Methodologies

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General Approach

The statistical methodologies and conversion factors are in line with the International Energy Agency (IEA) and SOEC definitions.

Conversion Factors

Conversion factors are used to convert and express energy figures in different units. Energy units used are therms, tonnes of oil equivalent (toe – the energy content of one tonne of oil), megaWatt hours (MWh) and gigaJoules (GJ). The conversion factors used are not the same for each of the technologies. Combustion technologies do not convert all the energy released from the fuel into electricity so the conversion factor needs to take into account that lost during electricity generation.

Summary of Conversion Factors Used to Generate the Statistics

Conversion Factors	Technology	Adopted IEA/SOEC definitions
therms/toe	-	397
toe/MWh	-	0.08598
MWh/toe	-	11.63
MWh/toe	Wind	11.63
MWh/toe	Hydro	11.63
MWh/toe	Wave Energy	11.63
MWh/toe	Tidal Currents	11.63
MWh/toe	Biomass electricity conversions, including Others Category, landfill gas and sewage.	3.05*
GJ/toe	All heat conversions	41.868

*This is a two-stage process; x 11.63 to convert from MWh to toe thermal; x 0.262, the fractional electrical conversion efficiency, to convert from thermal to electrical toe.

Points to Note

One tonne of oil equivalent is defined as 397 therms.
Primary electricity contributions from hydro and wind are now expressed in terms of an 'energy supplied' model (previously they were expressed in terms of the notional fossil fuel needed to produce that electricity - 'substitution model').
Electrical capacities are quoted as Installed Capacities. For some statistical data, Declared Net Capacity (DNC), are quoted for hydro schemes.

Capacities

Information is presented on the amount of generation the renewable energy projects are capable of producing. This information is presented in the form of so called ‘capacities’. There are many different types of capacity figures that may be used:

Nameplate Capacity
Nameplate Capacity is literally what the manufacturer says the equipment is capable of producing; this is stamped on the side of the machine, hence the term ‘Nameplate’ capacity.

Installed Capacity
Installed Capacity is the same as the nameplate capacity.

Declared Net Capacity (DNC)
Declared Net Capacity (DNC), taking into account the intermittent nature of the power output from some renewable sources. This is defined as the maximum continuous rating of the generating sets in the stations less the power consumed by the plant itself and reduced by a specified factor (B) to take into account the intermittent nature of some of the renewable energy sources. DNC represents the nominal maximum capability of a generating set to supply electricity to consumers; it is calculated from the following equation:

DNC = (name plate capacity x B) - 'in-house' load

B has the values given in the table below for the different renewable sources.

B	RESOURCE
0.43	Wind
0.17	Solar
0.33	Tidal/Wave
1.00	All Others

Load Factors

Load Factor for a Calendar Year
As historically reported in DUKES, these have been calculated in terms of installed capacity and express the average hourly quantity of electricity generated as a percentage of the average capacity at the beginning and end of the year. This is given by:

Electricity generated during the year (kWh)/(
(Installed capacity at the beginning of the year + Installed capacity at the end of the year (kW))
x 0.5 x 8760 hours)

Load Factor on an Unchanged Configuration Basis
To overcome the biasing of load factors for for projects (particularly wind) caused by new plant coming on-line either early or late in a calendar year, a new statistic has been calculated that includes only those projects that have operated throughout the calendar year with an unchanged configuration. Originally this new statistic was termed the capacity factor to distinguish it from the traditionally calculated load factor, but as capacity factoris already used as an alternative term for load factor in some countries and its use could lead to confusion, the term load factor on an unchanged configuration basis has been used. This is given by:

Electricity generated during the year (kWh)/
((Installed capacity of wind farms operating throughout the year with an unchanged configuration (kW)) x 8760 hours)

Calorific Values for Biofuels

For biofuels, the estimated average Gross Calorific Values (GCV) table below is used to convert the data from tonnes of fuel processed by the plant; these feedstock figures are supplied in the survey returns.

Renewable Energy Source	Gross GJ/tonne
Domestic Wood	14.5
Industrial Wood	11.9
Straw	15
Poultry Litter (on-farm use)	13.5
Poultry Litter (off-farm use)	8.8
General Industrial Waste	16
Hospital Waste	14
Municipal Solid Waste	9.5
Refuse Derived Fuel	18.6
Tyres	32

Energy from Non Bio-degradable Wastes

The non-biodegradable element of some fuel feedstocks - Tyres, Hospital Waste, Municipal Solid Waste (MSW) and General Industrial Waste (GIW) - must be considered separately. Waste tyres and hospital waste are included under non-biodegradable wastes. Generation from these other sources are split between biodegradable and non-biodegradable sources using information on calorific values for the constituent parts. Approximately 62½ per cent of generation from MSW has been estimated to be from biodegradable sources.

Statistical Indicators

The following are used to highlight general trends in the development of renewable energy technologies:

Trends in the use of renewable energy for both heat and electricity
Increase in the electricity generation capacity from all significant renewable sources
Growth in the proportion of electricity produced from renewable sources, including the progress towards the renewables targets set under the Renewables Obligation and Renewables Directive
Renewable generating capacity from NFFO, former NFFO contracts (including equivalents in Scotland and Northern Ireland) and capacity outside of NFFO

Wind schemes

DNC for Wind

This, very broadly, the equivalent capacity of baseload plant that would produce the same average annual energy output as the renewable energy plant. For wind farms the DNC is calculated by subtracting the on-site electrical power consumption from the installed capacity and multiplying the remainder by 0.43 (ie 43%). The reason 0.43 is used, and not the commonly assumed capacity factor of 0.3, is because conventional generating plant also operate at less than their maximum output for much of the time. When DNC factors were originally established it was assumed that wind farms would operate with a capacity factor of 0.3 and conventional plant with a capacity factor of 0.7. The DNC was therefore defined as (0.3÷0.7) or 0.43.

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