2 grid tied Solis Inverters overvoltage issues.

[unsquashable]

I would very much appreciate input from other similar or related experience.

I have had a grid tied Solis 4G 3.6 Kw system for a number of years with 0 issues with the initial setup. A 2 string / 6 panel each with a total STC of 4.08Kw. It has worked flawlessly.

My local 220 Volts, 50 Hz, grid standard calls for undervoltage at 190 Volts and overvoltage at 242 Volts. In the past I only had very few and sporadic over or under voltage alarms in the inverter, which has the regulatory grid standard as its setup.

Since I was adding quite a bit of additional consumption to the house (swimming pool filter and heat pump), I decided to add a second inverter with a similar but not identical equipment.

Since I was adding this additional consumption and eventual grid energy injection, I upgraded my mains line from the original 4.4 Kw to the maximum locally allowed 8.8 Kw for residential mains single phase, changing mains cable size, breakers, etc.

The second inverter is as well a Solis S6 3.6 Kw inverter with 6 panels / 1 string for a total STC of 3.3 Kw. I installed the second system with the same local grid standard, but I started having overvoltage alarms on the new inverter at a rather alarming rate, that is 100 alarms of overvoltage in a couple of days. However almost all of the alarms only affected the new S6 inverter, the 4G inverter only showed 1 alarm in the same period.

Given the situation I changed the standard grid definition to a user defined setup, raising the 242 V overvoltage to 248 V. This reduced the number of alarms in the S6, but still getting at least 3 to 4 daily, specially at the best possible radiation hours when I expect to produce full load.

Any ideas ?? as to how eliminate the issue. (of course maintaining safety standards). According to Solis manual the first thing to do is change grid cable to a larger size, but I wonder if this will solve the issue if only one of the inverters seems to be affected by the overvoltage situation.

regards

 

[SeaGal]

Have you measured what your grid supply voltage is with the inverters disconnected.? If that is too high you will need to contact your supply company to reduce the grid voltage.

If the incoming supply is not too high but is at the upper end of the range, then it sounds if you have an voltage rise issue, which can be overcome by thicker cables = less resistance between the inverter(s) and the incoming grid supply, as you identified already.

If that does not fix the issue, you could configure the Solis to limit export power to the maximum that you can export without breaching the 242V limit. Though you may still get some over-voltage triggers occur when a large load (like your pool pump) switches off and momentarily more power is exported, causing the voltage to rise.

The best approach IMHO will be to monitor voltage at the inverter and grid, ideally logging it every few seconds to work out when and why the overvoltage conditions are triggered.