Renewable and low carbon energy solutions
The use of cost-effective renewable or low carbon (RLC) energy sources reduces the use of conventional energy and associated greenhouse gas emissions. The suitability of renewable energy technologies varies from project to project and is dependent on site factors, location and funding availability. The Hertfordshire Renwwable and Low Carbon Study provided a high level analysis of the feasibility and appropriateness of a range of RLC technology solutions across Hertfordshire, including the solutions presented below. Click here to download a copy of the RLC study.
Funding streams for RLC solutions
Increasing the use of renewable energy is important for Government to achieve its national and international targets. Various financial incentives have been recently introduced to enable renewable and low carbon solutions to compete on an economic basis with conventional fossil fuels. These include:
- Energy efficiency grants – discounts on wall and loft insulation and better boilers and controls. Developers and tax-paying building occupiers can gain cash flow discounts on energy efficiency products using Enhanced Capital Allowances (ECA). Existing building owners in Hertfordshire can benefit from the HEEP scheme. Click here for more information.
- Feed In Tariffs (FIT) – incentives for low carbon electricity generation from micro-technologies such as photovoltaic panels and micro-CHP. The utility company pays the consumer for electricity generated. Click here for more information.
- Renewable Heat Incentive (RHI) – to be introduced in late 2011 to incentivise low carbon heat generation from micro-technologies such as solar thermal, biomass boilers and ground source heat pumps. Click here for more information.
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Renewable Obligation Certificates (ROCs) – tailored towards large energy installations such as wind farms and biomass power plants. The options above are more appropriate for building projects. Click here for more information.
In addition to the consideration of technical and economic feasibility on projects, it is vital to address planning issues associated with the installation, including local environmental and visual impacts.
The following gives an overview of available RLC technologies:
Combined Heat and Power (CHP)
Both electricity and thermal energy (for space heating and/or hot water) are produced from a single energy source, which is typically natural gas. Although not a renewable energy technology, this can be a very efficient use of fuel for some buildings and reduces their overall carbon emissions.
This technology is most efficient when sized to operate at a thermal ‘base load’. Both CHP and Biomass boilers perform best when sized to meet the thermal base load. The thermal base load is the amount of heat continuously required by the building. This is illustrated in the following graph showing a generic demand profile:
The base load is that below the dotted line. Peak energy demands result from increased activity and heat requirement throughout the day. Peak demands are typically met by using conventional gas boilers.
Additional systems meet the peaks of demand. This technology is best suited to buildings where there is a heat demand that matches electrical demand, such as process industries, swimming pools, community heating systems and hospitals. Possible variations on the basic system include the addition of absorption chillers, or the use of biomass as a fuel source, although it should be noted that these options will impact on the economics of the system.
Solar thermal
Solar collectors or solar thermal panels generate hot water using the thermal energy of sunlight which is used to offset conventional energy use for provision of hot water for showers and taps. This technology is well established, reliable and typically provides reasonable economic paybacks.
Panels are ideally applied to south facing roofs pitched at 30-45 degrees and can be freestanding or integrated into the roof, with pipework leading into the building and connected to a storage tank with a back-up heating supply.
Solar photovoltaics
Photovoltaic (PV) panels or tiles convert solar energy into electricity and are available in a variety of styles, colours and materials. Panels can be freestanding, or can be integrated into the south facing facades or roofs of buildings. Systems are best elevated at 30-45 degrees from horizontal. It is also possible to manufacture the PV cells into glass laminates providing the dual benefits renewable electricity and solar shading to internal spaces.
Source: Kawneer
PV tiles are a relatively new form of the technology and have been designed to match the colour and appearance of conventional slate tiles. They therefore can be a good solution to use on buildings within Conservation Areas.
Source: inhabitat.com
The installation of photovoltaic panels has been boosted by the Feed In Tariff for small scale electricity generation and the Green Deal in coming years. The FIT dramatically reduces the payback period of photovoltaic panels and has enabled very interesting options to emerge such as free PV using third-party finance. The applicability of these options depends on who actually owns the panels once installed.
Wind turbines
Turbines generate electricity from wind and are available in a variety of sizes and scales. Suitable sites must be exposed and have an average wind speed of at least 6 metres per second for a large portion of the year.
Source: Quiet Revolution
There are various options for the configuration of turbines. Small scale models can be roof mounted. Typically they have a rated output of around 1.5kW. Alternatively, small scale freestanding models are available at rated outputs of 15-250kW. These range in size up to industrial scale models that can be seen on wind farms at rated outputs of 2-7 MW.
Turbines are categorised as either horizontal or vertical axis, which relates to the axis the blades rotate around. Horizontal axis turbines are more powerful for their size, although some people consider vertical axis turbines to be more aesthetically pleasing.
When considering wind turbines of any scale it is crucial to consider the difference between the rated power output and the annual average output. The rated output is the maximum possible output under perfect wind conditions, which rarely occur during the year. The ratio between this maximum output and the average output over the year is called the ‘utilisation factor’, which typically ranges between 20-30% for a commercial wind farm. Small scale turbines in an inappropriate location without strong winds have been found to have utilisation factors of less than 10%.
Ground Source Heat Pumps (GSHP) and Air Source Heat Pumps (ASHP)
Source: grenergy.co.uk
GHSPs are better suited to new build applications as their efficiency is highest when supplying low temperature distribution systems such as underfloor heating. The use of GSHP is restricted to sites with enough land to either lay pipework in long trenches or with access to a suitable body of water such as a lake or aquifer.
Source: GroundwaterUK.co.uk
The high ‘coefficient of performance’ or COP of a heat pump means it is an energy efficient technology – for each unit of electricity used to operate the heat pump, around four units of heating energy is produced via a GSHP and 2-3 units of heating energy via an ASHP. The average COP over the course of a year is known as the Seasonal Performance Factor. The CoP of GSHP over a year may gradually reduce if the thermal energy of the heat source (the ground or body of water) is not sufficiently 'recharged' naturally or managed.
Biomass
The burning of energy crops in a biomass boiler to provide heating and hot water is considered to be a ‘carbon neutral’ process, as the amount of CO2 released during combustion is equivalent to that which is absorbed during the growing cycle of the crops.
Source: building.co.uk
Biomass fuel can be delivered in the form of either woodchips or pellets. Pellets contain much more energy within them, so a smaller volume needs to be stored between each delivery. Pellets can also be pumped like a fuel between the delivery lorry and the storage hopper, which makes deliveries quicker and more straight-forward. Automated systems feed the fuel through to the combustion chamber from a hopper, which needs to be refilled on a regular basis. On domestic scale systems, this is typically once per week, but depends on the system size and energy demand. Ash also has to be removed approximately once every month.
Both wood pellets and wood chip require space for storage, with woodchips requiring a larger storage volume, and delivery. It is therefore important to consider the storage and delivery access arrangements, for both new build and retrofit projects, early in the design stage if a biomass boiler is to be used.
Although it is always desirable to grow the biomass crops locally, crops are almost always grown by a separate company who sell the crop via fuels agents on the open market. Installers of biomass boilers can advise on local options. The carbon and ecological footprint associated with the cultivation and transportation of biomass fuel is something that should therefore be considered before opting for a biomass solution.
If considering this technology on an urban site, care should also be taken to ensure that the specified equipment meets the requirements of any designated smoke control zone.
District heating networks
The circumstances of new development may make it difficult to utilise on-site RLC solutions to achieve significant carbon savings. Therefore, when seeking to achieve low or zero carbon developments, it may be necessary to consider off-site solutions or 'allowable' solutions. A recognised and widely used off-site solution in the UK and Europe is district heating networks.
District heating is an alternative method of supplying heat to buildings, using a network of super insulated pipes to deliver heat to multiple buildings from a central heat source. Heat is generated in an energy centre and then pumped through underground pipes to the building. Building systems are usually connected to the network via a heat exchanger (also known as a heat interface unit (HIU)), which replaces individual boilers for space heating and hot water.
Whilst there is some amount of thermal loss from the heat distribution infrastructure, the aggregation of small heat loads from individual buildings into a single large load allows the use of large scale heat technologies, including the capture of waste heat from industrial processes or power generation, or other large scale heat generation technologies which are not viable at a smaller scale. Of particular interest is combined heat and power (CHP) technologies (see above).
A Department of Trade and Industry commissioned a survey into public attitudes towards renewables in 2006 and found that 85% of the general public support the use of renewable energy.
81% are in favour of wind power and just over three fifths would be happy to live within 5km of a wind farm development.