A token system / cryptocurrency (WASHED) is to be linked to the service. It will allow to incentive the lowest CO2 consumption and good environmental practices like using cold/shorter programs. Going deeper in that way, you could also reward (token) the users that become subscriptors of green utility providers, which are thus attracted to engage in the smart contract. The utility costs and/or CO2 emissions will get down and this will in turn make the service more appealing to the user.
The machine itself would mine the cryptocurrency associated to the system.
A proof-of-use would be generated each time a washing cycle is done and then the fee would be charged to the user wallet, by means of a smart contract that should also involve the utility providers.
From a financial point of view, a possible improvement could be a token-rewarded crowdfunding done by users of the first washing units, or even a (recurrent) crowdlending of the (upfront) capital requirements