'green transport' ?? think not..........
Discussion
Having a think, being an electronics engineer, about this 'green transport' issue. One of the things is electric cars, and how clean and 'environmentally friendly' they are. Where do they think the electricity comes from?. Power station, either nuclear (boo!!), coal (boo!!), oil (boo!!) or gas (boo!!) hydro (hurray!! - except, you need to pump water to the dam using one of the others, unless it rains a hell of a lot) wind (hurray!!, except you would need 72000 turbines (115 square miles) to produce the same power output as just 1 coal fired station).
So, these power stations are usually only about 30% efficient. You then transform the voltage up to HT, through large transformers (about 98% efficient), along perhaps hundreds of miles of wires (resistive losses) to step down transformers (98% efficient) down lower voltage cables (even more resistive losses due to higher currents) into your house. You house wiring is resistive right up to te actually plug and the charger. The charger will be switch mode, which is about 80-90% efficient, and dumps high current down the cables to the car batteries which are pretty lossy due to these high currents. The batteries only soak up about 60% of the charge put into them, and have a continuous leakage anyway across the plates - a bit like a leaking water tank.
So, that's the batteries charged.
To actually drive the car, you need to control the power from the batteries along the resistice vehicle wiring through a semiconductor controlled control system, which need heatsink to disipate the heat (quite a lot with such high currents). Then you have the motor, which is about 75% efficient which finally drives the wheels, which have to lug around the 1.5 tonnes or so of batteries everywhere you go.
All in all, the raw fuel to power at the wheel could be VASTLY improved if you took the fuel round with you and cut out all these very inneficient 'middle men'.
Answer - you could use an internal combusion engine burning petrol which has a really high energy content, there are far less efficiency losses, and the vehicle would be much lighter.
oops, sorry. That's already been though of hasn't it?
B35.
So, these power stations are usually only about 30% efficient. You then transform the voltage up to HT, through large transformers (about 98% efficient), along perhaps hundreds of miles of wires (resistive losses) to step down transformers (98% efficient) down lower voltage cables (even more resistive losses due to higher currents) into your house. You house wiring is resistive right up to te actually plug and the charger. The charger will be switch mode, which is about 80-90% efficient, and dumps high current down the cables to the car batteries which are pretty lossy due to these high currents. The batteries only soak up about 60% of the charge put into them, and have a continuous leakage anyway across the plates - a bit like a leaking water tank.
So, that's the batteries charged.
To actually drive the car, you need to control the power from the batteries along the resistice vehicle wiring through a semiconductor controlled control system, which need heatsink to disipate the heat (quite a lot with such high currents). Then you have the motor, which is about 75% efficient which finally drives the wheels, which have to lug around the 1.5 tonnes or so of batteries everywhere you go.
All in all, the raw fuel to power at the wheel could be VASTLY improved if you took the fuel round with you and cut out all these very inneficient 'middle men'.
Answer - you could use an internal combusion engine burning petrol which has a really high energy content, there are far less efficiency losses, and the vehicle would be much lighter.
oops, sorry. That's already been though of hasn't it?
B35.
I thought an average internal combustion engine in a car was around 30% efficient, although I'd have thought a power station would be more efficient than a car engine.
Even if the car engine was just 20% efficient, all the losses between burning the fuel at a power station and getting it to drive your car means an electric version is still less efficient than a convention ic engine.
Even if the car engine was just 20% efficient, all the losses between burning the fuel at a power station and getting it to drive your car means an electric version is still less efficient than a convention ic engine.
parrot of doom said:
What if I charged my electric car with a mini wind-turbine attached to the roof of my house?
Attach it to the roof of your car, then the further you drive, the more charge you get...
Why is that instantly recognisable as being silly but other things like the "engine that runs on water" keep cropping up every now and then and people seem to believe it even without seeing one?
parrot of doom said:
Except even the most economical engines are highly inefficient devices, most of the energy ends up as wasted heat.
What if I charged my electric car with a mini wind-turbine attached to the roof of my house? Such wind turbines will be available next year for about £1500.
Typical petrol engine is about 30-35% efficient, typical diseasal is about 40% efficient. So you have your very own power station without all the other losses. In fact, with catalytic convertors on pretty much every car on the road now, this is a lot more efficient than remote gneration. America is doing everyhting it can to avoid cleaning its power stations any further, due to the immense cost involved.
Electric cars at the moment are a complete waste.
parrot of doom said:
What if I charged my electric car with a mini wind-turbine attached to the roof of my house? Such wind turbines will be available next year for about £1500.
Being a bit of a Dilbert, this got me interested, so I've had a look at these turbines
They are available now - £700 plus accessories. But! they only put out max 0.8 kW flat out (Grauniad article says 750W).
That's not a lot in car terms. Even if you could charge at full power all the time it works out something like 23 1/2 hours charging to drive a 40hp car for 30 minutes.
They need to crack:
1. photochemical hydrogen generation
2. lightweight hydrogen storage
3. lightweight fuel cells
Progress on 3 has been creeping forward for some time... there have been some recent promising developments on 1. 2 is a bit of a bugger; metal hydrides seem to be the best so far but are definitely not free from problems.
Trouble is if we fuel our cars from energy hitting the roofs of our houses the bloody government won't be able to tax fuk out of it, so I'm not too hopeful of decent progress any time soon.
1. photochemical hydrogen generation
2. lightweight hydrogen storage
3. lightweight fuel cells
Progress on 3 has been creeping forward for some time... there have been some recent promising developments on 1. 2 is a bit of a bugger; metal hydrides seem to be the best so far but are definitely not free from problems.
Trouble is if we fuel our cars from energy hitting the roofs of our houses the bloody government won't be able to tax fuk out of it, so I'm not too hopeful of decent progress any time soon.
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