Future Resources: The ways towards a sustainable energy economy
Future Resources: The ways towards a sustainable energy economy Download PDF
Energy is always needed in the form of certain services like a comfortable room climate, hot water, illumination, powering of machines, or mobility. During the conversion of primary energy to such energy services, energy carriers run through several steps, all of which are associated with efficiency losses. These losses can be reduced considerably by modern conversion technologies and energy management techniques.
Besides even greater efficiency in the energy conversion and a more rational use of energy in all equipment, the substitution of high-grade energy by less valuable energy is also part of this strategy (e.g. substituting electricity used for heating rooms with heat from co-generation or with improved thermal insulation). The efficient use of the energy in unavoidable, non-recyclable waste materials is also of great importance.
Consistency: Currently, fossil and nuclear energy resources are taken from beneath the surface of the earth, yet their conversion products are disposed of in the environment. The present energy system is “open”. Only “closed” systems are however sustainable in the long run.
To a great extent, closed systems provide energy without the consumption of raw materials and always return the material to the energy cycle. Energy systems that use relatively small parts of the natural energy cycles driven by the sun, by gravitation, or by geothermal heat are very close to this ideal.
The materials employed within these processes (like e.g. solar collectors) can be recycled to a great extent as these are not contaminated or otherwise modified in an irreversible way: thus they are not “consumed” in the sense of fossil or nuclear energies.
The energy needs depend on the lifestyle and consumer habits. Changes in the human activities and needs, e.g. in recreational behaviour, can have a strong impact on the resulting energy consumption.
The scope of self dependent responsibility is rather large, ranging from a deliberate renunciation of energy-intensive products or exaggerated mobility to an intelligent assortment of foods and transportation means. From an awareness that old habits calling for “further, faster, and more” will not be sustainable in the long run, a change of values in the industrial countries calling for “living better instead of having more” would have a considerable influence on future energy demands.
Wind power has been used by man from time immemorial. Before the steam engine was invented, trade across the oceans was only possible by means of sailing vessels. Windmills ground grain and drove water pumps for irrigation and drainage purposes.
The first endeavours to revive this environmentally friendly technology were undertaken in the fifties. However, it wasn’t until the oil crisis of the seventies, together with an increasing awareness of the environment, which helped to revive wind power in recent times.
Modern wind turbines utilise the lift principle rather than the resistance principle. Similar to the wing of an aircraft, the wind flow passing over the rotor blades of the wind turbine generates a lifting force, which makes the rotor turn around.
While only a maximum of 15 % of the wind energy can be transformed by applying the resistance principle, a yield of up to 60 % can be achieved by applying the lift principle.
Depending on the wind velocity, it is possible to differentiate between four phases of operation. At very low wind speed, the wind energy is not sufficient to overcome the system’s moments of friction and inertia, and the rotors remain stationary.
The towers of the largest wind turbines today are more than 120 metres high, so that together with the rotor blades the wind turbines reach a height of up to 170 m. As a rule: the higher the tower, the less interference from air turbulence caused by ground roughness and the mean wind velocities are higher.
The towers are generally realised as steel-jacketed constructions which least influence the surrounding countryside due to their slim design.
Hydropower was already used in preindustrial times for driving mills, sawmills, and hammers works. Both the kinetic energy and the potential energy from flowing water can be converted into mechanical power by a turbine wheel, which in turn can drive machines or generators.
Hydropower is a mature technology which, world-wide, generates the second largest share of energy from renewable sources, after the traditional use of biomass. 17 % of the electricity consumed in the world today is generated by hydroelectric power stations.
Solar cells directly convert sunlight into electrical power without any mechanical, thermal, or chemical intermediate steps. At the core of all solar cells is a semiconducting material, usually silicon. Solar cells utilise the photovoltaic effect: for certain arrangements of superimposed semiconductor layers, free positive and negative charges are generated under the influence of light (photons).
These charges can then be separated by an electrical field and flow as electrons through an electrical conductor. The direct current thus generated can be used for powering electrical devices or stored in batteries. It can also be transformed into alternating current and fed into the national grid.
There are solar cells in all conceivable sizes. Miniature cells can be found in pocket calculators and wristwatches. In the kilowatt range, whole households can be supplied with power from solar cells. Put together in solar fields, solar cells have recently entered the megawatt range.
SOLAR THERMAL POWER PLANTS
Solar-thermal power plants use the high-temperature heat from concentrating solar collectors to drive conventional types of engines.
The plants generate electricity or coupled heat and power, which is when both electric power and process heat are generated at the same time.
In this way, a solar-thermal power plant can simultaneously produce electricity, provide cooling by means of an absorption chiller, generate industrial processing steam, and produce drinking water with a seawater desalination plant, thereby converting as much as 85 % of the absorbed solar heat into useful energy.
Efficient thermal storage of the generated solar heat and the additional firing of fuel are indispensable in order for the power plant to continuously meet the load. The power plants can be used in two ways: during the day as a solar power plant and during the night as part of the conventional power system.
Not only is the overall fuel consumption reduced in this way, the construction of conventional back-up power plants also becomes unnecessary. Thus the benefits to the environment are two-fold and the costs of generating electricity can be halved compared to purely solar operation.
The use of biomass for generating electricity and heat is a particularly attractive form of energy conversion from the climate point of view. When growing, the biomass first removes the greenhouse gas CO2 from the atmosphere and binds the carbon in the biomass.
This carbon is later released into the atmosphere again – e.g. as a result of combustion or when the biomass is rotting. Therefore, when biomass is used for energy purposes, then only that CO2 is released which was previously removed from the atmosphere when the plant was growing.
The biomass regulation, which determines which substances are considered as biomass for the renewable energy regulation, defines them as “energy carriers from phyto-mass and zoo-mass”, i.e. materials originating from vegetation and animals, including the “consequential and secondary products, remains and waste, the energy content of which originated from phytomass or zoo-mass”.
Furthermore, the biomass regulation specifies which processes are allowed and the environmental requirements.
Included amongst the most important biogenous fuels are of course wood and leftover timber accumulating from forestry, in sawmills or as old timber. Fast-growing trees, e.g. poplars and willows, can be planted in so-called short-turnaround plantations and be harvested within a few years.
Organic residuals are also suitable energy sources. Liquid manure, bio-waste, sewage sludge, and municipal sewage and food leftovers can be converted into high-energy biogas. Biogas is also released from landfills.
However, biogas from landfills and sewage-treatment plants is not recognised as a biogas in the context of the biomass regulation, because it falls under a special clause of the Renweable Energy Sources Act.
The alcohols ethanol and methanol are very suitable for use as fuels in transportation, proven by years of experience
Bio fuels offer a good opportunity to partially substitute petroleum as an energy carrier in the transport sector, since its use addresses all three problems at once. The feedstock can be produced in the country of consumption – the reliance on imports is thus reduced, and they grow again – so they are renewable.
And, finally, a further enormous advantage of biofuels is that they are in principle CO2-neutral, because the CO2 emitted by their combustion was absorbed from the atmosphere during cultivation.
Pure ethanol can only run special motors, like those found in Brazil’s vehicle fleet in the eighties, or those used in the so-called “Flexible Fuel Vehicles”. A small fleet of these is operating in Sweden and in the United States. A more simple method is to add bio-ethanol to petrol, by which means bio-ethanol could be introduced into the market with little effort.
Geothermal energy, or heat from the earth, is heat which reaches the surface of the earth from the earth’s molten core. On the way to the surface, both the layers of earth and the rocks, as well as any underground water reservoirs, are heated. In some locations, hot water and steam reach the earth’s surface in the form of hot springs or geysers.
The deeper one penetrates the interior of the earth, the warmer it becomes. In Central Europe the temperature increases by an average of 3 °C per 100 m depth. The temperature in the uppermost mantle is approximately 1,300 °C; in the earth’s core it is probably around 5,000 °C.
The heat stored in the earth is inexhaustible by human standards. Several times as much energy as is used world-wide ascends from the depths of our planet every day and escapes unused into space. Most of this heat flow originates from the continuous decay of radioactive elements in the mantle and in the earth’s crust, a process which will continue for billions of years. This source of energy can be used practically everywhere.
Either this transport medium is already available underground in the form of steam or hot water. In this case, it is brought to the surface where it cools down and is then normally returned underground again; or a medium, e.g. water, must first be pumped to the required depths and returned heated to the surface again.
The heat thereby acquired can then be used directly for heating purposes or for other heat consumers. Equally attractive is to use geothermal energy for electricity generation, because it is available round the clock. Geothermal energy power stations could thus provide a major contribution to the basic supply of electricity from a renewable source.
The utilisation of ambient heat with the help of heat pumps differs in one major aspect from using other sources of renewable energy. Namely, a heat pump is driven by a considerable amount of external energy, amounting to anywhere between a quarter and one half of the energy which is used as heat, depending on the exterior conditions.
This technology is therefore also considered as a rational use of energy, i.e. the same category as low-energy heating boilers.
Yet there is also a major difference from these techniques: Heat pumps do not only use the energy supplied for running the pump, but also energy from the surroundings. Decisive is whether or not the renewable energy proportion predominates. Thus the heat pump is a hybrid between an economical conventional use of energy and a source of renewable energy.
Absorption heat pumps are different than compression heat pumps. In an absorption heat pump, the mechanical compressor is replaced by a thermal compressor, run on a two-component mixture.
The absorption heat pump can be operated by any type of thermal energy with a sufficiently high temperature level, e.g. with heating oil, natural gas, or with bio fuels.
This pump is characterised by low-maintenance operation since, apart from a small solvents pump, there are no moving parts. Absorption heat pumps are frequently used in industry for utilising waste heat.
Natural gas, a fossil fuel gift from nature, is composed of methane (96 %) with small amounts of propane and ethane. Natural gas deposits often accompany oil deposits or may occur independently.
It is the cleanest source of energy among fossil fuels. Natural gas can easily be transported through pipelines. It has a high calorific value and burns without any smoke. Natural gas can be used as a source of energy for domestic or industrial use.
It can be used for power generation and as a raw material for petrochemical industries and fertilizer plants. It results as a by-product during crude oil refining and from fractional distillation plants. About 40 percent of total natural gas is found in Kazakhstan, Russia.
India has a huge reserve of natural gas of which a large amount flares up due to lack of adequate storage, compression and transportation facilities as a result about 17 million cubic meters of gas a day is wasted or Now the gas is distributed from Bombay High to Rajasthan, Gujarat, Madhya Pradesh and Utter Pradesh by a 1730 km pipeline, the Hazira-Vijapur-Jagdishpur pipeline.
A similar pipeline is proposed for South India to feed the natural gas of Bombay High and the gas imported from West Asia to southern states. A gas grid is also proposed for Assam.