California 2009 Power Mix

[Yodrak]

This is where your argument is flawed - marginal emission rates (like marginal costs) do not apply only at peak generation time. There is a marginal emission rate at all times. Like the marginal cost, it's based on the generator(s) that will supply, or back off, the next MW of power as the total system demand changes from instant to instant.

My contention is that neither the marginal utility emission rate (which applies at peak generation time) ...

Ray

 

[EricH]

This is where your argument is flawed - marginal emission rates (like marginal costs) do not apply only at peak generation time. There is a marginal emission rate at all times. Like the marginal cost, it's based on the generator(s) that will supply, or back off, the next MW of power as the total system demand changes from instant to instant.

Because economic dispatch is based on fuel costs, only the most efficient (more kWh/btu) plants are running off-peak, so off-peak charging has the lowest possible carbon footprint.

 

[Yodrak]

Keep in mind that there's different kinds of gas power plants.

There's combined cycle gas plants which can now reach over 60% efficiency, and then they're your peaker plant which might only be 30% efficient.

Yes, I believe that's exactly what I said in my post that you quoted.

Historically the high efficiency combined cycle gas plants could not ramp up or down very quickly - any quick rise or drop in power requirements would have to be satisfied by peaker type plants which may only be 20-30% efficient while doing so.

Combined cycle plants have always been better at load following than steam plants, and they can be more efficient at partial loads than steam plants, but I will agree that the newest ones are better than the older ones.

So what this really means is that these peakers only really would be called into service due to your charging when you first start or stop - the rest of the time it's all steady state - best case scenario.

Peakers are only called into service at times of peak loads, which occur only a few hundred hours or so of the year. Or, when there is a severe system upset such as perhaps when a very large, or several smaller, generators trip off line and there are not enough generators running at less than full output to cover the shortage. A combustion turbine peaker can start in minutes, a steam plant takes hours.

Ideally everyone would gradually start/stop charging at the same time every night during times of lowest grid-load - that would give the utilities plenty of time to adjust power output to match demand.

Power output matches demand instantly, in accordance with the laws of physics. What the utilities have to do is have enough generation running at less than full output so that when the generators automatically adjust their outputs they do so within limits that allow them to keep operating properly.

increasingly in the future we will see battery based grid regulation products - so no "burning" of fuel will need to be done. Earlier this year a 8MW flywheeel based grid storage system went online.

Gotta charge those batteries and get those flywheels spinning somehow. Until the day comes when there is more renewable generation than there is load, fuel is going to be burned to accomplish that.

Hopefully down the road very very of these inefficient gas peaker plants will be needed to run and more of these battery or flywheel based grid regulation products will make it to market - meaning the grid will be cleaner, more efficient - and hopefully also cheaper.

Agreed. But the 'cheaper' part will be the most difficult to achieve. Gas-fired combustion turbine peakers are are relatively inexpensive.

Wouldn't the marginal numbers apply only if you were charging your LEAF in the afternoon? I do virtually all of my charging during off-peak hours. I seem to remember reading that natural gas generation can be dialed up or down fairly easily, while nuclear cannot.

That leaves the fossil fuel plants to follow the load demand second to second, minute to minute, hour to hour. In California that's primarily natural gas. Most of the time that gas is fueling highly efficient combined cycle generation and somewhat less efficient steam generation. At peak times, very few hours per year, it's also fueling highly inefficient combustion turbines (big jet engines).

 

[ElectricVehicle]

Thing is, buying offsets or not buying offsets does not change where the electricity comes from, it only changes who is paying how much for it. A wind turbine somewhere does not increase output when you plug in your Leaf, and decrease output when your Leaf finishes charging, because you bought an offset. All those wind turbines out there keep right on generating whatever the wind passing by will allow them to generate. The flow of electrons from the various generators does not change one iota, the flow of dollars changes.

As EricH and I have explained, when a Californian plugs in or unplugs their Leaf it's the gas-fired generators that adjust to accomodate the change in electric demand.

if your worried about the Carbon from using grid electricity to charge your LEAF, just purchase some carbon offsets, in the whole picture of vehicle ownership - they're dirt cheap! And depending on how you account for it they get you very close to True Zero Emissions Vehicle.

In the case of a Terrapass, the utility still generates the power the same way, emitting the same amount of carbon - but the Terrapass cancels that carbon out by funding projects that eliminate carbon emissions from other sources that would not have happened without the Terrapass funding that comes from your and many other people's Terrapass purchases. In the case if a wind energy certificate, the utility can't count the wind energy you purchased in it's renewable mix, because you purchased the green attribute (0 carbon, 0 emission, etc.) of that electricity, no one else can "double claim or double count" the green attribute. It also means you want to research your carbon offset or green energy certificate provider to make sure they are monitored and certified.

You buying offsets just means that you get to pay a little bit more for your electricity and the rest of us get to pay a little bit less for ours. Thank you!

- That's just not true, at least from reputable carbon offset / green energy certificate providers. I'm presuming you have not researched this. Please check the links in my original post for more information on how green energy certificates work, and that they DO work to reduce global carbon emissions. There are a variety of rules and certifications to make sure that they do work.

 

[Yodrak]

Steam plants are designed to be most efficient when running at or near full output. At off-peak times, when running at partial output, they are less efficient, burning more fuel per MW of output.

Combined cycle plants have flatter efficiency curves, but do have 'sweet' and 'sour' spots at different load levels.

At all load levels the marginal concept still applies - the next MW to be generated will come from the generator(s) that have the lowest incremental cost to produce that next MW. (Except, perhaps, at extremely low loads when minimum generation can become a problem. I expect that you understand what I mean by that.)

This is where your argument is flawed - marginal emission rates (like marginal costs) do not apply only at peak generation time. There is a marginal emission rate at all times. Like the marginal cost, it's based on the generator(s) that will supply, or back off, the next MW of power as the total system demand changes from instant to instant.

Because economic dispatch is based on fuel costs, only the most efficient (more kWh/btu) plants are running off-peak, so off-peak charging has the lowest possible carbon footprint.