One way would be to use the following formula in a cell (assuming all the solar values per minute are in column A - change as necessary).

**=(SUM(A1:A1440)/164)/(COUNTIF(A1:A1440,">0")/60)**

which adds up all the solar values of the day and divides by 164 (the average over the entire earth per day) then divides that result by the total number of minutes with a solar reading above zero divided by 60 (giving the number of hours for the day) to produce a kWh value which is close but not exact to the value from WD as I have tested with my data, so not sure what formula WD uses.