Lecture (7) ASDAKMAJAIWJEWUEWWEEWRR.pptx

DSFA

1. 4-PERSPECTIVES 4.2 The energy scene – its history and present state 4.3 Suggested topics for discussion

2. 1.2 The energy scene – its history and present state The speed of the Earth in its orbit around the Sun is about 3×10 4 m s -1 , corresponding to a kinetic energy of some 2.7×10 33 J. The Earth further rotates around its axis with an angular velocity of about 7.3×10 -5 rad s -1 , furnishing an additional kinetic energy of some 2.2×10 29 J. The work required in order to pull the Earth infinitely far away from the Sun, against the gravitational attraction, is about 5.3×10 33 J, and the corresponding work required to separate the Earth from its Moon is of the order of 8×10 28 J.

3. About 10 21 J is on average present as kinetic energy in the atmospheric and oceanic circulation and the potential energy of the continental height-relief, relative to sea-level, is about 2×10 25 J, taking into account density variations in the crust. 1.2 The energy scene – its history and present state

4. Much larger amounts of energy are involved in the chemical and nuclear bindings, which determine the state and structure of matter. The carbon compounds of biological material provide an example of chemical energy. During earlier periods of the Earth’s history, fossilisation of biological material created the deposits of coal, oil and natural gas, of which at least 10 23 J is presently believed to be recoverable in a form suitable for fuel uses. Current standing crops of biomass correspond to an average of 1.5×10 22 J. 1.2 The energy scene – its history and present state

5. 1.2 The energy scene – its history and present state The amount of solar energy intercepted by the Earth and hence the amount of energy flowing in the “solar energy cycle” (from incident radiation flux via reflection, absorption and re-radiation to heat flux away from the Earth) is about 5.4×10 24 J per year.

6. 1.2 The energy scene – its history and present state Energy fluxes of other than solar origin which occur naturally at the surface of the Earth are numerically much smaller. For example, the heat flux from the interior of the Earth through the surface is about 9.5×10 20 J y -1 , and the energy dissipated in connection with the slowing down of the Earth’s rotation (due to tidal attraction by other masses in the solar system) is of the order of 10 20 J y -1 .

7. 1.2 The energy scene – its history and present state The minimum energy requirement of man may be taken as the amount of “exchangeable” chemical energy that can be associated with the amount of food necessary to maintain life processes for someone performing a minimum of work and not losing weight. This minimum depends on the temperature of the surroundings, but for an adult man is generally considered to lie in the region of 60–90 W on average for extended periods, corresponding to (6 to 8)×10 6 J per day.

8. 1.2 The energy scene – its history and present state The maximum average rate of food energy intake that a human being can continue for extended periods is about 330 W, and the maximum average rate at which work can be delivered for extended periods is of the order of 100 W. During work periods, the “man-power” output level may be 300–400 W, and the maximum power which can be delivered by an adult male for a period of about a minute is roughly 2000 W.

9. 1.2 The energy scene – its history and present state Nuclear energy may be released in large quantities from nuclear reactions, such as fission of heavy nuclei or fusion of light nuclei. Except for spontaneously fissioning nuclear isotopes in the Earth’s crust, which release about 4×10 20 J per year, an initial amount of energy must be provided in order to get the energy-releasing fission or fusion processes going. With necessary additional improvements in the technology of fast breeder reactors, recoverable resources of nuclear fuels are estimated to be of the order of 10 24 J.

10. 1.2 The energy scene – its history and present state If fusion of deuterium nuclei to form helium nuclei could be made viable on the basis of deuterium present in sea water, this resource alone would amount to more than 10 31 J

11. 1.2 The energy scene – its history and present state Energy conversion processes depleting certain materials of the Earth may be said to constitute irreversible processes. This is often true from a practical point of view, even if the reverse process may be theoretically possible.

12. 1.2 The energy scene – its history and present state

13. 1.3 Suggested topics for discussion 1.3.1 Find out what has happened since year 2000 to the mounts of renewable energy used, based upon available statistical data, either globally or for your region. 1.3.2 Order the prices given on pages 13 and 14 according to type of energy (heat, fuels for industry or transportation, electricity) and type of customers (wholesale, retail). Try to find out what has happened to these prices since year 2000 (e.g. using the annually updated sources such as OECD, IEA or Danish Energy Agency). Have the relative prices changed?