solar cells for charging electric car.

[jflorey2]

315w x 4 hours = just a bit over 1Kwh harvest, in a golf cart, maybe a couple hundred feet difference.

Hmm. 1kWhr in a Leaf would get me about 3.5 miles at 65mph. Are golf carts really that inefficient?

[SunEagle]

Hmm. 1kWhr in a Leaf would get me about 3.5 miles at 65mph. Are golf carts really that inefficient?

I understand that once you get up to speed it does not take much power to maintain it. How far would a single kWh get you from a standing start?

[bcroe]

I understand that once you get up to speed it does not take much power to maintain it. How far would a single kWh get you from a standing start?

My car weighs about 1818 KG. 65mph is 29.06 meters/sec, Kinetic energy = 0.5 m times V squared, or 767,494 newton-meters, or
joules, or watt seconds. Thats 0.213 KWH.

I would say that rolling (air, etc) friction (on the level) is quite significant at 65 mph. More on my car than an economy "blob" Bruce Roe

[jflorey2]

I understand that once you get up to speed it does not take much power to maintain it. How far would a single kWh get you from a standing start?

Not much difference. I get about 3.5mi/kwhr at 65mph, about 3.3 in stop and go traffic, about 3 at 75-80mph.

[SunEagle]

Not much difference. I get about 3.5mi/kwhr at 65mph, about 3.3 in stop and go traffic, about 3 at 75-80mph.

Unless there is some type of "restrictor" on the electric motor I would imagine that every time you start up from a complete stop the motor will draw much more energy than just maintaining a cruising speed. Stop and go running is much less efficient than driving at a constant speed.

Most golf carts do a lot of stop and go.

[J.P.M.]

The power required to overcome rolling (moving) friction is roughly proportional to vehicle velocity.

The power required to overcome air resistance is roughly proportional to the square of the wind velocity relative to the vehicle - usually the vector sum of the vehicle velocity and wind velocity, times the drag coeff. of the vehicle.

As a practical matter, the going rate of power required to overcome those two terms and move the vehicle seems to be about 0.3 -0.35 kWh/mile, or about 3miles/kWh +/- some, maybe a lot, depending on driving conditions.

HVAC considerations like A/C and heat, and other convenience features that require power will reduce the range of a vehicle and reduce the "fuel economy".

Your mileage will vary.

[sensij]

As a practical matter, the going rate of power required to overcome those two terms and move the vehicle seems to be about 0.3 -0.35 kWh/mile, or about 3miles/kWh +/- some, maybe a lot, depending on driving conditions.

HVAC considerations like A/C and heat, and other convenience features that require power will reduce the range of a vehicle and reduce the "fuel economy".

Your mileage will vary.

Yes, it varies quite a bit, depending on the car. The Spark EV doesn't do much worse than 250 Wh / mi even under lousy driving conditions... worst I've experienced is probably on the highway with rain and the heater running. Mostly, under normal conditions, it is 10-20% lower, approaching 200 Wh / mi.

Stop and go is really efficient driving. The regen braking recovers enough of the kinetic energy that Bruce calculated that acceleration and deceleration losses are reasonably well balanced by the fact that the velocity is low so friction and drag are better than at cruising speeds.

[jflorey2]

Unless there is some type of "restrictor" on the electric motor I would imagine that every time you start up from a complete stop the motor will draw much more energy than just maintaining a cruising speed. Stop and go running is much less efficient than driving at a constant speed.

Well, don't forget the "stop" part of "stop and go" driving. In an EV much of the energy you used to accelerate all that mass is returned to the battery via regen braking. Overall EV's (and to a lesser degree hybrids) are a lot better in stop and go driving than ICE cars.

[J.P.M.]

Yes, it varies quite a bit, depending on the car. The Spark EV doesn't do much worse than 250 Wh / mi even under lousy driving conditions... worst I've experienced is probably on the highway with rain and the heater running. Mostly, under normal conditions, it is 10-20% lower, approaching 200 Wh / mi.

Stop and go is really efficient driving. The regen braking recovers enough of the kinetic energy that Bruce calculated that acceleration and deceleration losses are reasonably well balanced by the fact that the velocity is low so friction and drag are better than at cruising speeds.

Good to know. Thanx.

Whether or not they all turn into vehicles, maybe the 300,000 preorders for the new Tesla will light a fire under the rest of the auto mfgs. I figure I'm about 2-3 yrs. out for an EV, maybe more.

[SunEagle]

Well, don't forget the "stop" part of "stop and go" driving. In an EV much of the energy you used to accelerate all that mass is returned to the battery via regen braking. Overall EV's (and to a lesser degree hybrids) are a lot better in stop and go driving than ICE cars.

I forgot about the regen feature. That is missing from most golf carts which probably makes them a lot less efficient that a Leaf.

[bcroe]

Well, don't forget the "stop" part of "stop and go" driving. In an EV much of the energy you used to accelerate all that mass is returned to the battery via regen braking. Overall EV's (and to a lesser degree hybrids) are a lot better in stop and go driving than ICE cars.

The reg braking is good, but probably greatly over rated. I haven't seen a number, but suppose the motor recovers
80% of the inertial energy and puts it into an 90 % efficient battery. Getting back to speed will cost another 80% use
of the motor, so 58% or the original inertia is recovered.

The amount of energy per mile to overcome air friction is proportional to the square of the velocity. The instantaneous
power is proportional to the cube, but since faster gets there sooner, less time drops to the square. Bruce Roe

[Sunking]

Maybe this is not relevant enough, but I know a fellow who installed a 315W Sun Power panel on top of a golf cart, using a Morning Star charge controller and it works really nice! While other golfists have to exchange carts in order to finish a game,

You are either making the story up, or you guys have a lot of shot batteries. Please tell me what is the voltage output of this 315 watt panel and the battery voltage. I do not believe a word of it.

Built too many Racing Golf carts and know better.

[Sunking]

Well, don't forget the "stop" part of "stop and go" driving. In an EV much of the energy you used to accelerate all that mass is returned to the battery via regen braking. Overall EV's (and to a lesser degree hybrids) are a lot better in stop and go driving than ICE cars.

While it does help, regen is far from 100% efficient. Most of the power is generated faster than the batteries can absorb it and the extra is burnt off as heat. Newer designs can use Super Caps to store th eexcess and slowly release it back in accelerations, but still round trip is on the order of 70% which beats nothing. Regen biggest feature is not having to use the mechanical brakes.

[Sunking]

I understand that once you get up to speed it does not take much power to maintain it. How far would a single kWh get you from a standing start?

I can help you out there. Lot's of calculators out there on line. But HP for Dummies builders like myself have a few simple rules of thumb. 10 wh/mile for every 100 pounds of vehicle at 60 mph speed. On average a EV uses 300 wh/mile when you look across the spectrum for a 3000 pound vehicle. It works pretty good.

I also use this calculator and a few more from Wallace Racing. To determine what size motor to go a specific speed. Example my last golf Cart my target was 70 mph. I entered weight of 1100 pounds with my butt in the cart, 8/ft2, and .7 CoD and you get 13 Hp. But that is to maintain 70 mph, not get there. No problem with electric motors, you use a motor with 4 times the hp which is a piece of cake with electric motors. I use a HPEV AC15 motor rated at continuous 16 Hp @ 6000 RPM. Peak HP is 80 Hp @ 5500 RPM wiht 90 lbs of torque from 0 to 5400 RPM. I need no transmission, just a 6:1 differential ratio and 23 inch tires. 0-70 in about 7 to 8 seconds. Not many ICE cars can beat it. It will scare the chit out of you. 96 volts @ 60 AH Leaf Battery. It gets around 120 wh/mile. Yes it has Regen.

If you look at any production care with ICE, take the HP, and divide by 4 you get real close to what the engine HP is at cruise. Genrally speaking it takes a 1 HP motor to equal a 3 to 4 hp engine.

[J.P.M.]

You are either making the story up, or you guys have a lot of shot batteries. Please tell me what is the voltage output of this 315 watt panel and the battery voltage. I do not believe a word of it.

Built too many Racing Golf carts and know better.

I seem to remember Ford had some tree hugger's wet dream/advert. about 3 or 4 yrs. ago and put a Sunpower panel on the roof of a vehicle sort of as a concept. At the time, I also seem to remember Russ lead the charge on Calling B.S. on that one.