Curtailment of energy can be defined as involuntary reduction in the output of the power plant from what it could produce in normal conditions. Curtailment of energy generation is generally observed in non-dispatchable renewable sources like wind, solar and wave. This issue can be regarded as one of the biggest disadvantages of renewable energy supply systems, so this is significant to address such problem and try to find solutions.
When these non-dispatchable renewable energy sources are considered, solar energy tends to form ‘embedded generation’ at local level and is well integrated into the distribution network. Wind is by far the most extensive new large-scale renewable energy resource in UK, so in UK the energy curtailment mostly occurs in wind energy generation.
Grid operators command wind generators to reduce their outputs for two main reasons; first to minimize transmission congestion and secondly to prevent penetration of oversupply into the grid. Transmission congestion generally occurs with wind farms that are located far from cities or towns. For those places transmission lines are generally weak, because the small local population required comparatively weak transmission lines to be installed before the construction of wind farm. Thus, during the times of full capacity generations from the wind farm, they may be asked to reduce their output to prevent overload and any damage to the transmission system. In the other case, when the demand is low or base load generators’ minimum generation thresholds are enough to cover demand, wind farms are asked to reduce their output to prevent oversupply because of frequency or voltage balance or interconnection issues. The oversupply curtailment generally occurs during night time when there is a abundance of wind resource available, but the demand is considerably lower than in daytime. Apart from these main curtailment reasons, environmental reasons such as birds and bats in migration, unusual meteorological conditions and similar issues might cause curtailment.
In order to understand curtailed wind energy in UK, as a first step ‘Transmission and Distribution’ system should be understood. The main duty of the transmission system in UK is to deliver generated electricity from large generation systems to the distribution networks. Transmission and distribution systems are connected at a point which is known as a ‘Grid Supply Point’ (GSP), so each distribution system is known as a GSP group. GSP groups and their distribution over regions are as shown in Map-1. Smaller power sources such as combined heat and power, solar power and some wind turbines (approximately one third of the total installed capacity) are connected to the Distribution Network, in other words the low voltage network. Roughly two thirds of the total installed wind capacity in UK consists of large wind farms and these are connected to the Transmission Network, i.e. the high voltage network. Nuclear, gas and coal fired power stations are other participants of the Transmission Network. Transmission Network participants are members of a trading system of National Grid which is known as the ‘Balancing Mechanism’ (BM).
Curtailment of wind generation is arranged by the BM. As wind energy generation increases, curtailment is becoming more widespread. Curtailment affects the energy output of the wind farm therefore it affects the revenue and related financial liabilities of the wind farm. To compensate wind farms for losses caused by curtailment, National Grid makes payments to the wind farms. These payments are known as ‘Constrained Payments’. National Grid has been making constrained payments to the wind farms since 2010. Before that time, gas and coal power stations might be called for output reduction. Renewable Energy Foundation (REF) records data from the BM which includes wind farm constraint payments and volume of constrained wind generation from 2010 to date. The data is sourced variously from Renewables Obligation Certificates, Renewable Energy Guarantees of Origin and in the case of some municipal waste generation, from Climate Change Levy Exemption Certificates. According to REF, the annual data of curtailed wind energy is as shown in Table-1 below,
Note that constraint volumes and constraint payments shared above only include the trades carried out as a part of the BM. There might be further constraints that are based on private contracts between National Grid and the generators which are not published or available to the public. As can be seen understood, the amount of curtailed wind generation has increased with the increase in installed capacity. Table-2 shows the comparison of total produced wind energy and the volume of curtailed wind generation.
Total Produced Wind Energy (GWh)
Volume of Curtailed Wind Energy (GWh)
Curtailment Ratio (%)
Table-2: Comparison of produced vs curtailed wind energy
The ratio of volume of curtailed wind generation and produced wind energy varies over the years. Figure-1 shows the change in ratio of produced vs curtailed wind energy according to years.
Figure-1 shows that the increase in wind energy penetration into the grid resulted in an increase in curtailed wind energy. The main point is that curtailed wind energy increases faster than the increase in capacity of generation, so it is seen as the increase in ratio. Future estimation of curtailment ratio is a challenging task, because supply and demand are two dynamic parameters which are also the main drivers of the curtailment. However, it is possible to make reasonable comments on the likely behaviour of the curtailment ratio in future.
 Due to aggregation of data and rounding of calculated results there may be small apparent inconsistencies
 There are missing data (Months of Jan, Feb and Mar) for 2011
The term ‘sustainability’ is firstly used in the Brudtland Report of 1987. In this report, sustainability is defined as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” Thus, following this definition, sustainable development can be understood as any action on behalf of development must meet the needs of present by not having negative impacts on future generations. After the emergence of the term ‘Sustainable Development’, many frameworks about the concept have been thought and put forward. In Brudtland Report, sustainable development is found in the intersection set of three mutually dependent areas of sustainability which are environmental, social and economic. What is important about these areas is any change in one area will disturb the other two. So, their effects overlap.
Energy is a key element of economic development, key factor of environmental concerns and vital for social welfare. Hence, energy can be regarded as the most important element of the concept of sustainable development and it can be shown as the most significant point of intersection set of three mutually dependent areas of sustainability. Due to highly invested know-how in extraction of fossil sources and developed industry to use them as fuels lead Energy Sector to grow through non-renewable generation in last two centuries. This phenomenon proceeded until 1973 Oil Crisis. Such a big crisis raised a resource security question in developed countries. The question leads a development in renewable energy sector. However, today the vast majority of the energy generation is still supplied by fossil fuels. When the Brudtland’s three mutually dependent areas are taken into account, it is not possible to achieve sustainable development with energy generation by fossil fuels, because any change in one area must not impact any other in a negative way. When we look into the energy generation from fossil fuels, we simply realize that non-renewable energy generation can accelerate economic growth while it produces harmful emissions for environment and social well-being. Thus, the basic requirement of sustainable development is failed due to the high demand on fossil fuel energy generation.
According to US Energy Information Administration (EIA) in 2008, total primary energy consumption of world was 485.718 Quadrillion Btu (British Thermal Units) and in 2012 that became 524.076 Quadrillion Btu and due to increase in technological developments, industry and access to electricity, this value keeps growing by every seconds. Thus, the required energy must be supplied by other type of sources. As it is mentioned, supplying energy by fossil fuels is violating the nature of sustainable development. After the rising of the concept of renewable energy, it becomes a strong candidate to replace fossil fuel domination in energy market. However, can renewable energy generation meet the basic requirements of sustainable development? This report argues how renewable energy affects the sustainable development considering the three mutually dependent areas (environmental, social and economic) of Brudtland Report.
When the environmental effects of an energy system are taken into account, as a first step the effects on ‘global warming’ is considered. Then, the effects on air, water and soil can be thought and finally the impacts on animals and plants are taken the place. For mostly used and different kinds of renewable energy resources, their direct environmental impacts can be seen in Table-1 below:
Impacts on Global Warming
Impacts on Air,Water,Soil
Impacts on other living creatures
Solar Power(PV and CSP)
No Pollution – Land use for PV 3.5-10 acre/MW For CSP 4-16.5acre/MW
Occupied land cannot be used for agriculture during operation.
No Pollution – Land use 1 acre/MW
Bird and Bat deaths from collision
No Pollution – possible conflict with fishing and shipping
Possible damage to marine habitat during construction
No Pollution – Flooding of useful area in large scale deployments
Fish and other organisms might be injured and killed by turbine blades
No for closed loop systems- Open loop systems emit H2S, CO2, CH4,NH3
No Pollution for closed loop Systems- Open loop systems emit H2S which causes acidic particulates in atmosphere
No Effects for closed loop systems – Acidic particulates caused by open loop systems damage crops,forests,soil, lakes and streams
Combustion produces CO2, but the amount released equals to amount absorbed during growth
Table-1: Environmental Impacts of different kind of renewable sources 
As it can be seen from the Table-1, in terms of greenhouse effects which cause global warming, the only risk is caused by open loop geothermal power plants. The problem can be overcome by building geothermal power plants as closed loop systems. However, if it is not possible, the most effective filters can be used to capture H2S which might decrease their impacts importantly. On the other hand, none of the renewable resources do not cause environmental pollution, except Tidal/Wave and Hydro power sources. Possible conflicts arising from fishing and shipping can be overcome with policy regularities, but flooding big amount of area can be regarded as a considerable problem for useful lands. When the impacts on other living creatures are examined, the point of birth and bat deaths from collision is noticed. This has been argued by some environmental circles. About this issue David MacKay notes that “It’s been estimated that 30.000 birds per year are killed by wind turbines in Denmark where windmills generate 9% of the electricity. Horror! Ban windmills! We also learn, moreover, that traffic kills one million birds per year in Denmark. Thirty-times-greater horror!”  When the benefits of the cars are taken into account, no one would think of banning them from a country, because of its effects on birds. Hence, arguing about impacts of wind mills on birds and bats is as meaningless as the effects of cars on birds. The effects of hydro plants on fish are also given in the table in the same equation with previous wind turbine case. Therefore, if geothermal power plants are built as closed loop systems and large scale hydro plants would not cause floods; renewable energy generation will cause zero environmental effects which means that sustainable environment can be achieved by renewable energy generations.
The social aspects of human life have been debated as ‘basic’, so when basic requirements are met, then other needs can be considered. The term ‘basic’ is understood within different concepts, but the undeniable and the most ‘basic’ need of human is security and health. The air pollution which is caused by fossil fuels is one of the most controversial topics of the recent news around the world. Many countries like China, India, Italy, England, etc. declare ‘high alert air pollution’ for some of their metropolises. According to U.N, about 3.5 million deaths a year are caused by indoor air pollution while another 3.3 million are caused by outdoor air pollution which means air pollution kills more people than AIDS and malaria combined. Besides these death rates, Scientific American released the data of death rates from energy production accidents among OECD countries which is shown in Table-2:
Deaths from Energy Production Accidents (per 100 GW of power generated for a year)
Table-2: Death rates from energy production accidents among OECD countries
When the provided data are examined, the danger of fossil fuel generation for health and related safety risks can be understood. Also, when zero air pollution and the least death rates about energy production accidents are taken into account, the respect of renewable energy towards the most ‘basic’ and the most important social aspect of human life can be realized. One would consider that in 21st century, electricity access should be regarded as another basic right of human. This is because access to electricity is important for the provision of clean water, leads huge improvements in health services and reduces poverty so that it boosts the quality of human life. However, today around 1.1 billion people still do not have access to electricity which corresponds to 20% of the world population. The costs of grid extension and conventional power generation are still considerable challenges for some developing countries. Moreover, the rapid population growth leads to increase the number of people who lives under the same poor life conditions. In order to overcome this challenge, investments in small scales renewable energy supplies and micro scale grids can be regarded as the best possible solution. In IEA’s World Energy Outlook (2015) , it is noted that power generation projections under the new policies scenario for methodology for energy access analysis, the rural generation is divided between mini-grids and off-grid generation, including oil, solar PV, mini-hydro, wind and bioenergy in the mix.  Although, IEA pointed out that using oil and bioenergy as an electricity generation method, their maintenance costs may not be coverable by the people of developing areas. Thus, the most feasible solutions for them are other renewable sources which are noted in the list. To conclude, one can understood that the renewables are the most supportive type of energy generation in terms of promoting social welfare.
The effects of renewable energy deployment on sustainable economic development might be the most controversial part of this topic. High initial investment costs per kW, reliability problems which occurred due to intermittencies in supply and non-dispatchable generation in most of the renewable energy technologies are noted as the negative impacts on sustainable economic development. However, when the concept is taking into account from a broad perspective, it can be understood that sustainable economic growth can be gained in long term. Researches show that the effect of traditional energy sources is statistically significant and positive in sustainable economic development and among the fossil fuels, oil is the one that has mostly contributed to economic growth. In recent days, since the volatile prices of oil, the world is witnessing hard times of some exporter countries. Fixed prices and long term contracts of renewable energy generation keep the suppliers and customers from volatile prices. Therefore, the country does not face with economic crises which are related with the devaluation in prices of an energy supply. There is also a hidden cost of fossil fuel energy generation. As it is mentioned in previous part, there are significant health impacts of fossil fuel emissions on people’s health and the hidden cost of this health impacts can lead to irrevocable consequences. A recent study about how much would electricity cost in US if the retail price reflected the health impacts of burning fossil fuels shows that accounting for such costs would add an average of 14 to 35 cents per kilowatt-hour to retail cost of electricity.(2013) When the hidden cost is taken into account as nationwide, these hidden health costs add up to as much as $886.5 billion annually, or 6% of GDP. Since, renewable energy systems has not any negative impacts on health, there is no need to consider such kind of hidden costs. Another positive impact of renewable energy on economic growth is that it promotes employment. Worldwide renewable job creation has been compiled by the Renewable Energy Agency (IRENA,2013). Various kinds of renewable sources provide employment opportunities. Table-3 shows the total direct and indirect employment in renewable energy sector for selected countries and world.
Table-3: Employment in Renewable Energy Globally and for Selected Countries(result/1000 people)
As it can be seen from the Table-3, in 2013 renewable energy sector promoted 5279000 jobs in worldwide. Thus, it creates not only a big opportunity for economic welfare but also increase the employment rate of individuals which will result in economic development of the countries.
To conclude, this report discussed the effects of renewable energy sources in the eyes of economic, social and environmental aspects of sustainable development. As a result, it is now clear that among energy supply resources, renewable energy can be regarded as the most suitable source for sustainable development. Repeatedly, parallel to the definition of sustainability, renewable energy brings development without giving any harm to future generations. So, in order to achieve sustainable development, one can be sure that alternative energy resources bring social, economic and environmental sustainability which can be achieved by renewable energy generation.