arj1 wrote:
I’d probably disagree – producing electricity at a power station is going to be always more efficient.
Also, you could produce electricity using different methods, and so you might be able to use clean(-er) methods in the future.
Indeed. Changing 1 power station to be less polluting (with 1 decision maker – the government) is always going to be easier to do than changing 100K cars (with 100K decision makers).
Re power station efficiency, look up the steam cycle.
The only bulk capable for most countries alternative is a gas turbine but Putin owns a lot of that business in mainland Europe.
Graham wrote:
@ gallois but electric doesn’t work for the big vehicles. They need too much power to move and cannot absorb the weight/space penalty of the batteries necessary.Same reason you can make an electric two seat ultralight but not an electric 300-seat airliner.
@Graham, could you elaborate? I always thought that if have a large lorry, then you could put more batteries and the weight increase is not going to be that big.
Am I mistaken?
Peter wrote:
The only bulk capable for most countries alternative is a gas turbine but Putin owns a lot of that business in mainland Europe.
But it’s not so difficult to replace a coal/oil/gas fired power plant with lots of wind farms and solar arrays.
Interconnectors or small gas fired power plants cover the issue with intermittent supply. It’s rare that the wind isn’t blowing and the sun isn’t shining somewhere across Europe.
Graham wrote:
@gallois but electric doesn’t work for the big vehicles.
I thought that too. But I seem them being used here successfully for large double decker buses.
I suspect it’s the recharge time that is the problem for commercial vehicles. Large batteries take longer to charge. You can’t have an international heavy truck stopped for 12 hours while it recharges.
But you could introduce trams as in many cities in France or even the old trolley buses as once transported people all over Derby.
They all ran off a central power station, so yes you can move heavy weights via electricity. Certainly in the case of trams they are becoming very prevalent again now.
But pf course trams and trolley buses are great if you don’t need to go to the door of a shop to load a heavy wardrobe. Or if you live in the city and the nearest/cheapest hypermarket is on the edge of town and you don’t have a car to get there. There’s that hole in the bucket again.
arj1 wrote:
could you elaborate?
A large (44 ton) truck burning diesel gets about 8 miles per gallon, constant speed cruise on a motorway. That is 5-10 (say 7 as an average) times fewer miles per gallon than a diesel car. In terms of carrying the stored energy necessary to do the work, it’s at a 7-fold disadvantage compared to a car – it needs to carry 7 times more diesel than the car in order to achieve the same range. Their fuel tanks are actually much bigger than this 7-fold factor, generally more than 10-fold, they carry something approaching 1,000 litres or even more, because range (and not stopping) is important.
Now, electric cars (as we have discussed previously) suffer a further weight-of-fuel penalty compared to ICE cars. The designers manage to absorb some of it but it’s still a factor – the electric cars available generally have a significantly-reduced range compared to the ICE equivalent. With modern diesel saloon cars we got used to 700-800 mile ranges, but the ICE versions don’t even get half that. Now consider that you need (at least) 7 times as much power to take this into a truck, and the trucks can’t deal with the compromised range – so probably a lot more. Hanging around charging (which takes longer, as the batteries are that much bigger) is a non-starter for trucks.
dublinpilot wrote:
I thought that too. But I seem them being used here successfully for large double decker buses.
Buses don’t (usually) go far from home and can re-charge overnight. Plus you can manage it with a fleet – if it doesn’t last all day (my bet is it doesn’t) then another one replaces it in service.
All vehicles which carry their fuel suffer from this problem of diminishing returns as they get larger. In the 1930s they built bigger and bigger steam locomotives to haul heavier trains faster over longer distances, but eventually ran up against a practical limit where the weight of the additional coal (and more significantly water) you needed to carry in the tender became so great that you needed even more power just to move it, which meant bigger cylinders, so a bigger boiler, which used more fuel, so you needed to carry even more, etc.
gallois wrote:
They all ran off a central power station, so yes you can move heavy weights via electricity.
Trams (and electric trains) don’t carry their power source with them. That’s the crucial difference. Electric propulsion is fantastic if you don’t have to carry the power source on the vehicle.
As a ground vehicle gets bigger, its energy consumption to travel a given journey at high speeds (the speed range where you typically operate when needing range) tends to rise as the square of the increase in linear dimension, in proportion to the increase in frontal area. The volume of the vehicle meanwhile increases as the cube of the increase in linear dimension. This means a larger EV has more room for batteries in relation to its energy consumption, and from first principles the larger vehicle can achieve longer range.
For sure the weight increases rapidly too when the car grows and much more batteries are on board, which is the issue with scaling aircraft up – when scaling up the wing area doesn’t grow as fast as the mass. But on a ground vehicle the energy to carry batteries with rolling friction supporting the load rises only in proportion to weight and is unaffected by speed. As a result the predominant use of energy at higher traveling speeds is parasitic aerodynamic drag and range is increased for a scaled up larger car.
The logical way to carry more batteries to increase range on a smaller EV traveling at higher speeds would be an auxiliary battery trailer aerodynamically tucked in behind the car, not increasing frontal area. You would for sure use more power plant generated energy for the trip, probably more energy than the equivalent, lighter gasoline car would use for the same trip, but you wouldn’t need to stop for a lengthy recharge like an EV without the trailer.
That’s true but then a central power station + grid system could be used to recharge electric vehicles every 200 to 300km. You wouldn’t need the cost of a garage pumps and reservoirs plus tanker delivery etc. You can just plug in and pop into the café for a coffee. Now, many on here who have experience of driving electric cars say it only takes 10 to 20 minutes to recharge and go another 200km to 300km. Do many wish to travel more than 600km in a day on a regular basis? Or is it like the true 4 seater aircraft that one buys but is only used to full capacity every few months or less?
The hole in the bucket is that it will take some time to build, possibly about the same time as it takes to build HS2 or a nuclear power station.
By then I am optimistic that either battery technology will improve or maybe lines could be laid within motoways and perhaps using induction chargers the batteries could be recharged on the move on any motorway.
To some extent the technology
exists. The question would be, how to set up the grid and how to get a return on investment, rapidly enough to make it worth an investors while.
