Finding an alternative power source

The UK has signed up to the EU Renewables Energy Directive which includes a UK target of 15 per cent of our energy to come from renewable sources by 2020. To achieve this it is likely that between 30 to 40 per cent of the UK’s electricity will have to be generated from renewables which is a significant increase from the current levels of about five per cent.            

In addition to this Directive the Climate Change Act of 2008 sets a legally binding greenhouse gas emission reduction target of 34 per cent for 2020 and a challenging 80 per cent reduction by 2050 (against levels of 1990). To achieve these tough targets the government has put in place revised building regulations and incentives like the feed-in-tariff that encourage the use of renewable technologies for energy generation.

Alternative power
Renewable energy (or sustainable green energy as it is sometimes called) is derived from inexhaustible sources, in other words it will not run out, unlike fossil fuels like oil, gas and coal. Renewable energy sources include the sun, wind, stored heat in the ground, air and water, fast growing crops and hydro power.   

Renewable energy sources are clean, often producing no harmful greenhouse gases (like carbon dioxide), or are classed as carbon neutral. Therefore renewables will play a key part in achieving a sustainable future.    

In April 2010 the Feed In Tariff (FIT) scheme was launched where energy suppliers make regular payments to householders and communities that generate their own electricity using renewable sources. To qualify for the FIT the generating technology must have been installed by an MCS (Micro generation Certification Scheme) certified product installer. The FIT scheme allows people to benefit in three ways:
•    A set rate is paid by the energy supplier for each kilo Watt hour (kWh) of electricity that is generated by the renewable system. The rate differs depending on the technology used. The rate set for photo voltaic systems is 41.3 p per kWh for a retrofitted system on an existing building.
•    A further three pence is paid for each kWh that is exported back into the grid (i.e. electricity that is not used by the householder).
•    Electricity that is generated and then used by the householder results in savings on their electricity bill.
The duration of the FIT agreement is different depending on the type of renewable source; the tariff agreement for a photo voltaic system is set for 25 years and for wind turbines the tariff agreement is for 20 years. This reflects the estimated life expectancy of these different technologies.

Local authorities
Since August 2010 local authorities have been able to benefit from tariffs for generating energy using renewable sources.   

Examples show that photo voltaic systems can generate an annual income of approximately £800, which can help to pay off the initial investment of the system in roughly 12 years, meaning that for the rest of the scheme the householder can benefit from the income.    

There is a proposal to launch a Renewable Heat Incentive (RHI) in 2011, which will provide financial support for people installing renewable heat sources. It is proposed that householders will receive an annual payment. Eligible technologies are likely to include: solar thermal, air, water and ground source heat pumps, biomass boilers, bio gas and bioliquids and renewable combined heat a power.

Renewable energy sources
Solar thermal: Liquid is pumped through solar panels (either flat plate or evacuated tubes) fitted onto the roof of a building where it is heated by the sun. In most systems the hot liquid passes through a heat exchanger where it heats water to provide about half the domestic hot water needs or can be used to help heat the building. It is essential that hot water is stored in a very well insulated cylinder to avoid the hot water being wasted. These systems work best in summer months when the sun is hotter, therefore in colder months the system will rely on a back-up which is usually a more traditional boiler.

Photo voltaic (PV) systems
Energy from the sun is converted to electricity using PV panels that are exposed to sunlight. It is essential that the panels are not shaded by other buildings or trees. They work most efficiently when positioned on south facing roofs with an incline of 30 to 40 degrees. Electricity that is generated during daylight hours can either be exported back into the grid, thus benefiting from FIT arrangements or be stored in batteries for use later in the day.

Wind power
The UK is a very windy place, having about 40 per cent of Europe’s wind resource. Wind is a free and plentiful source and can be harnessed to generate electricity using wind turbines. To be effective the turbine must be located in a windy site free from obstacles like buildings and trees. Turbines work particularly well on top of a gentle sloping hill, on the coast or out at sea. Small turbines attached to buildings in urban areas often struggle to get enough exposure to wind to be effective.

Heat pumps
Heat pumps draw low grade heat from either the air, water or the ground to provide domestic hot water or heating for the building. The temperature at one metre below the surface stays at a fairly constant level of 10-12 degrees Celsius throughout the year. Coils of plastic piping are either laid horizontally in water or in trenches or in deep bore holes in the ground. A mixture of water and antifreeze is pumped around the pipe work absorbing the heat from the ground (or water), it is then pumped through a heat exchanger; low grade heat is then passed through the heat pump compressor providing a higher grade useful heat that can be used for heating a building or heating hot water. The cooler fluid is then pumped back into the ground to absorb more heat and the process repeats itself.

The heat pump requires electricity to operate, however for every unit of energy used by the system it is often possible to extract three times the energy back in heat.    

Heat pumps are best suited to under floor heating systems as these run at lower temperatures than radiator heating systems.

Biomass
Biomass is plant material or animal waste that is burnt to provide energy. As trees and plants grow they absorb carbon dioxide, when burnt they release carbon dioxide which is absorbed by new trees and plants that are grown to replace them. Crops that grow quickly, for example willow and elephant grass are most appropriate. This process is known as ‘carbon neutral’. It is important to source biomass fuels locally to avoid transportation associated carbon emissions.    

In dwellings biomass is in the form of small wood pellets which are mechanically fed to boilers to provide heating and hot water, in larger buildings the fuel is usually in the form of woodchips, which are cheaper but require more robust feeding mechanisms to the boiler. The biomass fuels need to be stored in a dry space and flues from the boilers need to be adequate to withstand the aggressive combustion gasses.

Choosing the right source
Choosing the most appropriate renewable source is dependent on many factors. The most important being the location and orientation of the building. Buildings that are in sheltered locations may be inappropriate for wind turbines, however if they have large south facing roofs that are not sheltered by trees or neighbouring buildings they may be very suitable for solar thermal and or photo voltaic systems.    

It is important to consider every building individually to ensure you select the most appropriate system that will provide you with the most rewards. If you are uncertain you should seek the advice of expert renewables consultants who will provide guidance to ensure you achieve the most returns from your investment.

Training
What is renewable energy? What are the different types of renewable energy? Which renewable energy will work best in a given building scenario? These questions and more will be addressed by the BRE Introduction to Renewable Energy Technology course. The course will provide a good understanding for those that are responsible for specifying renewable energy technologies and provide practical advice on how the different renewable energy technologies available to the built environment in the UK can be applied to building projects.

For more information

Web: www.bre.co.uk/training

Tel: 01923 664829