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Renewable energy technologies

 

Combining energy efficiency with the installation of renewable energy technology can be a very effective way of demonstrably improving a building's energy performance.

 

Renewable energy technologies have now largely discarded their 'alternative' tag. Formerly of interest only to committed 'greens' and trendy designers, renewable technologies are an increasingly mainstream and familiar source of energy, and a key element of Government energy policy.

 

One of the issues influencing that policy is the EU Energy Performance of Buildings Directive - which comes into force in January 2006 - requiring minimum energy performance standards to be set for new buildings and large buildings being refurbished. It also requires the provision of energy performance certificates whenever buildings change ownership or tenancy.

 

There are few better ways of improving energy performance and demonstrating a commitment to energy efficiency, as well as safeguarding against future energy price rises, than using renewable energy. So important is this technology to the UK's energy and emissions targets, that the Government is committed to increasing the proportion of UK electricity from renewable sources to 10% by 2010. This is a very ambitious aim when you consider that in 2000 the UK generated just 1.3% of its electricity this way.

 

Renewable energy technologies

Renewable energy technologies offer virtually free energy in return for an initial capital outlay. There are currently two main Government grant schemes that help with equipment and installation costs - the BRE-managed Clear Skies scheme which provides support for a range of technologies in public-sector buildings such as hospitals, schools and community buildings, and the PV Grants scheme which provides funding towards the costs of photovoltaic systems. A new initiative to supersede both schemes is planned for sometime in 2006.

 

The most familiar sources of renewable energy are the wind and the sun.

 

Wind turbines

Wind energy is one of the most cost effective methods of renewable power generation. Wind turbines typically have three blades mounted on a horizontal axis, which is free to rotate in the wind on a tower. The blades drive a generator, either directly or via a gearbox, to produce electricity that can link to the grid or charge batteries.

 

Modern, quiet wind turbines are increasingly seen in lower-density urban areas, where ease of maintenance and immediate connection to the grid - or the direct use of the electricity in a building - can make them cost effective, despite lower wind speeds than in open areas.

 

 

While large wind turbines are generally less suited to dense urban areas, a number of companies are developing small, roof mounted turbines. If successful these are likely to be an increasingly popular way of providing buildings with energy.

 

Wind turbines are available with outputs ranging from 600w to 3.6 MW. Average wind speed is the main factor affecting output. It varies for different areas of the UK, but increases with the height of the turbine above the ground. A database on www.bwea.com can be used to predict the approximate wind speed at a particular set of co-ordinates at different heights, although for larger commercial installations it is advisable to measure the wind regime at a given site for a number of months.

 

According to the Clear Skies grant scheme website (www.clear-skies.org) the typical cost of a small wind turbine ranges from £2,500 - £5,000 per kWe installed. The Clear Skies site has a list of registered suppliers that must be used by those applying to the programme.

 

Photovoltaics

Photovoltaic (PV) systems convert energy from the sun into electricity through semi-conductor cells that are connected together and mounted into modules. Photovoltaics supply electricity to the building they are attached to or to the electricity grid. Electricity can be sold to the National Grid when the amount generated exceeds local needs.

 

PV systems require only daylight, not sunlight, to generate electricity (although more electricity is produced with more sunlight), so they can produce energy in overcast or cloudy conditions and can be used successfully in all parts of the UK.

 

Photovoltaic cells come in modular panels that can be fitted to the tops of roofs (looking similar to rooflights) and in slates or shingles that are integral parts of the roof covering (looking similar to normal roof tiles). Photovoltaic cells can be incorporated into glass for atria walls and roofs, or used as cladding or rain screens on building walls - this is particularly suitable for prestige offices.

 

PV systems can be discreet when designed as an integral part of the roof. An 'invisible' design using slates or shingles, as opposed to an architectural statement, is likely to be preferable in sensitive areas.  

 

Ideally, photovoltaics should face between south-east and south-west at an elevation of about 30o-40o, but even flat roofs in the UK receive 90% of the energy of an optimum system. They are particularly suited to buildings that use electricity during the day, such as offices, retail premises and schools.

 

There is rarely a standard PV project so it's difficult to give cost details, but ball-park figures for fully installed systems are:

  • £5000 - £8000/kWp for a 1kWp (the peak output of the panel) roof mounted system
  • £10,000 - £15,000/kWp for façade or atrium systems.

See www.est.co.uk/solar for details of grants for PV systems.

 

Solar water heating

Solar water heating systems use a heat collector, generally mounted on the roof, in which a fluid is heated by the sun. The fluid heats up water stored in the building. As these systems can function in diffuse lighting conditions, they work successfully in all parts of the UK.

 

They are suitable for any building type that has sufficient year-round hot water needs and a south (or south-east/south-west) facing roof. Offices, retail units or other buildings with canteens, washrooms, etc, are particularly suited to this technology.

 

Likely cost details, and a list of registered suppliers and installers, are available at www.clear-skies.org.  

 

Other systems

Among several other renewable energy technology systems are:

  • Biomass heating - biomass, usually in the form of wood chips or pellets, can be burnt to provide heat in buildings
  • Ground source heat pumps - these draw heat from the ground, concentrate it and deliver it to the building
  • Ground sourced cooling - space cooling for a building can be provided by circulating water cooled directly by the ground
  • Fuel cells - currently being developed and trialled, fuel cells convert energy stored in chemical form into electricity - as do batteries, but fuel cells use externally supplied fuel (hydrogen) and so do not need recharging.
  • Biogas - obtained from the breakdown of organic materials by bacterial action (eg landfill gas from waste sites) or enhanced digestion methods.
  • Hydro turbines - are turned by water to generate electricity - most hydro power is produced in hilly areas or river valleys.

More information

More information on renewable energy technologies is available in the London Renewables publication 'Renewable energy toolkit for planners, developers and consultants', which is available at http://www.london.gov.uk/mayor/environment/key-documents.jsp.

 

resource05

The latest renewable energy and energy efficiency developments will be on display at resource05, a three-day showcase being held at BRE near Watford on 13-15 September 2005. Leading industry figures will discuss advances in low carbon technologies and how they are being applied in building projects across the UK.

 

Indoor and outdoor exhibitions areas will showcase a wide range of products and materials - solar thermal, advanced insulation, innovative cooling, biomass boilers, lighting, photovoltaics, ground source heat pumps and many others.

 

For more information contact BRE Events on 01923 664800, Email events@bre.co.uk or visit www.resource05.com.

 

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