Comment by redleader55

The variability of France’s nuclear fleet is harder on the generator (valves and structures susceptible to thermal stresses in particular), and a possible contributor to their inability to keep their fleet in good repair.

Arguably, if cost effective, nuclear is best run at full output as consistently as possible, with other systems buffering that supply with demand (hydro storage, batteries, demand response, etc).

https://www.laka.org/nieuws/2022/so-how-flexible-is-nuclear-...

https://www.ianfairlie.org/news/french-report-nuclear-power-...

An interesting complicating factor here is that much of the UK's installed base of CCTG stations were built during the 90s with the intention of replacing many of the smaller coal-fired stations, which would typically be doing 2-shift operations (i.e., day and evening). Now, those CCGT stations are increasingly used to counterbalance renewables, and (as you point out) are now running on much shorter cycles than they were designed for.

A report from a few years back (which I'm afraid I've utterly forgotten the source) examined the data on this, and argued that as a result of this changed pattern of use, these CCGT stations were now not achieving nearly the kind of efficiency figures they were designed for, which from a carbon point of view is not good news - we might still be emitting lots of the stuff, but just not getting as much practical benefit from it as we used to.

Now, I'm not meaning to suggest that this is a disaster, or that is somehow invalidates the entire of concept of renewables, but it does point to the need to be careful about what we take to be a useful measure of progress - and that merely the quantity of supply to the grid in GWH isn't necessarily it.

And the article under discussion here is of course picking away at another strand of this same idea - when we connect these generators together, it gives rise to system-level effects, and we need to be thinking about the outcomes, both beneficial and harmful, in system-level terms as well.

(Edited for spelling.)

Varying output from a nuclear plant is mostly achieved by simply releasing the generated steam into the atmosphere instead of sending it through the turbine[1].

But operating a nuclear plant in this fashion pushes up the price per MWh considerably given their very high cap-ex and op-ex. And while fuel cost is negligible for nuclear, creating more nuclear waste per useful MWh generated is a further drag on costs.

So as a solution, it "works" if the nuclear plant does not have to compete in terms of price with other sources of electricity. But nuclear fails to compete on cost even if operated continuously - it's uncompetitive with cheap, quick to deploy, low op-ex, modern tech like CC gas turbines or renewables in most western electricity markets and can only survive with government subsidy[2].

[1] https://www.nrc.gov/docs/ML0703/ML070380209.pdf [2] https://www.washingtonpost.com/business/2022/04/19/biden-adm...

But using a nuclear power plant as a backup when there is no wind doesn't make any sense. If you build a nuclear power plant you might as well use it, costs the same either way. And if you use it, why building wind?

The problem is taking the most expensive power source with a large portion of the costs being the initial investment and then not running it 100% is economical suicide.

Most reactors in service operate at a constant load, and don't vary output according to demand. Certainly in the UK they do not. Sometimes reactors are operated for extended periods at reduced load for various reasons (eg: to conserve fuel and extend the time before a refuelling shutdown is required), but they don't vary output day-to-day.

Ramping it up is likely the problem, since all plants can reduce power on a dime by just varying the generator coil current I think.

You could just keep it spinning nonstop without a load I suppose, but for anything but nuclear it's not gonna be economical.

Not a nuclear engineer, but Im curious to know how they do it - throttling nuke is hard. I only know the stream "dumping" method.

There's good reason why they are hard to throttle. For starters thermal contraction shortened lifespan; but also because the nuclear cycle itself doesn't lend itself to throttling safely - nuclear products create "retarded (?) neutrons" which are the cornerstone of a stable control system (as opposed to prompt neutrons) and also significant amounts of neutrons poisons which are normally "burned" at equilibrium steady state power levels but which accumulate if you throttle down (therefore be needing even more prompt neutrons).

My understanding is that the more you need to rely on prompt neutrons for your neutron balance the more unstable your reactor (starting them up, therefore, is delicate). Throttling the power upsets this balance by at least two different mechanism.

It can be designed for, but it wasn't designed for when current UK nukes were built; they were intended to replace baseline coal plant.

There's this incredible project to build a 10GW solar farm in Morocco (1/3 of UK peak consumption) and bring the power to the UK via HVDC cable. Amazingly they estimate only 10% losses despite being over 3800km long:

https://xlinks.co/morocco-uk-power-project/

Surely HVDC links between Scotland and England could be built?

And then there are pumped hydropower storage project like this one with a proposed storage capacity of 200 GWh and 1.5GW of power:

https://www.coireglas.com

In the worst case, couldn't the excess power simply be used in electrolyzers to generate hydrogen? They may not be very efficient but it's better than throwing free energy away.

To be clear, Sun Cable entered administration this week. I wouldn’t hold your breath.

https://www.abc.net.au/news/2023-01-11/sun-cable-enters-admi...

Thank you. People laughed when I suggested an HVDC link between North America and Europe.

Nordstream 1 was 1222km, and Britpipe now, is 60km shorter.

Boston to Lisbon is 5100km. Churchill Falls (home of a giant hydro dam project in Labrador Canada which got screwed by Hydro-Quebec because the only via transit was through Quebec), would be just under 4000km subsea.

The transit contract expires in 2039 I believe...

"Under construction now."

Wiki says: https://en.wikipedia.org/wiki/Australia-Asia_Power_Link

    projected to begin construction in mid-2023

And:

    In January 2023, Sun Cable went into administration, the equivalent of Chapter 11 Bankruptcy.

The current problem, as I understand it, is the capacity to build HVDC isn't high enough to meet global demand.

The project has stalled due to the two billionaires funding the project having a “spat”.

But it’s expensive and takes a long time. The U.K. isn’t building enough quickly enough to take benefit of production in the north.

Maybe if variable prices encourages energy intensive demand to shift to Scotland that will help, but that’s not quick either.

The North Sea Link between Norway and the UK is already up and running and has a capacity of 1.4 GW. It is currently (10:53 UTC) supplying 3% of the UK load.

See https://gridwatch.templar.co.uk/

The quickest gas generation (gas engines) can go from cold start to fully ramped up in 4-5 minutes. A typical OCGT/CCGT is a bit slower and has a higher start cost (and a CCGT won't reach peak efficiency for hours). Pumped storage hydro takes 20 seconds or so.

However, turning generation on or off isn't the only way the grid is balanced in the short term - turning up/down tends to be a big part of it too and most conventional generation can do that faster (sometimes a lot faster) than startup/shutdown.

It depends on the type of natural gas plant. Some of them are designed for efficiency which takes longer to spin up and down while some are peaker plants which can spin up in a matter of seconds/minutes.

Yep, 15 minutes to full load is not uncommon with gas plants.

There is a hierarchy of time availability of power supply:

  1. power available when you want it, and you can choose on the fly
  2. power available when you want it as long as you know in advance
  3. power available at a time that you don't choose, but you can predict
  4. power available at a time that you can neither choose not predict

Examples are (roughly) 1: gas or hydro, 2: nuclear or coal, 3: sun or tidal, 4: wind. You can also think of demand types that require each of these levels or better. Of course each of these categories contains its own sliding scale of how far in advance you have to decide or can predict. Wind is not completely unpredictable, but it is further down this hierarchy than almost any other source of generation.

Moving generation up this hierarchy, or demand down it, is always going to give some benefit. Well designed power markets should make sure that there is some fair incentive for any such step.

I believe GP meant by predictability "power is available for generation whenever we want it".

What you are saying is that its possible to map out in the future when power is available for generation.

I think “intermittent” is what was meant.

Usually the problem with this kind of thing, is that the initial capex requirements are high, and it's just not profitable given how rarely it happens.