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Microgeneration: Electricity Generation Technologies

(Solar PV, Wind Turbines, Small Hydro)

The following is a description of the current state of technology.  For analysis of technology potential, please see 'Related Documents'.  For a list of current installers and  products, see the 'Accredited Installers and Products' page of the Low Carbon Buildings Programme (under 'External Links').

Solar PV (photovoltaics)

There is a small but growing market for photovoltaics (PV) in the UK. It is estimated that by the end of 2004 around 8,164 kilowatt peak (kWp) [Note 1] of PV was installed in total in the UK. The cumulative installation of PV has grown substantially over the last years:

Cumulative levels of PV installations in the UK:

In addition the Renewables Innovation Review estimated that PV could contribute 6-8% of overall electricity supply by 2050 and lead to a 3 million tonnes of carbon (MtC) reduction in carbon emissions.

PV systems consist of semi-conductor cells that are linked and encapsulated into modular panels - often a rectangular shape about a metre long. These are then interconnected to provide electrical power, which can be harmonised with grid electricity and fed back into the network. For grid-connected installations an inverter is required to turn the electricity generated from direct current (DC) to alternating current (AC) and for off-grid installations, a storage mechanism and control system are generally needed. A typical household system of 2kWp could provide an average of between 40-50% of total annual electricity needs. The cost of installing a PV system varies depending on whether it is a standard bolt on system or a more integrated system, but the average cost is around £6,300 per kWp [Note 2].

Wind Turbines

There are a number of established wind developers and installers both at the small (household) level and at the large (commercial) scale. It is estimated that there are around 650 – 700 [Note 3] small scale installations in the UK. Current small scale installations are not generally mounted directly onto buildings, but small building mounted machines are under development and becoming more widely available.

A wind turbine converts wind to electricity. The most common design is for three blades mounted on a horizontal axis, which is free to rotate into the wind on a tall tower. The blades drive a generator either directly or via gearbox (generally for larger machines) to produce electricity. The electricity can either link to the grid or charge batteries. Small wind turbines (less than 20 kilowatt (kW)) produce "wild" AC (variable voltage and frequency) current which is converted to DC via a system controller. This DC is then converted to normal AC (240V 50Hz) current by inverters as with PV. Modern designs tend to be very near silent in operation.

A typical small scale system costs between £2,500 - £5,000 per kilowatt electricity (kWe) installed [Note 4]. A small wind turbine of 6kW capacity (sufficient for all of the electricity requirements of two or three typical UK households), costing about £20,000 to install, will generate about 10,000 kilowatt hours (kWh) per year [Note 5]. This might amount to financial savings of around £700 per year [Note 6] and would equate to carbon saving of 4.3 tCO2/year [Note 7]. The pay back time on an average 6kWp system would therefore be around 29 years (based on current electricity prices).

Small Hydro

There is a small, limited market for small and micro-hydro in the UK. A total installed capacity of around 100 megawatt (MW) is currently operating at about 120 small hydro sites, each with installed capacity of <5MW. In addition there are an unknown number of operational micro-hydro sites, with installed capacities <20MW. Growth is estimated to at about 10MW per year. There are a number of small but established companies currently operating in the UK that specialise in micro-hydro installations. [Note 8]

Water is used by "hydro turbines" to generate electricity. Water flowing down rivers, for example, turns the turbine round; this movement is used to produce power. Most hydro power is produced in hilly or mountainous areas, or in river valleys. The amount of electricity that can be produced is determined by how much water is available and how fast it flows. Additionally of all renewable energy technologies, it is the most consistent at providing electricity.

Costs for hydro projects depend greatly on the site and vary considerably, but can cost anything between £1,000 and £3,000 per installed kW.

Footnotes:

[Note 1 - ref] Based on IEA PVPS data for up to 2003, and estimate of PV in 2004.
[Note 2 - ref] Cost is based on data from the Major PV Demonstration Programme Stream 1.
[Note 3 - ref] BRE.
[Note 4 - ref] Summary of renewable energy technologies characteristics, from the London Renewable: Toolkit for planners, developers and consultants, section 3; London Renewables.
[Note 5 - ref] BRE. Based on case study from Clear Skies programme.
[Note 6 - ref] The price assumes a net metering arrangement where the community receives similar rate for export as for import of electricity of around 6 – 7p/kWh.
[Note 7 - ref] Carbon saving calculated using the DEFRA electricity displacement coefficient of 0.43 kgCO2/kWh used since 2000.
[Note 8 - ref] Definition Study of the Community and Household Renewable Energy Grants Scheme, ESD Ltd and EST, September 2002.