far the first two cells came out with 118ah and 124am. How that is possible with damaged cells, I don't know. The third cell is now being charged to 3.65v then will be tested using a new capacity tester - suspected the previous tester.

 

[Nakinto]

I have two MPPT's, Epever 30a and Epever 60a.

Configuration now is 4x100 watt panels set up as 2s2p (is that right symbol?), using 30a CC with a 12v Battery pack consisting of 8 120ah cells. Has been working great

but....

I will eventually use 16 120ah cells configured to be a 24v battery pack and using the 60a Epever CC with 8x100 watt panels set up as a 4s2p (?) configuration. 4 pairs of panels, each pair a series connection, then those 4 in parallel to the CC (or is that 4s4p?). I am currently capacity testing remaining 8 120ah cells (which I overcharged!) to see what damage was done (diminished capacity).

So far the first two cells came out with 118ah and 124am. How that is possible with damaged cells, I don't know. The third cell is now being charged to 3.65v then will be tested using a new capacity tester - suspected the previous tester.

8 panels would be either a 2s4p or 4s2p. It sounds like you are doing a 2s4p system. 4s means 4 panels in (S)eries 4p means 4 (P)arallel strings(or panels). So 2s4p would be 2 panels in series and then 4 parallel strings of those 2 panels so 2*4 or 8 panels. Below is a 2s4p configuration of panels . Remember, series adds Voltage, parallel adds Amperage. So 2s panels of 24v each panel would be a 48v configuration. And if you took four 7 amp panels in parallel you would get 28 amps. I am borrowing an example of series vs parallel from Mind Research.

 

[willo]

Hmm. I’d do some testing - make sure that you don’t have a bad panel here. (Or bad wire)
A a minimum, you can connect to the BMV and watch data as you make changes.

I’d also check panel output voltage. Do you have the display for the ep ever? It may help you with some of the diagnostics.

You may get better results with partial series wiring to get a higher voltage to the controller.
You may also be suffering from shading. Even one cell shaded can kill panel output. How clear is the sky to your setup?

 

[DIDDLYV]

I am planning using 4 210 Watt panels running 2 s each set of 2 connected to its own 40 Amp solar controller just because I would need at least 60 Amps on a single controller and looks like 2 40 Amp SCCs are less expensive than the 60 amp models.
Am I missing something??

 

[MisterSandals]

Am I missing something??

No, redundancy is a good thing. Which panels, SCC and batteries?
And you REALLY should start your own thread so we can keep issues and solutions from being confused.

 

[DIDDLYV]

No, redundancy is a good thing. Which panels, SCC and batteries?
And you REALLY should start your own thread so we can keep issues and solutions from being confused.

build my own 310 AH cells 2 4s cells each wired with its own 150 Amp Daly BMS with fan Hitech solar 210 pannels 2 each EPever Tracer BN 40 AMP MPPT

 

[Gertundan]

Solar panels must be used and installed correctly. When the sun's rays hit the panel at an angle of 90 degrees, that is, perpendicular, this allows you to get the highest percentage of electricity generation. It is very important to monitor the inclination angle and set it accordingly, according to the recommendations of specialists, at least once a season. Our solar panels were installed by the company https://www.energyaustralia.com.au/, and we got a result that significantly exceeded our expectations.