Low Carbon Power Generation

Technology to produce Low carbon forms of energy has been developed and is being strongly marketed (Wind Generation, PV Cells, Solar Thermal, Biomass Products). The technology is, however, relatively new in that development and is often prohibitively expensive.  As progress continues in this area, investment in research and development will increase, making strides forward in efficiency as well as increasing availability. Solar panels, heat pumps and biomass systems are all improving in efficiency with costs falling as time goes on. It is a lengthy process, but it is set to continue with increasing momentum. The installation, maintenance and convenience of such systems are all factors that need to be considered carefully as there are both benefits and drawbacks. 

Solar Panels

Solar water heating systems use directheat from the sun to work alongside your conventional water heater.  In the UK particularly, this is unlikely to be sufficient on its own.  The technology is well developed with a large choice of equipment to suit many applications. They can provide around a third of domestic hot water needs, reducing impact on the environment - the average domestic system reduces carbon dioxide emissions by around 330kg per year, depending on the fuel replaced.

Solar panels - or collectors - are fitted to the roof. They collect heat from the sun's radiation and the heat transfer system uses the collected heat to heat water. A hot water cylinder stores the hot water that is heated during the day and supplies it for use later. Preferably 3-4m2 of southeast to southwest facing roof is required receiving direct sunlight for the main part of the day.  The hot water cylinder used will  be larger than previously, and suffient space to locate an additional water cylinder may also be required.

Solar Powered Cells on the roof directly heat water, and a water system has to be plumbed to run directly through them.  Hence the labour costs for fitting these, together with the necessary upgrade to the boiler, makes the installation costs higher than that of photovoltaic cells.

For more extensive information on Solar and PV power generation, please see the Solar Century Website, acessed from the LINKS page.

PV Cells

Photovoltaic cells use the sun to create electricity, like having a sun-powered re-charging battery on the roof.  The technology is expensive, but the actual fitting of these to the roof involves minimal disruption as they are simply wired back into the dwelling’s electricity system, and no wet plumbing is involved. There is a double benefit in this technology in that any excess power generated can go back into the national grid, thus providing a positive figures as well as a negative figure on the monthly invoice.  As prices drop, photovoltaic cells will probably become the norm for new houses, and will also provide a benefit to existing properties.

Photovoltaic cells (and wind generators, see below) can benefit a dwelling by providing cheap, low carbon power to fuel heating systems, as well as contributing to payback by potentially supplying power to the national grid.

PV requires only daylight - not direct sunlight - to generate electricity. The systems use cells to convert solar radiation into electricity. The PV cell consists of one or two layers of a semi conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers, causing electricity to flow.  PV systems generate no greenhouse gases, saving approximately 455kg of carbon dioxide emissions per year - adding up to about 11 tonnes over a system's lifetime - for each kilowatt peak (kWp - PV cells are referred to in terms of the amount of energy they generate in full sun light).

PV arrays now come in a variety of shapes and colours, ranging from grey 'solar tiles' that look like roof tiles, to panels and transparent cells that can be used on conservatories and glass to provide shading as well as generating electricity. As well as enabling the generation of free electricity they can provide an interesting alternative to conventional roof tiles.

PV systems can be used for a building with a roof or wall that faces within 90 degrees of south, as long as no other buildings or large trees overshadow it. If the roof surface is in shadow for parts of the day, the output of the system decreases.

Prices vary, depending on the size of the system to be installed, type of PV cell used and the nature of the actual building on which the PV is mounted. The size of the system is dictated by the amount of electricity required, but also by the size of the installation. The roof must be strong enough to take the weight of the panels, especially if the panel is placed on top of existing tiles. Most domestic systems usually require between 1.5 and 3 kWp.

Solar tiles (immitating roof tiles) cost more than conventional panels,but PV tiles can partially offset the cost of roof tiles.

Grid connected systems require very little maintenance, generally limited to ensuring that the panels are kept relatively clean and that shade from trees has not become a problem. Stand-alone systems, i.e. those not connected to the grid, need maintenance on other system components, such as batteries.

Biomass Fuel

Often called 'bioenergy' or 'biofuels', these biofuels are produced from organic materials, either directly from plants or indirectly from industrial, commercial, domestic or agricultural products. Biomass Fuel is created from organic matter of recent origin. It doesn't include fossil fuels, which have taken millions of years to evolve. The CO2 released when energy is generated from biomass is balanced by that absorbed during the fuel's production. This is called a carbon neutral process.  Biofuels fall into two main categories:

• Woody biomass includes forest products, untreated wood products, energy crops, short rotation coppice (SRC), e.g. willow.  For small-scale domestic applications of biomass the fuel usually takes the form of wood pellets, wood chips and wood logs.

• Non-woody biomass includes animal waste, industrial and biodegradable municipal products from food processing and high energy crops, e.g. rape, sugar cane, maize.

There are two main ways of using biomass to heat a domestic property: Stand-alone stoves providing space heating for a room. These can be fuelled by logs or pellets but only pellets are suitable for automatic feed. Generally they are 6-12 kW in output, and some models can be fitted with a back boiler to provide water heating. Boilers connected to central heating and hot water systems are suitable for pellets, logs or chips, and are generally larger than 15 kW. Stoves can be 80% efficient. They're normally used for background heating. They also add aesthetic value in the living area of the house itself. Many wood burning stoves act as space heaters only. But the higher output versions can be fitted with an integral back boiler to provide domestic hot water and central heating through radiators, if needed.

There are many domestic log, wood-chip and wood pellet burning central heating boilers available. Log boilers must be loaded by hand and may be unsuitable for some situations, such as sheltered accommodation with centralised services. Automatic pellet and wood-chip systems are available, but can be more expensive. Many boilers will dual-fire both wood chips and pellets, although the wood chip boilers need larger hoppers to provide the same time interval between refuelling.

Boilers can be designed with an integral hot water energy storage or accumulator tank that stores water up to 90º C, enabling the supply of heat to be further decoupled from the combustion of the fuel. This is particularly helpful with log boilers where systems operate at full load and the matching of demand with load is performed by the accumulator.

It is important to have storage space for the fuel, appropriate access to the boiler for loading and a local fuel supplier. The vent material must be specifically designed for wood fuel appliances and there must be sufficient air movement for proper operation of the stove. Chimneys can be fitted with a lined flue. Wood can only be burnt on exempted appliances, under the Clean Air Act. This mainly applies to domestic appliances.

Capital costs depend on the type and size of system you choose. But installation and commissioning costs tend to be fairly fixed. The cost for boilers varies depending on the fuel choice; including the cost of the flue and commissioning, a manual log feed system would be slightly cheaper than a pellet boiler of the same size. And of course, unlike other forms of renewable energy, biomass systems require payment for the fuel. Fuel costs generally depend on the distance from the supplier. As a general rule the running costs will be more favourable in an area that doesn't have a gas supply.

Producing energy from biomass has both environmental and economic advantages. It is most cost-effective when a local fuel source is used, which results in local investment and employment. Furthermore, biomass can contribute to waste management by harnessing energy from products that are often disposed of at landfill sites.

Ground or Air Source Heat Pumps

Heat pumps use the same principles as fridges and air conditioners. Ground source heat pumps (GSHP) transfer heat from the ground into a building to provide space heating and, in some cases, to pre-heat domestic hot water. For every unit of electricity used to pump the heat, 3-4 units of heat are produced. As well as ground source heat pumps, air source and water source heat pumps are also available.

There are three important elements to a GSHP:

1. The ground loop. This is comprised of lengths of pipe buried in the ground, either in a borehole or a horizontal trench. The pipe is usually a closed circuit and is filled with a mixture of water and antifreeze, which is pumped round the pipe absorbing heat from the ground.
2. A heat pump. This has three main parts - the evaporator which takes the heat from the water in the ground loop; the compressor which moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit; the condenser which gives up heat to a hot water tank which feeds the distribution system.
3. A heat distribution system, which may consist of under floor heating or radiators for space heating and in some cases water storage for hot water supply.

The ground loop can be a borehole; it may be a straight horizontal trench costing less than a borehole, but needing more land area; or a spiral horizontal (or 'slinky'), needing a trench of about 10m length to provide about 1kW of heating load.

The efficiency of a GSHP system is measured by the coefficient of performance (CoP). This is the ratio of units of heat output for each unit of electricity used to drive the compressor and pump for the ground loop. Typical CoPs range from 2 to 4 although some systems may produce a greater rate of e. The higher end of this range is for under-floor heating, because it works at a lower temperature (30-35ºC) than radiators. If grid electricity is used for the compressor and pump, then you should consult a range of energy suppliers to benefit from the lowest running costs, for example by choosing an economy 7 or economy 10 tariff.

Wind Generators

Private wind generators are on the increase and have the potential to provide electricity into the home and also sell back to the grid.  There is presently a noise implication, however, and planning permission may not be granted.  Also, the cost of purchase, installation, and upkeep is fairly prohibitive if a system large enough to be viable is employed.

Modern wind turbines use the wind's lift forces to turn aerodynamic blades that turn a rotor which creates electricity. In the UK we have 40% of Europe's total wind energy. But it's still largely untapped and only 0.5% of our electricity requirements are currently generated by wind power.
Wind power is proportional to the cube of the wind's speed, so relatively minor increases in speed result in large changes in potential output. Individual turbines vary in size and power output from a few hundred watts to two or three megawatts (as a guide, a typical domestic system would be 2.5 - 6 kilowatts, depending on the location and size of the home). Uses range from very small turbines supplying energy for battery charging systems (e.g. on boats or in homes), to turbines grouped on wind farms supplying electricity to the grid.

Wind speed increases with height so it's best to have the turbine high on a mast or tower. Generally speaking the ideal siting is a smooth-top hill with a flat, clear exposure, free from excessive turbulence and obstructions such as large trees, houses or other buildings. Small-scale building-integrated wind turbines suitable for urban locations are also available to install in homes and other buildings.

The electricity generated at any one time by a wind turbine is highly dependent on the speed and direction of the wind.  The windspeed itself is dependent on a number of factors, such as location within the UK, height of the turbine above ground level and nearby obstructions.  Ideally, a professional assessment of the local wind speed should be undertaken before proceeding.

Costs will include the turbine, mast, inverters, battery storage (if required) and installation - however it's important to remember that costs will vary depending on location and the size and type of system. Turbines can have a life of up to 20 years but require service checks every few years to ensure they work efficiently. For battery storage systems, typical battery life is around 6-10 years, depending on the type, so batteries may have to be replaced at some point in the system's life.

• Thermal Properties
• Thermal Mass
• Thermal Bridging
• Cylinders & Measured Heat Loss
• Dimensions
• Boilers & SEDBUK (Seasonal Efficiency Database of Boilers in the UK)
• Ventilation Systems & the Appendix Q database
• Solar Gains
• Insulation
• Space Heating Systems
• Water Heating Systems
• Low Carbon Power Souces
• Condensation & Dewpoint Analysis
• Heat Pumps