As we approach the major climate summit this autumn in Glasgow, many Hampshire residents are wondering when to switch to an electric car, or whether it is worth waiting to run a new vehicle off hydrogen.

The marketplace will be crammed with suppliers saying their cars are the greenest ever.

But what is the truth out there?

Electric cars are getting better. It is now possible to drive away a vehicle that will do 300 or more miles on a full charge, albeit for a hefty price. That means it becomes entirely possible to charge a car and head from Hampshire to the Lake District with just one stop for a shorter charge each way. The day will come when you can do the whole journey on a single charge. But there are substantial hidden costs to the planet.

The first is the manufacture of the battery and the related engine parts. In the manufacturing process there are still substantial costs in terms of carbon dioxide emissions.

So when you are choosing a new vehicle make sure you read the small print. How many tonnes of CO2 equivalent will have been emitted during the manufacturing process?

Just last week I reviewed a car which described itself as “the greenest sports car ever”. But the irony was in the last paragraph which stated “24 tonnes of CO2 were produced for each vehicle manufactured.This is the equivalent of driving a petrol vehicle for 66,000 miles”.

That means you would need to drive your car for 66,000 miles before it becomes carbon neutral. So not so green after all?

Then you have the charging costs. The carbon emissions for charging are entirely dependent on your energy supplier.

If you are with a truly green tariff (which is one in which the company invests directly in alternative energy) then the carbon costs will be low.

If on the other hand you invest with a company that “offsets” its carbon (through tree planting or paying a sum of money to another organisation that helps reduce carbon) the costs in carbon will be far higher.

If you want to invest in an electric car the key needs are:

1) Make sure the electric car you purchase has a low carbon footprint. If the emissions to manufacture mean you must drive more than 35,000 miles before it becomes carbon neutral, I would suggest you avoid purchasing.

2) It is always better to wait and buy second hand.

Remember that the energy costs by purchasing a car that may have already driven 30k are much lower. It far less costly for the planet to get a pre-owned electric car.

3) Check your electricity supplier to make sure it is a true green tariff that invests directly in alternative energy sources. Don’t let your supplier con you into believing its green when it isn’t!

Hydrogen vehicles are not far behind; and in the autumn I will be reviewing whether there is more benefit in hydrogen technology than electric.

For now shop wisely for electric and watch for green washing.