Friday Reads – 3 January 2020

1. With regard to the Guardian article on York banning private cars, I find it ironic that the two most polluted spots are a bus stop and taxi rank, neither of which are covered by the ban. It also doesn’t make any mention of electric cars, so presumably those are banned even though they don’t contribute (directly) to pollution. Sounds more like an anti-car measure rather than an anti-pollution measure.

   So I wonder if York will publish any regular stats to show how this measure is affecting pollution in the city, what the desired reductions are and whether they will rescind this policy if it doesn’t work?

2. They need proper 100% electric buses and taxis also. (Not daft things like the Boris bus.)

3. I would love to ride those NY historic Subway Trains, the NY Transport Museum has a great collection and being in a disused station itself, feels really atmospheric in comparison to the LT Museum or Acton depot.

4. @Mikey C From what I recall of the NY Transport Museum, having visited about 25 years ago, it was mostly the old train cars in the disused station. Like you say, really atmospheric, with old turnstiles, station fareboxes, and old Subway maps on the platform. I liked the Acton depot for its massive completeness, workshop atmosphere, signs, buses, equipment of all types. And the LT Museum told more of a story of transport in London from hundreds of years ago.

5. @ Jimbo, the main reason for banning cars in York is to support the council’s objective of reducing CO2 emissions, rather than improving air quality. However, it seems to be more of a publicity stunt than a serious bid to reduce emissions as the number of cars inside the walls is tiny already.

6. @RogerB – my point is that if you want to reduce CO2, why would you ban electric cars but allow diesel buses, vans and taxis? If you want to ban private cars to reduce congestion, then that is a fine policy. Similarly, if you want to reduce CO2, then get rid of sources of CO2. They seem to picked a policy and an answer that don’t match up.

   This smacks more of virtue signalling rather than the concrete policy to fix a problem. It is worth pointing out that unless the levels of CO2 in the city are significantly higher than the surrounding area, any reductions in the city will literally blow away in the wind.

7. In the “Electric car owners can be paid to charge” article, it says, referring to 14 Dec 2019 that “The weather conditions meant that the UK’s wind farms generated a record 16GW”. In fact gridwatch.co.uk data shows that the contribution of wind to the grid on that day did not exceed 11.7GW (as an average over an hour – I’m looking at hourly data as that is easily visible – you can get 5 min data if you download it). As for it being a record, well that level of wind contribution was exceeded by up to 1.8 GW on several other days in the month. And that 13.5GW has already been equalled or beaten 3 times since New Year. And I have half a memory of it getting up to about 14GW one day last winter. But certainly it has never got materially beyond that.

   It is not uncommon to see claims like “UK wind farms generated…” an amount considerable in excess of what the grid has ever said it is. I wonder where this comes from. In a journal like Air Quality News, the usual explanation of “journalist can’t do numbers” doesn’t really wash.

   It says “At times, this was more electricity supply than the grid needed” and I expect this was true. In fact 258 GWh of wind generation was constrained off during December 2019. So on average 0.35GW was constrained off every hour of that month. But since most of the time nothing is being constrained off, then actually there are times when quite a lot is being constrained off. After all, our wind capacity is currently about 22GW, and it is on only a handful of occasions in a year that more than 13GW actually gets onto the grid. In other countries, we see the maximum generation is a substantially higher fraction of the total capacity.

   So maybe what they mean is “we might have had 16GW that day, if so much of it hadn’t had to be forcibly constrained off”. But actually given that the 11.7GW hourly peak we saw that day isn’t so very high, I would be surprised if that was the day with the highest potential wind generation, ie including constrained off. Unfortunately you have to pay to get constraint data at a daily granularity, it is only free at monthly granularity.

   But there are two quite different reasons why wind farms get constrained off, and only one of them corresponds to the explanation here. Quite a lot is constrained off due to local grid constraints, which is different from the reason stated in quote. And when the reason is local constraints, generally in remote parts of Scotland, increasing demand doesn’t reduce the problem, unless you can increase demand in just the right remote part of Scotland. Because it isn’t a case of more electricity than the grid needs, it is more electricity than some local network in some area can transmit. There are several wind farms in Scotland that have over 20% of their generation constrained off, because those local constraints tend to be reached whenever it is rather windy around there. So you wouldn’t be giving out free car charging to all and sundry at times when that is the dominant reason for constraining off.

   But it is also true some of it is constrained off for the reason given. I expect this was true in particular in the early hours of 14 Dec, ie before about 0600. During this period, there was (averaged over an hour) up to 10.5GW of wind on the grid. (And during those early hours wind might just have got up to 45% of supply briefly, as quoted in the article, around 0400 to 0500 ish, though in the hourly averaged data it doesn’t quite get there.) This reduced gas to close to 3GW, which is about the minimum we see, for reasons of grid stability. As things stand, the grid tends to need at least 3-4GW of gas on it to remain stable. There are actually things other than gas that also help stability, but in practice gas is the key indicator. So at this time, when wind is being constrained off for reasons of grid stability, it is worth paying people to consume electricity. That avoids having to make constraint compensation payments to wind farms to switch off.

   So there is some sense in the article, even if the numbers look odd, and the explanations are rather partial and garbled. But the real thing I worry about plainly wrong numbers like “we had 16GW of wind generation that day” are so often reported, when in reality we never get that high.

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