When the aim is a balanced grid, is intermittent power easier/better than nuclear?

While cleaning up some old files, I found a link to a tweet that I used one year ago in a post on windmills “balancing” the grid. To recapitulate, during the first lockdown in Belgium, there was a lot of solar and wind power, but there was low demand. However, nuclear produced flat out, as usual. Not wanting to produce at negative prices (because of high production and low demand), windmill owners started to shut down some of their windmills. This curtailment was then framed as wind “balancing” the grid.

Below this tweet was another one written by the same author. It is his answer to the question whether there are quantified estimates on what would eventually be realistically possible with dynamic demand response:

Tweet Dieter Jong 2020-04-21

I apparently glossed over this tweet at the time I made the post, but that is an interesting question. So, in what way is that left graph easier/better than the right one when the aim is a balanced grid at all times?

The tweet shows two graphs. One with a constant level of generation (nuclear) and the other one with two peaks (wind or more generally intermittent power). None of the two fits demand. The left graph because it overproduces most of the time and the need for support at the very peak, the right graph because generation is not in sync with demand. Both need a balancing mechanism in order for the system to be balanced.

It is presented as a binary choice. Or generate loads of power, store some of it and curtail/lose the rest, risking frying the grid when demand is low. Or shift the generated power to when it is needed, risking frying the grid when generation is plentiful.

I don’t think this are the only two choices to chose from (and the first is not even an option for our politicians anyway), but let’s assume for the sake of the argument that these are our only two options. Which one is the easiest/better choice?

Looking at his other tweets, it seems he is not that fond on nuclear, so I guess he is in favor the the graph on the right. I also think that he doesn’t want filling in with gas or another fossil fuel, but with low emission power sources like pumped hydro or batteries.

The first option (with nuclear power, see the graph on the left) reminds me of what we currently have, but then on steroids. Currently, about 50% of our demand is provided by nuclear power and that would put the generation curve somewhere below the lowest point on the demand curve. The rest is filled in by primarily gas and pumped hydro at the peaks. This pumped hydro (Coo-trois-ponts) is specially built for this purpose. When there is excess generation (at night when the combo nuclear/gas produces more than the demand), water is pumped to a higher elevated reservoir and the kinetic power of the water in this reservoir is used to fill in the peaks.

In this option, not only nuclear power needs to be overdimensioned (to provide enough overproduction so the excess could be stored and used to fill in the top of the peaks), also pumped hydro (or another backup technology) needs to be jacked up tremendously. Knowing how little current pumped hydro contributes to the grid, there will be a need for huge amount of backup capacity.

Dynamic demand response will not be that problematic. Since there is base power generation, dynamic demand response will probably be limited to the top of the peaks.

The second option (with intermittent power sources, see the graph on the right) is something that is not tried before. Now not only the top of the peak needs to be filled in, but potentially almost the entire peak. Looking at the example graph at the right, the complete production during the period of low demand will have to be stored in order to fill in almost the entire peak demand when production is low.

An additional problem will be that production and demand will not always that symmetric. This scenario is also possible:

Now the entire deficit needs to be available in backup in order to be able to fill in almost the entire demand for that time frame. This means the need for longer term backup, which will be pretty expensive to build and to operate. If this lull continues for a couple days, then the deficit of all those days will need to be available beforehand.

The reverse is also possible:

This excess then need to be absorbed or curtailed. In the former case, an insane amount of backup will be required. In the latter case, curtailment is surely an option. Remember, curtailment was framed as wind energy “balancing” the system (although that sounds pretty neat, this was not really appreciated by the windmill owners who demanded extra financial compensation for their, ahem, “balancing”).

Dynamic demand response will probably have less impact, just compared to the energy that potentially needs to be displaced.

Concluding, both options presented in the tweet will have their share of problems, certainly when the infilling is done by for example pumped hydro or batteries instead of by dispatchable power sources like gas. Then just looking at the amount of energy that potentially needs to be stored, I think it is the first option that is the easiest/better one when the aim is to balance the grid at all times.

6 thoughts on “When the aim is a balanced grid, is intermittent power easier/better than nuclear?

  1. Linley

    I am no expert, but it seems France have managed to balance the grid for 40 years or so even though they have a large amount of nuclear. They have had cheap, low emissions electricity.


    1. Chris Morris

      From what I understand of the European grid (I live half a globe away), one cannot consider a country in isolation. The interconnectors make an effective supergrid.


      1. trustyetverify Post author

        It is true that EU countries are interconnected, but there are quite some limitations. As far as I know, we are still far from a supergrid. I think the situation is similar to Australia where there are transmission networks in each state and territory, but having cross‐border interconnectors that link some networks (the same here, I live at the other side of the globe).


    2. trustyetverify Post author

      France has a high share of nuclear power and indeed, prices and emissions are low. Contrary to Germany that has a high share of intermittent power, but has the second highest prices in the EU and also has high emissions that don’t seem to go down.

      In general, nuclear power reactors don’t follow load well, but most nuclear reactors in France have some load following capabilities. By the sheer number of them, France is able to reasonably follow load. It also is capable of shutting down reactors for a short time and there are other things like hydro that help with load balancing.

      That makes that they were able to help us out on several occasions when our grid was overloading (due too much intermittent energy combined with low demand on for example holidays) or saving us from blackouts in winter when our grid was ill-prepared.


  2. Chris Morris

    No country or group of countries have a true supergrid, as they all have significant choke points. There are problems with parallel transmission paths causing circulating flows that limit development. It is why the Poles had to put phase shifters on their German interconnectors to stop Germany exporting its problems. . The HV engineers tried to explain it to me, but it rapidly turned into me not understanding the vectorial maths they talk about.
    This document here says the goal for the EU is 10% of each country’s capacity in interconnectors https://ec.europa.eu/energy/sites/ener/files/documents/report_of_the_commission_expert_group_on_electricity_interconnection_targets.pdf That should be significantly larger than any single generator on the country’s grid. It recognises that more of the unreliables increases the need for interconnectors for grid balancing. I didn’t explore the document’s links, which may yield some nuggets.
    This one shows the links outside the EU.

    Click to access 2nd_report_ic_with_neighbouring_countries_b5.pdf

    Liked by 1 person


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s