Tesla's MPGe offsets carbon emission of other cars.

[Archduke]

I'm *terrible* with math and logic problems, so I'm hoping someone will help me here.

If a Toyota Prius hybrid were to get 50 combined MPG, while a Tesla charged on particularly clean electrical grid achieved 100 MPGe, would the Tesla effectively offset the carbon emissions 2 Toyota Priuses (Prii) or does it offset only 1 Toyota Prius (which is my guess)? Or is it some other number entirely? Thank you in advance for not making fun of me.

 

[Saghost]

Nothing the Tesla does eliminates the harm that the Prius is doing, so I'm not sure how you're expecting it to "offset" anything.

Maybe if you have some target pollution level that cars are both above and below? But in that case, how much pollution is acceptable?

 

[Archduke]

Nothing the Tesla does eliminates the harm that the Prius is doing, so I'm not sure how you're expecting it to "offset" anything.

Maybe if you have some target pollution level that cars are both above and below? But in that case, how much pollution is acceptable?

Okay, if we express it in terms of pounds of carbon dioxide released into the atmosphere per 1000 miles driven and agree that the Prius, at 50 MPG releases 5 pounds of carbon monoxide (I'm making up the CO values) into the atmosphere while the Tesla, at 100 MPGe releases only 2.5 pounds of carbon monoxide into the atmosphere, then the Tesla effectively negates 50% of the environmental impact of the Prius. Right?

 

[Visscher]

If we express in ml of urine released into the toilet per 1000 minutes lived and the Prius releases 5 litres of urine into the toilet and the Tesla releases only 2.5 litres of urine into the toilet, then the Tesla effectively negates 50% of the pollution of the Prius, right?

 

[Saghost]

Okay, if we express it in terms of pounds of carbon dioxide released into the atmosphere per 1000 miles driven and agree that the Prius, at 50 MPG releases 5 pounds of carbon monoxide (I'm making up the CO values) into the atmosphere while the Tesla, at 100 MPGe releases only 2.5 pounds of carbon monoxide into the atmosphere, then the Tesla effectively negates 50% of the environmental impact of the Prius. Right?

No. That's my point. The Prius released five pounds - and nothing about the Tesla changes that, unless it could somehow absorb those five pounds.

If there's a requirement that the average car release no more than four pounds, then a fleet of half Prius and half Tesla meets that requirement, though.

(This discussion is normally about carbon dioxide, the inevitable result of combustion, not carbon monoxide which comes from not having enough oxygen in the mix and kills people much faster and should be minimal in any modern car.)

 

[SageBrush]

I'm *terrible* with math and logic problems, so I'm hoping someone will help me here.

If a Toyota Prius hybrid were to get 50 combined MPG, while a Tesla charged on particularly clean electrical grid achieved 100 MPGe, would the Tesla effectively offset the carbon emissions 2 Toyota Priuses (Prii) or does it offset only 1 Toyota Prius (which is my guess)? Or is it some other number entirely? Thank you in advance for not making fun of me.

Best to flip your question around and look at in terms of pollution per mile:

A gallon of petrol combusted releases about 25 pounds of CO2 and moves a Prius ~ 50 miles, so about 0.5 pound CO2 per mile
A kWh of electricity from the grid in Los Angeles was produced from about 1 pound of CO2 emissions and moves a Tesla about 3 miles, so about 0.3 pound CO2 per mile

So then we can see that a Tesla in Los Angeles leads to about 60% of the CO2 emissions per mile compared to a Prius. And perhaps in terms you prefer, 1.66 Teslas emit the same CO2 amounts as one Prius for the same distance.

Which is all fine and dandy, but a Tesla is more expensive than a Prius so these answers are apples to oranges. If CO2 reduction is your goal, Prius+PV does a lot more than Tesla+grid for the same amount of money.

 

[Archduke]

Best to flip your question around and look at in terms of pollution per mile:

A gallon of petrol combusted releases about 25 pounds of CO2 and moves a Prius ~ 50 miles, so about 0.5 pound CO2 per mile
A kWh of electricity from the grid in Los Angeles was produced from about 1 pound of CO2 emissions and moves a Tesla about 3 miles, so about 0.3 pound CO2 per mile

So then we can see that a Tesla in Los Angeles leads to about 60% of the CO2 emissions per mile compared to a Prius. And perhaps in terms you prefer, 1.66 Teslas emit the same CO2 amounts as one Prius for the same distance.

Which is all fine and dandy, but a Tesla is more expensive than a Prius so these answers are apples to oranges. If CO2 reduction is your goal, Prius+PV does a lot more than Tesla+grid for the same amount of money.

Thank you for that very thoughtful answer!

@Saghost (and SageBrush): Yes, I do understand that you can't 'undo' the emissions of the Prius (or the Tesla) because once the fuel is used, the pollutants are released. I was trying, and failing miserably, to ask what SageBrush has answered. Namely, I wanted to know just how much better the Tesla is for the environment than the Prius is. The thing that brought on this question is that a friend has taken me to task for buying a Tesla. She sees the cars as pretentious and ostentatious and posed the question "Why not just buy a Prius and donate the extra money to a charity that helps the environment?" The obvious first response for me would be, "Because I drove a Prius for a year and *hated* it", but I wanted facts and figures that addressed environmental issues because that is the main reason I ordered a Tesla. I also wanted to make sure she understood that the Teslas she hates, and the owners who drive them, don't deserve her derision.

@SageBrush, you said, "If CO2 reduction is your goal, Prius+PV does a lot more than Tesla+grid for the same amount of money." You mean standard, gasoline burning Prius hybrid + PV cells to power the home reduces CO2 emissions more than just driving a Tesla instead of the Prius, right? That's an interesting way to look at things, and one that I had not considered. I looked into PV for my house a few years ago, but Solar City said a large tree on the south side of my house would obscure too much of my roof, so solar is not much of an option for me until/unless I cut that tree down. Even if/when I do cut down the tree, I'd still drive a Tesla so Tesla+Tesla Solar Roof+Powerwall beats Prius+PV, eh?

 

[ecarfan]

She sees the cars as pretentious and ostentatious and posed the question "Why not just buy a Prius and donate the extra money to a charity that helps the environment?"

Because buying a Tesla advances us towards the goal of powering the global transportation network with sustainable energy. If you charge your car using sustainable energy no CO2 is emitted other than whatever was produced to manufacture the car and the energy infrastructure, both of whic will last for a very long time. A Prius not emits Co2 over it's entire life but the fossil fuel energy production process emits huge amounts of CO2.

Your friend doesn't seem to grasp the fact that Tesla will shortly begin manufacturing BEVs at a price that the average person in the developedd world can afford, and that Tesla Energy is working towards making solar power ubiquitous and battery storage progressively less expensive. She is only focused on the fact that right now Tesla cars are very expensive. Help her to see the big picture.

 

[brucet999]

I'm *terrible* with math and logic problems, so I'm hoping someone will help me here.

If a Toyota Prius hybrid were to get 50 combined MPG, while a Tesla charged on particularly clean electrical grid achieved 100 MPGe, would the Tesla effectively offset the carbon emissions 2 Toyota Priuses (Prii) or does it offset only 1 Toyota Prius (which is my guess)? Or is it some other number entirely? Thank you in advance for not making fun of me.

Your Tesla will offset Prius CO2 production only in the sense of your decision not to buy and drive a Prius.

I ran a spreadsheet before buying my S70, using SoCal Edison's power generation sources information and found that on 12,000 miles per year a Lexus 300h hybrid (roughly equivalent to Prius) would produce 6.534 lb of CO2 per year versus my SCE-popwered S70 (89 MPGe) at 4,066 lb CO2. That calculation included an 85% charging efficiency converting AC line power to DC into the battery.

 

[Archduke]

Your Tesla will offset Prius CO2 production only in the sense of your decision not to buy and drive a Prius..

Yes, that is what I was trying to get at...that the decision to drive a cleaner vehicle would offset the carbon emissions that would have been created had I gotten a Prius instead. Thanks!

 

[SageBrush]

Why not just buy a Prius and donate the extra money to a charity that helps the environment?"

I think my answer would be "because a Tesla in LA is better than a Prius for the environment, because I enjoy the Tesla a lot more than a Prius, and because the environmental benefit of the money to a charity is an unknown."

So fwiw, while your decisions may* not be the optimum use of money for environmental gain, they are pretty darned good and your girlfriend is ... uninformed.

*I say "may" because there are lots of venues besides PV on your roof available to most people to either reduce energy use or add clean energy production to the grid. Look into home energy conservation. That tends to be an even better green investment than PV.

 

[SageBrush]

You mean standard, gasoline burning Prius hybrid + PV cells to power the home reduces CO2 emissions more than just driving a Tesla instead of the Prius, right?

Yes

The benefit to the grid depends on PV generation, cost of PV, and the fossil fuel that is displaced.
In Los Angeles, you can probably find a way to build a watt of PV for somewhere in the range of $2 - $4 , generate 50 kWh over it's lifetime, and displace fossil fuel that would otherwise emit 50 pounds of CO2 over the same PV lifetime.

If you figure that a Prius lifetime (in your hands or with successive owners) runs 200,000 miles,this leads to 100,000 pounds of CO2 emissions by the 0.5 lb/mile result I posted earlier. The PV offset then would be 100,000/50, = 2000 watts of PV that would cost $4,000 - $8,000. This does not take into account the CO2 emissions of the Tesla, which over the same 200,000 miles will be (according to the earlier post,) 60,000 lbs of CO2. So the Prius owner only has to offset the difference of 40,000 lbs CO2 to equal the Tesla owner, and build 40,000/50 = 800 watts of PV. That would work out to somewhere in the range of $1,600 - $3,200.

Since you probably paid tens of thousands of dollars to get into a Tesla, it follows that had the money been spent on PV instead the net CO2 reduction would have been quite a bit more. Probably somewhere in the range of 10 - 30 Prius owners with all the car savings of one Tesla spent on PV emit the same CO2 as one Tesla owner.

Needless to say, your answers will vary tremendously depending on your priorities, your POV, and who or what you use for comparison. Before you presume that I agree with your friend, keep in mind that Model S purchases are what allowed the Model 3 to come to market, and the Model 3 will push more people to install residential PV. The leveraged effect of your Model S purchase is difficult to put a firm number on but as a greenie through and through, I applaud your choice.

Cheers!

 

[brucet999]

Since you probably paid tens of thousands of dollars to get into a Tesla, it follows that had the money been spent on PV instead the net CO2 reduction would have been quite a bit more. Probably somewhere in the range of 10 - 30 Prius owners with all the car savings of one Tesla spent on PV emit the same CO2 as one Tesla owner.

If I understand correctly, you posit that buying a Prius and investing the $50,000 price difference vs a Tesla into PV would be environmentally better. Unfortunately, in my area SoCal Edison controls how much PV you may install on your roof for net-metering, only allowing capacity equal to your previous 12 months of electricity usage from the Grid. In my case, that would be about a $15,000 6kW array.

I'm guessing the PoCos in other areas have similar control over the amount of net-metering capacity as Edison does here.

 

[dgpcolorado]

The CO₂ offset for PV panels depends on the generation mix of the particular electrical grid. In California the grid is relatively "clean" compared to many other states. My state uses mostly coal and natural gas electricity generation so solar production here could be said to offset more CO₂ than the equivalent solar production in California.

I try to charge my car in the middle of the day when the sun is shining to use my solar production (and some of that of my neighbors) directly. The middle of the day is also off-peak here since the highest demand is mornings and evenings.