The nuclear magic bullet

A virtue of The Economist's focus this week on the vulnerability of our energy systems, regardless of whether they have got everything right (and there's plenty that's good as well as some that's bad) is that it has brought attention to the issue. Unfortunately, for every sensible comment, there are usually several from people who have picked their magic bullet and just trot out their usual unthinking platitudes without considering the complexities.

The favourite magic bullets are usually one form or another of renewable electricity, or nuclear power. For example, several nuclear freaks gave us the benefit of their opinions in response to a perfectly sensible post on Raedwald's blog.

I provided some information on there to explain why nuclear won't be a magic bullet, but I want to provide a bit of supporting analysis here.

The nuclear lobby often points to our import of power from France as illustration that the French nuclear-based system is more reliable than our mixture of generating technologies. They like to paint the story as though we are reliant on French nuclear power. Let's see how well that holds up to scrutiny.

I have looked at half-hourly system-demand data for the current year to end of May, available from National Grid/Elexon. The total or average volume of the flow over the French interconnector doesn't tell us much. We are net importers of a relatively small volume of our power (partly constrained by the capacity of the interconnector). But the more interesting question is when that power flows.

Looking first at how it varies by time of day:

Flows over French interconnector for each half-hour period of day

It's a mixed bag. System demand is (not surprisingly) higher during the day than at night, and has two peaks during the day, morning and evening. The French send the most power during our evening peak, so that is definitely them responding to our demand. But they send more over at night (when we don't need it) than they do in the morning and early afternoon, suggesting that we are providing an outlet to dump the inflexible output from their nuclear plant at night time. That's a fairly 50:50 relationship, then. They give it to us when we most need it, but we take it from them when they most need to dump it even though we don't need it then.

That is an average of winter and spring performance. Our needs are greater in winter (i.e. we are getting closer to using the full capacity available in order to meet demand), so let's see how they help us out at that time. Taking just the first three months of the year:

Flows over French interconnector in winter for half-hourly periods of the day

Our system demand is higher over a 3-month winter average than over a 5-month winter/spring average. But the French send us significantly less power during the winter than they do for the 5-month period. In fact, during most of our morning peak of demand, they are taking power from us (negative flows), rather than the other way round. They are still helping us out during the evening peak, but to a lesser extent. And they are still dumping their power on us at night, though again to a lesser extent. That's not 50:50. At the time of the year when supplies are tightest, they are using us more than we are using them.

We can see that picture more clearly if we look at the weekly averages:

Flows over French interconnector, weekly averages

As average system demand decreases, as the weather improves and the days get longer, the French send us more of their power. That's back to front, if French nuclear is helping to meet our needs, but consistent with the UK acting as a dumping ground for excess French nuclear production. Most noticeably, in the week with the highest demand so far this year (week 2), they were actually net importers from the UK. How very helpful of them.

If nuclear is not subsidised and the safety and environmental factors are rigorously controlled, then it is a useful part of our electricity mix. But it is an inflexible part of the mix, which is why France pushes her power out to her neighbours when demand is lower at home, and pulls it in when demand is higher. We can't all do that. We can use hydro to store the power to some extent, but it depends on the geographic and political constraints (the UK's potential is very limited), and even France, with massive hydro investment, cannot fully balance supply and demand in this way. To the extent that nuclear output cannot be matched to demand through stored hydro-power, there is a limit to how much of our electricity can be supplied by nuclear. In the UK, with limited hydro, but grand plans for inflexible, intermittent wind power, the practical limit is probably in the region of 10-12 GW, operating at fairly constant output to provide around 20-25% of our electricity. As electricity is only a minority of our total energy consumption, that equates to around 4% of our final energy consumption, or 8% of our primary energy supply.

As I said, nuclear can be a useful part of our systems, but it's no magic bullet for our broader energy issues.