To assess whether you need Wattson Solar Plus or Wattson Solar Plus with Easifit, try to answer the following question:
Does the active from the inverter, wire-into the active of the load circuit prior to the consumer unit ?
If so, you require Wattson Solar Plus and you will need to place the 50 Amp Sensor Clip (CT Clip) for measuring usage on the load side of the circuit breaker. In that way Wattson can work out whether the current is flowing into or out of the house. Refer to the Installation without Easifit page.
If not, you require Wattson Solar Plus with Easifit. Please refer to the Installation with Easifit page.