I’m getting close (I think).
I have the following query set up in grafana
SELECT cumulative_sum(sum("value"))/1360 AS "kWh" FROM "export" WHERE ("sensor" = 'export') AND $timeFilter GROUP BY time($__interval) fill(null)
Taken from @Jam 's post on this thread
Which gives me a guage display of sorts.
I have IotaWatt set to export data every 10 seconds (post interval).
The sums don’t seem to add up though.
My solar installation is showing 2.8 kWh exported today but this query shows 1677244?
I’m dividing by 1000 to get from wH to kWh and 360 as the sample rate is 10s.
I know there is something wrong with my logic but I’m stumped 
Plus, I’m not sure but I have set the calculation field in the panel settings to Total?