when will electric cars take over from diesel and petrol?

The primary driving factors in the large scale adoption of electric vehicles are likely to be the cost coming down and the charging time being reduced. They're great for getting around town if you finish up at home every night, but if you want to go 600 miles down the motorway and only have a 300 mile range then you have a problem. When you can drive into the service station, plug the car in, go get a coffee and a doughnut and them drive off again 15 minutes later with a full charge there will be a much higher uptake.

Not for a while. Electric cars aren't viable for long-range travel. They don't last long enough, take too long to charge, and don't provide as much power for their motor size.

Also, unless and until all electricity comes from, nuclear, wind, solar, geothermal, or tidal power sources, you're literally just centralizing where you're doing all your burning of fossil fuels to a power plant, and a lot of that raw energy gets lost between the generation of electricity and that little motor in your Nissan Leaf, so it's less efficient to use electricity to power your car than to run it on gas.

Edit: Dr. Redthumb corrected me on the efficiency thing... so nix that part. The practicality problem still stands, though.

When they solve the refuling and range issues.

When an electric Mini was driven from London to Edinburgh it took 6 days

It was quicker with horses. It was charging time that beat them.

In poor weather with lights, heat and wipers the range plumets.

And again I tell you there will never be flying cars that everyone has.Humans are too stupid to pilot them.Most of you can't dve 25 down the road without hitting something.

When some one invents 'the electric' horse, albeit a bit slower, but no polusion or having to shovel!

When we run out of oil to make diesel and gasoline.

When the Earth runs out of fossil fuels...

in a while when the earth runs out of fossil fuels

when their is more than one brand of them, or if there is more post to stop and charge your car.