what could cause grid tie mppt to decease over time?

balee123

After 11 years, the mppt voltage on the inverter display appears to be decreasing....mppt voltage is now around 58V,
it used to be much higher. What could be causing this? Panel age? Inverter age? Doesn't appear to be due to yearly or temperature fluctuations.


Inverters:

Xantrex STRX2500 and Xantrex STRX1500 are 10-11 years old....same age for panels.

Cariboocoot

Re: what could cause grid tie mppt to decease over time?

What was the Voltage before?
How dirty are the panels?

Otherwise it would be a good idea to inspect the wiring connections. Weather gets in to even "weather tight" connections causing corrosion. That's increased resistance and a loss of power. You may have some panels producing a fraction of their power due to this.

balee123

Re: what could cause grid tie mppt to decease over time?

Voltage has been 64-67 volts
Panels have been cleaned recently.
I'll take a look at some of the wire connections.

Could the efficiency of the grid tie output change with age?

What types of changes could/would one expect to see as a grid tie inverter ages? Or would it "just stop working" some day, like a switch being turned off?

Cariboocoot

Re: what could cause grid tie mppt to decease over time?

We're talking about the DC input to the inverter, not its output. The output will be a function of this, as it will be as much power as can be gathered from the panels. The Voltage in should be a factor of the array moreso than the inverter. If the MPPT function is pulling down 10 Volts lower than normal it is probably due to a lack of power from the array. This could be a small loss per panel (or connector) adding up or the degradation of one or more panels.

You're going to have to do the "disconnect and inspect" routine. You can look at all the connections and test each panel individually for Isc, which is a good indication of its power potential. But also look at the panels themselves for signs of discolouration or any other abnormalities. Sometimes panels fail and have to be replaced.

BB.

Re: what could cause grid tie mppt to decease over time?

Watch the current... Voltage is dependent on solar panel temperature. As we get into spring/summer, Vmp-array voltage will drop (upwards of 20% or so) as they get good and hot (especially if you have sub freezing weather where you are at).

When my panels failed--It was obvious because the maximum current fell by ~1/2 and the total power (Vmp*Imp=Pmp) fell dramatically too.

If you have parallel strings of panels, you can find bad wiring connections with a DC Current Clamp Meter (here is a ~$60 unit that is "good enough"). DC (and AC) current clamp meters are great for use around paralleled solar panels and battery banks--You can check each string and make sure it is contributing its share to the system performance without having to disconnect cables (note you have to measure the current in one wire at a time... If you put + and - Leads together in the current clamp, you will read ~0 amps--The sum of +10 amps and -10 amps is zero amps).

Also note, solar panels should current share very well (close matches between identical strings). Battery banks will tend to current share less evenly and may change over time (nature of batteries).

-Bill

solar_dave

Re: what could cause grid tie mppt to decease over time?

As others have said the incoming voltage from the panels does decrease a measurable amount due to temperature. I get a peak power drop of up to 10% in summer because of hot panels and I consider that pretty good considering the angle of incidence on the panels is better than in winter. My panels get really hot here in summer.

Cariboocoot

Re: what could cause grid tie mppt to decease over time?

I don't think the OP is referring to seasonal variation but rather a drop in operating MPPT Voltage over a span of eleven years.

solar_dave

Re: what could cause grid tie mppt to decease over time?

Cariboocoot wrote: »

I don't think the OP is referring to seasonal variation but rather a drop in operating MPPT Voltage over a span of eleven years.

I don't think he made that clear. He would have to have a data point eleven years ago with the same environment conditions. I didn't see anything saying that his overall harvest is down.

Cariboocoot

Re: what could cause grid tie mppt to decease over time?

Just to cover all bases, what panels are these?
Weird thought that they might be amorphous type which are known to go down over time (more so than crystaline type).

ggunn

Re: what could cause grid tie mppt to decease over time?

Just riffing here, but it seems to me that one thing that could dramatically lower the MPPT voltage would be a mid-string ground fault somewhere in the array. I would open the DC disconnect and string fuses and check all the string voltages (+ to - as well as + to GND) to make sure they are reasonable and virtually the same. GFP should catch this, of course, but stuff happens.

Cariboocoot

Re: what could cause grid tie mppt to decease over time?

If it was installed 11 years ago, would it even have had GFP?

ggunn

Re: what could cause grid tie mppt to decease over time?

Cariboocoot wrote: »

If it was installed 11 years ago, would it even have had GFP?

All the more reason to check those voltages, IMO.