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1: Renewable energy requirements

Many regulations are changing in the drive for greater energy efficiency and more sustainable buildings. The combination of new Part L, the Code for Sustainable Homes, the European Performance of ºÚ¶´ÉçÇøs Directive, the Sustainable and Secure ºÚ¶´ÉçÇøs Act and Planning Policy Statement 22 will all have a substantial effect on buildings in the UK.

PPS22 has really caused a stir because it enables local authorities to demand that a percentage of a building's energy be provided from on-site renewable energy sources. Since this provision has been available, about 70 local authorities require a 10% contribution from on-site renewables, one requires 15% and several are thought to be considering 20%.

Meeting these requirements is quite a challenge and specifiers will have to adopt appropriate technologies and consider using innovative materials and designs.

PPS22 is a substantial document (see link below). The guidance states "renewable energy sources should be promoted and encouraged and due justification should be sought from those not utilising these sources".

2: Putting PPS22 into practice

The specifier should consider the details when considering renewable energy sources and make a careful judgment over which are appropriate to use. There is a risk that inappropriate placement of technologies will mean they will fail and we will see a whole generation of buildings with useless systems. See the London Energy Partnership for good clear advice (link below)

In practice, PPS22 demands that a percentage of the building's primary energy consumption must come from a "sustainable source" - in other words, from a source that does not consume hydrocarbons.

This includes energy from the sun, wind, the ground, water courses or biomass. It is also accepted that heat pump technologies can contribute to making these sources more practical so this is classified as a renewable energy technology. Combined heat and power is also acceptable providing it is powered from fuel from a renewable source.

Many of the renewable technologies have a long history in Europe so the specifier should use this wealth of knowledge and experience when deciding on appropriate equipment for their building.

3: Sources of renewable energy

The technologies include:

• Solar water heating Delivers hot water and has a good payback period. Thermal solar panels need to face the sun and can provide cooling, too, if coupled to an absorption chiller.
• Solar photovoltaic Still a developing technology with a lengthy payback period. Produces relatively small amounts of direct current power and needs to face the sun.
• Wind turbines Relatively expensive with a large range of equipment available. Needs an appropriate site and may have aesthetic implications.
• Boreholes Water from the ground can deliver heating or cooling depending on the location.
• Ground source Liquid is pumped around a long tube buried in the ground - this can absorb or release energy.
• Biomass In the appropriate location, biomass can be used in conjunction with a number of technologies such as combined heat and power.

These sources need to be considered alongside the building's requirements - in particular the desired internal environment and anticipated use-pattern.

These technologies have to be considered in this way to maximise the potential gains. For example, solar thermal can be combined with absorption chillers to produce cooling, generate heat directly for hot water, contribute to general heating or generate heat to be fed to a thermal store for use later.

Photovoltaic cells are expensive, provide a relatively small output but have low maintenance and can be virtually regarded as "fit and forget". They can contribute some useful electrical energy to the building's systems although losses occur if the direct current output has to be converted to alternating current. It also takes a lot of cells to get up to the 10% figure.

Depending on the site, wind generators are simple and effective, although aesthetic issues and maintenance should be taken into account. Several types are available other than the conventional "windmill"-bladed configuration.

If they are available on site, energy can be extracted from boreholes or from the ground and large areas of water. Large areas of collector can collect energy at a low temperature; this can be raised to a useable temperature by a heat pump.

4: Future developments

European makers have been producing heat pumps, collectors and control systems for many years. It is clear that systems currently in development or not now seen as viable will receive a significant boost from the demand created by new regulations. Developments in wind generators and complex systems using several different sources are available, but experience of them in this country is limited.

Watch points

Seven factors to bear in mind when specifying …

• Ensure you know what the policy of the local authority is and the level of renewable energy required
• Identify site attributes early in the design process
• Discuss your proposals with the local authority and client and get agreement before detailed design starts
• Ensure you understand exactly how the renewable source will work
• Avoid easy fixes or systems that seem to good to be true
• Some grants are available to encourage renewable technologies
• Most of the technologies are on display somewhere so visit an installation before specifying.