Energy from biomass refers to the production of heat from the annual growth of a field crop; the triennial harvest of a specially grown timber crop; the trimmings from standard woodland management; or the recycling of wood from buildings etc. It can also refer to the pulp resulting from the pressing of oilseeds etc. as this may also be used as fuel for a solid fuel boiler.
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Use of this form of Renewable Energy is ideal for you if you have the space to grow your own, or if you live in the vicinity of a grower; and if you need to have the burner running continuously during the winter months NB if you only want occasional heating then go for Solar heating or Photovoltaic. As a rough guide: a farm, using timber for fencing etc. as well as fuel will require an area of woodland of approx. 6ha. It is worth bearing in mind that the first thinning even at 5 years will not yield enough to heat the house. However, if some of the area is put into coppice in the first year, this will greatly increase the 5 year yield. From year 10 onwards, there should be a good range of timber available, especially from fast growing species such as Sweet Chestnut and Hazel coppices, and single stem Ash. Naturally if you wish to go into the Biomass supply business you will be thinking in terms of 10s of hectares of Miscanthus or Short Rotation Coppice. The latter usually means the growing of specific cultivars of Willow for a 3 yearly harvest. Other species that can be grown range from: Spruce for Saw Log production for specific burners; to Popular and Larch which are best grown as single stems. In actual fact any wood may be chipped, the only dangers to be aware of are: toxic fumes from poisonous species when burnt; and nails or other metal in recycled wood from buildings etc. - these do not agree with Chippers.Top of page
- Use of home-grown wood and chipping provides heating at a cost equivalent to 17p/l for Oil - presently ca. 45p/l.
- A large old house, its estate office, greenhouse and swimming pool use 110t of wet wood/annum from 340ac (137.65ha) of established woodland.
- Another large old house has installed a 120kW wood boiler that runs on chips from low-grade woodland. This saves 40% of their fuel costs and reduces their annual carbon emissions by 67t/annum.
- In June 2011, the new RHI scheme (Renewable Heat Incentive Scheme) will provide owners of biomass boilers with 1.6 - 9p/kWh of heat generated. This is based on the rating of the specific boiler (see note below).
- 500ac of established woodland could produce 400t of wood fuel/annum.
- The ash from 30t of woodchips, burnt in a modern high-tech boiler, just covers an area of approx. 1m2. The weekly ash output from a 3 - 4 bed house is likely to fill less than a kitchen waste bucket; depending on usage. Therefore, this amount is easily bagged and disposed of with the normal domestic rubbish.
Approx. costs not including VAT or Delivery, but including the full system connected up plus the accumulator tank(s), range from: £4,355.00 for an 18kW boiler system to £9,995.00 for an 80kW system. The former will heat a housing height of 2.7m, up to 150sq.m; whilst, the latter will heat up to 750sq.m. of the same height of building.
From June 2011, even renewable heat will attract RHI (Renewable Heat Incentive) payments for any installations completed after 15th July 2009; with the proviso that they are burnt in a biomass burner and not just in an ordinary wood burning stove or grate. These are to be like the FiTs for production of electricity, only they will apply to Renewable/Sustainable Energy Installations that produce heat directly and are not connected to the Grid. Their installation does of course mean that fossil fuel is not being used for heating; and there is therefore a saving of Grid electricity, and fossil hydrocarbons that would otherwise combine with oxygen to form carbon dioxide thus accelerating global warming.Top of page
- Small wood burners can be used to heat individual rooms. Some wood burning stoves/ranges, can be used for cooking and also to heat radiators throughout the house.
- Modern pellet burning stoves will burn for two weeks and only produce the equivalent of an unheaped garden barrow load of ash whilst heating a domestic and business complex.
- Miscanthus does not require additional energy input for drying before processing to pellets and burning, since the pelleting process works best with material at 12% Moisture Content (Range 9 - 15%MC).
- Use of biofuels recycles the carbon dioxide currently in the atmosphere rather than recombining fossil carbon with our oxygen to increase the CO2 and deplete the O2 in our atmosphere.
- Wood ash, unlike coal ash, is non-greasy and excellent for providing grip on icy surfaces in winter. It is also suitable for spreading on the garden or fields as a soil conditioner, unlike coal ash that will act as a poison to most plants.
- Heat may not be required in the summer apart from the provision of Hot Water. Therefore, it may be necessary to achieve summer water heating by use of Passive Solar, Ground Source or an electricity supply. This could of course be provided by Photo-voltaic or a Wind Turbine.
- Biomass burners, are not normally efficient producers of electricity and therefore the house's electrical energy needs will need to be supplied by a second form of Renewable Energy generation even in winter.
There are many crops that can be grown to supply both houses and work buildings with Heat, the main crops are listed below.
SRC Willow - Many new cultivars of this well known small tree species, have been developed to reduce disease susceptibility; induce maximum growth rates in various challenging environments; and promote even growth of the basal multi-stem system. Planting is usually carried out in the autumn to ensure that the short slips do not get dried out. Two or three buds will break in the first summer and this first years growth must then be cut back to approx. 4 inches (10cms). This severe cutback (coppicing) in the second year is necessary to encourage more buds to develop from the base. The ideal is to produce a bush with about 6 - 10 good strong branches growing from near the base. Future harvesting cuts will be above this structure; the aim being to avoid uneven growth with a lot of thin sticks. The presence of thin sticks mean that there is an high percentage of bark which tends to turn to dust in processing, or flash burns when it does reach the boiler. SRC is cheaper to establish than Miscanthus; after the first coppicing a reasonable harvest can be obtained in the 3rd and every following 3rd year with modern stock. This means that the only window for input of disease control and fertilizer application is in spring after a harvest. This in turn means that the land selected for this crop must be dry enough in the early spring to take harvesting machinery and fertilizer in the form of Farm Yard Manure or Slurry. SRC is harvested, stacked on hard standing to air-dry and then chipped; though it can be powdered and pelleted to make small dense high calorific value logs. The yield here is likely to average 35 Oven Dried t/ha every 3rd year when grown on Yield Class 2 or 3 land. The poorer the land, the poorer the crop and the more management problems are likely to be incurred. Willow will stand some flooding, but loss of yield and susceptibility to disease attack is likely if the crop is flooded for more than a couple of weeks.
Miscanthus - a tufted rhizomatous C4 grass. This likes warmth and soil moisture throughout the growing season. However, unlike the Reeds, it does not like to stand in water, and the land must be dry in the early spring for harvesting before the new year's shoots start to break the surface (damage to the new shoots means that these do not produce a full crop in the year of damage, and thus the rhizomes' full potential is not achieved). The costs of establishment are ca. £2,000/ha before the first full crop at 5 years NB a trim is not necessary at the end of the first year; in fact the first two season's growth will survive to be cut with the 3rd season's harvest. Unlike seed grasses, cutting does not increase tillering in the rhizomatous grasses. After the 3rd year harvesting is annual and a mature harvest should garner a crop of 25 - 30t/ha in the UK without irrigation. If cut when dry at the end of winter and before sprouting starts, this material will be at 15%MC at harvest. The ideal MC (moisture content) for pelleting is 12%MC, thus air drying under cover is usually sufficient before processing and sale. In Greece the yield can be as high as 45t/ha with irrigation.
Switchgrass - This is a seed grass meaning that establishment is as cheap as that for an ordinary grass lea, except that this can be considered as permanent grassland! The annual harvest, from year 1, can be pelleted for ease of fuel supply, baled for burning in a straw burner, or potentially converted to bio-ethanol - it is unlikely that the sugar content will be high enough for this to be suitable for secondary processing, i.e. to produce a liquid fuel.
Straw - There are several straw burners on the market, most of which take one or more large round bales.
Coniferous Forestry & Woodland Management - Minimum processing means that wood from these sources can be supplied to the end user as simple saw log of ca. 1m in length. Or, all this material can be chipped, piled and stored in an open fronted shed to allow air circulation and avoid overheating. In the chipped form it is immediately useable as a fuel conveyed directly into the bottom of the modern wood burners.
These forestry and biomass products can be sold in a variety of forms.
- Pelletted Logs - ca. 30 cm
- Saw-mill Logs - ca. 1m length
The natural lignins, celluloses and oils in wood are inflammable; they are a naturally cycling living hydrocarbon. Produced by all plants, they use carbon dioxide from the atmosphere and water from the soil in the process of Photosynthesis. This is backed up by the same sort of Cellular Respiration using oxygen from the atmosphere that is common to all other life on the planet. The action of burning simply recombines the oxygen with the carbon to form carbon dioxide again; combines the Hydrogen with the Oxygen to form Water; and in the process releases lots of heat.
Both chips and pellets can be conveyed directly into the base of a central heating boiler where they are fired in the normal way. The gases are then passed through a secondary burning phase, thus abstracting all the useful heat from the wood and its volatile oils and tars, before the 'purified' smoke is passed up the chimney. This means that the chimney does not get sooted up and the only deposits in the boiler are friable and easily brushed out during a weekly clean of the pipes.Top of page
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