Salinity differences

Useful chemical energy may be defined as energy that can be released through exotermic chemical reactions. In general, chemical energy is associated with chemical bindings of electrons, atoms and molecules. The bindings may involve overlapping electron wave-functions of two or more atoms, attraction between ionised atoms or molecules, and long-range electromagnetic fields created by the motion of charged particles (notably electrons). In all cases, the physical interaction involved is the...

Atmospheric electricity

The Earth is surrounded by a magnetic field, and from a height of about 80 km a substantial fraction of atmospheric gases is in an ionised state (cf. section 2.3.1). It is thus clear that electromagnetic forces play an important role in the upper atmosphere. Manifestations of electromagnetic energy in the lower parts of the atmosphere are well known, in the form of lightning. Speculations on the possibility of extracting some of the electrical energy contained in a thunderstorm have appeared...

Energy storage and auxiliaries

The intermittency of several renewable energy flows makes it imperative to include features in systems relying on renewable energy inputs that can assure a match between demand and supply in time and place. For less than 100 renewable energy systems, the non-renewable units can be used for back up, but for pure renewable energy systems, storage of energy is necessary. To some extent, the storable biofuels can serve this purpose, but it is highly likely that additional components will be...

Info

An electric vehicle of mass 1000 kg excluding the battery is designed for a 50 km range in a city driving cycle. The vehicle is equipped with a new 500 kg battery and the average energy consumption is measured to be 0.3 kWh km-1 (from the battery). At a speed of 36 km h-1 the required acceleration is 2.0 m s-2, and the power required to overcome the frictional losses is one third of the total power required. Do the same calculation for an acceleration a 1.5 m s-2. - Calculate the required...

Current penetration of renewable energy technologies in the marketplace

The penetration of renewable energy into the energy system of human settlements on Earth is from one point of view nearly 100 . The energy system seen by the inhabitants of the Earth is dominated by the environmental heat associated with the greenhouse effect, which captures solar energy and stores it within a surface-near sheet of topsoil and atmosphere around the Earth. Only 0.02 of this energy system is currently managed by human society, as illustrated in Figure 1.1. Within this...

Treatment of the time variable

In order to predict the performance of systems consisting of one or several energy converters, stores and transmission devices, a mathematical model of the energy flow may be constructed. Such a model is composed of a number of energy conversion and transport equations, including source and sink terms corresponding to the renewable energy input and the output to load areas, both of which are varying with time. The conversion processes depend on the nature of the individual devices, and the...

Solar heat or heatandelectricity producing systems

The examples described in this subsection will be based on flat-plate solar collector devices (cf. section 4.2.1) in various configurations, and the system simulations will use as a data base the Danish Reference Year, which was summarised in section 3.1.3 (cf. Figs. 3.11-3.15). It is clear that use of the same systems at latitudes with higher levels of solar radiation will improve the performance and make it possible to cover loads with smaller and less expensive systems. On the other hand,...

Variability in wind power

Non Renewable Energy Sources

An example of short-term variations in wind speed at low height is given in Fig. 3.35. These fluctuations correspond to the region of frequencies above the spectral gap of Fig. 2.110. The occurrences of wind gusts, during which the wind speed may double or drop to half the original value over a fraction of a second, are clearly of importance for the design of wind energy converters. On the other hand, the comparison made in Fig. 3.35 between two simultaneous measurements at distances separated...

CHAPTER

Adjustments in blade profile and regulation features of the blades are likely to follow the widespread interest in offshore wind. Currently, essentially the same turbines are sold for deployment on land and at sea. However, the wind conditions at sea are so different, that the land design, typically chosen to optimise total annual production at good sites on land, far from does so when the same turbine is placed off-shore cf. the difference between the two patterns in Figs. 4.91 and...

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Natural Gas Industry Layout

Layout of PEM fuel cell layer, several of which may be stacked. Figure 4.109. Expected part-load efficiencies for a 50 kW PEM fuel cell, projected from measurements involving 10-20 cell test stacks Patil, 1998 . Figure 4.109. Expected part-load efficiencies for a 50 kW PEM fuel cell, projected from measurements involving 10-20 cell test stacks Patil, 1998 . For use in automobiles, compressed and liquefied hydrogen are limited by low energy density and safety precautions for...

Geothermal flows and stored energy

Heat is created in some parts of the interior of the Earth as a result of radioactive disintegrations of atomic nuclei. In addition, the material of the Earth is in the process of cooling down from an initial high temperature, or as a result of heat released within the interior by condensation and possibly other physical and chemical processes. Regions of particularly high heat flow Superimposed on a smoothly varying heat flow from the interior of the Earth towards the surface are several...

Heat Of Reaction Versus Equivalence Ratio

Energy change for idealised cellulose thermal conversion reactions. Source T. Reed 1981 , in Biomass Gasification T. Reed, ed. , reproduced with permission. Copyright 1981, Noyes Data Corporation. a Specific reaction heat. b The negative of the conventional heat of formation calculated for cellulose from the heat of combustion of starch. c Calculated from the data for the idealised pyrolysis oil C6H8O AHc - 745.9 kcal mol-1, AHf 149.6 kcal g-1, where Hc heat of combustion and Hf heat...

Augmenters and other advanced converters

In the preceding sections, it has been assumed that the induced velocities in the converter region were half of those in the wake. This is strictly true for situations where all cross-wind induced velocities ut and ur can be neglected, as shown in 4.45 , but if suitable cross-wind velocities can be induced so that the total stream-wise velocity in the converter region, ux, exceeds the value of -V. uxin uxout by a positive amount Suxind, then the Betz limit on the power coefficient, Cp 16 27,...

Heat production from biomass

Heat may be obtained from biological materials by burning, eventually with the purpose of further conversion. Efficient burning usually requires the reduction of water content, for example, by drying in the Sun. The heat produced by burning cow dung is about 1.5x107 J per kg dry matter, but initially only about 10 is dry matter, so the vaporisation of 9 kg water implies an energy requirement of 2.2x107 J, i.e. the burning process is a net energy producer only if substantial sun-drying is...

Crosswind converters

Wind energy converters of the cross-wind type have the rotor axis perpendicular to the wind direction. The rotor axis may be horizontal as in wheel-type converters in analogy to water-wheels or vertical as in the panemones used in Iran and China. The blades ranging from simple paddles to optimised airfoil sections will be moving with and against the wind direction on alternative sides of the rotor axis, necessitating some way of emphasising the forces acting on the blades on one side. Possible...

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1 rl -ii. l chain 1 1 .I f amp ES amp f 20 X gt .v gt 11 i050.FM amp r .' . .-i V i 1 Figure 7.28. Overview of LCA calculations for present and future Danish energy systems. Total impacts and impacts per unit of energy used are given for each scenario. F monetised full chain, D domestic evaluation Kuemmel et al., 1997 . The reason for basing the examples of Chapters 6 and 7 on scenario work is the following, For the purpose of assisting decision-makers, a way must be found of describing a given...

Spectral composition of solar radiation

Practically all of the radiation from the Sun received at the Earth originates in the photosphere, a thin layer surrounding the convective mantle of high Figure 2.2. Variation in the solar radius as a function of time bottom , together with selected milestones in the development on Earth, associated with the building-up of oxygen in the Earth's atmosphere top . The rapid development of phytoplankton in the upper layers of the oceans at a relative oxygen concentration of 10-2 is associated with...