My experience is that the Denver area has cool, very clear skies, near ideal for PV
solar. My guess is that the working system is not in perfect working order, beyond
14 years aging. I am guessing that system has at least 2 strings of panels to reach
4KW. Here I would go out at best sun with my clamp on DC ammeter and see if the
operating strings are producing identical current, or some problem is degrading one.
Do check the DC voltage and current into the inverter, and compare that with predicted
at your temperature.

Here with 2 inverters, one glance reveals if they are delivering identical power. They
usually agree within a couple percent, a fault is quite obvious. good luck, Bruce Roe

ClmpOnAmm.JPG

The short ans. to your question is probably yes.

According to PVWatts, on a clear day at around noon an unshaded south facing array in Denver ought to be producing ~ 725 -750 W/installed STC kW for a new array.

BTW, most any PV system will only produce its STC rated output in cold(er), clear weather.

Run PVWatts, use 10 % system losses, use the hourly output option and look for dates around this time of year with high output.

Interesting. PVWatts says 30% loss when I consider 14 years age and some shading which I do have. Had to order a voltmeter with loop and when that arrives I can confirm for sure. Thanks.

You're welcome. That PVWatts modeled # was for a new system. If reasonably correct, it'll mean with the numbers you provided, you're doing pretty good.

Check voltage and current under full sun.

Turns out my capacity is actually 7800 W, and just now saw my meter read 3300 W (with 1 broken inverter) so I think my panels are doing just fine. Thank you JPM and bcroe.