Technical Support

(Due to swings in energy import/export)

Has anyone else seen problems with excess energy import when enabling AC coupling of a second (non Sunsynk) inverter?

After many months attempting to resolve a problem with excess energy import, including having the house grid feed re-routed so that CT can be placed close to the inverter and to allow bulk of house to be fed by the load port I ended up with basically the same issue i.e. 1-1.5KWh of excess energy being pulled during peak tariff period.

As part the above works I had an Eastron SDM230 installed on the incoming grid feed, unfortunately this couldn't be enabled due to the version of my controller board, however I was able to use it to closely monitor import/export to the grid.

The monitoring revealed that the inverter is generating swings of +/- 200-300W (or higher) to/from the grid (below, active power readings every 0.5s, averages taken over 10 readings, clamped value ignores export giving value that roughly corresponds to import reported by smart meter). The swings happen irrespective of the string inverter generating any output. These swings are ultimately what is cause the excess import, see clamped average below.

I then found that if I turn off AC coupling (aux port set to gen instead of micro inverter) the fluctuations drop to a more reasonable level and daily import falls to ~200-300Wh, not perfect but at the acceptable end of the scale.

Sunsynk are currently investigating this issue for me, but have any installers or other users seen similar issues with AC coupling of second inverters?

Note changing string inverter to feed directly into AUX doesn't help (it actually makes matters worse).