Should EVs have efficiency standards?

[MarcusMaximus]

Ok, revision:
Solar panels produce a charge at a rate of
25 Watts per sq ft per hour

1 sqft = 25 Watts/hr
40 sqft = 1000 Watts/hr
So 8000 Watts for 8 hours.

Which would be a much larger battery getting only 15 miles per 8000 Watts charge rate. But that also places it outside the stated weight range of the Cybertruck which Elon said would be the same as the F150 (4000lbs-5600lbs).

And cost; there’s an assumption here that the reason they can sell the base version for $39k is that the body assembly costs are lower AND the battery size is in the 75-85kWh range.

Check your units. A watt is a unit of instantaneous power. X watts per hour makes no sense, unless you’re talking about something that increases its power generation consistently over time.

(I’m guessing you actually mean watt-hours, with watt-hours per hour becoming... watts)

 

[CoyoteJim]

Check your units. A watt is a unit of instantaneous power. X watts per hour makes no sense, unless you’re talking about something that increases its power generation consistently over time.

(I’m guessing you actually mean watt-hours, with watt-hours per hour becoming... watts)

Yes, I suppose I mangled it a bit. My hope is that someone should be able to figure battery size based on what is known:

• should be able to get exact dimensions of tonneau by studying photos
• Charge rate based on 25 Watts per sq ft.
• Total miles gained per day is 15
• Best guess as to number of hours of sunlight used to produce a charge

with that you could figure out charge rate and Wh per mile consumption rate. The constraints for the vehicle are:

• Vehicle including battery cannot weigh over 5600 lbs
• Cd of .30
• Cost limit of $39k for Cybertruck with smallest battery and range of 250 miles

Cost limit is the biggest factor. People keep assuming it’s a heavy vehicle and will require a large battery. But based on cost this doesn’t seem right...unless all other components of the Cybertruck are very inexpensive to produce.

 

[keeney]

That is not always true. If the car is powered entirely by electricity generated from, say, existing solar panels, there is no environmental or societal cost from using it, regardless of how much is used per mile.

Except for the energy used to make the solar panel, and the costs of disposal of it when you are done with it...

 

[MarcusMaximus]

Except for the energy used to make the solar panel, and the costs of disposal of it when you are done with it...

...which is constant regardless of the amount of energy you use from them, or how said energy is used. So still 0 societal/environmental cost from running the truck.

 

[Daniel in SD]

Yes, I suppose I mangled it a bit. My hope is that someone should be able to figure battery size based on what is known:

• should be able to get exact dimensions of tonneau by studying photos
• Charge rate based on 25 Watts per sq ft.
• Total miles gained per day is 15
• Best guess as to number of hours of sunlight used to produce a charge
• Vehicle including battery cannot weigh over 5600 lbs
• Cd of .30
• Cost limit of $39k for Cybertruck with smallest battery and range of 250 miles

Cost limit is the biggest factor. People keep assuming it’s a heavy vehicle and will require a large battery. But based on cost this doesn’t seem right...unless all other components of the Cybertruck are very inexpensive to produce.

I think you need to look at all those things as very aspirational.
The Model X weighs 5400lbs and is made of aluminum, is it likely that the Cybertruck is the same weight while being much larger and made of steel?
The Model X has a drag coefficient of 0.25 and less frontal area. Remember that total drag is the drag coefficient multiplied by the frontal area. The current truck design does not have a drag coefficient of 0.30 so there will need to be changes to the design to hit that number. The Cybertruck will be significantly less efficient than a Model X.
I would expect that the $39k version of the Cybertruck will not be available until years after launch. The only way to reconcile everything is that Tesla expects to dramatically cut the cost of batteries in the next few years.

 

[richtrav]

Agreed; I apologize for feeding the troll. I have estimated the battery size to be more comparable to the Model S rather than the X, though:

Elon Musk tweeted that a solar power tonneau cover option would be available that would provide 15 miles per day. I decided to try using this estimate, given the dimensions of the tonneau cover to figure out what the battery size of the Cybertruck would be.

I measured the area of the tonneau cover at about 77 in. x 77 in. This is equivalent to 41.2 sq ft. To account for error I rounded it to 40 sq ft.

77x77 = 5929/144 = 41.2

Solar panels produce a charge at a rate of
15 Watts per sq ft per hour
1 sqft = 15 Watts/hr

At 40 sq ft the solar tonneau cover would produce 600 Watts per hour
40 sqft = 600 Watts/hr

I’m guessing that the calculation was made anticipating 8 hours of full sun.

600 Watts x 8 hrs = 4800 Watts or 4.8 kW.
4.8kW gives the model S 75kWh 15 miles
4.8kW gives the Cybertruck 15 miles

The Cybertruck battery size is very close to the model S

The Model X is a heavier vehicle so it only gets 11 miles per 4.8kwh and has a range of 237 miles for a 75kWh battery. But the Cybertruck and the Model S both gain 15 miles per 4.8kWh, so they must have similar range and weight.

However, if the cd for the Cybertruck is higher than the cd for the Model S but they both charge at the same rate, the Cybertruck must weigh less than the Model S.

So for both the Model S and the Cybertruck that would be 75kWh for 250 miles, 90kWh for 300 miles, and 150-160kWh for 500 miles.

There's something wrong about this, probably that Elon's claim of 15 mi/day is too optimistic, but it would be fantastic if the CT uses about the same amount of power as the Model S.

I was thinking it's going to use a bit more power than the X and the battery would be around 100 kWh for the RWD and 120 kWh for the AWD (which both neatly work out to 2.5 miles/kWh or 400 Wh/mile. The LR Model X is rated at 350 Wh/mi). The RWD will weigh less than the AWD so it may have a slightly smaller battery than 100 kWh but not by much (maybe 95 kWh, with 380 Wh/mi).

You can massage your numbers a bit to get something close to 15 miles/day with a 95 kWh battery and efficiencies near 380 Wh/mi, mainly by adding a couple more hours of sun. Battery prices will have to come down but there's no reason to think they won't.

 

[DarthPierce]

You can massage your numbers a bit to get something close to 15 miles/day with a 95 kWh battery and efficiencies near 380 Wh/mi, mainly by adding a couple more hours of sun. Battery prices will have to come down but there's no reason to think they won't.

Yes, getting 15 mi/day in Arizona in June seems quite feasible. That same panel might not keep up with vampire drain in Seattle in December... Solar insolation just isn't the same everywhere.

 

[Blup85]

25watts/sqft is way high.. more like 15-18 maybe.. in Arizona pointed due south... in summer... at 70deg f..

 

[Daniel in SD]

25watts/sqft is way high.. more like 15-18 maybe.. in Arizona pointed due south... in summer... at 70deg f..

GaAs cells can achieve that efficiency
All competitive solar powered cars use GaAs cells!

 

[Blup85]

Wow! Thanks for sharing that. That is amazing! Totally makes his charge rate possible, assuming the cost isn't crazy? I checked out some rollable GaAs cells right away, Would be great for camping trips. Light weight, flexible, high power!

 

[Saghost]

Why are there no government fuel economy standards for EVs?

I think it's mostly because there has never been a foreign country that held our electricity hostage and nearly brought our economy to its knees among massive lines and rationing. CAFE was enacted shortly after and in response to the first oil embargo...

 

[juliusa]

That is not always true. If the car is powered entirely by electricity generated from, say, existing solar panels, there is no environmental or societal cost from using it, regardless of how much is used per mile.

Sure - when electricity just magically appears in your battery.

Until then, there is an environmental cost in the production of electricity (for example manufacturing solar panels - and their eventual disposal). There is societal cost of paying for the electricity instead of other things - like food and health care.

 

[juliusa]

I think it's mostly because there has never been a foreign country that held our electricity hostage and nearly brought our economy to its knees among massive lines and rationing. CAFE was enacted shortly after and in response to the first oil embargo...

Good - so no need for EV efficiency standards, and since we are no longer dependent on foreign oil we can get rid of the needliess efficiency standards for ICE.

 

[MarcusMaximus]

Sure - when electricity just magically appears in your battery.

Until then, there is an environmental cost in the production of electricity (for example manufacturing solar panels - and their eventual disposal). There is societal cost of paying for the electricity instead of other things - like food and health care.

As I noted later, any cost in manufacturing or disposal of panels is constant, irrespective of how that energy is used, or whether it’s used at all. Whether you drive a car that gets 100mpge or 1mpge makes absolutely no difference if all that energy comes from a set of solar panels. Neither has any cost.

 

[juliusa]

As I noted later, any cost in manufacturing or disposal of panels is constant, irrespective of how that energy is used, or whether it’s used at all.

So why the concern about petrol? Any cost in manufacturing or disposal of petrol is constant, irrespective of how the petrol is used, or whether it is used a all.

If we get electricity from solar, and we use less electricity, we will have less solar panels. Nobody is manufacturing solar panels not to be used, just like nobody is manufacturing petrol not to be used.

 

[brucet999]

As I noted later, any cost in manufacturing or disposal of panels is constant, irrespective of how that energy is used, or whether it’s used at all. Whether you drive a car that gets 100mpge or 1mpge makes absolutely no difference if all that energy comes from a set of solar panels. Neither has any cost.

Your statement appears to assume that the solar panels were installed for some other reason, but, if so, the car's use subtracts from the building's use and so shifts the power demand back to The Grid. My PV array was sized to cover both house and car, so the portion of lifetime panel costs that covers my MS usage may appropriately be applied to the car.

 

[Fredneck]

And, comparing the efficiency of an EV car to an ICE car is sort of pointless, but not for the reasons you suggest. EVs are ridiculously more efficient than ICE vehicles: a gallon of gas contains about 132,000 btu’s worth of energy, or 38kWh. So a 75kWh battery contains about the equivalent energy as two gallons of gas. An ICE vehicle with an MPG of 36 can go 72 miles on 2 gallons of gas...a Tesla Model 3 LR with 75kWh hour battery can go what - 310 miles?

I must not be explaining it very well. You clearly are not getting the concept. A Tesla can't go anywhere on 2 gallons of gas because it requires electrical energy to run. I would make some silly analogy to putting a Honda generator on the roof, but it would be just that, silly.

Rather than argue pointlessly about this, I'll just let it slide. Enjoy.

 

[MarcusMaximus]

So why the concern about petrol? Any cost in manufacturing or disposal of petrol is constant, irrespective of how the petrol is used, or whether it is used a all.

If we get electricity from solar, and we use less electricity, we will have less solar panels. Nobody is manufacturing solar panels not to be used, just like nobody is manufacturing petrol not to be used.

Because you don’t load up an electric car with ground up solar panels. Using the electricity generated from the panels in no way reduces the amount that can be produced going forward.

If you want something analogous to the solar panels, that would be the gasoline refinery, which does, in fact, have a cost for building, a set lifetime during which it generates the fuel, and then another cost for demolition. It also adds another yet another cost for generation.

 

[MarcusMaximus]

Your statement appears to assume that the solar panels were installed for some other reason, but, if so, the car's use subtracts from the building's use and so shifts the power demand back to The Grid. My PV array was sized to cover both house and car, so the portion of lifetime panel costs that covers my MS usage may appropriately be applied to the car.

Not assuming that, just saying it’s not relevant to the operating of the car. I mentioned this in my other comment, but it’s the same reason we don’t typically apply the societal/energy cost of constructing and deconstructing gasoline refineries to the cost of operating a gas car.

 

[Fredneck]

Your statement appears to assume that the solar panels were installed for some other reason, but, if so, the car's use subtracts from the building's use and so shifts the power demand back to The Grid. My PV array was sized to cover both house and car, so the portion of lifetime panel costs that covers my MS usage may appropriately be applied to the car.

I have the means to monitor my power usage hour by hour. I've noticed that my usage without heat or AC is often below 1 kW. So there would be plenty of times when even if I only had a 2 kW solar install, which would be a tiny install, there would be power left to charge the car much of the day. I don't want to remove the trees shading my house or I would likely install PV. I'm currently on TOU and the utility won't let the two be combined. I could still install a stand alone system to only charge the car, even 2 kW would be good.