You can sometimes charge for free or daily at minimal cost by using a tariff based on wholesale electricity prices. These vary by the half-hour, they peak in the early evening but are exceedingly cheap in the early hours of the morning. However, they do vary according to supply and demand.
Sometimes there is so much electricity being supplied to the grid that your supplier will actually pay you to use the excess!
Some chargers can be set for the maximum that you wish to pay to charge your vehicle, for example zero. You will need a Smart meter and a half-hourly tariff such as Octopus Agile.
Join Octopus Energy as a new customer and receive a £50 discount for joining any Octopus tariff including the ones designed for Home charging. Also, have them donate £50 to keep this site running, please click through to the Octopus site.