Renewable Energy Fuels and Technologies in the UK

Which fuels and technologies are used for renewable energy generation in the UK?

In the UK, most renewable energy technologies qualify for subsidies under the Renewables Obligation (RO).

The list of renewable energy fuels and technologies that qualify for the RO is published by Ofgem, who administer the Renewables Obligation scheme in England and Wales. The ROCs earned by these renewable fuels and technologies are called Banding Levels. This article draws on information from Ofgem and other sources to provide a comprehensive review of those fuels and renewable technologies.

Our aim is to provide a brief (but comprehensive) summary description of those technologies. Although the list is long, please note that many of the technologies listed by Ofgem are just sub-categories of a wider technology. In many cases, the classification is merely a reference to a fuel source rather than the technology itself. So, to try and keep things simple, and to remove unnecessary duplication, we have grouped similar technologies into tables.

This article focusses on listing and describing the fuels and technologies from the perspective of the Renewals Obligation. It does not provide detailed descriptions of the technologies. However, there are links to more detailed descriptions of the main technologies throughout the article. More descriptions will be added over time. So, if it’s not there yet, it will be soon. Please do check back.

Technologies are listed alphabetically.

Anaerobic Digestion

Anaerobic digestion is the process, or sequence of processes, by which microorganisms break down biodegradable material in the absence of oxygen. It is used in various processes including to manage waste, produce fuels and to produce food and drink products.

For the purpose of the Renewables Obligation, anaerobic digestion is classified as electricity generated from gas formed by the anaerobic digestion of material which is neither sewage nor material in a landfill. Anaerobic digestion earns 1.8 ROCs per MWH of electricity generated.

Biomass

Biomass, as a renewable energy source (as opposed to the biological / ecological definition of the word), is plant or animal material used for energy production, or in various industrial processes, as a raw material. It can comprise purposely grown energy crops (such as miscanthus, switchgrass), wood or forest residues, waste from food crops (wheat), garden waste, food processing waste (corn cobs), animal farming (manure), or human waste from sewage plants.

Burning plant-derived biomass releases CO₂. However, it has still been classified as a renewable energy source in the EU and by the UN because photosynthesis recycles the CO₂ back into new crops. This recycling of CO₂ from plants to atmosphere and back into plants, can even be CO₂ negative. It depends how much of the recycled CO₂ is moved and stored in the soil with each cycle.

For the purposes of the Renewables Obligation, biomass is split into numerous categories.

Electricity generation where biomass is used jointly with other fuels (Co-firing Biomass) is covered separately below. Dedicated biomass is where biomass is the only fuel source used.

Technology	Condition(s)	ROCs per MWh (2016/2017)
Biomass - Dedicated	Electricity generated only from regular biomass by a generating station which is not a relevant fossil fuel generating station.	1.4
Biomass – Dedicated with CHP	As above but generation is by a qualifying combined heat and power generating station.	1.8

Co-firing

Co-firing is the combustion of two (or more) different fuels at the same time. One advantage of co-firing is that an existing power plant can be used to burn a new fuel, which may be cheaper and/or more environmentally friendly for the generator. Another, of course, is that the renewable component may qualify for ROCs.

For the purpose of the Renewables Obligation Co-firing comes in many different flavours. The categorisation depends upon;

the renewable fuel being co-fired,
the proportion of renewable fuels to fossil fuels, and
whether CHP is also involved.

Generally speaking, Co-firing qualifies for less than the default 1 ROC (Renewables Obligation Certificate) per MWh of eligible renewable electricity generated. This is because the station operator is not making a dedicated investment in renewables generation. Rather they are either optimising or converting existing generation capacity. The higher the proportion of renewables generated by the generating station, the higher the ROCs earned. And if CHP is added into the mix, the ROCs earned can exceed 1.

Co-firing – Biomass (common definition)

The common definition for Co-firing biomass, which applies to all elements of the table below, is… Wait for it. It’s a long one.

Electricity generated from solid and gaseous biomass or energy crops in a month in which the generating station generates electricity partly from fossil fuel and partly from renewable sources; and where the energy content of the biomass burned in a combustion unit (in that unit in that month) as a proportion of all the energy sources burned, is as per the proportions in the Table below.

To summarise. From a renewables perspective…

Burning more renewable fuels is better than burning less.
Using CHP is better than not using CHP.
Burning biomass is better than burning bioliquids.
Burning energy crops (which are a type of biomass) beats biomass and bioliquids.
The reward (ROCs) you earn is not a linear function of the proportion of renewables used – odd but true.

All clear?

Technology	Condition(s)	ROCs per MWh (2016/2017)
Co-firing Biomass
Co-firing (High-range)	At least 85% biomass but less than 100%.	0.9
Co-firing with CHP (High-range)	At least 85% biomass but less than 100%. Fossil fuel and biomass burned in separate combustion units.	1.4
Co-firing (Mid-range)	At least 50% biomass but less than 85%.	0.6
Co-firing (Mid-range with CHP)	At least 50% biomass but less than 85%. Fossil fuel and biomass burned in separate combustion units.	1.1
Co-firing (Low-range)	Less than 50% biomass.	0.5
Co-firing (Low-range with CHP)	Less than 50% biomass. Fossil fuel and biomass burned in separate combustion units.	1.0
Co-firing Bioliquids
Co-firing of regular bioliquid	Electricity generated from regular bioliquid. Part fossil fuel, part renewable sources with no minimum conditions attached.	0.5
Co-firing of regular bioliquid with CHP	As above but generation is from a qualifying CHP generating station.	1.0
Co-firing Energy crops
Co-firing of relevant energy crops	Only applicable to generating stations with net generating capacity of < 50kW. Energy content of biomass is less than 50% of the energy content of all energy sources burned,	1.0
Co-firing of relevant energy crops (with CHP)	As above but with the energy crops burned by a qualifying CHP generating station.	1.5

Dedicated energy crops

Energy crops are crops grown solely for energy production by combustion (not for food). They are generally selected for being low-cost and low-maintenance. The crops are processed into solid, liquid or gaseous fuels, such as pellets, bioethanol or biogas, which are then burned to generate electricity or heat.

For the purposes of the Renewables Obligation, dedicated energy crops covers electricity generated from energy crops by a generating station (which is not a relevant fossil fuel generating station), and which in any month, generates electricity only from energy crops. This is a definition of a fuel source as opposed to a technology. Dedicated energy crops earn 1.8 ROC’s per MWh of electricity generated.

Gasification

Gasification is a process that converts biomass, or fossil fuel-based carbonaceous materials, into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam. The resulting gas mixture is called syngas (from synthesis gas) or producer gas, and is itself a fuel. The power derived from gasification, and combustion of the resultant gas, is considered to be a source of renewable energy but only if the gasified compounds are obtained from biomass. The advantage of gasification is that using the syngas is potentially more efficient than direct combustion of the original fuel because it can be combusted at higher temperatures or even in fuel cells,

For the purpose of the Renewables Obligation, gasification has two classifications; Standard and Advanced. Both classifications currently earn the same number of ROCs although this was not the case previously.

Technology	Condition(s)	ROCs per MWh (2016/2017)
Gasification - Standard	Generated from gaseous fuel which is produced from waste or biomass by gasification and which has a gross calorific value of at least 2 MJ/m3 (megajoules per metre cubed) but less than 4 MJ/m3 (measured at 25⁰C and 0.1 megapascals at the inlet)	1.8
Gasification - Advanced	As above but which has a gross calorific value of at least 4 MJ/m3	1.8

Geothermal energy

Geothermal energy is the thermal energy generated and stored in the Earth. The geothermal energy of the Earth’s crust originates not only from the original formation of the planet but also from radioactive decay of materials within the earth.

Electricity generated using naturally occurring subterranean heat (geothermal energy) earns 1.8 ROC’s per MWh of electricity generated.

Geopressure

Geopressure is a geological term meaning the pressure within the Earth, or formation pressure. For those who would like to know more, there is a detailed technical definition and discussion of geopressured here.

For the purposes of the Renewables Obligation, geopressure is defined as electricity generated using naturally occurring subterranean pressure. It earns 1.0 ROC’s per MWh of electricity generated.

Hydro-electricity

Hydropower, or water power, is power derived from the energy of falling or fast-running water, which can be harnessed for useful purposes.

Hydro-electricity is, in turn, electricity produced from hydropower.

For the purposes of the Renewables Obligation, hydro-electricity is more narrowly defined as electricity generated by a hydro generating station. A “hydro generating station” is then defined as a generating station which is wholly or mainly driven by water (other than a generating station driven by tidal flows, waves, ocean currents, geothermal sources or using a difference in tidal levels). So, it basically means that only certain types of water qualify. Other types of hydropower (wave, tidal) are covered under separate classifications.

Electricity generated from hydro-electric power earns 0.7 ROCs per MWh of electricity generated in England and Wales. However, hydro-electricity generation in Scotland earns a more generous 1.0 ROCs.

Landfill Gas

Landfill Gas is a complex mix of different gases created by the action of microorganisms as they decompose organic waste within a landfill. Organic waste includes, for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane, with the remainder being mostly carbon dioxide. Trace amounts of other volatile organic compounds (VOCs) comprise the remainder (<1%). Because CO₂ and methane are both greenhouse gases, landfill gases have an influence on climate change. However, those gases can be used as input fuels to generate electricity.

For the purposes of the Renewables Obligation, landfill gas is split into 2 categories based on rather technical characteristics. Landfill gas generation attracts minimal ROCs, because is not particularly clean or green.

Landfill gas – closed

This is electricity generated from landfill gas in which the generating station generates electricity only from gas formed by the digestion of material in a landfill which no longer accepts waste for disposal. But this excludes electricity generated using the heat from a turbine or engine which forms a seperate category. This earns 0.2 ROC’s per MWh.

Landfill gas heat recovery

This is electricity generated using the heat from a turbine or engine which is generating electricity from landfill gas. Landfill gas heat recovery earns the minumum amount of 0.1 ROC’s per MWh of electricity generated.

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Pyrolysis

Pyrolysis is the thermal decomposition of materials at elevated temperatures in an inert atmosphere. It involves a change of chemical composition.

Pyrolysis is most commonly used in the treatment of organic materials. In general, pyrolysis of organic substances produces volatile products and leaves a solid residue enriched in carbon. Extreme pyrolysis, which leaves mostly carbon as the residue, is called carbonization. Pyrolysis is considered as the first step in the processes of gasification or combustion.

For the purposes of the Renewables Obligation, pyrolysis comes in 2 flavours earning the same level of ROCs. These are summarised below.

Technology	Condition(s)	ROCs per MWh (2016/2017)
Pyrolysis - Standard	Generated from gaseous fuel which is produced from waste or biomass by pyrolysis and which has a gross calorific value of at least 2 MJ/m3 (megajoules per metre cubed) but less than 4 MJ/m3 (measured at 25⁰C and 0.1 megapascals at the inlet)	1.8
Pyrolysis - Advanced	Generated from a liquid or gaseous fuel which is produced from waste or biomass by pyrolysis and which has a gross calorific value; (a) for gaseous fuels of at least 4 MJ/m3 (b) for liquid fuel lof at east 10 MJ/kg (measured at 25⁰C and 0.1 megapascals at the inlet)	1.8

Solar photovoltaic

Solar power is the conversion of energy from sunlight into electricity. When the electricity is generated directly from sunlight, the technology is called Solar photovoltaic or photovoltaics (PV).

For the purposes of the Renewables Obligation, solar photovoltaic power is categorised depending upon whether the solar panels are building or ground mounted. Building mounted solar photovoltaics attract a slightly higher subsidy – 1.4 ROCs per MWh of electricity generated, whereas ground mounted solar panels earn a more modest 1.2 ROCs per MWh of electricity generated. This is to incentivise greater use of existing infrastructure assets – basically buildings – for this type of generation.

Station Conversion / Unit Conversion

This is not a technology per se, but rather the modification / conversion of an existing fossil fuel burning plant (or a unit within it) to burn renewables rather than fossil fuels. Under the RO, there are 4 classifications in this category, which are summarised in the table below.

Technology	Condition(s)	ROCs per MWh (2016/2017)
Station conversion	Electricity generated from regular biomass or energy crops by a relevant fossil fuel generating station (RFFGS).	1.0
Station conversion with CHP	Electricity generated from regular biomass or from energy crops by a relevant fossil fuel CHP generating station.	1.5
Unit conversion	Electricity generated from regular biomass or energy crops burned in a combustion unit in any month in which that combustion unit burns only biomass or only energy crops, and the generating station generates electricity partly from fossil fuel and partly from renewable sources.	1.0
Unit conversion with CHP	As for Unit conversion above but in respect of a qualifying combined heat and power generating station.	1.5

Hang in there…not much longer now.

Tidal Power

Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity.

For the purposes of the Renewables Obligation, tidal power comes in 4 flavours which are summarised in the table below.

Technology	Condition(s)	ROCs per MWh (2016/2017)
Tidal Impoundment – Tidal Barrage	Electricity generated by the release of water impounded behind a barrier using the difference in tidal levels where the barrier is connected to both banks of a river and the generating station has a declared net capacity of less than 1 GW.	1.8
Tidal Impoundment - Tidal Lagoon	Exactly as above except that the barrier is not a tidal barrage.	1.8
Tidal Stream	Electricity generated from the capture of the energy created from the motion of naturally occurring tidal currents in water.	2.0
Tidal Stream - Enhanced	As for tidal stream above with some bureaucratic conditions about where the funding comes from. Applies to Scotland only and (again) gets a higher ROC contribution.	3.0

Wave Power

Wave power is the capture of energy of wind waves to do useful work, such as electricity generation, water desalination, or pumping water.

It is distinct from tidal power, which captures the energy of the current caused by the gravitational pull of, predominantly, the Moon. Waves and tides are also distinct from ocean currents which are caused by other forces including breaking waves, wind, the Coriolis effect and differences in temperature and salinity.

For the purposes of the Renewables Obligation, Wave power comes in just 2 flavours. Regular and Enhanced.

Wave

This is electricity generated from the capture of the energy created from the motion of naturally occurring waves on water. It earns 2.0 ROC’s per MWh of electricity generated.

Wave – Enhanced

As for wave above with some conditions about where the funding comes from. Applies to Scotland only and earns a massive 5 ROCs per MWh of electricity generated. Because, of course, Scottish waves are more renewable than non-Scottish waves.

Wind Power

Wind power, or wind energy, is the use of wind to provide mechanical power through wind turbines to turn electric generators. Traditionally is has also been used to do other work, such as milling or pumping with windmills. For the purposes of the Renewables Obligation, wind power is categorised into onshore and offshore; offshore wind is then further broken down by technology type.

Onshore Wind

This is a bit of a circularity, but onshore wind is defined as electricity generated from wind by a generating station that is not offshore (see offshore definition below).

Offshore Wind

This is electricity generated from wind by a generating station that is offshore. Yes, that really is the definition given by Ofgem. Seems obvious enough. However, to avoid possible “cheating”, this is qualified as a generating station which has its wind turbines situated wholly in offshore waters, and is not connected to dry land by means of a permanent structure which provides access to land above the mean low water mark. This is to designed to prevent onshore wind turbines claiming to be offshore wind turbines by building them on a platform that merely extends into the sea.

Why would someone want to claim onshore was offshore?

Well, onshore wind generation earns 0.9 ROC’s per MWh of electricity generated. However, offshore wind generation earns double that at 1.8 ROC’s per MWh of electricity generated. You can see the incentive.

Offshore wind – demonstration turbines

This is defined as electricity generated from offshore wind using only eligible turbines, and which are located on a particular area of seabed which is subject to a demonstration lease issued by the Crown Estate. There are tight definitions of what constitutes an eligible turbine and a demonstration lease for the purpose of testing, demonstrating and approving the viability of new (post 2014) wind turbines.

Offshore wind – floating turbines

This is defined as electricity generated from offshore wind using only floating wind turbines. A floating wind turbine in this context is one which is fixed or connected to the seabed by means of a chain, tension leg or other flexible mooring.

Demonstration turbines and floating turbines earn generous ROC allowances . However, they are restricted to Scotland only.

Offshore wind categories are summarised in the Table below. In summary, from a renewables perspective;

Offshore wind is better than onshore.
Offshore wind in Scotland is way better that offshore wind in England and Wales.

Technology	Condition(s)	ROCs per MWh (2016/2017)
Onshore Wind	Not offshore	0.9
Offshore Wind	Wholly offshore	1.8
Offshore wind – demonstration turbines	Wholly offshore. Only eligible turbines which are located on a particular area of seabed which is subject to a demonstration lease.	2.5
Offshore wind – floating turbines	Wholly offshore. Uses floating wind turbines only (fixed or connected to the seabed by means of a chain, tension leg or other flexible mooring).	3.5

And the rest…

For completeness, the remaining fuel sources in the Renewables Obligation mix are listed below. They cover fuel sources excluded elsewhere.

Sewage Gas

This is electricity generated from gas formed by the anaerobic digestion of sewage (including sewage which has been treated or processed). It has its own category as it was specifically excluded from the definition of anaerobic digestion. This earns a paltry 0.5 ROCs per MWh of electricity generated.

Waste with CHP (energy from)

This definition basically picks up the scraps. This earns the default 1.0 ROCs per MWh of electricity generated We are guessing that the bureaucrats who came up with some of these definitions lost the will to live by the end it and just plumped for the default.

Here is the definition. Enjoy!

Electricity generated from the combustion of waste (other than a fuel produced by means of anaerobic digestion, gasification or pyrolysis) in a qualifying combined heat and power generating station in a month in which the station generates electricity only from renewable sources and those renewable sources include waste which is not biomass.

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