Adding new panels to old?

[modernhistorian]

I designed and built a grid-tied PV system back in 2009, using 14 KyoceraKD210GX-LP panels in series, feeding a Solectria PVI3000 inverter. The system is still producing, but output has declined significantly, and I'm considering adding panels to the string. Here are the specs:

Each panel stated with a Vmpp of 26.6 and Impp of 7.9, producing 210 watts. When new, in full sun the panels produced 372 VDC and 2942 watts, but they now only produce about 304 VDC and about 2400 watts, max. The inverter is rated for a max of 600 VDC and 3600 watts.

I am thinking of adding four 24 VDC nominal panels, one each at beginning and end of string, and two in the middle of the string. If these each added a max of 26.6 VDC, then the panels would be restored to slightly more than new specs and be well within the inverter's capabliities.

Are there and problems with adding new panels to old, as I've described, and are there recommendations for brand and type of panels? Thanks for any help.

[littleharbor2]

If the current rating is close and preferably slightly higher than the Kyoceras you should be fine. The Kyocrea panels shouldn't have lost more than maybe 12 % of their output.. You might want to look for a problem panel or two in the array while you're up there. A good visual inspection could turn up a problem panel. Look for small burnt areas on the buss tabbing near the top/bottom of the panels If you can see the back of the panels give the backsheet a good looking at. Any bubbling or charred areas are certainly going to reveal problematic panels.

[bcroe]

My thought, some of your panels have sections that have faded,
no longer can put out within the current range of the others, and
they are being bypassed. That is directly indicated by the large
drop in operating voltage. Track them down and get the bypassed
sections out of the series string.

It is not impossible, that you could have a (shorter) string of full
capability panels, and a second string of somewhat lesser current
panels, to keep them working for you. Voltage measurements on
individual panel terminals under good sun, will find them. I
described my method in another string. Bruce Roe

[modernhistorian]

These are excellent suggestions and I will certainly inspect the panels, front and back, before proceeding further. The array is set up on the hill below my house (we live on a south-facing mountainside) so it is easy to access.

I was lucky in timing when I designed and built this PV system. In 2009 Colorado Springs Utilities offered a cash payout for grid-tied solar systems, a program since discontinued. The materials cost me 12.5K and CSU sent a check for 9.5K after the work was completed. Federal and state tax credits further reduced the outlay and the system has long since paid for itself. For power fed into the grid, CSU pays me the same rate they charge (.1342/kWh). In August, according to Home Assistant, I produced 293 kWh, sending 160kWh of that to the grid.

Thanks again for the help.