January 26, 20242 yr Hi everyone, Installed for myself my first solar system: 3200VA off grid mppt solar inverter (has bypass to grid capability), 6x440w panels, 2x280Ah 12V Lifepo4 batteries in series. Works all the time as it powers my heat pump to heat the house, nicely switches solar and battery power and back to the grid depending if there is sun or the batteries are empty. As an extra measure of protecting the inverter and the heat pump I though to add a DC 250V SPD to the PV string after the DC fuses, but then the RCBO trips (this is installed by the utility grid provider right after the meter). If I disconnect the DC fuses (so no solar power) the inverter continues to work from battery or utility, no RCBO tripping. Interesting enough if I disconnect the negative lead of the PV string from the SPD then the RCBO does not trip anymore. The measured voltage on the PV string in full sun is 200V, this is very close to the working voltage from the PV panel specs, and far from the 250V where the SPD should start surging. Is the SPD bogus or the inverter back-feeds something when there is PV power? Ohmmeter shows around 0.3Mohms between each pole of the disconnected SPD and ground. I plan to measure each individual panel's leads resistance to the frame (that's grounded), maybe there is a defective panel (I doubt as they are less then two months old), but then I'm out of ideas. Any thoughs what can cause this?
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