# Cars, cars and electric cars

Discussion in 'Just Talk' started by joinerjohn1, Jul 26, 2017.

1. ### btiw2Screwfix Select

If you can cut a hole through the car to reduce air resistance, then that should be done. That's free efficiency. Although it's interesting that no car manufacturers do this and there's probably a reason for that.
But don't put a turbine there.
Newton's third law states that for every reaction there's an opposite and equal reaction.
Put simply getting the fan to move means you have to put energy into moving the car forwards, and the energy needed to turn the fan will be needed from energy you're putting in.
You're now having to put energy into moving the car forward and turn a turbine.
And because nothing is 100% efficient, you'd lose energy.
I suppose you could stick a wind turbine on the car when it's on a car park, but it'd probably be better to stick the turbines on the roof of the car park instead (and even then I think they'd be too small to power much).

Solar energy is free. But as a rough calculation say 5 sq m at 200 W/m^2 = 1kW.
I chose 5 sq m to make the numbers easier. In truth getting 5 sq m on car all facing the sun seems very optimistic! 200W/m^2 is pretty optimistic for the uk too, but let's allow technology to improve a bit.

We need 450kJ (thanks to 2shortplanks for reminding me about the 1/2) to get 1000kg to 70mph (we could reduce this by making the car lighter).
So that would take 450 seconds (7 and a half minutes) for solar power to get us to 70mph (even with my very generous solar panels).
This is ignoring friction and air resistance in getting the car up to 70mph though, so it'd really take much longer than this.
There again, if your car could collect and store that energy whilst sitting on the driveway, then that's a good thing.
Free energy is nice (free if we ignore the cost of the panels), but again you'd probably just put the solar panels on the garage roof instead.

But back to DA's point. Braking wastes a lot of energy, so it's a good place to collect it.
Convoy systems and better traffic management can also reduce the wasted energy that cars brake away, by reducing the need for so many braking events.

longboat likes this.
2. ### Mr. HandyandyScrewfix Select

Ah, but there's the rub. The car is moving forward anyway. No extra energy needed to make it do that. So any obstruction in a tube will still be less obstruction than a solid part of the car.

3. ### btiw2Screwfix Select

But we had to put the energy in to make the car move forward.
The turbine now acts as a brake - slowing the car down.
We'd have to put more energy in to overcome that braking.

If the tube is less obstruction than a solid part of the car, then great, do that. Just don't stick a turbine into it - it'll cost you more than you gain.

4. ### joinerjohn1Screwfix Select

Just a thought here,, The government is going to be pushing for all electric cars in 23 yrs, yet at the same time has stopped the continuing electrification of the Midland Main line .. Wonder if some government bod would care to comment,,,,,,,,,,,,,,,,,,,,,,, thought not.

5. ### Mr. HandyandyScrewfix Select

Well, no. The energy you put in to move the car hasn't increased. The car is moving anyway. Cut a hole through and there is less resistance. Blocking the hole would return the resistance to what is was originally. Allowing the airflow to push a turbine round is less that blocking the hole. It's free(but take into account of any extra weight of the fan/turbine). That turbine will be turning with no extra drag on the car.

6. ### btiw2Screwfix Select

Okay. Let's look at this another way.

We agree that sticking a wind turbine on the top of the car is a bad idea. Why? There was little air resistance over the top of the car before. But you could see why that didn't work.
All you've done create another area of low air resistance and then, for some reason, stick a turbine in it. If you could see why it was a bad idea on the top of the car, why not in this new tunnel?

The benefit you're inventing is in designing a hole which would reduce overall air resistance - not in adding the turbine.
Also, I have no idea what this hole you're envisioning looks like. Is it like a tube from the windscreen to the rear view mirror? I can't think of anywhere where this would work in existing designs. Cars are already designed to minimise air resistance where practicable.

7. ### chippie244Super Member

You are forgetting that Handy is very stupid and uneducated.

8. ### Harry StottleScrewfix Select

I've often wondered why trolley buses were phased out, they took their electric power directly from the mains. There were a few disadvantages; overhead wires etc. but no batteries needed, no exhaust fumes, less maintenance.

9. ### Harry StottleScrewfix Select

Handy is not stupid or uneducated, he's thinking laterally. I believe he's wrong about his hole in the car theory but he's not just sitting back and accepting things, he's using his brain. Most people who've improved civilisation have had failures along the way. The old saying "The man who never made a mistake never did anything" is as valid as Newton's laws.
Lets have more way out ideas, even if they are unworkable they are interesting and may lead to something really good.

10. ### Deleted member 33931Guest

That was a rubbish answer 'cos you didn't use any cutting sarcasm.

11. ### Deleted member 33931Guest

A 5MW turbine planted on 'arry's head with its blades rotating in a horizontal plane to catch the thermals from his gob.

Wait - that is workable. And it would lead to something good.

12. ### Deleted member 33931Guest

Calm...calm...calm...

13. ### btiw2Screwfix Select

I'll judge not, lest I be judged.

14. ### facilitiesGuest

I'm with Harry on this, I remember years ago before blue tooth when someone came up with this handsfree on a mobile phone and it wasn't long before it was improved upon

15. ### Deleted member 33931Guest

Hang on, pal - you judge all right

16. ### Deleted member 33931Guest

Did he delete all his German contacts?

17. ### btiw2Screwfix Select

I got the equation for kinetic energy wrong (I used "em vee squared" not "half em vee squared").
2shortplanks corrected me (for which I'm grateful).
So I'm already on pretty shaky foundations if I want to criticise others on this topic.

18. ### Deleted member 33931Guest

Did you really write that, or did The Mooch do it for you?

19. ### btiw2Screwfix Select

My manic-argumentative disorder isn't in its sarcy phase at the moment.

Manic-argumentative disorder? Schizopolemic? I quite like the idea of calling it "Bitroller disorder", but it reads like "bit roller" and if I hyphenate it to "bi-troller" then it's ummm... let's say ambiguous.

Deleted member 33931 likes this.
20. ### Mr. HandyandyScrewfix Select

Starting with "cars are already designed..etc" there will be fresher designs when cars go electric and shape will probably alter a lot, because a lot that goes to make a petrol/diesel car work, won't be needed.
Turbine on the roof is extra resistance. a no-no.
Take a look at the front of a car and imagine a hole in some part of it going straight through and out the back of the car. The front of the car has many areas that are just 'car' offering resistance. It's inevitable. either side of the number plate, or near the headlights etc, all unused bodywork just offering resistance. What's behind it is the important part. With electric cars things can be moved to make way for a tunnel from front to back. It could even pass through the door panels, sealed when doors are shut.
Doesn't have to be a big round stupid looking hole, any ducting could be used