The solar PV that the UK added between in the single year to March 2015 reduced overall UK power needs by 2.6% in spring this year. Over the daylight portion of the day the reduction was 4.3% between April/May 2014 and the same months a year later. In the early afternoon, when the sun is at its strongest, the reduction over the one year period was almost 7%.

PV is having a marked impact on UK electricity need. At 1.30pm, the typical April or May day saw a reduction of 2.6 GW in the total electricity supplied by the big generators. That’s after taking into account the higher winds this year and the overall fall in electricity demand.

This year compared to last year

I looked at the total amount of electricity being transported by the National Grid from big generators, including the large wind farms, coal stations, gas and nuclear. This number excludes solar and smaller wind farms which are connected to local electricity networks and which aren’t metered in real-time by National Grid. Electricity need is tending to fall across all parts of the year and was down about 1% in April and May compared to last year.

The wind blew a bit harder in spring this year. This matters because if small wind farms are producing lots of electricity the amount of power the big generators need to produce goes down. More power produced by local turbines further reduced the flow of electricity across the National Grid by about 0.7%, taking the reduction to 1.7%, before considering solar.

During the year from May 2014 to May 2015, the UK added slightly over 3 GW of solar PV. (For comparison, the UK’s biggest power station complex at Drax in Yorkshire has a maximum output of just under 4 GW). My estimate of the additional solar capacity isn’t firm. DECC produces estimates every month but I think it is falling to capture some of the new solar farms that were hastily installed across England in the weeks of February and March as developers raced to beat the end of the Renewable Obligation subsidy. I think the UK now has about 7.1 GW of solar, not the 6.5 GW that DECC says. (It’s only when the new farms finally get fully accredited at Ofgem that we’ll know who is right).

The other thing to mention was April and May were sunnier this year than last. The panels on my roof produced 27% more in April and 5% more in May than in 2014. When we look at the impact of PV on the electricity that the big fossil fuel generators needed to produce we have to remember that it was windier and sunnier and we had more turbines and a lot more PV.

Nevertheless, the results are impressive to look at. The chart below shows the how April/May 2015 compared to the same days last year. The world of electricity divides the day up into 48 half hour periods and in summer the peak output from solar is sometime just after 1pm BST. (Remember that most of the UK solar capacity sits slightly west of the Greenwich meridian and so the sun will be at its zenith after 1pm BST/noon GMT).

These figures contain an adjustment to ensure that both years have the same number of weekend and weekday days because weekends have lower demand.

In the dark hours the UK’s big power plants were producing about 98% percent of what they did in 2014. As the sun rose, the difference increased. In early afternoon, the average demand on the Grid was a little over 91% of what it was in 2014. The dip was well over 2 GW for several hours and peaked at 2.6 GW. If the weather’s OK, June, July and August will be the same.

A dent in overall electricity generation need was already apparent in 2014. This year, it had become far more obvious with the need for conventional power now falling sharply after 9 am. The usual early evening peak has disappeared because the sun is still shining when people come home, turn the TV on and cook dinner.

The pattern in the chart above is perfectly explicable because of the sunnier days of 2015 and the larger base of installed capacity. Sadly, the PV rush is over. Unless things change, we’ll only see a small increase in solar output each year. But if anyone ever says PV is irrelevant in the cloudy UK, you can show them this chart. Or take a look at www.solarforecast.co.uk where I use meteorological data to estimate how much electricity the UK’s PV will produce for the next five days. On the best days, we’ll see about 6 GW pouring into the electricity distribution system, as much as 25% of the UK’s need on sunny weekend day. Saturday doesn’t look too bad, with over 5 GW expected by my forecast and that of National Grid’s.