Earth Notes: On GB Grid Electricity CO2 Intensity vs Record Wind (2012-09)

Did Record GB Wind Generation 2012-09-13 Decarbonise The Grid?

Not much more than usual in this case.

I deduce this from the FUELINST figures from bmreports.com. Partly because wind is still small beer, maxing out for now at around 10% of demand.

Wind generation did not hit the near-100% capacity factor predicted (of the the 5GW that is visible to and metered by National Grid), though it did still hit a very respectable near 80% figure, and quite a large chunk of it was outside peak-demand hours when intensity tends to be highest (eg being supported by coal).

Maximum and minimum intensity figures were not unusual (eg for summer months) ranging from about 358gCO2/kWh to 499gCO2/kWh on the 14th (29% swing), compared to about 423--539gCO2/kWh on the 12th for example. These are generation intensity figures; for domestic consumers, due to losses in transmission and distribution, add about 7%.

Peak Generation 4GW

The very peak was 4.01GW at 2012-09-13 21:00 GMT (ie 10pm BST) out of National Grid metered capacity of 5.066GW on the GB grid according to the bmreports.com FUELINST data (Reuters quotes 4.13GW on the morning of the 14th which may have been a spike too short to see in the FUELINST data). Total UK capacity to date according to RenewableUK's UKWED (UK Wind Energy Database) is 7.391GW of which probably 10% is in Northern Ireland, ie not on the GB grid. So another ~1.5GW of capacity that is connected to the distribution networks will not show here but reduce apparent demand instead, like solar PV microgeneration. The NI grid is not run as part of the rest of the UK, ie the GB grid of England/Wales/Scotland.

Questions

Mark Lynas prodded me with the following questions:

1. How much did the 2012-09-13 record wind event help decarbonise the UK grid?
2. What actually happened? How long was the wind blowing for etc?
3. Does the event tell us anything about how far wind can help decarbonise UK electricity?

How much did the 2012-09-13 record wind event help decarbonise the UK grid?

Not much given that ~2GW of nukes were off-line so day-ahead wholesale prices did not move much either; they would drop if much other generation were being displaced. Since gas has been expensive and can probably be ramped faster than most coal, it seems that more gas (CCGT) than coal moved off the grid. See also Platts. Note that nuclear at the start of September was a little over 8GW, down to about 6.6GW as wind was peaking 13th/14th.

What actually happened? How long was the wind blowing for etc?

Peaks of ~4GW (80% of name-plate capacity, ie capacity factor) were touched at about 21:00 (13th) and 09:00 (14th).

About 36 hours at >50% capacity factor (2.5GW) from about noon on the 13th until midnight on the 14th (typical capacity factor is nearer 30%), and >70% between about 18:00 on the 13th until early afternoon 14th, all times GMT, all generation from the National Grid's metered 5GW.

Numbers derived from bmreports.com FUELINST data, with one clearly bogus zero value manually removed. (See also gnuplot code.)

Does the event tell us anything about how far wind can help decarbonise UK electricity?

Not much: every day can be somewhat different, 'baseload' generation such as nuclear can come and go rather than be its idealised steady state, and the addition of new interconnectors (such as INTEW, the East-West Interconnector, going live October 2012) adds more complication to predictions. National Grid does not seem worried about accepting a lot more wind into the mix and as is often pointed out deals with bigger daily slews in demand than the slews in wind generation just seen.

The new peak did not break anything, and wind stood in for supposedly reliable nuclear baseload and had a similar or better capacity factor!

Correlation Analysis

I performed some extra analysis to look for the overall effect of wind on GB grid carbon intensity.

Like many other renewables, wind is not 'demand callable' by the grid to meet demand, ie the wind is not at our command, though wind generation can be curtailed, ie shut off, in rare circumstances such as transmission failure. (2% of available wind generation over winter 2011--2012 for example, see National Grid Winter Consultation Report 2012-13.)

As a nominally zero-carbon generation source, its carbon intensity is lower than anything else metered by National Grid on the grid except hydropower, and there's only a fairly limited amount of such 'non-pumped-storage' hydro. So in general, as wind input to the grid increases, carbon intensity of the grid (gCO2/kWh, ie CO2 emitted per 'unit' generated) should decrease. And because wind is an 'independent' variable that would suggest a negative correlation between wind generation levels and GB grid carbon intensity.

Looking back over 2009--2011, and using a simple Pearson correlation, I see small correlations (essentially wind is small enough to be noise, and/or swamped by other noise) of ~-0.0062 (2009), ~0.0335 (2010) and ~0.0614 (2011) for each whole year with 5-minute FUELINST data. Those may also indicate wind happily coinciding with high demand a little more than not.

For early September 2012 (1st--17th inclusive) correlation is slightly negative at -0.1400 (cf all fuels/sources CCGT=0.6303 COAL=0.9417 INTEW=0.3609 INTFR=-0.3491 INTIRL=0.6369 INTNED=-0.2284 NPSHYD=0.3641 NUCLEAR=-0.2143 OCGT=-0.7199 OTHER=0.4118 PS=-0.0052 WIND=-0.1400). Note for example that nuclear which does not significantly load-follow on short timescales in the UK is more negative than wind in this sample.

For the days of 12th/13th/14th/15th, ie around the peak, however, correlation ranged from -0.1630 (with everything else positive that day) to -0.5 and upwards. Wind seemed to be having quite an impact on the grid, presumably in part because the volume was significant enough to displace other fuels in decent quantities even if gas seemed to buckle more than coal.

If lots of wind on the grid forced wastage elsewhere, eg with lots of OCGT (less-efficient open-cycle gas turbines) for extra 'balancing' and increasing carbon footprint as wind's detractors assert is necessarily the case, then I'd expect these correlations to be positive and getting more so, under high wind conditions. But this does not seem to be the case from my limited analysis so far, even though I was initially taken aback by the weak positive correlations over significant data sets.

I intend to compute correlation between the fuels and demand, to see how well in particular wind matches demand better than chance. I also intend to compute the correlation between demand and intensity, bucket results as I have for intensity in the yearly analyses, and then find a grown-up statistician to help me do it again, right! I may also ask Elexon very nicely to give me access to more accurate figures than the FUELINST approximations to see how much difference that makes to the results. I may also make an effort to compensate for reduction in apparent demand from wind, solar and other (micro)generation 'embedded' in the distribution low and medium voltage networks.

Caveats

• Note the significant volatility of nukes and the mainly-nuke INTFR French Interconnector flows to us (each varying by ~2GW quite quickly in the scheme of things).
• Note the effect of high-intensity COAL inability to ramp quickly (and the EU combustion plant directive) vs low-intensity CCGT/NPSHYD and pumped storage.
• Note the size of normal slews and daily/weekly consumption patterns.
• Note significant fraction of wind (and other renewables) not visible to Elexon, and that show as reduced demand.