Talk Morgan Forums Community The Malvern Arms efficiency of electric vehicles

Hope I have got my maths right in doing the conversions.

1 gallon of petrol contains approx 40 kwh of energy and you might do 40 miles on that so 1 kwh per mile.

1kwh of energy will power an electric car for between 2 miles and 4 miles according to wiki " Miles per gallon gasoline equivalent". The difference comes about because a good petrol engine is still only beatween 25% and 50% efficient - diesel being inherently more - and an electric motor is way more.

There is the debate about the efficiency of power stations and line losses but there is no realistic way of quantifying this given the changes going on as new capacity comes on line both from solar / wind and nuclear. It takes 6 kwh of energy to distill petrol so really that gallon only gives 34 kwh

As for range, a 15 gallon petrol tank hold 600 kwh. A Tesla battery pack is somewhere around 100.

Hmm.

Electric transmission (AC) can loose q fair bit - DC even more. I do not fully recall but at uni I seem to recall 60% losses overall.

Order of magnitude out, Richard. National Grid transmission and distribution losses are a bit under 8% overall.

It was a long time ago

Great post Howard. Efficiencies aside, no matter how battery capacity improves, we already don’t have the infrastructure to cope with home charging if even just 10% of cars were electric. Domestic supply is only rated at 9kw per hour, blocks of flats less per household. By the time batteries improve to offer decent range on twisty roads and cold conditions, they’ll need all day and all night to recharge.

Put it this way, you get your 600kw hour of petrol in 5 mins, and how may petrol pumps are available per car? If you need 50 mins to fill your tank, we need 10 times as many pumps.

Sorry ewn, 9KW per hour makes no sense, wattage is a delivery of power (energy per second).

Max current rating on a UK domestic consumer unit is 100A, beyond that you need multiple supply points / consumer units at the same location (not a problem, we have 2) and for very high consumption you can go 3-phase.

100A means that at 240V you could in theory charge at 24KW, but you'd have to leave a bit to enable your other homes systems to run and you would need dedicated wiring to the charge point.

But in exactly the same way that we don't expect people to provide their own petrol refuelling systems at home, there's no particular reason why we should expect people to provide their own home charging.

There is, of course, a very good reason to do so, as it will enable owners to make money from their EVs using the Vehicle to Grid technology that's already available and is going to be expanding rapidly over the next few years. The early adopters now who are going for domestic battery installations are going to be able to take even more of an advantage.

Much of the development work in the industry is focused on 'opportunistic' charging, doing things like using the existing network for things like street lighting to provide charge points.

Your consumer unit and wiring might be rated at a maximum of 100A but I very much doubt that its rated at 100A continuous which is effectively wht is needed to charge a car battery.

However, the key is the capability of the incoming supply to the house. Is there a maximum rating for a domestic dwelling or can you have as much power as you want by agreement with the power distribution company?

Sure the architecture of the national system has to be based on non domestic charging if only for the reason that lots of people dont have drives or garages to put the car whilst charging

Depends on the DNO, but they are usually very keen to provide their customers with as much power as they need. There are many domestic customers with high power demands even without EV charging.

For domestic EV charging I really can't see a problem with overnight top-ups, this idea that you have to get a full range charge every evening is a canard, most cars only do a max of 30 miles a day, an amount easily replaced between 22:00 and 06:00.

It is more efficient to transmit high voltage DC than high voltage AC. You do not have the losses associated with Inductive and Capacitive effects. The reason it is not done is because the power stations generate electricity as AC and the equipment required to convert AC to DC and back again would be very expensive and large and not cost effective. In any case it will still have to arrive at your home as AC.

As far as car chargers are concerned, if you want an OLEV grant to install a charging point there are 3 sizes. 3.7.kw or 15.5 amps, 7kw or 29 amps both single phase and requiring separate wiring to the consumer unit and 22kw which would require a 3 phase supply.

I can only speak for the situation in Aberdeenshire but farmers local to us therefore in rural locations that do not have 3 Phase electricity supplies installed have very big problems getting and in many cases are refused 3 phase supplies.

I assume it is probably the existing local network capacity is at it's limit and that would require the supplier to reinforce the local distribution network

In another case of a very large house in the country side that was being refurbished, where the electrician approached the electricity supplier for more than 100 amps he was very firmly advised that 100 amp was the maximum that the supplier would provide. They refused a second supply to an outbuilding.

Again this may well be a local capacity problem and not a country wide issue.