Awhile back I worked out a somewhat convoluted way to accumulate the exported (negative) energy. It involves using both a signed (allow negative values) and unsigned CT on a main.
In a split phase system, you have two mains. If you don’t really need to know the individual measurements of the two mains (only interested in the total) and the total doesn’t exceed 200Amps, it would be possible to do by using a splitter to combine the mains and some under the hood sleight of hand to share the combined CTs between two inputs.
The just of it is that the two mains are combined with the splitter and fed into Input_1. Allow negative values is set and the single input delivers what was Main1 + Main2. Well cal that netMain because it will accumulate the net power through the mains.
A manually inserted config file parameter makes Input_2 use the CT plugged into Input_1. It is configured without the “allow negative” check so it accumulates the sum of the imported and exported power as a positive number. Well call that absMain.
So now energy for netMain is import-export.
Energy for absMain is import+export.
netMain - absMain = (import - export) - (import + export) = 2 * export.
The calculator function
export = (netMain - absMain) / 2. Over any interval - hours, days, months.
I dont have solar, I have trees, so I have not been able to try this at home. I believe a guy in Australia is doing it but I lost track of that effort. If your mains don’t come close to 200A combined, and you want to try it out, I can send you a splitter and help you set it up.