Embedded Data Generation
An explanation of how the Embedded Data is generated
Solar PV generation:
Solar Photovoltaic (PV) generation is calculated using an estimate combining registered capacity, minutes sunlight in the hour, time of year and average load factor.
Solar photovoltaic generation encompasses Solar Wind farms, domestic roof-top panels and ground mounted panels.
Solar photovoltaic generation is completely Embedded or Distributed capacity, this means that none of the Solar Photovoltaic capacity is connected to the National Grid via its balancing and reporting mechanism. Because of this distributed nature of the PV capacity there is no way to report on what the total UK PV output is at any one time.
However the solar PV capacity is now a sizeable amount and is growing continually - the increased solar PV capacity shows as a decrease in the Demand on the National Grid
To be able to report this solar PV output and thus see the reduced impact on NG demand we have started to track the estimated solar PV output at hourly granularity
Output Estimate calculation
The output value is calculated from:
Total UK Solar PV Capacity * Annual Average Load factor * Time of year weighting * Percentage sunshine in the hour
Total Solar PV capacity
Under UK government rules all renewable energy capacity must be registered with the government, the govermnent report on this data weekly and monthly and this allows for a good estimate of UK solar PV capacity per week
The total UK solar PV capacity is calculated as the total of Feed in Tarriff (Fit), RooFIT, MCS (micro-generation certified) and RO (Renewable obligation) capacity. This covers domestic roof-top and ground mounted as well as commmercial and solar farm capacity. All capacity that is installed is totalled including non-certified capacity.
Annual Average Load Factor
Using 2012 data the average annual load factor for the UK is calculated as 0.08525 - dividing total GWh / ( Total GW capacity * hours in year) = 2015 / (2.698 * 8760) = 0.08525. Data is sourced from this wiki page
Time of year weighting
The insolation from the sun is calculated for the day of the year using data from here . This is applied as a weighting to the value, decreasing the value in winter and increasing it in summer. The hours of sunlight in the day is taken into account to produces a weighting for the strength of sunshine for month of the year.
Percentage Sunshine in the hour
The hourly level of sunshine is calculated from UK weather station data that use Campbell-Stokes sunshine recorders to measure the number of minutes (0-60) of sunishine in each hour of the day. This is compared to the average UK value of 4.67 hours of sunlight a day or 11.67 mins an hour and then applied as a weighting to the data. Data is sourced in near real-time from here
Example of calculation
As an example on 10:00 26 March 2013:
Total UK Solar PV Capacity: 2.405719GW
Annual Average Load Factor: 0.085
Time of Year weighting for March, average hours sunlight = 4, average hours sunlght for year = 4.67, March insolation = 2.2, average year insolation = 2.51. March insolation weighting = (24 / 4.67) * ((2.2 / 2.51) / (4/4.67) = 5.2574
Percentage sunshine in the hour: mins = 47.8 /60 = 0.797 = 79.7%
UK Solar PV Output 12:00 23 March 2014 = 2.406 * 0.085 * 5.257 * 0.797 * 1000 = 856.9 MW
Consisderations on estimated calculation
The minutes of sunshine in the hour recorded using the Campbell-Stokes recorder produces a binary view of the sunshine viz. the sun is shining or not for each minute. Thus there can be times when the estimate is too low because the minutes sunshine is actually lower than is real and at other times where there is weak sunshine the estimate is too high
Because of this limitation with the calculation the data is more spiky than would really be the case.