Exported PV being subtracted from grid

Durung this recent sunny spell I’ve noticed that exported PV (-ve kWh) is being subtracted from imported grid value displayed on emoncms.local. I prevent this happening on emonGLCD with a simple ‘if’ statement. Is it possible to prevent this in the ‘feeds’ section of emoncms.local?

Reminds me of my old spinning wheel electricty meter where the wheel would spin backwards when exporting PV

I don’t think so, but it’s certainly possible to create a (new) feed that follows an “Allow positive” or “Allow negative” operation on the Inputs page. Then you can add that feed to another input (or subtract it from, as appropriate).

Does ‘allow positive’ mean it will block negative?

Correct, only positive values will pass on to the next process.