Embedded Generation Technologies

Some conventional generating technologies can be used at a scale appropriate to

embedded and decentralised generation e.g. CCGT. But, a number of newer technologies using a variety of fuel sources are beginning to enter the fray. Embedded generation plant ranges from established technologies such as diesel generators to more recent technologies such as fuel cells. It is necessary at this juncture to analyse the important embedded generation technologies. “Understanding the interaction of embedded generation with the

power system requires an appreciation of the technology… … the characteristics of the energy sources and… … the conditions in which the embedded generation plant is operated” (Jenkins et al, 2000).

The output of embedded generators can be classified under two, not necessarily mutually exclusive, categories. Certain embedded plant’s output is intended for use on-site and tends to be in the form of combined heat and power. The other category of embedded plant generates output for the supply of third parties and is often renewable in nature, e.g. biomass or wind.

CHP and wind generation technologies are discussed in detail, a reflection of their likely major contribution in the near term to Government targets. Characteristics of other embedded and renewable technologies are overviewed in Box 12.

Combined Heat and Power (CHP)

CHP is the most significant form of embedded generation in the UK contributing 4,239 MW of electricity and 15,093 MW of thermal capacity from 1,313 sites in 1999 (Digest of United Kingdom Energy Statistics, 2000). CHP is often referred to as cogeneration, a reflection of the technology’s simultaneous production of electrical and heat energy. CHP plant tends to be located on industrial sites. For example, in the UK, the chemical industry has constructed CHP plant that generates 1,180MW of electricity and 5,970MW of heat. The electricity produced is consumed by the host of the CHP plant, any surplus or deficit sold to or purchased from the local DNO. The generated heat may be utilised for industrial purposes on-site, for on-site space heating and/or linked to a local district-heating scheme. CHP schemes are fuelled either exclusively or by a combination of gas, coal and bio-fuels such a wood chip and sewage gas. CHP expansion has appeared to avoid the locational bias evident in the previous geographical pattern of generation location. In England and Wales, the installed capacity of CHP schemes has an approximate distribution of 53% in the North and Midlands and 47% in the South (NGC SYS, 2001). Figure 6 indicates that over 80% of total generation in England and Wales is located in the North and the Midlands

The location of embedded CHP plant is defined by the location of the heat demand. CHP schemes are conventionally designed to meet the electricity and heat requirements of the host sites or defined district-heating scheme. That said, this convention is a commercial choice rather than a necessity. Should policy and economic incentives allow, CHP plant is capable of being designed to provide electricity and associated ancillary service to the distribution and transmission networks to which they are connected.

CHP efficiencies reach as high as 80%, this high efficiency rating contributing to a

reduction in greenhouse gas emissions relative to traditional fossil-fuelled generating units. The UK Government has set targets for at least 10,000MWe of CHP by 2010. The

potential for industrial, commercial, domestic and household CHP may be as high as 27,000MWe, more than 40% of UK supply (DETR, 1997)

Wind

The utilisation of wind energy is not new, documents suggesting that wind powered

irrigation schemes were common in China as far back as 2,000 years ago (Waugh, 1994). However, it was not until the late 1970s that work began on the development of wind power to contribute large amounts of electricity to the interconnected electricity networks. Wind power, both on and offshore, is among the more developed and promising renewable

energy technologies and contributed 9% of UK’s renewable electricity generation in 1998 (Electricity Association, 2000). However, this still represents less than 0.2% of total generation. ETSU have estimated that onshore and offshore wind could supply 150 TWh of cost effective electricity (less than 4p/kWh) to UK electricity by 2010, over 40% of total UK electricity consumption in 2000 (ETSU, 2001).

Expansion of the industry, from the first mass production of a wind turbine in Denmark in May 1980, has been rapid. From 1993 to 2000, the market for wind turbines in Europe grew by an average of 40% per annum, total worldwide installed capacity meeting the equivalent of the electricity demands of 10.6 million households by January 2001 (James & James, 2001).

Box 12 Embedded and Renewable Energy Technologies

Fuel Cells

A fuel cell converts chemical energy in a fuel source directly to electrical energy. Although originally invented in 1839, fuel cell technology development has been slow, the main source of funding and research being the space industry. Multinational companies, including GE, Alstom and Siemens- Westinghouse are developing a variety of fuel cell technologies. Efficiencies can reach over 50%, twice that of the equivalent internal combustion device (Hart et al, 2000). They are a clean technology relative to the emissions from traditional fossil fuel generation units. Potential fuel sources included natural gas, biomass and hydrogen. They are modular by nature, outputs ranging from 5kW to 1MW per unit, being well suited to embedded and distributed generation. They allow generation to be located near to demand and can operate persistently at high capacities and efficiencies.

Renewable Technologies

Renewable energy is derived from renewable sources, i.e. the use of which does not deplete the resource. Such sources include the sun, wind, rivers, waves, tides, heat from inside the earth and the sustainable growth of crops. In the UK, Government includes landfill gas and municipal and industrial wastes in its classification of renewable sources eligible for financial support. The location and potential output of renewable electricity plant is primarily determined by the availability of the renewable resource, one of the most lucid examples being the choice of location for hydro-electric plant. Some of the key renewable energy technologies include:

Hydro-electric power

This is the most widely utilised source of renewable electricity in the world, in 1998 contributing 17.9% of the world's electricity generation and 2.3% of the world’s total energy supply (IEA, 2001). 1.38% of UK electricity supply is generated from hydro-power, the majority of which is in Scotland (Digest of United Kingdom Energy Statistics, 2001).

Hydro electric schemes often involve the construction of large dams across valleys and the flooding of vast areas of land, villages and towns. This has led to widespread criticism of such large schemes from both an environmental and social perspective, best highlighted by the ongoing debate concerning the Ilisu dam project in Turkey. Lack of remaining suitable sites limits the potential in the UK. There may remain some potential for the development of small-scale hydro projects and river run-off schemes with generating capacities under 5 MW.

Solar

Solar photovoltaics (PVs) convert solar radiation into electricity. Costs remain high, but may fall alongside increased R & D, increased production and associated economies. Building integrated PV systems, e.g. building facades and solar roofs, have been identified as a key commercial application of PVs in the developed world (Hart et al, 2000).

ETSU have suggested that nearly 80% of the UK's energy needs could be met by PVs. Even on cloudy days, solar panels are capable of generating power. The cost of PVs dropped fivefold over the last 15 years and is set to fall further once a mass market is established for it (TXU Europe, 2001). Although UK solar programmes have traditionally been much smaller than other countries, some growth is anticipated from DTI's market incentives and reduced VAT. (continued over…)

Box 12 Embedded and Renewable Energy Technologies (continued from previous) Biomass

Biomass is biological matter such as trees, grasses and agricultural crops which can, primarily through combustion, be used as fuel for the production of energy. Biomass can also be used with coal in conventional power plant. Co-firing is the most economical near-term option for introducing new biomass power generation, and lowers the air emissions from coal-fired plants (Hart et al, 2000). ETSU estimates the potential resource for energy crops and agricultural and forestry wastes is 20 TWh and 15 TWh respectively by 2010. Energy crops have also been mooted as an area of great potential for the troubled UK agricultural industry.

Wave and tidal

The UK is blessed with some of the largest wave and tidal power resources in the world. A recent report by the House of Commons Select Committee acknowledged the high capital costs and need for further R & D and highlighted that energy from waves and tides was predictable and reliable.

Micropower

Some of the most radical developments in electricity generation technologies are in the area of heat and power systems for hotels, offices, small businesses and homes (Fabian Society, 2001). Multinational companies such as ABB, BG, BP Amoco, Shell, Turbec and Capstone are investing, researching and developing fuel cells, solar photvoltaics and microturbines. Stirling engines are being developed for small-scale generation and domestic CHP systems. Capstone and BG are offering power plant down to the 10 to 100 kW level (Hart et al, 2000).