Designs and Projects (update August 2013)
The designs were developed to enhance the use of the basic Owl energy monitors when used in conjunction with solar PV panels. The original design was later expanded to enable the circuit to be used for a more ambitious task.
Typically, the shop-bought Owl monitor consists of a clamp-on current sensor, a transmitter and a desk-top monitor. See here for further details of the Owl monitor
In most domestic Solar PV installations there is nowhere to clip the current sensor to read just the imported or the exported energy. If there is no suitable place to clip the sensor and the sensor is clipped to the cable between the import meter and the consumer unit the Owl does not know in which direction the current is flowing; it can be into or out of the house.
The original design detected the direction of the current flow and switched the current signal to the Owl transmitter on or off depending on the direction of the current flow. The Owl will only read the current when it flows in the desired direction.
The modified design enabled the circuit to drive a phase-angle control block so that a load (such as an immersion heater) could be connected to use up any excess energy produced by the PV panels. It uses the fact that the circuit knows in which direction the current is flowing and, if the current is export, the current to the load is increased so that there is no nett export.