"Rod Speed" wrote in message
...
And we'll all have to stop every 200 or so miles for an enforced and
prolonged recharging stop - that's the hurdle that really hasn't been
overcome yet: limited range coupled with *very* long recharging times.

And that’s just one of the reasons I can't see a ban happening.

When they bring out an electric car with a 700 mile range which can be
recharged in 5 mins to give another 700 miles, then I might be
interested.

Can't see that happening in just 20 years either, but I could be
wrong there with the faster charging given what has been seen
with phones. But it remains to be seen what that will do to the
useful life of the battery. Can't see that anyone will be prepared
to swap by far the most expensive part of the car every 2 years either.

Yes I think when the date of the ban starts to become imminent, they'll
decide that technology just hasn't moved on far enough for "no fossil-fuel
cars" to be realistic.

It's a *very* tall order being able to recharge an electric car in the same
time that you can fill a car with petrol or diesel.

My car has a 60-litre tank and that gives me a range of 650-700 miles (it's
diesel, so the economy is better than for petrol). I can fill up in 5
minutes (at the most, with a painfully slow pump).

Diesel has an energy density of 38.5 MJ/litre. So 60 litres in 5 minutes
(300 seconds) is:

60*38.5/300 MJ/sec = 7.7 MJ/sec, aka 7.7 MW (gulp!)

That is one hell of a lot of power. Even if 99.9% of the electric power goes
into chemical energy, and only 0.1% is wasted as heat, that's

7.7 * (0.1/100) = 7.7 kW

of waste heat that you need to dispose of, to avoid the batteries
overheating. I bet my estimate of 99.9% efficiency is wildly optimistic.

Irrespective of the battery technology that you use, you're still got the
problem of needing to get the same amount of energy into the battery in the
same length of time.


OK, so electric cars are probably more efficient. You may not need as much
electric energy as you do petrol/diesel energy to propel the car the same
distance at comparable speeds and accelerations. You can also use
regenerative braking to charge the batteries a little bit when the brakes
are applied. But I doubt it's going to be an order of magnitude difference.


So, maybe the way forward is replaceable batteries. Or else replaceable gas
in a fuel cell, so you are taking on board chemical energy rather than
electrical that has to be converted to chemical. The husband of one of my
mum's friends is (or was until he retired) a professor of fuel technology. I
remember him talking about fuel cells back in the 1970s as being a more
energy-dense way of storing and generating the electricity needed for
electric vehicles.