Sum up time with value below 0

I am logging the power consumption from my smart power meter to an Influx DB.
A new log entry is written once a minute as average of the last minute.

When my solar system is producing more than I consume, the smart meter is logging a negative value.

I am now trying to display one value of how much produces energy I didn’t consume. (during all time and during the last day)

So I need to sum up all time frames where the value is below 0.

I tried but don’t find the right approach.
I think this should be the right Influx query. (from Chronograph)

SELECT sum(“CurrentConsumption”) / 60 / 1000 * -1 AS “mean_CurrentConsumption” FROM “Sensors”.“autogen”.“Power” WHERE time > :dashboardTime: AND time < :upperDashboardTime: AND CurrentConsumption < 0 AND “tag1”=‘Smartmeter’

Would be great if someone could help.