Solar Power

From Factsheets: Limiting UK Emissions
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So how much sun do we get in the UK? Using this tool [1] FLUKE has created graphics for the average mid-day intensity of sunlight month-by-month and also the total monthly sunlight received

The sunlight intensity around noon averaged 700 W/m² over May 2016 making it the sunniest month that year, although individual days had more intense noon sunshine. Sunlight intensity exceeded 1,000 W per square metre on 36 days; but on no day did it reach 1,100 W. Note that the rated power of a solar PV panel is based on it receiving 1,000 W/m² of sunlight. So for example a 150Wp Solar PV panel RS Components Model 9046156[2] measuring 1.49m x 0.67m (area of 1 square metre) is rated 150 Wp (p standing for 'peak') with an implied efficiency of 15% (although the brochure states 17%)
The monthly figures are cumulative and also confirm May to be the sunniest in 2016 with 170 kW-h/m². At 15% efficiency this will have generated 25.5 kW-h/m² of electricity. Multiplying this figure by 1000 to convert to Watts and dividing by 31 days and by 24 hours the average power output over the whole month (sunniest of the year), day and night for a "150W" panel is 34W
Another way to look at the figures: for 4 hours around noon, if the panel received the average 700W of sunlight and produced 15% as electricity (105 W / 0.105 kW) then 4 hours x 31 days x 0.105 W = 13 kW-h/m² which is half the monthly total. Half the electricity is produced over a four hour slot (1/6 of a day), the rest over the remaining 5/6. To effectively 'smooth' the power over 24 hours you would need to be storing approaching 50% of the energy produced at the peak period
Compensating for the lack of sunlight at night by using battery storage is therefore technically possible although expensive. However the monthly graphic shows that across seasons there is a four-fold difference in the energy received from the sun (170 kW-h/m² in May compared to 40 kW-h/m² for December or January). Inclement weather (more dull days in winter) plays a role but the root cause is the geometry of the Earth's orbit about the sun. The 23.5° inclination of the Earth's axis means the North pole point towards the sun in summer and away in winter resulting in the:

  • short winter days
  • sun low in the sky during winter

we're all familiar with

In conclusion

Solar PV can produce significant amounts of electricity under the most favourable conditions (sunny summer days a few hours either side of noon) but is subject to peaks and troughs (including zero output) across both 24 hours period and across the seasons.


  1. Photovoltaic Geographical Information System
  2. RS Pro Datasheet 12V Solar Panels