When adding electric usage, you need to “bill” it at the marginal costs to generate that electricity
Yes, but marginal analysis requires identifying the correct margin. If you charge your car during the day at work, you are increasing peak load, which is often coal. If you charge your car at night, you are contributing to base load. This might not even require building new plants! This works great if you have nuclear plants. With a sufficiently smart grid, it makes erratic sources like wind much more useful.
Yes, but marginal analysis requires identifying the correct margin.
I do agree using the rate for coal is pessimistic.
On further research, I discover that Li-ion batteries are very energetically expensive to produce. Their net lifetime energy in production and then recycling is about 430 kWh per kWh of battery. Li-ion can be recharged 300-500 times. Using 430 recharges, amortizing production costs across all uses of the battery we see that we have 1 kWh of production energy used for every 1 kWh of storage the battery accomplished during its lifetime.
So now we have the more complicated accounting questions, how much carbon do we associate with constructing the battery vs how much with charging the battery? If construction and charging come from the same grid, we charge the same.
And of course to be fair, we need to figure the cost to refine a gallon of gasoline. Its pretty wacky out there but the numbers out there range from 6 kwh to 12 kwh. The higher numbers include quite a bit of natural gas directly used in the process, which using it directly is about twice as efficient as making electricity with it.
All in all, it looks to me like we have about 100% overhead on battery production energy, and say 8 kWh to make a gallon of gas for about 25% overhead on gasoline.
Lets assign 1.3 lbs of CO2 per kwh electric, which is 2009 US average adjusted 7.5% for delivery losses.
Then a gallon of gasoline gives 19 lbs from the gasoline + 10.4 lbs from making/transporting the gasoline.
A Tesla costs 1.3*38 = 39 lbs CO2 to go 100 miles from electric charge + 39 lbs CO2 from amortizing battery lifetime over CO2 cost or producing the battery.
Tesla = 78 lbs CO2 per 100 miles.
A 78 lbs of CO2 comes from 78⁄30 = 2.6 gallons of fuel.
So using US average CO2 load for kwh electricity, loading the Tesla with 100% overhead for battery production and loading gasoline with 34% overhead from refining, mining, and transport, we get a Tesla S about equivalent to a 38 mpg car in CO2 emissions.
That number is actually extremely impressive for the class of car a Tesla is.
Nissan Leaf uses 75% as much energy as Tesla to go 100 miles. So Leaf has same CO2 emissions as a 51 mpg car.
If we use coal for electricity these numbers change to Tesla --> 19 mpg and Leaf --> 26 mpg. The Tesla still looks good-ish for the class of car it is, but the Leaf is lousy at 26 mpg, competing with hybrids that get 45 mpg or so.
Your lithium-ion numbers match my understanding of batteries in general: they cost as much energy to create as their lifetime capacity. That’s why you can’t use batteries to smooth out erratic power sources like wind, or inflexible ones like nuclear.
I’m skeptical that it’s a good idea to focus on the energy used to create the battery. There’s energy used to create all the rest of the car, and certainly energy to create the gasoline-powered car that you’re using as a benchmark. Production energy is difficult to compute and I think most people do such a bad job that I think it’s better to use price as a proxy.
Yes, but marginal analysis requires identifying the correct margin. If you charge your car during the day at work, you are increasing peak load, which is often coal. If you charge your car at night, you are contributing to base load. This might not even require building new plants! This works great if you have nuclear plants. With a sufficiently smart grid, it makes erratic sources like wind much more useful.
I do agree using the rate for coal is pessimistic.
On further research, I discover that Li-ion batteries are very energetically expensive to produce. Their net lifetime energy in production and then recycling is about 430 kWh per kWh of battery. Li-ion can be recharged 300-500 times. Using 430 recharges, amortizing production costs across all uses of the battery we see that we have 1 kWh of production energy used for every 1 kWh of storage the battery accomplished during its lifetime.
So now we have the more complicated accounting questions, how much carbon do we associate with constructing the battery vs how much with charging the battery? If construction and charging come from the same grid, we charge the same.
And of course to be fair, we need to figure the cost to refine a gallon of gasoline. Its pretty wacky out there but the numbers out there range from 6 kwh to 12 kwh. The higher numbers include quite a bit of natural gas directly used in the process, which using it directly is about twice as efficient as making electricity with it.
All in all, it looks to me like we have about 100% overhead on battery production energy, and say 8 kWh to make a gallon of gas for about 25% overhead on gasoline.
Lets assign 1.3 lbs of CO2 per kwh electric, which is 2009 US average adjusted 7.5% for delivery losses.
Then a gallon of gasoline gives 19 lbs from the gasoline + 10.4 lbs from making/transporting the gasoline.
A Tesla costs 1.3*38 = 39 lbs CO2 to go 100 miles from electric charge + 39 lbs CO2 from amortizing battery lifetime over CO2 cost or producing the battery.
Tesla = 78 lbs CO2 per 100 miles.
A 78 lbs of CO2 comes from 78⁄30 = 2.6 gallons of fuel.
So using US average CO2 load for kwh electricity, loading the Tesla with 100% overhead for battery production and loading gasoline with 34% overhead from refining, mining, and transport, we get a Tesla S about equivalent to a 38 mpg car in CO2 emissions.
That number is actually extremely impressive for the class of car a Tesla is.
Nissan Leaf uses 75% as much energy as Tesla to go 100 miles. So Leaf has same CO2 emissions as a 51 mpg car.
If we use coal for electricity these numbers change to Tesla --> 19 mpg and Leaf --> 26 mpg. The Tesla still looks good-ish for the class of car it is, but the Leaf is lousy at 26 mpg, competing with hybrids that get 45 mpg or so.
Your lithium-ion numbers match my understanding of batteries in general: they cost as much energy to create as their lifetime capacity. That’s why you can’t use batteries to smooth out erratic power sources like wind, or inflexible ones like nuclear.
I’m skeptical that it’s a good idea to focus on the energy used to create the battery. There’s energy used to create all the rest of the car, and certainly energy to create the gasoline-powered car that you’re using as a benchmark. Production energy is difficult to compute and I think most people do such a bad job that I think it’s better to use price as a proxy.