In order to define a calculation formula go to Administration->Maintenance/Calculation Formula 

Find detailed instructions here:

1) Define a formula to calculating Active Energy Net Consumption

2) Define a formula to calculating Reactive Energy Net Consumption

Click button TEST to verify correctness of the definition and existing data for specific device in the system.

* Each relevant device should be configured appropriately to have next electricity consumptions types:

kWh Import, kWh Export, kVarh Import and kVarh Export.

Resulted consumption data will be available in reports.

3) Create new report. Choose "Single period comparison" type.

Choose Groups->Calculations and in Calculation choose a new created formula.