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The emissions of green house gases contribute to global warming. Consequently, renewable energies such as solar, wind power, hydropower and bio energy appear as alternatives for reducing these emissions. One promising source of renewable energy is forest biomass, for it is considered to have neutral CO2 balance. The problem is to quantify the amount of CO2 that is emitted for a certain amount of energy generated, compared to the CO2 emitted to generate the same amount of energy from a non-renewable source. In this paper we calculate biomass production and carbon dioxide balance of an eight-year-old Populus deltoides short rotation forestry (SRF) under two cutting cycles (harvesting every two years, biennial and every three years, triennial). We also compare the amount of energy generated per kg of CO2 emitted in the use of fossil fuels versus the amount of energy generated per kilogram of CO2 emitted. On the one hand, total biomass yield was 12.6 ± 0.9 Mg ha-1 year-1 and 15.1 ± 1.5 Mg ha-1 year-1 for biennial and triennial cutting cycles respectively. On the other hand, total emissions of CO2 for growing a poplar SRF with a cycle of eight year and biennial cutting sequence reached a value of 738.8 kg ha-1 year-1; however, triennial short total emissions are equivalent to 695.5 kg ha-1 year-1. We concluded that the use of biomass makes a positive contribution to the reduction of greenhouse gases, in particular CO2, reducing emissions almost five times compared with fossil fuels. Las emisiones de gases de efecto invernadero contribuyen al calentamiento global. En esta situación, las energías renovables como la solar, eólica, hidroeléctrica y biomasa, aparecen como una alternativa para reducir estas emisiones. Una prometedora fuente de energía renovable es la biomasa, considerada con un balance de CO2 neutro. El problema es cuantificar el CO2 emitido para una cierta cantidad de energía generada, en comparación con el CO2 emitido para generar la misma cantidad de energía de una fuente no renovable. En este trabajo se calculó la producción de biomasa y el balance de CO2 en una rotación de ocho años de edad de Populus deltoides bajo dos ciclos de corte (bienal y trienal). También se comparó la cantidad de energía generada por kilogramo de CO2 emitido en el uso de combustibles fósiles frente a la cantidad de energía generada por kilogramo de CO2 emitido en el uso de biomasa como energía. El rendimiento total de la biomasa fue de 12,6 ± 0,9 Mg ha-1 año-1 y 15,1 ± 1,5 Mg ha-1 año-1 para los ciclos bienal y trienal respectivamente. Las emisiones totales de CO2 fueron de 738,8 kg ha-1 año-1 y 695,5 kg ha-1 año-1 para los ciclos bienal y trienal, respectivamente. Se concluyó que el uso de biomasa constituye una contribución positiva a la reducción de gases de efecto invernadero, en particular CO2, reduciendo las emisiones casi cinco veces en comparación con combustibles fósiles.

Optimizing the harvesting of Miscanthus x giganteus: The effect of harvest time and system of biomass cost. Biomass and Energy Crops V

Given the energy challenges confronted by the world in general, where Chile is not an exception, forest energy crops have been positioned as a viable alternative to diversify this country's energy matrix. These types of crops, still under development, are based on short rotation shifts with high biomass production. The problem arises when assessing the sustainability of such crops. Accordingly, the energy balance is an important factor to assess sustainability i.e. we cannot spend more energy to produce biomass than what is released by the biomass combustion. This work presents the energy balance of harvest products at roadside in a Populus deltoides clone Lux short rotation forestry during eight years (2000-2008), comparing biennial (T2) and triennial (T3) shifts. Consequently, we calculated the energy cost of production and harvest and the amount of energy released in the combustion of the biomass generated. Both rotation shifts got positive results, being triennial shifts more energy efficient than biennial ones (34.7 T2 vs 25 T3)., Ante el desafío energético al cual se enfrenta el mundo en general, y Chile no es una excepción, los cultivos forestales con destinación energética se han ido posicionando como una alternativa viable para la diversificación de la matriz energética del país. Este tipo de cultivos, aún en fase de desarrollo, se basan en turnos cortos de rotación con altas producciones de biomasa. El problema surge a la hora de evaluar la sostenibilidad de dichos cultivos. El cálculo del balance energético es clave para valorar dicha sostenibilidad, es decir, no se puede gastar más energía en producir biomasa que la que esta otorga con la combustión. En este trabajo se calcula el balance energético, considerando los productos de la cosecha puestos a orilla de camino, de un cultivo de Populus deltoides clon Lux con fines energéticos durante un periodo de ocho años (2000-2008), comparando un turno de rotación bienal (T2) con uno trienal (T3) en un sitio con ambiente mediterráneo. Para ello se ha calculado el costo energético de la producción y cosecha, y la cantidad de energía liberada en la combustión de la biomasa generada. En ambos turnos de rotación se obtienen resultados positivos, siendo más conveniente energéticamente el turno trienal respecto al bienal (34,7 T2 vs 25 T3).

This work describes part of the research activities conducted within the ENERPAN project. The main aim of the project is to increase the agronomic and physiological knowledge concerning the suitability of switchgrass (Panicum virgatum L.) genotypes for energy use in the Mediterranean environment. Our research activity focused on investigating different crop management systems, in order to optimize switchgrass biomass production. Three field trials were carried out in spring 2010: (i) six switchgrass varieties were compared assessing their morphological and physiological responses to the Mediterranean environmental conditions; (ii) two switchgrass varieties were studied to investigate the influence of water and nitrogen level on crop yield, (iii) the sustainability of switchgrass cropping system was evaluated, at farm level for two different switchgrass varieties (e.g. production, energy balance, GHG emission etc.). Preliminary results on biomass yield response to the environmental conditions and to crop management seem to show a good suitability of some switchgrass varieties to our environment with promising biomass productions. Furthermore, nitrogen and water levels seems to affect switchgrass yield. Our results referred just to the first year of growth, for this reason, further studies are needed to evaluate switchgrass performances in the long term and to estimate the crop cycle length of this perennial species in our climate., Proceedings of the 19th European Biomass Conference and Exhibition, 6-10 June 2011, Berlin, Germany, pp. 615-618