And The Consequences Are
Wednesday, October 13, 2010 at 11:03AMAt Edison2 we try very hard to talk facts and only facts. For us, the numbers the Very Light Car made in coastdown testing both confirmed what we had hoped and opened some new vistas.
We’ve discussed the meaning of ABC coastdown numbers in previous blog posts; now let’s talk about the consequences.
By definition, a horsepower is 33000 ft.lb/min; it’s the work that a good horse could reliably deliver when, say, lifting coal out of a mine. A fit man can expend about a horsepower for short bursts: for example, a 200 lb man running up a 10 ft flight of stairs in 3 seconds (200 x 10 x (60/3) = 40000 ft.lb/min = 1.2 hp).
The beauty of ABC coastdown numbers is that we can calculate the overall drag for any given speed. From there we can then calculate the power required to drive the car and the energy needed to cover a given distance.
Consider the spreadsheet below. Based on our coastdown ABC numbers, this tabulates the power required for the VLC to run on a level road at a range of speeds.
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VERY LIGHT CAR |
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A |
B |
C |
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EFFICIENCY (%) |
BATTERY KWhr |
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6.31 |
0.1862 |
0.00433 |
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84 |
16 |
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SPEED |
DRAG |
POWER |
ENERGY |
RANGE |
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mph |
lb |
hp |
KW |
KWhr/100 Miles |
Miles |
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0 |
1.4 |
0.0 |
0.00 |
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10 |
8.6 |
0.2 |
0.17 |
2.04 |
785 |
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20 |
11.8 |
0.6 |
0.47 |
2.79 |
574 |
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30 |
15.8 |
1.3 |
0.94 |
3.74 |
428 |
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40 |
20.7 |
2.2 |
1.65 |
4.90 |
327 |
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50 |
26.4 |
3.5 |
2.63 |
6.26 |
255 |
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60 |
33.1 |
5.3 |
3.95 |
7.83 |
204 |
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70 |
40.6 |
7.6 |
5.65 |
9.61 |
167 |
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80 |
48.9 |
10.4 |
7.78 |
11.58 |
138 |
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90 |
58.1 |
14.0 |
10.41 |
13.77 |
116 |
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100 |
68.2 |
18.2 |
13.57 |
16.16 |
99 |
The power numbers are really quite astonishing – only 3.5 hp to drive the VLC at 50 mph. The great virtue of such a low power requirement is that energy requirements are also spectacularly low. Using our platform, the range of an electric car stops being a problem.
In the table, for a given speed in the left column, the ABC numbers are used to calculate overall vehicle drag in pounds; knowing drag and speed, we can calculate power in horsepower and kilowatts (1 hp = 0.746 KW). Knowing the power requirement in KW and speed allows us to calculate energy use per 100 miles. For example, at 50 mph, it would take 2 hours to drive 100 miles, so the energy required is 2 hours x 2.63 KW = 5.26 KWH.
Where this gets interesting is the Range column. The numbers here are calculated from energy use and battery size and efficiency. Here we’ve used 16 KWH for the battery size (like the Chevy Volt) and, based on our research and some very competent advice, assumed 84% for overall efficiency for the battery, controller and motor.
It is significant how this works out: 204 mile range at 60 mph reminds us why we chost an internal combustion engine for the X Prize. For the competition we needed to (and easily did) demonstrate a 200 mile range with our Mainstream cars, and 204 miles with a battery cuts it far too close. We could have fitted a larger battery, but the extra weight would decrease overall efficiency.
The numbers don’t lie and wishful thinking doesn’t cut much ice with physics. So the consequences are, if you want an electric car with realistic range it’s going to need to look pretty much like the Very Light Car. If it looks like an ordinary car, it’s not going to go very far before it needs recharging.
Reader Comments (10)
Can't wait to see what a real electric VLC prototype can do!
In the meantime, here's an idea: load up the VLC with extra weight to simulate a 16 KWh battery pack and show the world how close it gets to these calculated range numbers.
Great work, and thanks for communicating all this to the public.
I am new to the VLC discussion so forgive me if this topic has already been vetted. It is my opinion the the most economical, environmentally friendly and most efficient is power is produced locall. The same should stand true for an electric version of the VLC. The best and most efficient source of electric is to generate it on board rather than try and generate it on the grid or at a base station and then store it for remote consumption in the form of a weight prohibitive battery.
II see the most efficient form of propulsion for VLC's as a very small and efficient diesel engine turning a direct drive electric generator. There would be one small battery system used to handle the starting, surge loading of hard acceleration, and storage for regenerative braking. It would never be used for extended battery only operation so as to keep battery weight to a bare minimum. The diesel engine would be made to operate with a very narrow power torque curve and always operates at a preset, optimal RPM for maximum fuel economy and matched to the generator. Acceleration does not change engine throttle settings but rather controls electrical current. The current produced is transported to the battery and then through a controller to the wheels and integrated wheel motors eliminating transmission, drive-line, and brakes as well as eliminating multiple heavy and complex steering components. Regenerative braking is used by the wheels. Heat from the small diesel engine is utilized for cabin heat in the winter and it provides enough auxiliary power while cruising to run reasonable accessories such as headlights, radio, gps, AC, etc.
It is in essence a hybrid vehicle although very unlike most of the current hybrids which use a conventional drive-train with heavy batteries and a central electric motor.
An advanced monitoring system would detect inclines and allow the vehicle to free wheel if desired. Steering would be assisted through continuously variable wheel speed control lowering tire and drivetrain friction, wear, and improving cornering, handling and fuel mileage.
When dealing with VLC 's the name of the game as I see it is efficiency. Getting more power and usefulness from every gram of weight on board is the goal. Diesel/Electric is the best way to maximize power transfer.
Recent changes in US Diesel formulations have made diesel much cleaner and it is lower in CO2 emission than a comparable gasoline engine as well as safer. Newer CRD engines are propelling standard full weight and drivetrain vehicles with a fuel economy of 55mpg+. Earlier testing of a hybrid diesel electric in the GM EV1 prototypes showed 80mpg+ in the paralell hybrid version and showed performance specs that were impressive with a 550 mi. range. Later testing with the Opel Astra and now Mercedes E300 BluTEC confirm this is an efficient and viable hybrid system but both have used a transmission and drivetrain. All have been very heavy base vehicles. This is where the Edison VLC could shine. I look at a gas/fuel tank with ICE as a battery that is much more energy dense than any electrical storage battery we can currently manufacture and therefore yielding up more power per kg. of weight. and extending range. I would anticipate this system to yield up about 140 mpg with existing off the shelf components/ technologies and 150+ once engines, motors and controls are optimized for specific application.
I too am new to this forum but have been reading about and studying the Edison2 team's philosophy with great interest. As far as one can tell from reading their and other's published information, they are refreshingly honest and open about the cars' design and performance. I am a mechanical engineer who uses and trusts the KISS principle every day, just like the Edison2 team seems to do, so let me take a stab at "thehardway"'s post.
[Tho' KISS is almost always the better way to go, no MechE can dispute that the Prius's Hybrid Synergy Drive to totally cool: gas IC engine and two electric motors coupled to all three rotating shafts of a two stage planetary transmission giving complete and infinite torque/speed control. Awesome!]
First you are correct that the "most economical, environmentally friendly and most efficient power is produced locally", but the "best" local source is most likely solar or wind, producing electricity at your house.
But there are several issues with your concept.
1) a hybrid by definition means the car is carrying more weight (IC engine, generator, batteries).
2) a hybrid also has more places to lose power converting energy from one form to another (liquid fuel to mechanical, mechanical to electricity, electricity back to mechanical)
3) a hybrid's components also take up more volume making the car bigger in one or two dimensions
Both 1) and 3) increase coastdown distance.
In the long run VLC cars will probably -hopefully- end up being all electric, recharged from energy produced near the charging station.
Pauls,
You are correct about weight when you talk about today's conventional hybrids. I am not however talking about a conventional hybrid. This is a different breed of hybrid.
Let's say you build a true BPV VLC how would you provide heat/cooling for those who live in areas with cold winters and hot humid summers? Electric heat would rapidly kill any battery system you have as would driving an AC compressor. Diesel engines are very efficient and even more efficient when operating at a set RPM and their weight to HP ratio can be very high. Remember I am not adding a central electric motor, I am turning theexisting wheels (rotors) and axle (stator) into motors using ex removing the need for conventional brakes, transmission and mechanical drivetrain. There is very little weight if any added to the car. It may even weigh less than the ICE car alone and certainly less weight than a BPV with equal range and power.
Power produced by wind and solar needs to be consumed locally, we agree that local is most efficient. Use that solar/wind power to heat, cool, light and make your home livable and what you don't use, put back into the grid for those who don't have solar capacity. Fossil fuels are most efficient for mobile application. We shouldn't burn them for fixed loads Solar, wind and geothermal are most efficient for fixed location application. Its all about efficiency. Batteries are seldom if ever efficient even in a fixed location when you consider their total energy use cycle from manufacture to disposal. Add to that if you are charging your car at night you would be charging a battery with a battery as solar power is difficult to produce at night. Go to wind and we will only be able to drive after a windy night or once again charge batteries with batteries. Not very efficient. Charging batteries from grid power is even less efficient when considering line losses and conversion losses.
Today's green crowd often forgets net energy facts. It takes 2-4 years depending on availability of sunlight to reproduce the energy required to produce a PV array. Add batteries and transport into the system and you have about 10 years a little less than half the warranteed life expectancy of the array. If you are using the energy it produces in an inefficient manner (charging batteries to charge batteries to power a car) then the net energy gain is pretty low.
We have a bad habit of using our fuels in inefficient manners. If we use them properly and efficiently without waste their is plenty to last and go around. Good discussion.
The biggest problem with all of the other competitors is their price. Edison 2 was planning on making the car affordable. The only way you will get a lot of people to actually reduce their consumption, whether it be fuel, energy, fatty foods, etc. is to make it at least affordable to most people. It does not have to be cheap, nor should it be, but affordable. Designing and producing a bunch of advanced monitors and regenerative braking, as was already made quite clear in the case of the VLC in previous blogs, just does not have any positive gain, because the car does not weigh enough to make the system justifiable. How cool is that? That's pretty awesome if you think about it. A car gets you to work weighing 3,000 pounds or more, but so can a bike weighing 20 pounds and less. So if they haven' t put a regenerative braking system on a bike. Why should they for the VLC? Finally, there is a middle ground vehicle! All I'm saying is let's keep the car simple. If we keep the car simple, we keep it affordable, and more people can afford the change. Yes, CRD designs being engineered for a much smaller diesel engine is a very good idea. I like that idea, as well as electric. Now think about the thermo-dynamics of the situation of a hybrid. One power-train is always pulling the other, and what's more is that, all of the energy comes from the same source, the fuel tank. When considering the most efficient drive-train for a vehicle from the ground up for efficiency, that's just not the best choice. Too much weight, too little efficiency, not safe for accident avoidance, and no fun to drive on lonely country curvy roads.
Acceleration times I have measured a lot in regular traffic, and it takes everyone about a minute + to get to sixty miles per hour. Now we do have steeper graded roads in America, but I have had a less than 200 hp engine pulling over 6,000 lbs total no problem at interstate speed up a hill, and that includes a trailer, so six wheels total.
If you have to make the vehicle more expensive, to increase it's range, stand outside in the sun. Ok, you feel that heat? It takes me 20 minutes to cook like a lobster if I didn't move an inch. Now that's power! Having solar panel(s) on the roof top is the one thing that I thought was really cool about the Aptera. Not everywhere, but on the roof it would/could be cost effective in providing regenerative power without costing too much more. It would not provide infinite range like the solar racers, but it could help.
Now, cooling in the cabin: Ok, air conditioning would sap the battery due to running a hefty compressor, no contest there sir. However, my ideas for cooling are: a conduction cooling system similar to hyper computer cooling systems where they use refrigerant gel, except that the radiator cooled gel is inside your seat. Then you have a tiny vent in the body of the car close to the windshield just for the cabin, with a tiny motor-fan for traffic stand stills, and fitted with a filter like motorcycle helmets have to filter out rain, etc. It may not be ice cold, but enough to keep people from sweating. I haven't had working A/C for my entire driving experience in Alabama and I've managed to go on dates in the summer afternoon without sweating, just.
Heating, ok, how about an optional tiny propane tent heater? It would certainly work for those really cold days, have it even remote started so you have a warm electric car to get into. It could easily be re-filled.
I'm not against diesel, I like that idea very much too. It can run off of bio-diesel or traditional, all it takes is a fill up for long trips, of course it has to have alcohol, or gasoline added to it on cold nights so that it won't solidify, but diesels are more thermally efficient, as I'm sure Ron Mathis knows all about. They have lasted the test of time as a viable option.
So Mr. Hard Way, yes, I like the diesel idea, however, a diesel/electric hybrid, however much sense it makes to you, I just couldn't imagine in a million years that it would be an affordable power-train, when weighing in the simplification of deleting one. A quote I like that was said to me by a very good teacher was "You can be a jack of all trades, or you can refine your craft to become a master of one."
I agree about keeping it simple. Diesel electric is very simple and has fewer moving parts than gas, no spark plugs, etc. Tha fact is, if people are going to buy a VLC, it has to not only be affordable but it has to offer the amenities they are used to. That doesn't mean getting out your BIC and lighting a tent heater to keep warm on your way to work, although I give you some originality points there.
Diesels need not be heavy nor does the generator, especially when we are only talking about the equivalent of 5HP. This diesel electric combination without the batteries could give the VLC the kind of performance that is loved and expected by people that are used to driving sports cars along with all the amenities wile still staying within the spirit of the VLC of reduced weight and maximum efficiency.
If you throw out comfort and performance then we should all just ride bicycles or mopeds.
Light and powerful but efficient will sell. Check out the Ariel Atom. It is almost addictive to watch a car with the combination of low weight and lots of power.
Inductive delivery of power from the road to very light vehicles with small batteries is the future of human transportation. We can have the efficiency of the electric motor and carry only tiny batteries large enough to get us from road power into our garages.
Better yet, we can self-power Shweeb rail velomobiles and use no power for daily commutes. Of course, the red Chinese tried that, sorta.
No you're absolutely right on there Mr. Hard Way, it is absolutely addictive to watch the Ariel Atom, let alone driving it I'm sure must be exhilarating. Yes, design a small but powerful engine, for example a tiny diesel like used on a kubota mower, except designed for car use, add in the latest in CRD technology, then add a turbo with a boost controller of some kind (I would prefer a manual one), and voila! Plus it would just be fun to have a turbo button. Small size, efficient, and powerful. At that size it could even be air cooled, eliminating one fluid that could leek, leaving only three in the whole car.
Bubba Nicholson, you think ahead of many people, and maybe it is the future, but for right now, we just haven't burned up enough of the fossil fuel reservoirs yet, to make paying for an entire remodel of all of our roads justifiable. Other countries would laugh again as we plunge even further into debt. Of course, they would later be following our foot steps after the world begins to run out of fossil fuel, learning from our previous mistakes, so the cost to them would be minimal. So I think right now, just using less is certainly one key for getting our economy boosted back up, and once we have a better economy, it could pay for something as grand, and expensive as that.
Edison 2, tell us what your plans are. Yes, the car is awesome, no question about that, and we Americans don't have a whole lot of options for efficient cars, so we need it, but what are you doing/going to do now? I've seen where Oliver was talking about making a car for GM, but where has that gone or led to? I'm sure I'm not the only one who wants to know what is going on, and you've been excellent about it so far up until now. So what is going on Edison 2? What's your game plan now? Or are we all just stuck in pipe dream land like the GM EV? (Many people's dream manifested into a real, efficient, and great working car and almost instantly smashed to bits)
To put this into perspective, imagine watching a football game, or any sport, where only after the game or race does anybody watching get to know who won. If you never saw the score until after the game, wouldn't it seem slightly pointless to be a fan, cheerleader, or even the coach? We're all with you just tell us sometime soon what's going on.
Biologist,
You have almost grasped the concept but with a small caveat. There would be no turbo button or any other manual mechanism to vary the throttle on the diesel engine. There would basically be two engine speeds. Idle, (no-load) and WOT (optimal generator speed). The turbo would be designed for optimal boost at the speed which produces the most efficient generating capacity. When the accelerator is depressed, current from the generator is allowed to flow to the wheel motors. This sounds boring but remember, variable speed electric motors can provide a tremendous amount of torque throughout a wide operating range without any need to shift gears.
For example the Tesla Roadster, 0-60 in 3.7 and over 211 ft/lbs. of zero rpm torque almost constant to 14,000 rpm. In the Torque/weight ratio department it outperforms the Lotus Exige S which has to get up to 6500 RPM before it can match it in torque/weight. This is for a 2700lb car with 1000lbs of that being its massive battery bank.
I believe the VLC diesel electric version could out accelerate the Tesla Roadster and perhaps even the Ariel Atom. I can imagine sub 3 sec. 0-60 times. Using all wheel drive, having lower mass and wind drag, improved suspension technology, better weight distribution, and active traction control the VLC should pull away from the Tesla off the line and never look back.
Tesla uses one 70 lb electric motor with 248HP generated. It also uses a 1 speed transmission. The VLC could use 4 -20lb 10HP electric motors (one on each wheel) and a diesel/electric generator with battery package weighing less than 200lbs. No transmission is necessary and only a fraction of the 1000lb battery. I do not know the weight of the fuel, engine, transmission, drivetrain, brakes, and associated engine components of the existing Edison 2 vehicle. Maybe 200lb.? I’m talking about a power package under 300lbs. that gets the same 100mpg+ fuel economy and is capable of serious performance while still having a 500mi. range on a single tank of fuel.
For examples of what can be done with diesel engines check out the Gemini-100 from Powerplant Developments or the Z0-01A from Zoche aero-diesels. These are simplistic engines that offer reduction of parts and maintenance very low fuel consumption, very low installed weights and HP outputs exceeding their A/V gas counterparts.
These could be adapted in smaller versions.
Yes Mr. Hard Way you are correct there. I did miss that little detail about the engine being used exclusively for electric generation. Although, I am ok with slower 0-60 times, and only two wheel drive, (preferably rear wheel) so long as the car is still affordable for most people. I know now, even if I became super rich, I would still be concerned about less fortunate people having transportation that won't cost them so much to operate, and that also is much better for the environment. Today, the only option realistically out there is a Toyota Prius. The problem is, that it's just not a big enough leap in efficiency to warrant the extra expense when compared to a Toyota Camry or Corolla. The Prius that my step mother has gets an average of 40 mpg, the Corolla my dad has gets 35mpg at almost ten grand less. It's just not a big enough leap to make it worthwhile for me. A small diesel like the VW polo diesel would be a great option, but they won't sell them here. Nobody, not even Ford, an American company that makes a Fiesta diesel only for other countries. So there just aren't any viable options out there for people like me who are considered working class pay scale. These are the people who will most greatly affect changing our fuel consumption on the whole of the nation.