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Renewable Energy

The following article was researched and written in March 2013 by a member of our committee with input from a second committee member - both have strong scientific backgrounds. As you will see, the article draws on a variety of sources which are duly acknowledged. It was written, and published here, to help inform members of our community. It aims to be totally factual but inevitably contains some personal opinions.
The article makes reference to material from a recent presentation by Lord Stern. To watch the whole presentation go to http://www.youtube.com/watch?v=0S-QcOsOoRs&feature=youtu.be

 Renewable energy in the UK


Levels of carbon dioxide in the Earth’s atmosphere have now reached nearly 400 parts per million, higher than at any time in the last 800,000 years.  Carbon dioxide (CO2) is a `greenhouse’ gas that traps the sun’s energy causing the planet to heat up.  We can already see the effects as average global temperatures have risen by about 0.8°C since 1850 and 0.6°C in the last 40 years alone.  This may not sound much but in the past such changes have normally happened over tens of thousands of years so the changes we are seeing are very rapid indeed on a geological timescale.  Arctic ice is melting far quicker than expected and sea levels are now rising at about 3 mm per year, equivalent to just over one foot per century.  There is serious concern that sea level rises far greater than this will occur this century if the major ice sheets disintegrate.


From James Hansen’s webpage at http://www.columbia.edu/~mhs119/Temperature/

Many countries including the UK are committed to reducing their output of CO2 in an attempt to avoid the catastrophic effects of climate instability that some consider inevitable if we continue with `business as usual’. The government policy is to invest in low-carbon energy sources, improve fuel standards in cars and increase energy efficiency wherever possible. A target has been set to obtain 15 per cent of UK’s energy from `renewables’ by 2020. There are many definitions of renewable energy but generally it is taken to mean energy that does not run out because it comes from unlimited or constantly replenished sources such as sunlight, wind, rain, tides, waves and geothermal heat. It does not include energy from fossil fuels or nuclear reactors.
The total amount of electricity generated in the UK in 2011 was about 370 Terrawatt hours (One TWh is equal to one billion kWh). This generated about 180 million tonnes of
CO2 equivalent.
The total emissions of CO2 in 2011 from all sources including transport, manufacture, agriculture, domestic and so on were 459 million tonnes (Department of Energy & Climate Change. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/73148/050213_Ghg_National_Statistics_release__2011_final_results_.pdf  )Replacing the burning of coal or gas by energy obtained from renewable sources would certainly help reduce CO2 emissions but it is often not clear how much progress is being made in this direction, or how much energy might realistically be obtained from renewables. For example, plans for new wind turbines are often accompanied by statements that they `will provide power for 10,000 homes (or whatever)’ which sounds impressive but does not convey how this output compares with that from a conventional power station or how much it contributes to the nation’s total electricity supply. The following notes are an attempt to provide a brief perspective on generation of electricity from renewable energy in the UK. Please note that other sources of CO2 emissions such as transport are not considered here.


How we stand today

Renewable energy presently contributes about 10% to total UK energy supplies. This has been increasing slowly in recent years as shown in the following graph.

The breakdown of UK renewable energy by source is shown in the figures below. These are based on information published by the Department of Energy and Climate Change (DECC). https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/65850/5956-dukes-2012-chapter-6-renewable.pdf (Table 6.4 of the Report). Note that the information presented in the various government reports can be confusing because the data are presented in several different ways. Some summaries are based on `inputs’ meaning sources used for generation. These do not allow for losses incurred during generation (e.g. in electricity generated from combustion of waste). The following figures relate to actual electricity generated from each source.

Most energy comes from `bioenergy’ followed by onshore wind which currently exceeds that from offshore wind.  Photovoltaic energy contributes very little at present. 

The breakdown of the bioenergy component is shown below.

How does the UK compare with other countries?

The following figure shows how we compare with other countries. This information came from an article in New Scientist of 5th January 2013.  Data for Europe can be seen at: http://epp.eurostat.ec.europa.eu/tgm/table.do?tab=table&init=1&plugin=1&language=en&pcode=tsdcc330.

In Sweden and Norway most renewable energy comes from hydroelectric plants (88% in Norway, 65% in Sweden) whilst in Spain about 25% is from hydro, 25% from wind and 40% from combustion of biomass and waste.

Comments on some of the sources of renewable energy

Wind power

In December 2011 UK had a generating capacity of 4.6 GW from onshore wind turbines and 1.8 GW from offshore turbines. The Government target is for 18 GW total capacity by 2020. Variability in the amount of wind blowing means that this theoretical maximum generating capacity is never achieved.  The percentage of electricity generated relative the maximum capacity is known as the load factor and for wind this is about 30%.  The actual amount of electricity generated from wind in 2011 was 15.5 TWh representing about 4.2% of total UK consumption.

How many turbines would be needed to supply all our electricity? The largest onshore turbines currently deliver 2.5 MW and offshore ones up to 5.0 MW, though bigger 10 MW ones are being designed. If, for the sake of argument, we assume that large 5 MW turbines were to be used then we would need about 25,000 to supply all our electricity (see Appendix 1). Getting planning permission for, and building this number would clearly be a challenge.

Photovoltaic energy

The average amount of solar energy falling on the UK is about 100 Watts per square metre so in a year this amounts to 876 kWh.  Theoretically, if we could capture and store all this energy we would need an area of about 420 square kilometres, slightly larger than the Isle of Wight to supply all the UK’s electricity.  In practice we can only capture a fraction of the energy - typically about 20% for the more expensive panels so the area needed increases to 2100 square kilometres - about as big as Leicestershire. In practice the nominal efficiency of solar panels is reduced by shading of panels and reduced efficiency in hot weather. The theoretical maximum efficiency of energy capture for photovoltaic cells is 60%.  The best achieved so far is 40% but the technology required to do this is quite sophisticated and much too expensive for large scale production. However this is a very active area of research and improvements in performance with cheaper materials can be expected.

A major problem with both the above forms of renewable energy is that output varies considerably under different weather condition.  Apart from pumped storage hydro there are few methods of storing energy e.g. under very sunny or windy conditions and conventional power stations cannot be readily switched off and on.  Hence such renewable sources can potentially cause problems in balancing supply with demand

Biofuel crops

Plants capture the sun’s energy and use it to make biomass from carbon dioxide and water. The biomass can be burned to provide energy with no net release of CO2.  The conversion of CO2 and water to biomass is only about 0.5% efficient in biofuel crops grown in Europe.  If we perform the same calculation for plant biofuels plants as for photovoltaics above we find that the land area needed to capture the energy is 84,475 square kilometres-about the size of Scotland.  In addition, growth of crops such as willow or corn specifically for fuel production uses valuable, scarce supplies of fertiliser and fertile land needed for food production and a balance between competing priorities is required.


Bioenergy makes up a large proportion of the renewable energy budget of many countries. The inclusion of bioenergy as a genuinely renewable source is questionable because, with some sources, such as municipal waste, the amount of energy generated by combustion will be much less than the energy originally used to manufacture or create the material being burned so there is no net gain in energy captured. Nevertheless Bioenergy sources capture quite large amounts of energy that would otherwise be completely wasted.


Nuclear reactors are low-carbon sources of energy but are not included in the renewables statistics.  Currently, there are 16 operating reactors in the UK producing around 20% of the nation’s electricity.  Since the 1990s there has been a steady decline in electricity generated from nuclear power stations in the UK reaching a low of 13 per cent in 2008 due to maintenance shutdowns.  France gets three quarters of its power from nuclear energy from 58 nuclear reactors.   Belgium, Bulgaria, Czech Republic, Hungary, Slovakia, South Korea, Sweden, Switzerland, Slovenia and Ukraine get one third of their electricity from nuclear and the USA gets about 20%. (World Nuclear Forum http://www.world-nuclear.org/info/inf84.html )

All but one of the existing power stations in the UK are due to close by 2023.  Nuclear energy of course has its problems, particularly the public fear of serious accidents involving release of radiation, problems of disposing of radioactive waste and decommissioning costs.   Although the accidents at Chernobyl and Fukushima have caused general alarm over nuclear safety, the actual number of people who have died or developed cancer as result is very much less than generally perceived.  When viewed objectively nuclear power has had a good safety record when compared with other forms of electricity generation such as coal.  This needs to be considered against the implications of their being a major shortfall in energy supply.  There are however problems associated with the costs waste disposal and decommissioning. These can be dealt from a technical point of view but government and the industry have failed to grasp the nettle and make long term strategic decisions.  (Nuclear power will be discussed in a future notes from Cold Ash Greening.)  Following the Fukushima accident Germany decided to replace its nuclear power stations by coal-powered ones.  One estimate suggests that by 2020 Germany will have produced an extra 300 million tonnes of CO2 as a result of its nuclear closure, equivalent to almost all the savings that will be made in the 27 member states as a result of the EU’s energy efficiency directive http://www.monbiot.com/2013/02/04/out-of-steam/. 


These notes have highlighted some of the problems of generating electricity from renewable sources.  The main problem is that industrialised countries use massive amounts of energy and renewables are not a concentrated source of energy. Energy capture therefore takes up a lot of land area.  For example you would need about 400 onshore wind turbines to replace a typical power station.  However, in terms of planning for a low carbon future, all forms of energy generation have attendant practical problems. For example if we wished to copy France and generate most of our electricity from nuclear we would need to build another 40 nuclear power stations.  According to the eminent economist Lord Stern what is needed is a much clearer and more consistent government energy policy that will give industry the confidence to invest in low carbon sources of energy.  Also needed is a coherent strategy concerning the most appropriate balance of methods of energy generation. Lord Stern also believes that politicians and others need to understand and promote the scientific arguments as to why urgent action is needed on climate change, and examples of what can be achieved need to be presented to the public.

An excellent analysis of how renewables along with nuclear energy might provide low carbon energy is given in the book by Professor David Mackay (see Further reading below) who  is the Chief Scientific Advisor at the Department of Energy & Climate Change (DECC).  He is also Professor of Natural Philosophy in the Department of Physics at the University of Cambridge. He presents several possible plans each of which has advantages and drawbacks. Two of these are shown in the table below.


Note that David Mackay’s tables refer total energy requirements whereas these notes deal only with electricity generation.  The Department of Energy & Climate Change also has a calculator that allows you to simulate what a low-carbon UK might look like in 2050. https://www.gov.uk/2050-pathways-analysis.

A positive final thought is that micro-renewables are likely to play a very important part in developing countries, particularly in rural areas that have no electricity supply whatsoever. Solar panels and small wind-turbines are proving very useful in pumping water from boreholes and wells.  Portable solar-powered LED lights are being sold in Kenya and other Africa countries. These provide much better light and are cheaper than polluting paraffin lamps and can also be used to charge mobile phones.  Schools have reported that this has had a beneficial effect on education by enabling children to do their homework when light would not otherwise be available.  Other products are being developed to power computers. It is believed that this will be an extremely good way of aiding development by allowing people to participate in the `knowledge economy’.

Books and websites

1.       https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/65818/5955-dukes-2012-chapter-5-electricity.pdf 

2.       http://epp.eurostat.ec.europa.eu/statistics_explained/index.php/Renewable_energy_statistics

3.       David Mackay. Sustainable energy-without the hot air. UIT Cambridge England 2009. Available free to download at http://www.withouthotair.com/ 

4.       Nicholas Stern (2009) A blueprint for a safer planet. Bodley Head, London.


Appendix 1

Each turbine would generate a maximum of 5 x 365 x 24 MWh per year  = 43,800 MWh

= 0.0438 TWh 

Allowing for 30% load factor this is reduced to 0.0438 x 0.3                       = 0.013 TWh

Total electricity used in UK                                                                            = 370 TWh

Therefore to supply all our electricity we would need 370/0.013                  = 25,461 turbines.



Photovoltaic (PV)

Are you considering generating electricity yourself, possible using Photovoltaic cells, but are mystified by all the jargon? If so, see the attached document from The Greening Campaign that explains all.

Robert Pattison,
30 Dec 2010, 05:17