Solis OV-DC01 (Alarm 1020) — PV String Over-Voltage

What it means: The DC voltage arriving from your solar array is higher than the inverter is built to accept, so it shut down to avoid damaging itself. Solis logs it as alarm 1020 and the LCD shows OV-DC01 through OV-DC04. The manual's failure description is simply "over DC voltage" and its remedy is equally blunt: reduce the number of modules in series. On the single-phase S5 and S6, the maximum DC input is 600 V for the 3 kW to 6 kW models and 550 V on the 2.5 kW; the MPPT tracking window is 90–520 V on the 3–6 kW models and 50–450 V on the 2.5 kW. This is almost always a string that was designed or extended wrongly, not a component that has failed.

Why does Solis show OV-DC01?

• Too many modules wired in series for the model — the string's open-circuit voltage exceeds the inverter's DC input limit
• A string sized on the panel's nameplate voltage without correcting for cold temperature. Open-circuit voltage rises as the modules get colder, so a string that is fine at 40 °C can go over the limit at first light on a cold morning
• Panels added to an existing string during a later system expansion
• A different panel model substituted mid-installation with a higher open-circuit voltage than the one the string was designed around
• Two strings accidentally wired in series instead of in parallel
• On a healthy array, an internal DC measurement or boost-stage fault in the inverter

The Pakistan factor

Two Pakistani patterns produce this code. The first is geographic: a string sized with a Lahore-or-Karachi summer in mind can go over-voltage on a December morning in Quetta, Murree, Abbottabad, Skardu or the upper Punjab plains, where near-freezing dawn temperatures push open-circuit voltage well above what the designer allowed for. If your system was commissioned in summer and started throwing OV-DC in winter, that is the explanation. The second is far more common and entirely avoidable: panels being added to an existing string during an expansion. Systems here grow — a household adds two or three more panels after the first summer bill, and if those panels go into an existing series string rather than a new one, the string quietly crosses the inverter's DC limit. The inverter's over-voltage protection is the only thing standing between that decision and a dead input stage, so the alarm is doing you a favour. Anyone quoting to expand a Solis system should be recalculating string voltage as part of the quote; if they are not, ask.

How to fix it

1. Note when it happens. A fault that appears at sunrise on a clear cold morning and clears as the day warms is the classic signature of a string that only goes over-voltage at low temperature. That timing is the most useful thing you can tell your installer.
2. Do the arithmetic from the ground, with paperwork rather than tools. Count the modules in the string, read the open-circuit voltage and temperature coefficient off the panel's label or datasheet, and compare the cold-morning total against your model's DC input limit — 600 V on the S5/S6 single-phase 3–6 kW units, 550 V on the 2.5 kW. This is a reading and counting job and it is perfectly safe.
3. Do not unplug, rearrange or "shorten" the string yourself. A PV string is live at hundreds of volts DC whenever there is daylight, and this alarm means it is currently above even the inverter's rating.
4. Do not switch the DC isolator to try to clear it. The Solis manual warns explicitly that operating the DC switches while current is flowing damages the inverter, and that damage caused that way is not covered by the warranty. The safe sequence, when it is needed, is an installer's job with a clamp meter confirming the string current is near zero first.
5. Do not simply keep restarting the inverter. It is reporting an input above its design limit, and every restart puts that over-voltage back on the input stage.
6. The actual fix belongs to whoever built the string — reduce the number of modules in series, and re-check the temperature-corrected open-circuit voltage against the coldest morning the site will ever see, not against today's conditions. If the string was extended during an expansion, that is an installation design error and it is the installer's to correct.
7. If the string is comfortably inside the limit and OV-DC still appears, the fault is in the inverter's own DC measurement or boost stage. That goes to the Solis service centre with the model, serial number and firmware version. Nobody should be opening the case — the DC capacitors inside hold charge after shutdown.