UK solar PV installation companies have been in the news for the wrong reasons. The reduction in subsidies has seen a number of companies go bust. Should we be bothered by this? Regular readers will be familiar with my opposition to installing solar PV panels on north facing roofs in a land where the sun seldom shines for 3 months of the year.
The UK National Grid publishes model data for solar production in the UK so we can get an idea how much electricity all those roof mounted panels produce. The model data are published with 30 minute resolution and I have chosen to graph all the data for 2014, the most recent year with full cover. The idea is to try and show graphically how useful solar PV is in a high latitude country like the UK.
A good starting point is to look at the contribution solar PV made to UK production in January 2014 (Figure 1).
Figure 1 According to The Renewable Energy Foundation (REF), the UK had about 2700 MW installed PV capacity in January 2014. And according to National Grid, this produced 54 MWh of electricity, equivalent to 0.19% of total UK demand. The small, barely visible, blips along the x-axis is the solar PV output. The load factor was 2.7%. Click all charts for a larger and readable version.
I wanted to chart all the solar data for 2014 to show how the output varies across the annual cycle of seasons. This is quite a charting challenge. I have plotted individual charts for each month and grouped them into threes below (Figures 2 to 5).
Figures 2 to 5 Working from top to bottom, installed PV capacity increased from 2691 MW at the beginning of January to 5131 MW at the end of December. The charts clearly show, as is to be expected, PV output increases in Summer and declines in Winter. There is substantial variability within any given month reflecting changes in cloud cover. In winter months, this cloud variation is up to a factor of 8. In summer months, the peaks are also much broader reflecting the longer days (Figure 6).
Figure 6 January and July 2014 compared. The January output has been grossed up by a factor 0f 1.45 to reflect the growth in installed capacity between January and July. The summer peaks are taller, more regular and broader. The January and July peaks are also offset by 1 hour, January operating on Greenwich Mean Time (GMT) and July operating on British Summer Time (BST). Peak winter demand is always around 6 pm. At that time in January, UK solar PV production is always zero since The Sun has already set. In mid-Summer, PV output is less than half the midday peak come 6 pm.
Generation varies in proportion to the amount of sunlight that is in turn controlled by the length of day, the height of The Sun above the horizon and the amount of cloud cover. In the winter months, all of these factors work against solar PV in the UK, hence winter generation is a fraction of summer generation. Correcting for the growth in installed capacity, July PV generation was 8 times higher than January generation in 2014.
The monthly vital statistics are summarised in the Table below. Capacity has been increased linearly from 2691 MW in January to 5131 MW in December. Capacity factor varies from a low of 2.44% in December to a high of 20.45% in July (Figure 7).
Table 1 Summary of generation statistics from National Grid. Installed capacity from REF. The National Grid generation data combined with the REF installed capacity data yields a solar PV load factor of 10.3% for the whole year. This compares with 10.8% published by DECC and 11.8% determined from REF data (see A Note on UK Renewable Load Factors) and with 10.1% estimated by Roger Andrews.
Figure 7 Seasonal variation in UK solar PV load factors plotted from Table 1. UK power demand is highest in winter and lowest in summer, negatively correlated with the above.
Quite often the sustainable renewables solution to inadequacy is to over dimension the infrastructure. In January 2014 there was 2.7 GW of installed capacity that produced 0.19% of power demand (Figure1). Let us imagine this was increased by a factor of 10. This would mean 27 GW of installed capacity – enough to cover 50% of UK demand at 100% load, but it would still provide just 1.9% of gross UK demand in January and 0% of peak demand.
It is this latter point that is important. The 6 pm maximum demand peak in winter months sets the capacity requirement for dispatchable UK generation (Figure 1). If solar could be relied upon to always provide some power at 6 pm in winter this would reduce the required capacity of conventional generators and replacing one with the other may have made some sense. But solar PV will never ever produce a Watt of power at 6 pm GMT in the UK in the winter months meaning that 100% backup will always be required.
One final consideration is the ERoEI for solar PV. Prieto and Hall have estimated, somewhat controversially, that solar PV in Spain has ERoEI of 2.5 and Spain is a sunny country. The load factor in Spain is estimated to be 18% compared with 10% in the UK. Adjusting ERoEI for load (10/18*2.5) ERoEI for solar PV in the UK would be of the order 1.4. Solar panels are made using fossil fuels. The CO2 from the manufacturing process is in the atmosphere today and it may take 15 to 20 years for the panels to offset this CO2 that has already been produced.
Concluding ThoughtsLow CO2 electricity for free sounds like a great idea and too good to be true. It is. There are undoubtedly niche applications for solar PV. The Space Station for one, although notably the Mars rover is powered by nuclear. Hobby Greens wanting to indulge their fantasy living off grid surrounded by a stack of toxic lead acid batteries, pretending to save the planet are welcome to do so, so long as they pay the costs themselves and do not expect everyone else join their delusional path.
There may be other niche applications for solar PV in developing, sunny, African countries where it may provide valuable electricity to power the local cell phone network or communal computer. And there may be grid scale applications in sunny lands, but if Prieto and Hall are correct, this too is questionable.
Deploying and subsidising grid-scale PV in the UK appears to be plain stupid, especially in a country like Scotland where it is doubtful that PV panels will ever repay the energy used to create them. They are likely making the problems they are designed to solve, worse.
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