Mr Brown also said the government was launching a new website, ChargePlace Scotland, which will allow the public to find charging points and detail financial help available to switch to an electric vehicle.
Ministers know they need to switch the burden of tax from fuel to direct charges such as motorway tolls or urban congestion charging, but fear voters' reaction.
She oversaw its conversion in 2008 from a fee-charging school to a state-funded academy - one of the first private schools in England to make the switch.