If it works this could be a good idea for us if the site owners that I assume sell the electric to Chargemaster are prepared to buy it back from them at double or three times the price.Check with the customer service desk, they may have a card that can be used for a refundable £10 deposit. They do have at Perth but not sure if this will still be available when the charges come in. I prefer to use my own card so that I can keep a track of the power used but I have been told by a member of staff about the cards they hold for customers using.