Emissions measurement - a non-hippy view

[WyVern]

Great as the zero emission claim is for EVs, we are constantly reminded that our cars have an impact at the power station and a genuine CO2 figure is closer to 130g per Km (0.6 miles) travelled than 0 when taking into account a mixed power source.

Having purchased my iMiev for purely economic reasons I'm not really up to speed on how this is measured. My thought was that as I charge overnight, when there is a surplus of electricity generation, I am purchasing power that would otherwise have been generated anyway, its not like a power station has a throttle. How can my car have increased CO2 emissions when the power station would have generated that CO2 anyway?

Surely until EVs reach a point when there is so much demand the utilities companies have to actually burn more coal etc the the vehicle is effectively truly ZE?

Thoughts?

 

[alohart]

Electric grids generally have little electricity storage capacity, so they cannot generate more electricity than is being used unless they're burning off the excess electricity with some sort of large load. I haven't read that this is done, at least on a large scale (please correct me if I'm wrong). So power plants do indeed throttle back their electricity generation during periods of low demand which apparently results in less efficient operation. EV charging during low demand periods would increase the generation efficiency a bit, but it would still result in CO2 emissions for carbon-burning power plants.

But your figure of 130 gm CO2/km seems high from what I recall reading, especially when considering that a considerable amount of electricity is generated without burning carbon.

 

[WyVern]

From my understanding there is a limited throttling, however most power stations generate a "base load", unless this is forced to increase, especially overnight when many EVs are charged and grid loads are low.

The 130gm figure was based on generation here in Australia and is definitely a pessimistic view.

 

[Don]

Electric grids generally have little electricity storage capacity, so they cannot generate more electricity than is being used unless they're burning off the excess electricity with some sort of large load. I haven't read that this is done, at least on a large scale (please correct me if I'm wrong). So power plants do indeed throttle back their electricity generation during periods of low demand which apparently results in less efficient operation.

I believe that's how it works. There is a certain load with all of the line losses, transformers and other associated gear which consumes a percentage of what's generated, but you cannot generate significantly more power than what's being consumed at the time, so they throttle back less efficient plants which cost more to operate when the grid calls for less power - You are saving something by recharging at night when there's less demand . . . . the grid efficiency would be higher during those periods

I don't worry too much about the carbon footprint of my EV. I have no control over where my power comes from and what they use to generate it and driving an EV is still much, much less polluting than driving an ICE powered vehicle. I would still like to see a shift to natural gas powered vehicles for those which need more range than we can easily get with EV's. The technology is already here and we have an abundance of the fuel without importing anything . . . . .

Don

 

[aarond12]

I would still like to see a shift to natural gas powered vehicles...

Do I dare bring up fracking chemicals into this discussion?

130g/km seems excessive since there are diesels in Europe that claim far less than 100g/km. With ICE vehicles, catalytic converters help to reduce pollution. With EVs, that pollution reduction is done at the power plant. If the power plant is running on coal, it's still dirty, but even then, not as dirty as a typical ICE vehicle. If your EV is powered by hydroelectric power or geothermal power or solar or wind, then you are truly emission-free.

 

[misterbleepy]

Don't forget if you start taking CO2 output of electricity generation into account for electric vehicles, you need to take into account CO2 emissions of producing and transporting petrol/diesel fuel as well as the CO2 produced burning it in the car for a meaningful comparison.

How far can an iMiev travel on the electricity used to refine 1 gallon of petrol? I've seen figures between 3KWh and 12KWh for the power required to refine 1 gallon - call it 6KWh and I reckon an iMiev could go 20 miles on that electricity...

 

[misterbleepy]

In the UK we have at least one "Pumped Storage" power station, which uses off-peak power to pump a lake full of water up through a mountain to a high reservoir. There are huge turbines in the mountain, and the water in the top reservoir is released through these turbines at times of high demand. Basically it's a very big battery that can produce power very quickly - 0 to 1.8 gigawatts in 16 seconds. The interior is very impressive to visit.
I would assume most power grids would have something similar, as it's a very responsive way of coping with varying power demand.

 

[HParkEV]

I think this "Pumped Storage" facility is a great idea, but not something that would be used in North America, as it sounds expensive for something that does not actually produce any power, just storage.
I know in Ontario, the power supply to the grid is mostly adjusted by varying the water flow through hydroelectric dams (24% of total power generation in 2012) and varying output of natural gas fired generating plants (18%). Most of our base load power comes from 18 nuclear reactors (54%) which are pretty much running full tilt and their output is not variable. The remaining generation is coal (2%, and not easily throttled) and wind/solar (also 2%, obviously very variable).
Recharging at night, especially in the spring and fall, is VERY beneficial for the grid here and for the finances of Ontario Power Generation. Because of the high nuclear component, which can not be throttled down, there are occasional days when at 2-3 am there is such an oversupply of electricity that the spot price goes negative (OPG has to pay someone to take the power off their hands, or dispose of it in the ground). You can see it in the Independent Electricity System Operator data that you can download online.

I was actually considering getting a NLR PWRD vanity plate for my i-MiEV, but you can't order those for the 'Green' plates that we get on EV's.

 

[JoeS]

I think this "Pumped Storage" facility is a great idea, but not something that would be used in North America...

au contraire, many of the dammed lakes with hydro here in California have forebays which are used for temporary water storage. The water is pumped back up to the main lake during periods of excess power availability. Examples are San Luis Reservoir and Oroville Dam.

 

[HParkEV]

I think this "Pumped Storage" facility is a great idea, but not something that would be used in North America...

au contraire, many of the dammed lakes with hydro here in California have forebays which are used for temporary water storage. The water is pumped back up to the main lake during periods of excess power availability. Examples are San Luis Reservoir and Oroville Dam.

Well, I learn something new every day! Of course, it makes a lot of sense to make this 'pumped storage' arrangement as part of an existing hydroelectric station, since most of the infrastructure needed is already there, as opposed to a stand-alone system.

 

[alohart]

I wonder how efficient a water storage system is. I would think that it wouldn't be very efficient due to the resistance to flow of water in a pipe and efficiency losses in the pumps and turbines. But it must be better than other available alternatives up to this point. Hopefully using the excess generating capacity to charge EV battery packs will eventually become an important component of a smart grid.

 

[jray3]

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
If Wikipedia is accurate, pumped hydropower storage is reasonably close to battery efficiency- 70-80%, and the scale of pumped storage is orders of magnitude larger than battery banks, at relatively low capital cost, especially if it's just reversing an existing dam.

The Tennessee Valley Authority has a couple of pumped storage facilities, and I think the practice has potential for increasing the valus of some of the older, smaller hydro stations elsewhere. I'm sitting 2 miles from a mothballed hydro station that's ideally laid out for pumped storage, without salmon issues.

I've yet to try out the i-Pumped Storage Range Extender. :? It requires one to stop and fill a water bladder at the top of a hill, and gain greater regen on the way down thanks to the added weight. One must then dump the contents at the bottom of the hill (I'm picturing a fast acting dump valve/ripcord that you can use on the fly. Of course, use caution to not create hazardous conditions for a vehicle behind you- unless they are henchmen of Dr. Evil!

 

[misterbleepy]

I've yet to try out the i-Pumped Storage Range Extender. :? It requires one to stop and fill a water bladder at the top of a hill, and gain greater regen on the way down thanks to the added weight. One must then dump the contents at the bottom of the hill (I'm picturing a fast acting dump valve/ripcord that you can use on the fly. Of course, use caution to not create hazardous conditions for a vehicle behind you- unless they are henchmen of Dr. Evil!

The mk.2 version will include a small turbine on the outlet pipe to generate electricity to recharge the battery when the water is dumped.
In the UK the almost continuous rainfall will keep the battery topped up without the need to actually plug in to a charger.

 

[alohart]

The mk.2 version will include a small turbine on the outlet pipe to generate electricity to recharge the battery when the water is dumped.

Cool! That plus the propeller on the front of my car that spins a generator while I drive should result in almost no need for me to ever recharge. Perpetual motion will soon be realized!

In the UK the almost continuous rainfall will keep the battery topped up without the need to actually plug in to a charger.

How fortunate you are to reside in a location that provides such a nice benefit. Maybe I can modify my propeller to also be a water wheel so it will spin while parked in the rain. Now, where is that rain when I need it?

 

[Barbagris]

I know in Ontario, the power supply to the grid is mostly adjusted by varying the water flow through hydroelectric dams (24% of total power generation in 2012) and varying output of natural gas fired generating plants (18%). Most of our base load power comes from 18 nuclear reactors (54%) which are pretty much running full tilt and their output is not variable. The remaining generation is coal (2%, and not easily throttled) and wind/solar (also 2%, obviously very variable).

Each zone has different energy sources, and the distribution is changing with the time of day, is interesting to watch closely.

We can see, two days ago, how in my country we were pumping water up (hydraulic, negative) or how the wind provided much of the energy, if recharge at night.

 

[MLucas]

I was actually considering getting a NLR PWRD vanity plate for my i-MiEV, but you can't order those for the 'Green' plates that we get on EV's.

I think you are also getting some of our hydro power from the Niagara River as well. The OPG just enlarged the water inlets to use more of the agreed upon water intake with the United States. I see the transmission lines heading north from my house.

I like to tell people my car is Water Powered to get a rise out of them.

 

[Kuuuurija]

Don't forget if you start taking CO2 output of electricity generation into account for electric vehicles, you need to take into account CO2 emissions of producing and transporting petrol/diesel fuel as well as the CO2 produced burning it in the car for a meaningful comparison.

How far can an iMiev travel on the electricity used to refine 1 gallon of petrol? I've seen figures between 3KWh and 12KWh for the power required to refine 1 gallon - call it 6KWh and I reckon an iMiev could go 20 miles on that electricity...

You need to take into account, that fuel for thermal power plants is also mined, processed and transported. Even wind turbines and hydro plants have its CO2 footprint.
For instance, in Estonia, there are predominantly oil shale burning powerplants and an EV consumes for 100 km distance ca 50 kg of oil shale, dumping ca 50 kg of CO2, ca 15 kg of ashes and ca 20 litres of waste waters.

 

[misterbleepy]

You need to take into account, that fuel for thermal power plants is also mined, processed and transported. Even wind turbines and hydro plants have its CO2 footprint.
For instance, in Estonia, there are predominantly oil shale burning powerplants and an EV consumes for 100 km distance ca 50 kg of oil shale, dumping ca 50 kg of CO2, ca 15 kg of ashes and ca 20 litres of waste waters.

Indeed - what sounds like a simple to answer question is anything but.
If I charge my car during the day, I am probably using the electricity generated by my next door neighbours solar panels. At night, I am most likely using a mix of coal fired power station, nuclear, wind, and pumped storage. The actual CO2 footprint will vary depending on where you live, and even what the weather is (if your area has access to solar, wind, and hydro power).
Of course this all has to be taken into account for the electricity generated to run oil refineries too - it's a never ending calculation.

 

[Kuuuurija]

At least here in Estonia it is pretty obvious, that EV-s have much higher CO2 footprint than average ICE car. 50 kg of CO2 per 100 km is ca double of amount of gasoline engine wastes even if to into account all CO2 that is dumped by oil wells, pipelines, refineries, gasoline transporting tankers and gas station network.

If to take into account construction of powerplants, equipment for plants, power grid, ditching the mining areas (peat releases lot of CO2 after ditching), then the CO2 emission is even higher for EV.

Solar power cells hardly produce enough eletricity to cover its construction costs (in Estonian conditions) and during the construction so much CO2 is released, that per energy production it is not so different than our oil shale plants. There is no clean electric energy. Nuclear plants release huge amount of CO2 also. And lots of highly toxic wastes too. The bluff of CO2 clean EV-s is possible only when share of EV-s is marginal. As soon as the share will be considerable, the rise of pollusion will be obvious.

 

[HParkEV]

At least here in Estonia it is pretty obvious, that EV-s have much higher CO2 footprint than average ICE car. 50 kg of CO2 per 100 km is ca double of amount of gasoline engine wastes even if to into account all CO2 that is dumped by oil wells, pipelines, refineries, gasoline transporting tankers and gas station network.

If to take into account construction of powerplants, equipment for plants, power grid, ditching the mining areas (peat releases lot of CO2 after ditching), then the CO2 emission is even higher for EV.

Solar power cells hardly produce enough eletricity to cover its construction costs (in Estonian conditions) and during the construction so much CO2 is released, that per energy production it is not so different than our oil shale plants. There is no clean electric energy. Nuclear plants release huge amount of CO2 also. And lots of highly toxic wastes too. The bluff of CO2 clean EV-s is possible only when share of EV-s is marginal. As soon as the share will be considerable, the rise of pollusion will be obvious.

I think your 50kg per 100km number is an estimate that is way on the high side... The numbers I have seen for Estonia (which is actually the worst country in Europe in terms of CO2 production per kWh) are about 1 kg per 1kWh. Considering the i uses on average about 16kWh to travel 100km, that should mean 16kg CO2 per 100km. That is comparable to what some ICE cars produce.
Estonia is definitely a special case in terms of the CO2 production!

http://www.eea.europa.eu/data-and-maps/figures/co2-electricity-g-per-kwh