Renewable Energy System

B.TECH IV YEAR II SEM LECTURE NOTES RENEWABLE ENERGY SOURCES

POTENTIALS AND TECHNOLOGIES FOR UTILISATION OF RENEWABLE ENERGY SOURCES

NOMENCLATURE c cp cv F g h H I m p P Q t T u v V w W x y z speed of light specific heat at constant pressure specific heat at constant volume force acceleration of gravity specific enthalpy heating value electric current mass pressure power thermal energy, heat time temperature specific internal energy specific volume = 1/ρ electric tension velocity energy, general distance parameter defining physical state vertical distance η ρ energy efficiency density Subscripts el fuel heat loss marg th electricity fuel useful heat loss marginal thermal LIST OF ABBREVIATIONS ARC cap GNP IPCC PAH PV RME SEK USD VOC Anti-reflection coating capita Gross national product Intergovernmental Panel on Climate Change polyaromatic hydrocarbons Photo-voltaic rapsmetylester Swedish crown US Dollar volatile organic compounds

1. INTRODUCTION 1.1 Scope of these notes The objective of the lecture notes is to give an introduction to the current issues of energy engineering with a focus on the role of energy supply for development of the human societies. Technical issues are treated only to the extent that this is necessary for understanding of the limitations and potential of the current technologies. These notes discuss the potential and technologies of renewable energy sources for generation of energy carriers in industrial and developing countries. The approach is source-oriented rather than user-oriented, but this does not mean that it is implied that a switch from a “conventional” energy source to a renewable energy source requires that the same energy carrier or the same amount of energy shall serve the needs of the user after the switch. Since use of renewable energy is often more expensive than use of the conventional energy sources, introduction of energy conservation measures is often economically justified when the switch to renewable energy is made. 1.2 Definition of renewable energy In the strict thermodynamic sense energy cannot be destroyed or produced, only converted from one form to another. These conversions are associated with an increase of the total entropy, which means a loss in the “quality” of the energy i.e. a loss of exergy. Apparently, renewable energy is a contradiction from a strict thermodynamic point of view. The term is nevertheless used frequently, not only by politicians and laymen, but also by those who understand their thermodynamics. Renewable energy is then understood as energy that is supplied directly or indirectly from the Sun or the Moon and thermal energy stored or generated below the crust of our planet, the Earth. In other words, renewable energy represents energy that can be expected to be available for as long as the Earth is habitable for the human race. Certainly these energy flows will deteriorate at some stage, but in the human perspective they may be considered as perpetual. This is in contrast with the large but much more limited deposits of fossil fuels, coal, petroleum and natural gas and the likewise limited deposits of fissile uranium. Even though renewable energy is based on energy sources that are expected to be available very far into the future, there is no guarantee that an energy system is sustainable just because it relies on renewable energy sources. A discussion of different requirements for sustainability is the subject of a forthcoming lecture. It may be sufficient at this stage to mention two requirements for sustainability that must be fulfilled in addition to a sustainable energy source. These are economic sustainability and environmental sustainability. Economic sustainability requires that the resources generated by utilisation of the energy source exceed those needed for the utilisation. Environmental sustainability requires that first of all the resource base is not deteriorated by excessive utilisation. This can easily be the case when biomass energy is over-utilised. Environmental sustainability also requires that the impacts and risks caused by the utilisation are 1