Marginal power

[eledille]

I often see the following argument: Marginal electricity is coal, EVs represent a new demand, therefore EVs run on coal.

This is wrong.

As an electricity consumer in Norway, I can choose what power I want to buy. That destroys the whole marginality thing in one crushing blow. For the sake of argument, let's pretend that I don't have a choice.

If I lived in a more sunny country, I might have installed solar PV on my roof. Let's pretend I don't have that choice either.

Marginal power is the power that is least expensive to generate that is not already in use. If demand rises some small increment, marginal power will meet that demand. If it falls, marginal power will be shut down.

It's not quite that simple, however.

Marginality also assumes that no one is able to plan ahead and that everyone immediately finds out what the best course of action is. The world does not work that way.

There will also be different types of marginal power for different scenarios. There are four classes of power plants: 1) Base load, running 24/7 *EDIT deleted "full power" which I don't really know whether is true or not * 2) load-following, which follow the load curve throughout the day, 3) peak power which is only started up when load is approaching the average high and 4) reserve power, plants that are so inefficient that they have been closed down completely and are only started up when base power demand is higher than usual, like during a cold spell in the winter.

If load is very high and peaking plants are already running, then more demand will be met by injecting more gas into the turbines, or by building new gas turbine plants if the load is getting dangerously high. If we're talking about a general increase in night-time demand, the peaking plants are unaffected. This will be met by running base load plants harder or building new base load plants.

If, all of a sudden, huge numbers of new EVs were to be charged during the night, then reserve power would have to be fired up. They were shut down because of high fuel costs, so if the new demand can be expected to last, then it makes sense to build modern plants so they can be shut back down again.

The introduction of EVs will be a slow and predictable process. Reserve power will not be used to meet such a slow increase in base power requirements, this is something that can be planned for. I don't think the marginality concept is very useful in this situation.

Also, if marginal power is coal, then why are new gas turbine plants being built all the time?

Finally, with a smart grid and lower charge cycle cost, EVs can help smooth out the demand curve.

[rabar10]

You need to clarify the time-scale over which your reasoning is to apply, and whether it varies between the individual points. There is a big difference in day-to-day or week-to-week demand-following strategy (adjusting output of existing plants), as compared to demand planning 3-5 years from now or 15-20 years from now (building/expanding/retiring plants).

1) Base load, running full power 24/7, ...
...
This will be met by running base load plants harder...

As presented, these two statements are logically incompatible.

Finally, starting a logical path of reasoning with this declarative yet unproven (at that point) statement

"This is clearly wrong."

will throw off lots of people that aren't already convinced of your position. Lay out the facts and your deductive points, and allow the message to come out at the end.

Now as there are several others on here with actual utility power experience, I'll pipe down and let them review the finer points

[JRP3]

As the grid exists now, in most places, EV's are marginal demand, and if charged at night they will most likely be charged from coal power, and if during the day probably natural gas. You may be able to choose where you send your money but the power is coming from whatever is available and cost effective at that time. You might be able to pay only for wind power but you won't actually be getting any of it. The extra load your car puts on the grid can't be met by turning on a windmill.

[jerry33]

You may be able to choose where you send your money but the power is coming from whatever is available and cost effective at that time.

While true, choosing where you will send your money puts that amount of "type x" power into the grid at some nebulous point in the future, as opposed to not having it go into the grid at all. So even if it isn't running your car, it's running something that would otherwise be powered by coal. A kWh used is a kWh used whether is is running a car or watching TV.

[eledille]

As the grid exists now, in most places, EV's are marginal demand, and if charged at night they will most likely be charged from coal power, and if during the day probably natural gas. You may be able to choose where you send your money but the power is coming from whatever is available and cost effective at that time. You might be able to pay only for wind power but you won't actually be getting any of it. The extra load your car puts on the grid can't be met by turning on a windmill.

I'm aware that my electrons are not being moved by the utility I paid to do it. But you have to either accept that power can be traded or not.

In Norway we used to have 97% hydro. That's not true anymore, because the utilities now sell the green-ness of 60% of their power to Germany and the Netherlands. We don't have anywhere near half the transfer capacity to transmit the actual electrons there even in theory. If they can do that then I can equally insist that I'm charging with hydro because I paid extra for it.

Now anti-EV economists and statistics types are telling me that my EV is running on Danish coal, because the Danes have to power up some old mothballed coal plants during extra cold winters when there is little water in our dams (i.e. coal is the marginal power - true, but misleading). They simply cannot have it both ways - either the utilities sell green power to Germany and I buy green power for my EV, or my EV is still running on 97% hydro as it always did. And either way, it's crazy to label the power consumed by EVs as "dirty coal" just because we depend on Danish coal for 5% backup during extra cold winters. This is application of seasonal timeframe marginality to both longer and shorter timeframes, which leads to the wrong conclusion.

We also buy Danish coal and Swedish nuclear energy during the night and sell hydro back to them during the day. This does not mean that my EV is being charged with marginal Danish coal during the night. It means that we're helping the Danes use their generating capacity more efficiently by not having to ramp. They're paying us good money to do it - their power is cheap at night because no one needs it and we can take it. Our power is expensive during the daytime because they can buy it to avoid ramping. Our power is more valuable because it is more easily regulated, so it makes sense to use it to lower the peaks of the Danish supply curve and use spare Danish generating capacity to meet as much of the Norwegian base load as possible to save water for demand peaks and wind lows.

It would often be correct to say that during the night, Danish coal is marginal, so new night-time demand will be met with Danish coal power. It would be wrong to say that EVs are dirty because they charge during the night - we sell the same amount of hydro power back to them the very next day. Neither is correct when there is a lot of wind or rain. When the wind is blowing they need to get rid of their excess wind power first, and when our dams are full and the rain keeps falling, we need to offload excess water at any price higher than zero. Last summer and autumn the price of electricity was very low because the turbines had to run all out all the time because the rain would not stop. We hit a new electricity export all time high. In 2010 we had a dry autumn and extremely cold winter, and we broke the import record.

The marginality concept can be used to find out what will be used to satisfy the next demand increment within a given time frame, but I don't think you can use it to assign a CO² emissions value to a specific class of consumer. Demand is the sum of demand of all consumers and the blame can just as well be assigned to people not fixing their leaky windows, and too many variables, too many different scenarios and different effects over different time frames make it impossible to arrive at a simple number anyway.

I would love to hear what pro-EV economists and those with utility power experience think about this.

[eledille]

I think I am now able to formulate why blaming EVs for marginal coal emissions seems so unfair to me.

When you add another watt of load, that watt is going to affect the grid in some way. Marginality is useful for reasoning about its effect and what must be powered up or built to deliver the last added watt of load.

However, the last watt added would have had a different effect if no other loads were present. Every watt of load must take its share of the blame for the emissions caused by the last watt, because every watt of load is equally responsible for the total load being what it was when the final watt was added, and therefore also for the effect of adding the last watt. Thus the only reasonable way to assign blame is energy consumed multiplied by average emissions per energy generated.

Or what?

[JRP3]

EV's put an extra demand on the grid that did not previously exist. That power has to come from fuel that was not previously being used. More fuel will be burned to charge your EV. Depending on location that fuel is likely going to be coal at night and NG during the day.

[eledille]

You need to clarify the time-scale over which your reasoning is to apply, and whether it varies between the individual points. There is a big difference in day-to-day or week-to-week demand-following strategy (adjusting output of existing plants), as compared to demand planning 3-5 years from now or 15-20 years from now (building/expanding/retiring plants).


As presented, these two statements are logically incompatible.

You are absolutely right. I should have thought this one through a couple more times before clicking the send button.

I didn't separate the short-term and long-term effects.

If demand continues to rise over time, then new power plants must be built. If I as an individual plug in my EV one night, then some power plant must consume more fuel or water for a few hours. These effects have very different costs and time scales, and this is also part of the problem with the "coal is marginal, so EVs run on coal" argument.

The grid can't be powered only by plants running at 100% 24/7 even during the night. It is my understanding that even base load plants can be adjusted, but I don't know to what extent that is being done vs. running the base load plants at full power and using other load-following plants in addition even during demand lows.

Finally, starting a logical path of reasoning with this declarative yet unproven (at that point) statement

will throw off lots of people that aren't already convinced of your position. Lay out the facts and your deductive points, and allow the message to come out at the end.

You are right again. Thanks. I had realized that by myself and was hoping no one had answered so I could edit

My main points are 1) that this issue is more complex than some make it seem, there are many different classes of power plants and plugging in at different times of day has different effects, and 2) that you can't just say that EVs run on coal power based on what happens the instant you plug it in. A change in the demand curve that persists over time has a different effect.

[Doug_G]

A lot depends on your local grid characteristics. If you add gobs more night time EV charging in Ontario it will actually help Hydro One with their excess nighttime generation problem. Normally none of the carbon generators are running at night, because they are used for peak load.

Yes electrons are fungible - you get what the grid is producing, not what you "paid" for. But I don't see how it is legitimate to assign "marginal load" to an EV just because it is a "new" device. People are buying new big-screen TVs all the time and no one calls them "marginal load". As I see it, loads are just as fungible as the electrons.

[neroden]

A lot depends on your local grid characteristics. If you add gobs more night time EV charging in Ontario it will actually help Hydro One with their excess nighttime generation problem. Normally none of the carbon generators are running at night, because they are used for peak load.

This is probably true in the portions of upstate NY which buy great hunks of Niagara Falls energy, as well.

But anyway, analyzing marginally, I'm replacing the burning of premium gasoline in a car with 20 mpg, and of ordinary gasoline in a car with 40 mpg, with extra load on the electric grid. This is *clearly* an improvement to the overall carbon profile, unless you assume that I then resell the cars to someone who wasn't driving a car before.