Update 16/9/16 – Solar generated more electricity than coal during August. Its estimated 1,279 gigawatt hour (GWh) output in August was 1.5 times more than the 512GWh generated at coal-fired power stations. We’ve updated the charts below, including the first two weeks of September, when coal continued to be out-generated by solar.

Update 1/8/16 – Solar has once again generated more electricity across a whole month than coal. The estimated 1,273 gigawatt hours (GWh) of power generated by solar during July was two-thirds higher than the 778GWh output from coal. The charts below have been updated.

The UK’s solar panels generated more electricity than coal in May 2016, the first-ever calendar month to pass the milestone, Carbon Brief analysis shows. The feat was repeated in July.

Solar generated an estimated 1,336 gigawatt hours (GWh) of electricity in May, 50% more than the 893GWh output from coal. The finding follows on from Carbon Brief’s earlier analysis showing solar beating coal for the first full day on 9 April 2016, and for the first week from 3 May 2016.

While these milestones are largely symbolic, they do highlight the major changes going on in the UK electricity system. For further context, analysis and data details see the previous coverage from Carbon Brief.

UK monthly electricity from solar and coal

The chart below shows that solar generated 50% more electricity than coal during May 2016 and 64% more in July. This was due to a combination of low coal output and the impact of longer daylight hours.

Solar and coal shares of UK total

Total electricity generation from UK solar and coal during calendar months in 2016, gigawatt hours (GWh). Sources: Sheffield Solar and Gridwatch . Chart by Carbon Brief using Highcharts.

Solar generated nearly 6% of the UK’s electricity needs during May and July, against less than 4% for coal (see note below for details of this calculations). In January, the figures were just 1% for solar and 17% for coal. The solar share has hovered around 5-6% during May-July, whereas coal use has continued to fall.

There has been a huge reduction in coal-fired power generation in the UK since the start of 2016, as the chart below shows. Nearly a quarter of electricity generation in 2015 was from coal but since then, power market economics have shifted in favour of gas and several coal plants have opted to close.

UK weekly electricity from solar and coal

Shares of total UK electricity generation met by solar and coal during 2016 (%). Sources: Sheffield Solar and Gridwatch . Chart by Carbon Brief.

Solar has generated more electricity than coal in each of the past four weeks. Note that coal generation increased around the start of June, partly as a result of low wind power output.

UK daily electricity from solar and coal

Total electricity generation from UK solar and coal during each week from 1 April 2016, gigawatt hours (GWh). Sources: Sheffield Solar and Gridwatch . Chart by Carbon Brief.

Although solar cumulatively outpaced coal May and July, coal has topped solar on some days in those months, as the chart below shows.

The UK passed a historic milestone in mid-May as coal output hit zero on seven periods across the week commencing Monday 9 May. Total daily coal output was near zero during 12-14 May. The zero-coal periods were reported by the Financial Times, the Press Association, the Telegraph and others, citing Carbon Brief analysis.

Total electricity generation from UK solar and coal on each day from 1 April 2016, gigawatt hours (GWh). Sources: Sheffield Solar and Gridwatch . Chart by Carbon Brief.

Notes: The figures for shares of total UK electricity generation are estimates. They only include solar generation and other forms of generation that are connected to the transmission grid network. Embedded generation from wind or other sources is not centrally metered and data is not available. However, this missing data will not alter the relative positions of solar and coal generation.

Figures for solar output in the UK are estimates produced by Sheffield Solar. The project recently updated its estimates of installed UK solar capacity.

Main image: The solar panel of a parkmeter reflects the sky in a street of Durham, England. Credit: marcoventuriniautieri/Getty Images.

Note: Sheffield Solar recently updated its estimates of solar capacity in the UK.