The eco charge mode is a mixture of both green energy and energy imported from the grid. Eco mode minimizes the use of grid power, generally taking advantage of cheaper rates overnight, but can also charge using 100% green energy. Essentially giving you the ability to charge up your car for free! The charging power is continuously adjusted in response to changes in generation or power being used elsewhere in the home.
If the surplus generation drops below 1.4kWh, some power will be drawn from the grid to top it back up.