It may come as something of a surprise to many people that one of Co Mayo's most realisable long-term energy resource options, especially in terms of benefits to local communities and local economies, is the development of sustainable forestry.
A research project I was involved in a few years ago (the Mayo Energy Audit) found that Co Mayo could meet over one third of its total heating requirements from wood produced in sustainably managed deciduous woodland, in combination with a smaller area of coniferous plantation.
The most viable method of production was identified as medium-term rotation coppicing, whereby relatively slow-growing deciduous trees are coppiced on an 8-20 year cycle. Under a coppicing system, trees are cut to near ground level when they reach a useful size and then are allowed to grow back before being cut again at the end of the next cycle. Well-managed coppiced woodland can be maintained for many centuries without there ever being a need to replant. The only problem is, most of this woodland has yet to be planted!
A number of native and non-native species of deciduous trees are suitable for coppicing. These include ash, sycamore, alder, sweet chestnut, hazel and oak. Oak is a slow-growing tree so an oak coppice cut now will not be ready for its next cut until the children of the people doing the cutting reach adulthood! Generally, coppicing species do best on drier land, and will often thrive in rocky terrain where little else will grow.
What is not a good choice for coppicing is hybrid (biomass) willow, as it is very fussy in terms of suitable soils, demands heavy doses of artificial fertilisers in order to maintain yields, and requires specialist harvesting machinery. The only type of willow worth planting is the native grey or bog willow, on waterlogged ground where nothing else will grow.
Whatever the varieties of trees used, the wood harvested needs two to three years to dry properly so it pays to have good storage facilities where cut wood can be stockpiled. Anyone who cuts turf will be familiar with this concept of always cutting a few years ahead. Like turf, wood will dry outside moderately well if stacked properly. It is only necessary to move it into a shed after the first year of drying, by which time the moisture content should be down to 25-30 percent. Well-dried wood has a moisture content of around 16-18 percent.
Although there is a widespread belief that burning wet fuel somehow saves fuel (because it burns more slowly) the reality is that wet fuel cannot begin to burn efficiently until all the moisture has been boiled off. The result of this inefficient combustion is much lower heat output, and production of carbon monoxide combined with and lots of corrosive tarry residues that clog up flues and increase the risk of chimney fires. So if you're going to burn wood (or turf) burn it dry.
When it comes to burning wood, the choice is between purpose-designed wood stoves and multi-fuel stoves. The former generally are unsuited to burning anything else except wood, but are generally designed for maximum efficiency. Multi-fuel stoves are a very mixed bag - many are designed for burning coal or turf briquettes and have the wrong type of firebox for efficient combustion of wood. Wood requires a tall firebox that provides room for secondary combustion to take place. The three-sided wrap-around boilers often found in multi-fuel stoves are a particularly unsuited for burning wood, as they excessively lower combustion temperatures. Either find a stove with a boiler located only at the rear, or forget the boiler option completely.
The final word is on open fires - they're a disaster! >>> http://www.dslfarms.com
Monday, February 14, 2011
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