Introduction and Disclaimer
By Campbell Dunford, CEO Renewable Energy Foundation
The issues of security of supply and climate change are now being taken more seriously than ever, and public interest in renewable energy is not only strong but increasingly sophisticated. With indirect subsidy approaching £1 billion a year being channelled towards renewable energy by the government’s Renewables Obligation there is a real need for more information about the performance of the various technologies now benefitting from this support mechanism.
While Ofgem publishes data concerning the issue of Renewables Obligation certificates to renewable electricity generators, the database is cumbersome and laborious to interrogate. The Renewable Energy Foundation has therefore commissioned Mr James Oswald and Mr Michael Raine of Oswald Consultancy Ltd to analyse the Ofgem database and re-present this public domain information in a user-friendly form, bringing it together with other public domain information concerning the generators.
The data will be available only in electronic form, as five files:
1. Biomass and Biomass Co-firing
3. Landfill gas
4. Sewage gas
5. Windpower (on-and offshore)
The analysis is based on data obtained from the Ofgem Renewables Obligation Certificate Register (http://www.rocregister.ofgem.gov.uk/main.asp). Further information, such as the installed capacities of the generators has also been obtained from Ofgem. All this information is in the public domain. REF and Oswald Consultancy Ltd have taken all reasonable measures to ensure that this information and the subsequent analysis is correct (errors and omissions are excepted).
The charts currently provided display data downloaded in May 2006, and do not include superannuated Renewables Obligation Certificates removed by Ofgem from the online register. We intend to include this information in the next issue of UK Renewable Energy Data, which will also be updated with more recent performance statistics.
The Renewable Energy Foundation is a registered charity funding research into renewable and alternative energy technologies and policy. We have no political affiliation and no corporate membership. None of our work could take place if it were not for generous private donations. I wish to take this opportunity of thanking all our donors for their continuing support, and in particular Mr Vincent Tchenguiz, who has funded the current project.
8 December 2006
About the charts
The charts in the REF UK Renewables Energy Data volumes present generation statistics, and are based on the publicly available monthly Renewables Obligation Certificate issue data provided by Ofgem. One Renewables Obligation Certificates is issued to a renewable generator for every MWh (1000 kWh) of electrical energy generated. These certificates are freely tradeable and are the government’s way of
encouraging investment in renewable generation under the Renewable Obligation legislation (the RO). The certificates provide a valuable insight into the generation profiles of the UK’s renewable electricity, and since Ofgem also publishes the installed capacities of the generators, it is possible to calculate Load Factors (referred to as Capacity Factor in the case of wind).
Load factor is the proportion of the theoretical maximum energy generation which is actually attained under normal working conditions. For example the theoretical yearly maximum of a 1 MW plant would be reached by operating at full output for 8,760 hours, and which would deliver 8,760 MWh. In this case its Load Factor would be 100%. In the real world, however, generators are limited by market demand (i.e. the need to respond to fluctuating demand for electricity), and downtime for scheduled and unscheduled maintenance. Consequently they will produce less energy than their theoretical maximum. Imagine a 1 MW plant which generated 6,000 MWh in a year. Its Load Factor would be 6000 MWh / 8760 MWh, or 68%. In the case of Biomass, Biomass co-firing, Hydro, Landfill Gas, and Sewage Gas (which are all capable of following load) we follow common practice by referring to this proportion as the Load Factor in recognition of the fact that the output can in large part be market-determined.
In the case of some renewables the generation output is also or principally limited by energy input availability. For example, while the wind may be blowing for over 80% of the time it is not blowing at all times with sufficient force to allow a wind generator to reach its maximum output. Thus, the ratio of actual energy generated to theoretical maximum energy generation is a measure of the strength of the wind resource. At present the UK’s wind power, which cannot follow load, is not yet significantly limited by market demand, though the curtailment of output at times of low demand is possible, and already appears to occur in Germany. In recognition of the fact that the result of Actual Output / Theoretical Maximum Output is a reflection of wind resource rather than load following we refer to this proportion as the Capacity Factor.
In the case of Biomass and Biomass co-firing, we chart Load Factor, and also MWhs generated, since this extra detail seemed informative, especially in the case of cofiring. In the case of Hydro and Sewage Gas we chart Load Factor only, and in the case of wind, Capacity Factor only.
In the case of Landfill Gas the Load Factor graph is calculated, as all the other charts are, according to the total installed capacity as taken from the Ofgem web site. However, it should be noted that landfill operators have reason from time to time to alter the installed plant in response to gas evolution rates. It has not been possible to track these changes in detail and the load factor graph should be interpreted with a degree of caution.
Wind Power: A Note on Installed Capacities
The graph of capacity factor and the calculated 2005 capacity factor are both calculated based on Ofgem total installed generating capacity (TIGC) as listed in May 2006. During the research, three different sources of installed capacity have been found:
1. Ofgem installed capacity
2. Installed capacity provided by operators
3. Number of wind turbines and turbine size taken from internet searches.
It has become apparent that in some cases the Ofgem total installed capacity (TIGC) record is in error, due to repowering and for some other reasons. However, the dates of these changes are not easy to determine, and thus it has not been practical to factor this alteration into our calculations. The issue does not at present seem to be a major source of error, and for consistency through out the study, the Ofgem TIGC has been used.