Biomass is a natural biological material. In a renewable energy context, biomass is an animal waste and/or plant material that can be used as fuel to produce energy. There are many examples of biomass including wood, food waste, garden waste, slurry, algae, palm oil and willow as well as many more! Biomass is viewed as being a carbon neutral alternative in the sense that the amount of carbon absorbed during the material’s lifecycle equates to the amount of carbon that is released when used as a fuel source. However, a ‘carbon neutral process’ of collecting and extracting biomass material is almost impossible as it produces its own carbon emissions.
Fossil fuels, such as coal, oil and gas, are derived from old animal and plant life. So how are these materials not regarded as biomass? The chemical make-up of these materials has been changed over a period of millions of years due to geological processes. As a result, these fossil fuels contain a significant amount of energy that is released when combusted. Due to the long period of time in which they were formed, the carbon contained within these fossil fuels can no longer be regarded as being within the carbon cycle, and therefore, when they are combusted, you are effectively adding ‘new’ carbon to the carbon cycle.
Domestic Households
Biomass systems are available for domestic applications. The energy that is generated can be used for heating a single room, heating water and/or central heating. A new biomass system can be integrated into the existing heating system in your home. Below is an example schematic of how a wood stove may be connected to an existing hot water cylinder. The central heating network may also be connected to this to provide heating for your home as well as heating your water.
Where does the fuel come from?
There are three main forms in which you can source fuel for your biomass system. These are logs, chippings or pellets. Some fuel sources may not be compatible with all types of biomass systems. It would be sensible to look at what fuel stock a system requires and check that that fuel stock can be sourced locally to you. By sourcing a local fuel source, you can reduce transportation costs of the fuel and reduce your overall carbon emissions.
The chart above has been given to you as guidance on average fuels costs and the amount of energy that is given out by each when burnt. It shows energy density by mass and the price per kWh of common fuels and wood fuels. Most figures have been taken from the biomass energy centre. Others, including the price per tonne, have been calculated: log wood (£60/ton), house coal (£250/ton), and wood dried (£100/ton). The p/kWh has been calculated using these £/ton figures and energy density figures from the biomass energy centre.
When talking about wood fuels, the moisture content (MC) is usually given as a percentage. The moisture content of the wood can be reduced by drying processes (but this in turn will increase the cost of the resource). This is an important factor. Moisture content reduces the ‘energy’ that you can get out of a wood. The higher the moisture content is, the lower the energy you can get out of it, as some of the combustion process will involve evaporating the moisture. So if a wood is completely dry then the combustion process can use the maximum amount of energy contained within the wood.
Governmental Incentives
Unfortunately, there are no government incentives in place to support the installation costs for biomass at present. This used to be included under the Low Carbon Buildings Programme (LCBP) although this is now obsolete. However, biomass systems will be able to earn money through the new Renewables Heat Incentive (RHI) in April 2011. As biomass is a thermal technology (like solar thermal), it is to be covered by the RHI. If you have already installed a biomass technology then the RHI may be applicable to you IF you have not installed it prior to 15th July 2009.
Cost, Installation and Maintenance
There are two general types of wood stove that you may come across. Stand alone wood stoves and automatically fed wood boilers, both of whose names are self-explanatory as to what they are. Stand alone stoves are cheaper than automatically fed wood boilers at around £3,000 for stand alone boilers and £9,000 for automatically fed ones. It is recommended to shop around for quotes from different installers as this will bring the price down. If the wood stoves are part of a refurbishment, then the more you can refurbish yourself (i.e. installing your own mantle piece or hearth) the more you can bring the cost down further.
The cost of fuel varies. The less manufacturing or changing the wood there has been involved, the cheaper the fuel tends to be. For example, wood logs may cost around £50-£60 per tonne. The price will vary here depending on if the wood has been incensed with a smell (such as apple smoke) and the proximity to fuel supply. Transport costs will be reflected in the price you buy your fuel for, in relation to your distance from the supplier. Pellets tend to be more expensive due to manufacturing costs. Oven drying pellets will also increase cost, but this should be reflected in the amount of thermal energy you can gain from combusting it as the moisture content is very low.
The installation of a wood stove will involve installing a flue pipe, or chimney. To avoid requiring planning permission, the pipe must not exceed 1m above the surface of the roof. If this is not possible you will require planning permission. You will also need to line the cavern that your stove will be installed within. The lining will need to be fire proof, but should also offer insulation from the wall behind the stove. If you are not having a flue pipe installed because you already have a chimney then it would be a good idea to line the chimney as well. By lining it, the chimney now has a smooth surface where tar and soot will find it hard to condense and stick to. Any lining work done to your chimney may need to be consulted under building control. This type of work will need to be done under guidance of a building inspector or an installer under the ‘Competent Person Scheme’.
Maintaining a wood stove or automatic feeder is important, not just for performance but also for health and safety reasons. It is important to check that an automatic feeder wood boiler has its fuel (pellets) flowing freely and unhindered. The store should only contain wood pellets, as contaminants such as stone chippings or large pieces of wood will block up the feeding mechanism.
Regularly check your wood stoves and feeders for cracks within them as this will cause a weakness that heat can get into. The fireplace that your stove is installed in, should also be checked for irregularities as this will cause weaknesses within the brick work or lining, and produces a fire hazard.
Regular cleaning out of bottom ash will maintain the stoves efficiency. At the same time, you should check for holes and cracks within the bottom of the stoves pan, as these will allow hot ash to escape, and provide a fire hazard.
The glass will need to be checked for irregularities and any build up of tar deposits should be removed.
If you are using your stove for heating purposes only, it is unlikely that you will need it on during the summer. During the summer months, allow the door to be open on the stove. This prevents condensation building up within the chimney.
A free health check may be included within a quote from the company installing your stove.
Suitability
A general checklist of what you need to think about;
- Do you have ample dry space to store your fuel?
- Planning permission considerations, are you in a conservational area, smoke free zone? If you are, then you may need planning permission. (Although there is a smoke free wood stove!)
- Do you want a manually fed wood stove (logs), or automatically fed wood boiler (pellets).
- The Renewables Heat Incentive is set to come into effect April 2011. Installing it between July 2009 and April 2010 will mean you will receive the RHI when it comes into effect. However, payback costs are difficult to work out as the incentive has not been finalised.
- Shop around for cheaper quotes, such as one from ESW
