An ad hoc user is a person who wants to charge at a public charge point without having a preexisting contract with the EMP.
To do this they have to scan a QR-code sticker, accept both rates and the terms and conditions. By using a payment-provider they pay directly (“pay-as-you-go”). The ad hoc user gets a receipt but stays anonymous.
The opposite of an ad hoc user is the contracted user or roaming user, who usually are charged at some later point in time (“postpaid”).
