Differences in DECC and National Grid Power for 2009?

With some help of a reader from Bishop-Hill’s web site, some discrepancies have been noted.

Appears that the number used by DECC and National Grid for mean wind power/energy for the full year 2009 are different by almost three times.

As explained below, the difference could be related to DECC using a combination of actual and estimate (based on “typical load factor or the design”) generation numbers. I do not have, and probably can not get the source data from DECC (per their email this morning).

I therefore conclude, pending errors in my thinking, so far with the data I have that the National Grid numbers, which appear to be “actual” are more accurate than DECC’s actual/estimated generation numbers.  Further, DECC’s computed load factors may have some issues with circular logic.

Would welcome some “peer review” here to spot any errors.

JK on 1 November 2010 at 1:44 p.m. said at Bishop-Hill:

The energy statistics section on the Decc web site publishes the information on installed capacity and actual generation from renewable sources, which suggest that for onshore wind the generation is in the range 20-25% of installed capacity.

table DUKES 7.4 on http://www.decc.gov.uk/en/content/cms/statistics/source/renewables/renewables.aspx

This DECC table is reproduced here and I’ve highlighted the two areas of interest.  I’ve looked at nothing else so far.

For the only year where DECC data and the source 30-minute interval power generation data from National Grid is 2009.  The National Grid data is presented in GW as power. Comparing the two for the full year 2009:

The GWh (Gigawatt Hours) column above is from the DECC data in DUKES&-4-1.xls.  Assuming (24 h/day x 365 days/year) 8,760 hours per year this means an average power output of 9,304 GWh / 8760 h=1.06 GW.

The mean annual power from the National Grid data is obtained by averaging the 17,520 30-minute interval data points for power produced 2009. This worked out to be 0.379 GW.  The histogram of the data along with a fitted probability distribution is as shown below:

Digging further into the DECC data see Note 7 (highlighted above) where they say for the wind data:

(7)    Actual generation figures are given where available, but otherwise are estimated using a typical load factor or the design load factor, where known.

Since I don’t have access to the source data I don’t (yet) know how much of their data is actual and how much is estimated for 2009.  Further, if they are using “typical” and/or “design” load factors to estimate actuals, then this will certainly impact their computation of “actual” load factor.  Seem like a bit of circular logic here.

Would welcome any thoughts here in comments about what else could be wrong here.


9 Responses to Differences in DECC and National Grid Power for 2009?

  1. […] Grid Data vs. that reported by Department of Energy and Climate Change (DECC) for 2009. See https://rmschneider.wordpress.com/2010/11/01/467/ were we do an initial exploration of the issue.  Comments welcome.  The discrepancy is not […]

  2. martinbrumby says:

    I wonder which set of figures BigWind gets paid on?


  3. fujirobin says:

    Big wind gets paid on what it reports to OFGEM – look in the ROC Register (as was) and use those figures

    go here https://www.renewablesandchp.ofgem.gov.uk/ and click on “view public reports” then recalculate using those figures.

  4. HG says:

    I’m not sure if this will help. I looked into the apparent shortfall in installed capacity and the amount of wind power available to National Grid some time ago. Much of it seems to be explained by NG seeing a significant proportion of installed wind capacity as a reduction in demand. See “Measuring the Wind” at

  5. HG says:

    Addendum: the figures for metered capacity available to the Grid has changed since I wrote that piece. It now stands at 2430 MW. See:

    • fujirobin says:

      And I suspect even the 2430MW figure is wrong. When the Thanet windfarm came online a few weeks ago, the 2430 figure didn’t change… and Thanet is included as metered.
      I wrote to Elexon, then NGC to clarify, but didn’t get a response. I also asked how\whether they adjusted their demand forecasts for unmetered wind. Sept 6th was a record day for wind generation, but I couldn’t see a dent in their forecast demand.

      Interesting questions that deserve answers.

      • HG says:

        Thanet is now listed in the spreadsheet containing ‘Power Park Modules” connected to the grid – with two entries of 70MW each.


        I’ve just had a look through my old emails and the BSC Service Desk wrote that “[i]t is in fact National Grid which provides this data for the BMRS.”

        There’s no doubt that most of the country’s wind turbines aren’t included in the NG list. I think you’ll find there’s a disclaimer somewhere on the NG site that acknowledges that National Grid data doesn’t necessarily show everything that is connected and metered.

  6. fujirobin says:


    I know – but now Thanet is now 300 MW !

    which is why I think their info is out of date

  7. rms says:

    I asked BSC Service Desk (runs Elexon Portal) about the coverage of power generation and how to see all documents on their site. I provide their reply here for others to know. I will dig into the links and find clues about their coverage. Unfortunately, I’m travelling over the next few days and can’t get to this immediately. Will report results here when I learn something.

    The Tibco Relay Service provides users access to files containing balancing mechanism data published on the BMRS website for a chosen date. The file can be accessed via the following link (http://www.bmreports.com/tibcodata/YYYY-MM-DD/ – where YYYY-MM-DD is chosen date) which can be used to automatically view and download historic data. Further information on the Service can be found in the Tibco Relay User Guide which is accessible on the ELEXON Portal (www.bsccentralservices.com). Alternatively, we have already extracted Generation by Fuel Type data from these messages and have a file (Historic BMRA data 200811-201001) available for download from the ELEXON Exchange which might be of use. The file can be accessed by logging on to the ELEXON Portal (once an account has been created) and using the navigation links to open the ELEXON Exchange there is an option to view Historic Generation by Fuel Type Data Files under Most Viewed Content. To view this data you will need to read the Tibco Relay User guide to extract the files.

    Have you had a look at http://www.bmreports.com to see if the extent of coverage is the same between bmreports and the historic generation data on the Elexon Portal (www.bsccentralservices.com). If you navigate to General > Electrical Data Summary and look at the Generation by Fuel Type data, then hover the mouse over the “information” button, this will show details about National Grid’s operational metering.

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