For some time now my car charger has been linked to my solar panels so that it automatically turned on when enough surplus solar power was available enabling me to charge my electric car for free. This has helped me get up to an average of 70% of my generated electricity being used my me rather than export to the grid.

The latest refinement is intended to help me increase that beyond 70% while charging the car more quickly and reducing my use of bought electricity.

Variable rate charger

The new refinement allows the charger to switch between 0, 6, 10 and 16 Amps rather than simply off/on between 0 and 6 Amps. I needed a new case to get all the bits in, but the main technical difference is the use of a Programmable Logic Controller (PLC) to determine the desired charge rate.

The PLC is programmed from a laptop via a USB lead to create a programme in ladder logic which combines inputs (currently export threshold and contactor closed) with timers to switch on one of four different outputs corresponding to the four different charge currents (0, 6, 10 and 16 Amps).

Solar panels can generate significant amounts of electricity for example on March 25th our 4kW panels generated 22.4 kWh over the course of the day as shown.
ImmerSUN 25-03-2016
This generation typically substantially exceeds the load being drawn by the house leading to export of electricity to the grid – 12.3 kWh in this example or more than half the generated energy.

Moving loads such as the washing machine or dishwasher from night to day can help use this electricity, but done to excess risks increasing day time electricity import if changing cloud cover or other factors reduces generated power. The varying power demand from such devices is also unlikely to coincide the the surplus power available leaving some unused surplus. I was thus pleased to come across the ImmerSUN system.
The ImmerSUN is a device which diverts surplus power to a range of possible consumers such as an immersion heater. It has a current sensor that measures any surplus power being exported and then diverts a similar amount of power into the immersion heater. Normally of course an immersion heater is either on or off, but the ImmerSUN provides proportionate control between 0 and 100%. It can control several devices diverting power to a lower priority device once, for example, a higher priority immersion heater has raised the water temperature to the set point and power for that purpose is no longer required. In the top illustration the blue bars show 4.7kWh being diverted into water heating (and thus reducing my gas bill) that otherwise would have been lost to export.

For further details see ImmerSUN website .

At the time of writing if you order online quoting Referral Code 206505 you will receive £25 in department store discount vouchers or a free system upgrade to remote monitoring.