Today was sunny. Most predictions were for at least 5 gigawatts of solar PV arriving into the UK electricity system. This number hasn’t been reached for almost six months. (My website at Solar Forecast was a little more conservative and I think the algorithm was too pessimistic).

The electricity market didn’t predict the abundance of sun. As a result, it was hugely oversupplied in the middle of the day. If you’d been buying, you could have bought electricity for less than £10 a megawatt hour (1p a kilowatt hour) in the early afternoon. In fact, for the entire day so far the system price has been less than £30, a strikingly unusual state of affairs.

Phil Harper wrote to me a few minutes ago pointing out that today was the first obvious sighting of the California Duck in the UK this year. Electricity demand in the middle of the day was seriously dented by the superabundance of PV-generated electricity, an increasingly important feature of the Californian power market from March to September. Last Monday, the UK need for electricity was flat from noon to late afternoon at around 40 gigawatts. Today, it dipped sharply as the sun burnt off the haze. At 14.30, demand for other sources of power was around 35 gigawatts over 5 gigawatts less than a week ago. (I do not know why demand remains somewhat lower even now at around 10pm).

The chart below shows the dent in demand. The pattern will get even clearer over the next six months. Some sources suggest that UK PV installations will top 10 gigawatts by mid year, meaning that early afternoon power needs will dip by at least 8 gigawatts below usual levels on very sunny days.

As usual, DECC is either disguising these numbers in its monthly releases or is still unable to cope with the rate of installation. Despite being warned by National Statistics for fiddling with its estimates, it continues to make huge ad hoc changes in its statistics from month to month without acknowledging its problems in keeping up with solar volumes.

Solar is making a significant difference to the operation of the UK electricity market.