I need economy

[Yuriman]

WOW, not sure how you missed what I actually said but...

I've not driven all the hybrids out there but I have driven a few and my experience is that at a traffic light the engine shuts off -- and that's a good thing for mileage. In stop and go driving where you stop and a light, then move forward 200 feet to the next light it would be good if the hybrid had a battery that would allow the car to advance to the next light without starting the engine, but with the Prius I've driven the engine tends to cut back in within about 50 feet or so. But, again, when you get to the next light the engine shuts off again.

If I were making cars I'd design the hybrid with a larger battery and a smaller engine with fewer cylinders. I do away with the mechanical drive train a go straight to an electric motor at each wheel for true, TRUE 4WD. I'd work to make brake energy reclamation more effective. In a commuter situation you should be able to go 30 minutes or more on battery alone and should be rechargeable from home. In a stop and go situation as above the engine would likely be off anyway, but at a stop light the engine would be off and would not start when advancing to the next light.

But, even with current hybrid technology the advantage in stop and go driving is huge. My current car, a 2012 Ford Focus with 2.0L DGI engine gets great mileage and my net average after 56K miles is a shade less than 39mpg. I've achieved almost 50mpg for an entire tank of over 600 miles. But, the mileage in stop and go driving as pretty bad, like as low as 20mpg bad at its worst. There's a stretch of suburban road that I can get over 40mpg when the traffic is light and I hit the lights favorably, but when the traffic is heavy and the lights don't go my way it can drop to near 20mpg. This is where hybrids kick ass...


Brian

Most large sedan hybrids are shooting for ~1.8-2.0L engine sizes, because when you DO have to run on gas alone, this is roughly the displacement you need to cruise on the highway at a steady speed without revving it up and thus losing economy. The older Civic Hybrids and 2nd Gen Insight got away with a 1.3L, but it was very easy to run the battery down if you spend periods climbing anything but the smallest incline, and then the engine RPM would shoot up once the battery was empty. If you're running a quasi-Atkinson-cycle (as the Prius does), you need a bit more displacement because you're giving up torque for greater efficiency.

It doesn't make too much sense to go below ~1.2-1.5L in vehicles of that size unless you're consciously willing to sacrifice fuel economy on gasoline for weight.

 

[Brian Stirling]

Most large sedan hybrids are shooting for ~1.8-2.0L engine sizes, because when you DO have to run on gas alone, this is roughly the displacement you need to cruise on the highway at a steady speed without revving it up and thus losing economy. The older Civic Hybrids and 2nd Gen Insight got away with a 1.3L, but it was very easy to run the battery down if you spend periods climbing anything but the smallest incline, and then the engine RPM would shoot up once the battery was empty. If you're running a quasi-Atkinson-cycle (as the Prius does), you need a bit more displacement because you're giving up torque for greater efficiency.

It doesn't make too much sense to go below ~1.2-1.5L in vehicles of that size unless you're consciously willing to sacrifice fuel economy on gasoline for weight.

See, if you'd just included the next sentence I wrote in your quoted highlight my comment would have made more sense. So let me reiterate ... if you do away with the mechanical drive train entirely so there is no physical connection between engine and wheels and instead the engine only drives an alternator what you have is a Tesla with expanded range.

At highway cruising speeds the power needed to maintain speed will depend on many factors but is typically in the 20hp to 50hp range. In city driving the time weighted power needs are much less -- less than 10hp in fact. So, if you had the larger battery I talked about and an engine that's optimized for operation at a single rpm AND operates at nearly 100% load at that rpm the efficiency increases quite a bit. And, if there are times when more power is needed the engine can run at higher rpm albeit at lower efficiency.

The vast majority of miles put on private vehicles are in short trips or trips of less than 50 miles and in those cases a hybrid with a large battery could run for most of that trip from the batteries alone having been charged at home. Add a few m^2 of solar cells to the car and it could recharge enough while you work to cover most/all of your trip back home without starting the engine at all.

The vast majority of mountains you might encounter will be less than 4000 ft of elevation gain and most are much less than that. Lets say we have a car with a couple passengers and luggage so the total weight is 3850 pounds. The power needed to gain 1 foot in 1 second is 1 hp/550 pounds of weight so a car weighing 3850 pounds would require 7hp to climb 1 ft/sec. So, climbing 4000 feet would require 7.8hp*hours or about 5.8KWhrs to climb the mountain in addition to the power and energy needed to cruise at the given speed.

But, here's the deal, that value is a fraction of what a Tesla battery pack can handle WITHOUT an engine providing supplemental power AND, with some smarts you can plan to have the battery pack discharged enough so that going down the other side of the mountain instead of riding the brakes and wasting energy the surplus energy is stored in the battery. That's a twofer -- save your brakes AND save energy which equates to higher mileage.


Brian

 

[skyking]

Most of that is nice enough, but the solar cells on a car is not at all a good use of them. Much better to to put them at an optimal angle on a house roof, facing the sun. It has never penciled out.

 

[tortillasoup]

You couldn't put enough solar cells on a car to fully charge a car in a reasonable amount of time. Solar cells with significantly improved efficiency like 50% and being stupid cheap could be helpful/beneficial but that's so far into the future I wouldn't even worry about it. Solar panels made today are only crappy single junction stuff that maxes out at like 25% theoretical efficiency anyway.

 

[Yuriman]

You couldn't put enough solar cells on a car to fully charge a car in a reasonable amount of time. Solar cells with significantly improved efficiency like 50% and being stupid cheap could be helpful/beneficial but that's so far into the future I wouldn't even worry about it. Solar panels made today are only crappy single junction stuff that maxes out at like 25% theoretical efficiency anyway.

I think you're making the same mistake I did. Brian Sterling is right. A gasoline engine doesn't need to be able to power the car indefinitely to be useful. That's why it's a range extender. Same with panels. As long as the benefits outweight the costs (gradual self charge and slight range extension vs weight & cost), they're worthwhile. Maybe they're not topping the batteries off every day, but they're not going to be useless either.

 

[tortillasoup]

I think you're making the same mistake I did. Brian Sterling is right. A gasoline engine doesn't need to be able to power the car indefinitely to be useful. That's why it's a range extender. Same with panels. As long as the benefits outweight the costs (gradual self charge and slight range extension vs weight & cost), they're worthwhile. Maybe they're not topping the batteries off every day, but they're not going to be useless either.

No I know but at this point, to put solar on a car, you probably couldn't power the air conditioner for more than an hour a day on the car what with the poor square footage, low efficiency and poor angles. It just really depends on what you're willing to give up or if you're dead serious about the efficiency and don't care about anything. The solar car for example could give some semblance of range boost but it's a flat car with the most efficient, expensive solar cells on the market. But on a regular car, if you were to go with a "solar paint" then the efficiency would be several magnitudes less and the angles and whatnot would mean poor efficiency for the majority of the day.