• Energy Research

Abstract The oil price instability and the measures taken to reduce the increase in greenhouse gas emissions are the main factors promoting the development and use of environmentally friendly energies. From an energy efficiency point of view, biofuels constitute a renewable energy source and its use helps to reduce energy dependency on fossil fuels. The most used biofuels for transport worldwide are biodiesel (BD) and bioethanol. However, there are other options such as straight vegetable oil (SVO). SVO can be small-scale produced in local cooperatives through pressing, filtering and conditioning processes which are much simpler than the ones required for BD production. In this study a comparative life cycle assessment (LCA) of two biofuels obtained from Spanish rapeseed, namely small-scale SVO and large-scale BD, is performed. The LCA methodology allows the two biofuels’ production and their rate of consumption in a vehicle (a truck) to be compared. In this manner, it is possible to assess which is environmentally advantageous: to use SVO directly as biofuel or to convert it to BD. Moreover, LCA is used in the study to calculate the energy return on investment index (EROI) and an energy conversion ratio to evaluate which biofuel is more energy efficient. The obtained results show the environmental benefits of using SVO instead of BD by analyzing representative impact categories defined by the CML and EDIP methods. A sensitivity analysis has also been conducted. EROI indexes for SVO and BD production show a clear preference for SVO as compared to BD.

Abstract The oil price instability and the measures taken to reduce the increase in greenhouse gas emissions are the main factors promoting the development and use of environmentally friendly energies. From an energy efficiency point of view, biofuels constitute a renewable energy source and its use helps to reduce energy dependency on fossil fuels. The most used biofuels for transport worldwide are biodiesel (BD) and bioethanol. However, there are other options such as straight vegetable oil (SVO). SVO can be small-scale produced in local cooperatives through pressing, filtering and conditioning processes which are much simpler than the ones required for BD production. In this study a comparative life cycle assessment (LCA) of two biofuels obtained from Spanish rapeseed, namely small-scale SVO and large-scale BD, is performed. The LCA methodology allows the two biofuels’ production and their rate of consumption in a vehicle (a truck) to be compared. In this manner, it is possible to assess which is environmentally advantageous: to use SVO directly as biofuel or to convert it to BD. Moreover, LCA is used in the study to calculate the energy return on investment index (EROI) and an energy conversion ratio to evaluate which biofuel is more energy efficient. The obtained results show the environmental benefits of using SVO instead of BD by analyzing representative impact categories defined by the CML and EDIP methods. A sensitivity analysis has also been conducted. EROI indexes for SVO and BD production show a clear preference for SVO as compared to BD.

Abstract This work performs a cost evaluation of small-scale produced wood chips from forests in the Euro-Mediterranean region to be used for heating purposes. The study is focused on forests located in the Argencola municipality (Catalonia, northeastern Spain). The use of such easy-to-produce biofuel is appealing since it may be used as a valid substitute of heating oil to produce thermal energy in the same area where it is produced, thus minimizing transportation requirements and reducing dependence on the rising prices of heating oil. Additionally, it allows facing environmental and social concerns related to the current lack of management in the forests under analysis, which has led to an important increase in the biomass stock and wildfires risk. As wildfires in the Euro-Mediterranean region generate important impacts, an average economic cost of wildfires has been evaluated in this paper. The economic assessment of small-scale production and consumption of wood chips as proposed in this study has shown interesting economic benefits when compared with current heating oil prices. Results indicate that it is a realistic option since production costs range from 12.2 €/GJ to 18.5 €/GJ depending on the applied forestry practices, whereas current cost of heating oil is about 23.9 €/GJ. A sensitivity analysis has also been conducted to assess the impact of the data with higher uncertainty on the final results. It has been shown that the key factors that determine the viability of the proposed model are heating oil price, biomass stock growth rate, transportation requirements and applied forest management practices. Results presented prove that wood chips cost is quite independent of fossil fuel prices, thus higher fossil fuel prices greatly favors the use of wood chips when produced and consumed in the same area, thus minimizing transportation requirements. In addition, higher biomass growth rates than those considered in this work may reduce the final cost of small-scale produced wood chips.

Abstract This work performs a cost evaluation of small-scale produced wood chips from forests in the Euro-Mediterranean region to be used for heating purposes. The study is focused on forests located in the Argencola municipality (Catalonia, northeastern Spain). The use of such easy-to-produce biofuel is appealing since it may be used as a valid substitute of heating oil to produce thermal energy in the same area where it is produced, thus minimizing transportation requirements and reducing dependence on the rising prices of heating oil. Additionally, it allows facing environmental and social concerns related to the current lack of management in the forests under analysis, which has led to an important increase in the biomass stock and wildfires risk. As wildfires in the Euro-Mediterranean region generate important impacts, an average economic cost of wildfires has been evaluated in this paper. The economic assessment of small-scale production and consumption of wood chips as proposed in this study has shown interesting economic benefits when compared with current heating oil prices. Results indicate that it is a realistic option since production costs range from 12.2 €/GJ to 18.5 €/GJ depending on the applied forestry practices, whereas current cost of heating oil is about 23.9 €/GJ. A sensitivity analysis has also been conducted to assess the impact of the data with higher uncertainty on the final results. It has been shown that the key factors that determine the viability of the proposed model are heating oil price, biomass stock growth rate, transportation requirements and applied forest management practices. Results presented prove that wood chips cost is quite independent of fossil fuel prices, thus higher fossil fuel prices greatly favors the use of wood chips when produced and consumed in the same area, thus minimizing transportation requirements. In addition, higher biomass growth rates than those considered in this work may reduce the final cost of small-scale produced wood chips.

Abstract Straight vegetable oils may be used as fuel in existing diesel engines. However, some precautions should be taken into account because some of their physicochemical properties must be adjusted through temperature control to ensure enhanced combustion, thus avoiding premature aging of the engine. Although it is well known that surface tension plays a prevalent role in the fuel atomization process which affects the combustion quality, there is lack of published information about its variation with temperature when dealing with straight vegetable oils to be used as fuel in unmodified diesel engines. In this work, the surface tension of several vegetable oils is studied in a wide temperature interval. The optimal range of temperatures at which each vegetable oil should operate to adjust its properties to those of automotive diesel and biodiesel is found. Moreover, an empirical relationship between the dependence between surface tension and density is presented. Therefore, by means of this relationship, just measuring the density of a given oil, its surface tension can be directly deduced.

Abstract Straight vegetable oils may be used as fuel in existing diesel engines. However, some precautions should be taken into account because some of their physicochemical properties must be adjusted through temperature control to ensure enhanced combustion, thus avoiding premature aging of the engine. Although it is well known that surface tension plays a prevalent role in the fuel atomization process which affects the combustion quality, there is lack of published information about its variation with temperature when dealing with straight vegetable oils to be used as fuel in unmodified diesel engines. In this work, the surface tension of several vegetable oils is studied in a wide temperature interval. The optimal range of temperatures at which each vegetable oil should operate to adjust its properties to those of automotive diesel and biodiesel is found. Moreover, an empirical relationship between the dependence between surface tension and density is presented. Therefore, by means of this relationship, just measuring the density of a given oil, its surface tension can be directly deduced.

This work describes a methodology to optimize a grid-connected hybrid renewable energy system (HRES) that hybridizes photovoltaic, wind and forest biomass energy sources taking into account cost and environmental impact criteria from a life-cycle perspective. The developed model has been tested in a sample township in central Catalonia. The results show that life-cycle cost and life-cycle environmental impact are contradicting criteria. Low environmental impact layouts highly dependent on RES have higher costs than the ones more reliant on the electricity from the public grid, which present high environmental impact. A sensitivity analysis has been performed to analyze the trade-offs between different energy sources of the system, showing that wind power is the RE source with higher impact on the system since it presents lower cost and lower environmental impact, compared with biomass and photovoltaic power. Another important conclusion that can be drawn from such sensitivity analysis is that improving the rate of return on investment in HRES would be a very beneficial measure to encourage the use of renewable energies for electricity production, as it has significant positive outcomes in terms of both cost and environmental impact reduction. Peer Reviewed

This work describes a methodology to optimize a grid-connected hybrid renewable energy system (HRES) that hybridizes photovoltaic, wind and forest biomass energy sources taking into account cost and environmental impact criteria from a life-cycle perspective. The developed model has been tested in a sample township in central Catalonia. The results show that life-cycle cost and life-cycle environmental impact are contradicting criteria. Low environmental impact layouts highly dependent on RES have higher costs than the ones more reliant on the electricity from the public grid, which present high environmental impact. A sensitivity analysis has been performed to analyze the trade-offs between different energy sources of the system, showing that wind power is the RE source with higher impact on the system since it presents lower cost and lower environmental impact, compared with biomass and photovoltaic power. Another important conclusion that can be drawn from such sensitivity analysis is that improving the rate of return on investment in HRES would be a very beneficial measure to encourage the use of renewable energies for electricity production, as it has significant positive outcomes in terms of both cost and environmental impact reduction. Peer Reviewed