Question about the output from my DIY Solar

[pconroy328]

So I could use a "shove in the right direction."

My Solar is all DIY. Two 100 watt panels, an EPEver 30A MPPT controller. One group 27 (for now).

It's working. It's keeping the battery charged.
But I don't think it's working right, or even close to optimal.

The first 100 watt panel is two years old. I started with it, just one 100 watt. I added the second 100 watt panel a month ago - wired parallel.

Wire from panels to controller is 10g stranded from Home Depot.

Thing is I just started watching the power output recently!

Today is FULL SUN, No Clouds, Noon in Denver.
I'm getting 30 watts.

Looking back at historical data for the week, the best I've ever done is 85 watts from the two panels.


Does that happen?

I *am* plugged in and the battery is fully charged.
Is that what's happening?

The controller is smart enough to dial down the wattage since it's not needed?

If I unplugged and discharged the battery - will I see the controller display more wattage from the panels?


(As I'm typing this, I think I'll try that now. Unplug.)

But I'm a bit confused and wanted to hear from some of you.
Thank you!!!

[red31]

Isc and Vsc pair or Ioc and Voc.

by definition Vsc is zero & Ioc is zero.
both zero power conditions at each end of the IV curve.

Isc and Voc are the max, current and voltage

shorted again, clamp meter
2:40 https://www.youtube.com/watch?v=57R5CVi1j_k

[BFL13]

My wording was clumsy. Isc and Voc --open circuit voltage. (Edited out more confused stuff 🙂 )

BTW, I see they have Il (current from ambient light) to define what I mean by getting Isc as your expected amps. Max Il is the same value as Isc.

That solves the purist's argument that you can't get Isc to the battery--call it Il 🙂

[red31]

can you rephrase your question using Vsc or ZERO volts when + and - are connected via no resistance.

Clamp on should match ammeter with 8A reading shorted by a wire or shorted by an ammeter.

Short circuit current, short is in its name and definition!

see it done @ 2:15 of this video!
https://www.youtube.com/watch?v=hOjcaKmR4lE

[BFL13]

If the Isc of a cell is 8 amps, which you get with no voltage load (Voc), and you short the pos and neg wires from the panel, would you not get 8 amps on the wires using a clamp meter?

A "shunt" type solar controller controls by turning the panel on and off by shorting it. A "PWM" controller and an MPPT controller when in Abs or Float turn the panel on and off rapidly--AFAIK by shorting it too.

[ajriding]

Do not connect the positive and negative wires from the panel together using a wire!!!!!!!! That creates a short. That will damage the panel.

Using a meter between the pos and neg is not a short; it is a measuring method and has an element that can measure yet not short.

The term short is going to cause confusion. A light bulb's filament is not a short, a short is when the pos and neg wires touch.

[Housted]

Get the remote monitor for your controller called MT-50.
It will show the amps and volts from the panels and to the battery.
Amazon has for about $30 works really well.
BTW: I have one to monitor my 80amp controller and 1100 watt solar array.

Housted

[pconroy328]

Thank you all very much!!!

Today was the day I was going to experiment and run the battery down to 60%, but it's cloudy and rainy today! 🙂

But all of your explanations helped very much!
Thank you!

[BFL13]

Shorting the panel does not harm it. That is how you measure Isc and Voc with your meter.

You can do the whole array at once by shorting the wires with your meter at the controller's input terminals. ( Wires out of terminals) If result is unsat you can do one panel at a time if you can get at its wires on the roof

If your rated Voc is 22v, you will see more like 20v a few minutes after the panel is in the sun due to panel heating. Your Isc will vary with the sun's angle to the panel.

Mid-day in summer with panel aimed you should see amps to the battery at least to the Isc rating, which is what you will get with PWM. Might get a touch more with MPPT--I get the same amps in that situation either way. MPPT does better in the shoulder hours.

Don't confuse Imp at the array side with amps to the battery with MPPT. Don't use Imp with PWM at all--use Isc as expected amps to the battery

Watch out with a meter that says 10 amps limit! You can fry the meter if it does not have a fuse you can replace.

[red31]

yes, short panel via an ammeter (or short panel and use a clamp around ammeter), no need to do this test at this pt., add loads and/or discharge the battery to see if additional power is made.

[ajriding]

mexicowanderer.
Don't short the panels. I think you did not mean to say, "short out the panels with a wire".

Use the amp meter between the panel's positive and negative output to measure amps.

Shorting it out will probably damage something.

[naturist]

red31 wrote:
controller job is the LIMIT panel output, if your battery is charged it does not take much power to keep it there.

Yes, if there is a need for power and it CAN be made it will be used for whatever load you have and/or to recharge the battery.

Bingo!

If the battery is fully charged, you won't get much power from the panels. Wanna see full power from the panels? Disconnect them, run the battery down, and then reconnect the panels.

Question, "when the battery is fully charged, what happens to the excess power from the panels?"

Answer: "when the battery is fully charged, there is no 'excess power' from the panels. The controller shuts them off, and they don't make any excess power."

[MEXICOWANDERER]

To isolate a possible panel issue in clear weather

Disconnect from load. Short circuit THE ONE panel. 10 gauge wire

Put an ammeter in line with the shorted wire loop.

If sky is clear blue and it's near noon....

The panel MUST pit out sticker rated amperage

When aimed at the sun.

Period.

At this time of year

Cloud edging amplification can add + 10% error 110%.

[theoldwizard1]

pconroy328 wrote:
Today is FULL SUN, No Clouds, Noon in Denver.
I'm getting 30 watts.

Based on what measuring device ?

First get a Victron Battery Monitor, even just the base model.

Second, get meter with an "amp clamp" like a Uni-T UT210E

The battery monitor will show total power going into or out of the battery. With the meter, you can measure current on any positive wire.

[Lwiddis]

Your solar system numbers are showing you why charging with a generator is such a waste in the absorption phase. Solar = easy, quiet, efficient.