I am on a green tariff with SSE. Every kWh I take from the grid has to be matched by SSE putting one in from a renewable source (on my plan, it's hydro). This is audited by Ofgem.
Thus the money I pay them has to be spent on renewable sources. If all customers signed up for this tariff, they'd have to make a lot of investment in renewable sources. Maybe that is one reason why SSE just opened the country's first new full-size hydro station for 50 years and have so many new hydro and wind schemes coming online soon: SSE - Project portfolio
So while green and brown electrons mix in the grid, if you are paying for green ones to be put in, you are entitled to say that you are taking green ones out. If more customers vote with their wallets, the proportion of green ones will rise.
However there is another way we can power our cars that is often overlooked in these discussions and that is domestic solar.
A 3kW peak system costing around £10,000 is about 20 sq metres of panels - enough to fit on a typical 4x5 metre garage. Such a system will generate enough juice for 10,000 miles of EV driving a year, even in sunny ol' Britain (in the south of England it's about 11,000 miles and in Scotland about 9,000 miles per annum). You can check results for your location here: PVGIS home
As the EV would most likely be plugged in at night, you'd need to store the energy generated in the daytime. Some people would use the grid as the battery, but to be more independent you can store the energy in static batteries at home. 10,000 miles a year is under 28 miles per day - which is typically under 7kWh of electricity use in an EV. That would require 5 boat/caravan 130Ah "leisure" batteries costing £95 each
for daytime storage. In the winter you'd still have to top some up from the grid (or another local source like wind), but you'd put it back in the summer.
Furthermore, in the 25 years that a solar panel is normally guaranteed for, a 50 mpg diesel car will burn over £30,000 of fuel to cover the same distance (at 2011 prices), so your initial £10500 outlay really pays for itself.
So everyone with a garage or house roof that does average mileage (according to the AA
) in this country could be driving net emissions free and at significantly reduced cost per mile than they are now. The difficulty is getting over that "hump" of having to pay £10,000 before you enjoy decades of free motoring. Sounds like we need a new class of bank loan or mortgage extension to enable people to do this and perhaps legislate that all new-builds should have it as standard.