Showing what a mismatch PV generation is compared with our demand across the year is one thing, but what about comparing production and demand for all the days through the year?  Does it at least generate each day when we need it?

I have not seen this done before either, but it isn’t difficult and is hugely important.  To demonstrate the effect I have taken both the extremes and the average so we will analyse 21st June (the peak day for solar power); 21st December (when it is at minimum), and 21st March or 21st September (and here we have the precise data for 21/3).

The amount of electricity we use is easy as The National Grid has very precise data and publishes it live.  The amount produced has to be considered in two stages:

  1. Assuming the sun is shining across the whole of GB from dawn to dusk (even on 21st December).
  2. Taking what is analysed as the mean annual production of PV units which allows for average weather.

As Government wants lots of us to install it, and as this is precisely representative, we will assume here that enough PV is fitted to almost cover peak demand at midday on 21st June – which is about 32Gw.  Please don’t worry about these Giga Watt units as everything here is in them so it is all directly comparable.  No maths is needed, but one Gw is 1,000,000,000 watts or about what one nuclear plant produces.

The amount PV can generate is also known as there is more light in the middle of the day than early or late – and none before dawn or after dusk.  Much fuller figures and explanations are given on – hyperlink – but as this is a Blog, the 3 charts are shown beside each other:

21st June                                            21st April                               21st December

The black upper line shows demand through the day, and the red curve shows how much 32Gw of PV could generate at maximum.

The power produced by PV is the area with black and red cross hatching.  The amount of power other generators must produce is the area with vertical black lines only.  And all these charts assume wall to wall sunshine across the whole of GB.

So on 21st June PV could produce 42% of all the electricity we need (2/5), but will the same wall to wall sunshine it is just 15.6% (1/6) on 21st April and a paltry 5% (1/20) on 21st December.

Taking the weather into account the output is of course considerably less.  Our annual demand is 383Tw.hrs, and all this PV could produce would be not more than 20Tw.hrs – or about 5% of our national electricity demand.

It seems to be proving difficult to find any aspect of PV that makes any sense, so the next Blog compares commercial scale wind with PV – for all factors – but all this is on the Brief – Hyperlink