Biomass

Biomass is 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. We call this a carbon neutral process.

Biomass is 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. Biofuels fall into two main categories:

• Woody biomass includes forest products, untreated wood products, energy crops, short rotation coppice (SRC), e.g. willow.
• Non-woody biomass includes animal waste, industrial and biodegradable municipal products from food processing and high energy crops, e.g. rape, sugar cane, maize.

For small-scale domestic applications of biomass the fuel usually takes the form of wood pellets, wood chips and wood logs.

Biomass and your home

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. These 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. Automatic pellet and wood-chip systems 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.

Is my house suitable?

You should consider the following issues if you're thinking about a biomass boiler or stove. An accredited installer will be able to provide more detailed advice.

• Fuel: It's important to have storage space for the fuel, appropriate access to the boiler for loading and a local fuel supplier.
• Flue: 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.
• Regulations: The installation must comply with all safety and building regulations (see Part J of the Building Regulations).
• Smokeless zone: Wood can only be burnt on exempted appliances, under the Clean Air Act. This mainly applies to domestic appliances.
• Planning: If the building is listed or in an area of outstanding natural beauty (AONB), then you will need to check with your Local Authority Planning Department before a flue is fitted.

Costs
Capital costs depend on the type and size of system you choose. But installation and commissioning costs tend to be fairly fixed. Stand alone room heaters generally cost £1500 - £3000 installed. The cost for boilers varies depending on the fuel choice; a typical 20kW (average size required for a three-bedroom semi-detached house) pellet boiler would cost around £5000 installed, including the cost of the flue and commissioning. A manual log feed system of the same size would be slightly cheaper.

Running costs: Unlike other forms of renewable energy, biomass systems require you to pay for the fuel. Fuel costs generally depend on the distance from your supplier. As a general rule the running costs will be more favourable if you live in an area that doesn't have a gas supply.

Payback: This depends on the fuel being replaced and the type of wood fuel being used. It too is more favourable in areas that don't have a gas supply.

Local benefits
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 source heat pumps

Although we may not know it heat pumps are very familiar to us - fridges and air conditioners are two examples. 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.

How does it work?

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 - (e.g. the squiggly thing in the cold part of your fridge) takes the heat from the water in the ground loop;
• the compressor - (this is what makes the noise in a fridge) moves the refrigerant round the heat pump and compresses the gaseous refrigerant to the temperature needed for the heat distribution circuit;
• the condenser - (the hot part at the back of your fridge) gives up heat to a hot water tank which feeds the distribution system.

3) Heat distribution system. Consisting of under floor heating or radiators for space heating and in some cases water storage for hot water supply.

What options are available?

The ground loop can be:

1)       borehole;

2)       straight horizontal - trench costs less than a borehole, but needs more land area;

3)       spiral horizontal (or 'slinky coil') - needs a trench of about 10m length to provide about 1kW of heating load.

How much does it cost?

Installation

A typical 8kW system costs £6,400-£9,600 plus the price of connection to the distribution system. This can vary with property and location.

Running costs
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 2.5 to 4. The higher end of this range is for under-floor heating, because it works at a lower temperature (30-35ºC) than radiators.

Based on current fuel prices, assuming a CoP of 3-4, a GSHP can be a cheaper form of space heating than oil, LPG and electric storage heaters. It is however more expensive than mains gas. If grid electricity is used for the compressor and pump, then an economy 7 tariff usually gives the lowest running costs.

Ground source heat pumps and your home

What to keep in mind when considering a ground source heat pump.

• The type of heat distribution system. GSHPs can be combined with radiators but under-floor heating is better as it works at a lower temperature.
• Is there space available for a trench or borehole to accommodate a ground loop?
• Is the ground suitable for digging a trench or borehole?
• What fuel is being replaced? If it's electricity, oil, LPG or any other conventional fossil fuel the payback will be more favourable. Heat pumps are a good option where gas is unavailable.
• Want to be 100% renewable? Buy green electricity, or install solar PV or some other form of renewable electricity generating system to power the compressor and pump.
• Need a back-up heating system?
• Is there also a cooling requirement?
• Is the system for a new building development? Combining the installation with other building works can reduce costs.
• Can you incorporate insulation measures? Wall, floor and loft insulation will lower your heat demand.

 Small scale hydro

Hydro-power systems convert potential energy stored in water held at height to kinetic energy (or the energy used in movement) to turn a turbine to produce electricity.

A micro hydro plant is below 100kW. Improvements in small turbine and generator technology mean that micro hydro schemes are an attractive means of producing electricity. Useful power may be produced from even a small stream. The likely range is from a few hundred watts (possibly for use with batteries) for domestic schemes, to a minimum 25kW for commercial schemes.

Small scale hydro and your home

Hydro power requires the source to be relatively close to where the power will be used, or to a suitable grid connection. Hydro systems can be connected to the main electricity grid or as a part of a stand-alone (off-grid) power system. In a grid-connected system, any electricity generated but not used can be sold to electricity companies.

In an off-grid hydro system, electricity can be supplied directly to the devices powered or through a battery bank and inverter set up. A back-up power system may be needed to compensate for seasonal variations in water flow.

The capital cost is high but the prospect of not having electricity bills or making money by selling energy back to a power supplier may tempt you!

Provided the resource is there, community hydro projects can also be a viable proposition. Potentially, there are great benefits in clubbing together to increase buying power or sharing expertise - although the work involved should not be underestimated.

System sizing

Energy available in a body of water depends on the water's flow rate (per second) and the height (or head) that the water falls. The scheme's actual output will depend on how efficiently it converts the power of the water into electrical power (maximum efficiencies of over 90% are possible but for small systems 50% is more realistic). Hydro electric systems are generally divided into two categories, low and high head.

Reliable and efficient equipment - and sound advice - is available from a large number of experienced UK suppliers and consultants.

Will it meet my energy needs?

This depends, of course, on your energy needs and the resource available. For houses with no mains connection but with access to a micro-hydro site, a good hydro system can generate a steady, more reliable electricity supply than other renewable technologies at a lower cost.

Total system costs can be high but often less than the cost of a grid connection and with no electricity bills to follow. It should be noted that in off-grid applications the power is used for lighting and electrical appliances. However space and water heating can be supplied when available power exceeds demand.

Costs

Hydro costs are very site specific and are related to energy output.

For low head systems (not including the civil works - so assuming there was an existing pond or weir), costs may be in the region of £4,000 per kW installed up to about 10kW and would drop per kW for larger schemes.

For medium heads, there is a fixed cost of about £10,000 and then about £2,500 per kW up to around 10kW - so a typical 5kW domestic scheme might cost £20-£25,000. Unit costs drop for larger schemes.

Environmental impact

Turbines can have visual impact and produce some noise, but these can be mitigated relatively easily. The main issue is to maintain the river's ecology by restricting the proportion of the total flow diverted through the turbine.

You will need to talk to the relevant planning authorities to ensure the site and design are acceptable and identify any other permissions required.

Solar PV

Solar photovoltaic (PV) uses energy from the sun to create electricity to run appliances and lighting. PV requires only daylight - not direct sunlight - to generate electricity.

How it works
Photovoltaic 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.

The greater the intensity of the light, the greater the flow of electricity...

PV systems generate no greenhouse gases, saving approximately 325kg of carbon dioxide emissions per year - adding up to about 8 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 you can use on conservatories and glass to provide shading as well as generating electricity. As well as enabling you to generate free electricity they can provide an interesting alternative to conventional roof tiles!

Solar PV and your home
You can use PV systems 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.

Solar panels are not light and the roof must be strong enough to take their weight, especially if the panel is placed on top of existing tiles.

Solar PV installations should always be carried out by a trained and experienced installer.

Cost and maintenance
Prices for PV systems 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.

For the average domestic system, costs can be around £4,000- £9,000 per kWp installed, with most domestic systems usually between 1.5 and 2 kWp. Solar tiles cost more than conventional panels, and panels that are integrated into a roof are more expensive than those that sit on top.

If you intend to have major roof repairs carried out it may be worth exploring PV tiles as they can 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. The wiring and components of the system should however be checked regularly by a qualified technician.

Stand-alone systems, i.e. those not connected to the grid, need maintenance on other system components, such as batteries.

Planning considerations
Some local authorities require planning permission to allow you to fit a PV system, especially in conservation areas or on listed buildings. Always check with your local authority about planning issues before you have a system installed. Obtaining retrospective planning permission can be difficult and costly.

 Solar thermal hot water

Solar water heating systems use heat from the sun to work alongside your conventional water heater. The technology is well developed with a large choice of equipment to suit many applications.

Benefits

• can provide almost all of your hot water during the summer months and about 50% year round
• reduces your impact on the environment - the average domestic system reduces carbon dioxide emissions by around 400kg per year, depending on the fuel replaced.

Different types of system

What best suits your needs depends on a range of factors, including the area of south facing roof, the existing water heating system (e.g. some combi boilers aren't suitable) and your budget.  

A competent professional installer should assess your situation and discuss with you the best configuration to meet your needs. 

Solar water heating and your home

Solar water heating can be used in the home or for larger applications, such as swimming pools.

For domestic hot water there are three main components: solar panels, a heat transfer system, and a hot water cylinder. Solar panels - or collectors - are fitted to your roof. They collect heat from the sun's radiation. 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.

Is my property suitable?

Preferably you will need 2-4m² of southeast to southwest facing roof receiving direct sunlight for the main part of the day. You'll also need space to locate an additional water cylinder if required.

Cost and maintenance

The typical installation cost for a domestic flat plate collector system is £2,000 - £3,000. Evacuated tube systems will cost £3,500 - £4,500.

You can also fit or build the system yourself. It may be cheaper but will take longer and you'll need a certain level of skill. However, DIY jobs are not eligible for grant funding.

Solar hot water systems generally come with a 10-year warranty and require very little maintenance. A yearly check by the householder and a more detailed check by a professional installer every 3-5 years should be sufficient (consult your system supplier for exact maintenance requirements).

 Wind turbines

Modern wind turbines use the wind's lift forces to turn aerodynamic blades that turn a rotor which creates electricity.

Wind energy

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.

Small scale wind and your home

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.

However, small-scale building-integrated wind turbines suitable for urban locations are currently being developed and will be available to install in homes and other buildings within the next few years.

Knowledge of the local wind is critical to designing a wind energy system and predicting output. For domestic installations a good source of information on local wind speeds is the NOABL database which can be accessed from the British Wind Energy Association.

You can also collect primary information by setting up your own monitoring mast to record wind speed. An ideal way of doing this is with an anemometer. You can buy one online for around £120.

Planning issues such as visual impact, noise and conservation issues also have to be considered. System installation normally requires permission from the local authority.

Stand-alone or grid-connected system?

Small-scale wind power is particularly suitable for remote off-grid locations where conventional methods of supply are expensive or impractical. Most small wind turbines generate direct current (DC) electricity. Off-grid systems require battery storage and an inverter to convert DC electricity to AC (alternating current - mains electricity).

You also need a controller to divert power to another useful source (e.g. space and/or water heaters) when the battery is fully charged.

It's common to combine this system with a diesel generator for use during periods of low wind speeds. A combined wind and diesel system gives greater efficiency and flexibility than a diesel only system. It allows the generator to be used at optimum load for short periods of time to charge batteries when there is little wind, rather than by constant use at varying loads.

Wind systems can also be installed where there is a grid connection. A special inverter and controller converts DC electricity to AC at a quality and standard acceptable to the grid. No battery storage is required. Any unused or excess electricity can be exported to the grid and sold to the local electricity supply company.

Cost and maintenance

Systems up to 1kW will cost around £3000 whereas larger systems in the region of 1.5kW to 6kW would cost between £4,000 - £18,000 installed. These costs are inclusive of the turbine, mast, inverters, battery storage (if required) and installation, however it's important to remember that costs always 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.