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Posted: Jul 25, 2012

The joker card in the renewable energy game

(Nanowerk News) Local renewable energy sources such as woodchips offer the advantage of being sustainable and reducing dependency on energy imports. Yet, they are best used for combined heat and power production
Woodchips are one of the renewable sources of energy used in domestic and district-level heating systems. They can come from wood waste from construction, agriculture, landscaping, logging and sawmills. Woodchips can also stem from trees planted in less productive land. “Woodchips have an important value, first of all, to stimulate the care of a resource like the forest that has often been abandoned”, Stefano Dal Savio, tells youris.com. He is an environmental engineer and manager of the energy and environment area of TIS Innovation Park in Bolzano, Italy.
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“[They also] enable the production of a local and renewable fuel,” Da Savio adds. Used as a power source, woodchips could help nations “ensure [that] a part of their energy [production comes] from within the country,” sayd Ioana Ionel, Romania’s national co-ordinator of the EU funded BIO-HEAT project, based at Timisoara’s Polytechnic University. The project promotes the use of a forestry technique based on two to four year wood cutting cycles, called short rotation coppice (SRC), to produce woodchips for district heating systems in Eastern Europe.
As the main solid biomass fuel sources used for combined heat and power production, known as cogeneration, woodchips offer definite advantages as an energy source. “If you produce only heat from woodchips you have an energy efficiency of more than 80%, in cogeneration plants the efficiency is 65 % whereas in power-only production plants [it is down to] 30-40%,” Edita Vagonyte, European Affairs Manager from the Brussels, Belgium-based European Biomass Association, tells youris.com
“Since many power plants in Europe produce electricity only, the aim at EU level is to build only new cogeneration plants so that the efficiency is increased and we use the biomass more efficiently,” Vagonyte adds. In particular, trigeneration systems, which generate a combination of cooling, heating and power, are the best possible option, according to Ionel.
When it comes to energy production, woodchips offer an alternative to other energy sources. “From one hectare of land planted with poplar between 15 and 30 tons per hectar per year of biomass can be obtained,” Dal Savio explains, “The shorter the duration of the cycle, the greater the amount of biomass [obtained], even though of lower quality since it will have a higher quantity of bark.” He estimates that at an average value of 22 tons per hectar per year the amount of energy produced by woodchips would be of 77000 kiloWatt hours per year. This is equivalent to 45 oil barrels or to 23 photovoltaic roof systems each producing 1.8kw from solar power.
Woodchips not be as attractive an alternative in terms of carbon emissions performance as other renewable energies, such as photovoltaic, solar or thermal energy. Although its combustion is CO2 neutral as long as no more trees are cut than those that are replanted, planting, farming, harvesting, chipping and transporting it do cause net emissions. In particular, transport is, according to Ionel, where most of the CO2 is emitted.
Experts believe for woodchip to be a sustainable energy source, the transportation distance from the plantation to the power and heating plant would need to be limited to between 40 to 70 kilometers. Vagonyte remarks: “Woodchips contain around 50% of water; therefore, it is not even economically viable to transport them over long distances.”
Source: By Elena Ledda, Youris
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