UK Wind Drought July 2018


July 2018 was an exceptional month for fine anti-cyclonic weather in the United Kingdom.

The result was that overall wind power capacity for the month was significantly reduced to 11.7%, less than half the normal annual capacity percentage in 2017 of 27.3%.  On the other hand Solar PV power was at an maximum performance in the fine weather resulting in a capacity figure for the month of 21.2% as opposed to the annual capacity figure for 2017 of 9.96%.

This post outlines the detail of this significant variability which posed very significant problems to those managing the grid.


Data sources

Gridwatch.templar publishes a data set of generation values by technology at 5 minute intervals for all generation sources for the whole of the UK.  For the 31 days of July this results in 8928 data lines or 105,120 data lines for the whole year.

Each line of the data for 5 minute  intervals includes:

  • Demand, which omits Solar PV generation
  • Coal
  • Nuclear
  • Gas-firing CCGT
  • Pumped Hydro
  • Hydro
  • Biomass
  • Wind
  • Solar PV
  • Inter-connectors primarily from France and Netherlands

The July 2018 overall results in the following generation sources, which are regrouped for simplicity as follows.

Screen Shot 2018-08-18 at 08.10.42.png

For the purposes of this post these data have been condensed to 744 hours in the 31 days of July.  In addition

provides graphic presentations of the data, for example in July 2018.Screen Shot 2018-08-17 at 18.15.29.png

A subset of this detailed data at 5 minute intervals for July 12 -14 encompassing 2 weekdays and a Saturday is also used for more detailed presentations.


Generation performance for 12 – 14 July 2018

Screen Shot 2018-08-20 at 10.52.21.png

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This chart for the three days Thursday – Saturday, 12 – 14 July shows:

  • the huge variability of available power input from the 19 Gigawatts of UK installed wind power.  The variation ranges from about 0.1 Gigawatts to 13.0 Gigawatts even over the course of a single day.  The low level of actual Wind generation over the first two days of this 3 day period clearly gives the lie to the myth that “the wind is always blowing somewhere”.  For the three days 12 -14 July wind power capacity was 4.4% and it achieved only 2.8% of UK demand
  • the intermittent diurnal solar PV generation clearly attenuated somewhat on the Saturday by cloudy weather, generated from some 13 Gigawatt of installed Solar  PV installations.  The variation ranges from nil generation at night to up to 60% capacity at noon on fine summer days.
  • the very limited amount of hydroelectricity and pumped storage power available in the UK.
  • the variability of the generation from Gas-firing / CCGT to load follow the variations induced by the mandatory use of Wind and Solar generation whenever available can be extreme.  This intensely variable use of Gas-firing is inefficient and creates more unnecessary CO2 output to have a quickly available spinning reserve than running the plant continuously at full power and ignoring the Weather Dependent input if and when available.
  • there is occasional but minimal use of Coal for generation even though the summer period is a low demand season.
  • it should be noted that in 2017 there was substantially more generation from Coal-fired plants, this has been curtailed in 2018 thus loosing significant base load power input.  This essential input has been replaced by imports form France and Holland.
  • Native Nuclear energy still supplies a quarter of all the power in the UK.  As these plants are reaching the end of their service lives, their replacement for base load provision is progressively becoming more essential to avoid grid failure.
  • Interconnectors from France and the Netherlands in this low demand season are providing a very substantial proportion of UK power, (~9%).  This implies that about 1/3 of total UK power is presently provided by Nuclear energy, either locally or from the continent.
  • it should not be assumed that power imports are inevitably available, the availability of imports is not necessarily guaranteed.  French government policy is to reduce its Nuclear generation by about 1/3 to 50% of French generation.  If France requires that remaining power to service its local needs, it will not be available for export.  As it seems to be Government policy to impede further development this crucial Nuclear base load power source the UK is facing a substantial future supply crisis in power generation.
  • the electrical generation from “biomass”.  This is mainly the output of the Drax power site.  With substantial subsidies, this major UK power generation site has been converted to burn wood pellets.  They are imported from the East coast of the USA where clear felling of virgin forest, with resulting habitat loss, is continuing apace to meet this demand.  The combined processes of felling, pelletisation, sea transport, and wood burning immediately releases more CO2 per unit of power generated than the burning of Coal at Drax.  As Drax itself is located on very large Coal reserves this would seem to be a fatuous mechanism to control climate change.  The recovery of the American forest will take at least a century.

Screen Shot 2018-08-22 at 14.54.13.pngFrom the huge variability arising from Weather Dependence how here it should be clear that Renewables are not capable of providing sufficiently consistent power to be relied upon to supply a developed Nation.  Biomass burning is of course the only dispatchable form of “Green” generation, which is capable of being responsive to variations in demand.

Capacity and Demand percentages

The following diagram show the percentage of Weather Dependent Renewables supply in terms of the capacity percentage of Weather Dependent Renewables.

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The month of July 2018 showed the following Wind power statistics:

  • 92% of the hours in the month were below the 2017 annual average Wind capacity level of 27%
  • 55% of the hours in the month were below 10% Wind capacity level
  • 29% of the hours in the month were below 5% Wind capacity level
  • 9% of the hours in the month were below 2% Wind capacity level
  • the significant variability can be seen towards the end of the month with wind capacity figures ranging from ~10% to ~45% within 12 hours.

On the other hand July 2018 was exceptional for Solar productivity:

  • normal annual capacity accounting for the diurnal nature of Solar power and the seasonal variations over the year being ~11%.
  • the Solar capacity value for the month achieved ~21%
  • on brief occasions on 5 days during the month Solar capacity exceeded 70% for an hour or so at noon and Solar output exceeded 50% ~17% of the time.
  • July 29th was a cloudy, windy day and Solar briefly peaked at 20% capacity but Wind power achieved ~50% for several hours.
  • the diagram above shows the vast variability of Solar power ranging from nil at night to in excess of ~50% capacity on sunny days.

There diagram below shows the percentage of Renewables output when compared to actual electrical demand in July 2018:

Screen Shot 2018-08-25 at 15.57.11.png

  • Wind power was less than 5% of demand 51% of the time.
  • Wind power was less than 10% of demand 80% of the time.
  • Wind power actually achieved the average 2017 capacity level of 27% only 8% of the time in July 2018.
  • the diagram above shows the vast variability of Solar power ranging from nil at night to in excess of ~25% of demand at noon on some sunny days.

On the other hand July 2018 was exceptional for Solar productivity:

  • Solar power in this maximum month for Solar generation exceeded 25% of demand on one occasion around noon and in excess of 20% of demand on 11 days.
  • the times that this performance occurred were ~6% of the hours in the month.



July is a comparatively low demand month for electricity in the UK.  The UK has already invested in and installed ~32 Gigawatts of nameplate capacity of Weather Dependent Renewables, Wind 19.0GW and Solar PV 12.8GW:  this level of installation would account for some 85% of the UK power needs, were Renewables fully productive all the time.  The performance over the month of July 2018 shows how unpredictably intermittent and unproductive Weather Dependent Renewables really are.

Accordingly one can conclude from July 2018:

  • Wind power in July was very variable with a protracted period from 3/7/2018 to 27/7/2018 of Wind Drought where it was producing less than 5% of demand and on several occasions reducing to as little as ~1% of demand

  • at the same time Solar power in this highly productive period nonetheless it never exceed 10% of daily demand.

Screen Shot 2018-08-22 at 10.48.15.png

  • Solar power is diurnally intermittent and its peak production around noon does not match well with peak demand, which is usually in the evenings.
  • the impact of cloudy weather on Solar production can clearly be seen on 29/7/2018 where Solar production is suddenly only about 1/4 of it maximum output capability.
  • in total the contribution to demand from Weather Dependent Renewables ranged from ~5% to ~35% over a period of about 12 hours
  • 24.2% of UK generation came from native Nuclear generation
  • a further 8.6% was essential coming from French and Dutch inter-connectors amounting to ~3.2 Gigawatts, this is close to the maximum available interconnecter load.
  • thus total Nuclear generation supporting the UK power grid was about 32.8%.
  • 8.6% of power demand from overseas generation sources represents an existential National emergency, as the availability of inter connection power is not guaranteed and this is becoming particularly questionable as French Nuclear policy is now to reduce its Nuclear generation capability from 75% at present to 50% the near future.
  • the largest generation source was Gas-fired CCGT at more than  50%.
  • in order to load follow to compensate for the variability of the Weather Dependent Renewables power input, the Gas-fired stations have to be maintained as spinning reserve:  this is inefficient, costly and generates extra CO2 emissions unnecessarily.

To understand the excess costs of using Renewables as opposed to maximising generation by Gas-firing see:

To quote the late Professor David Mackay

“an appalling delusion”.