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Renewable/ Clean Technology Top Some general information about energy:
Source: www.enercon.de Hydro Power: Hydro power stations work by using water from dams, rivers or other sources to drive a hydro turbine that turns a generator, which creates the electricity. The development goes back thousands of years when hydro power was used for flour mills, saw mills and many other applications. Since the invention of the dynamo (electric generator, alternator), hydro power is used for the generation of electrical energy. Modern hydro power stations range from the biggest power plants in the world (Iquazu – Brazil, Three-Gorges-Dam – China) to very small stations in remote locations. Lately there have been new innovations in developing very small hydro stations as supplements to the larger power network, or as stand alone systems in remote villages, usually in the developing countries. Where they are used as supplements to existing power networks they generate primarily electricity to the owner of the hydro station and feed excess power into the network. They often use water flows that are available through other processes like waste water in processing companies or in sewage plants.
Tidal and Wave Energy Power generation is also possible where large tidal differences are available. There are many types of tidal hydro power stations, including ones that use the high flow rates when the tide is coming in or going out, in particular when the water flows through narrow gaps, such as between islands or rock formations. This type of station has been in use for a considerable time, such as on the Normandy coast in France. Other tidal stations place turbines with generators in fast flowing currents near the coast. Wave energy can be captured by converting wave actions into hydraulic energy, which is then processed through turbines and/or pumps, through generators and into electrical energy. Versions of the conversion of wave action are long tanks connected with flexible joints. The movement provides the power for pumps to drive a hydro generator. Another method is to place floats in shallow water under the water surface. These floats are connected to the ground but can move with the wave action. This movement drives pumps, which then drive hydro generators for electrical energy. Many of the tidal and wave energy capturing projects are currently still in the developmental stage.
Wave Energy Scotland has built a power plant using wave currents. Near the Orkney Islands this wave converter uses snake like segments that generate hydraulic pressure through their movements and the hydraulic pressure drives a generator. Output is around 750 kW; the system appears to be so impressive that Portugal has bought the station. A new one is being built. In the Orkney Islands the waves have a specific energy of 25 kW per m wave length. The currents between 10 and 50 m in depth have a speed of up to 3.5 m/second. VDI 11 – 16.3.2007 Energy from Waste Water Another type of hydro station is shown below. This type is robust and is used at the outlet of waste water treatment works to generate power from relatively low heights and flow rates. It works in other places as well.
Wind Power: The second most used and fastest growing sector of sustainable energy generation is wind power. Currently there are around 50 to 60 thousand wind generators providing electricity to the networks. Most of them are located in Europe, the next highest number is found in America. The size ranges from a few hundred kW to 5 MW per generator. These generators are simply propellers driving an electric generator. Wind farms are found in many countries, particularly in locations with reliable wind near coast lines or on mountain ranges.
Source: www.enercon.de Solar Power: As with hydro power generation there are several ways to generate electrical energy. The direct way is the use of solar cells. These are silicon wafers on specially designed conducting and insulating materials. Research is ongoing to increase the efficiency of these panels. Currently only 10 to 20% of sunlight is converted into electricity. One solar panel typically generates less that 1 kW (less than 0.001 MW), but connecting many panels together increases the power. The disadvantage however, is that sunlight, which is not constantly available, is needed to make a solar panel work. The advantages are that little to no maintenance is needed; and the conversion into electricity is direct, therefore moving parts are not required. Other methods let the sun heat up water and this drives a steam turbine, which, as with all other methods, drives a generator for electricity generation. There are different types of reflectors in use, from parabolic mirrors to flat mirrors heating up water in a central located boiler. Other methods use parabolic troughs with a water pipe running through the centre. This water becomes steam which again drives a turbine and generator. In some cases this hot water is used to increase the feedwater temperature for a fossil power station thus increasing efficiency. A newer development is a process that uses the sun to heat up air and then funnel the air through a high stack or chimney. This creates draught that is used to drive air turbines (wind mills) with generators making electrical energy. This is a hybrid between wind and solar power, but initially needs solar power to operate. A further development is that some of the heat during the day is used to heat up ponds filled with salt water (brine) and then pump the hot brine during the night under the solar collectors keep hot air moving through the stack. This allows electricity generation during the night, providing a base load. Currently only one of these plants exists in Spain but at least two are being planned. The size can be up to 200 MW, which is much larger than other power generators using sustainable energy.
Waste: Energy from Waste The integrated system uses household waste, which is sorted, treated and fermented in bio units. The resulting products are methane gas used for electricity generation, fertiliser and a small amount of waste for permanent storage or incineration. The electricity generated by the methane gas exceeds the plant use and the excess is fed into the grid. From “Clean energy from left-overs”, Pace Magazine, April 2007, p26.
The Böblingen Residual Waste Thermal Power Station is building a new biomass thermal power station, for which it has requested Siemens to supply a “Reject Power” system. This Reject Power system is based on the impeller method and uses also allows the use of combustible materials with high water content. In this case, such materials to be used are sifting coarse chip residue from hogging. These left-over residues were formerly wasted and so this new system is an efficient and economical way of using them. The unit has been designed for a thermal output of 6 megawatts; for thermal utilisation of approximately 18,000 metric tonnes of sifting residue; and to generate 6.4 metric tonnes of steam per hour with a 40 bar pressure and 390°C temperature. The steam will be used to generate electrical energy as well as district heat supply, through means of a steam turbine. The new biomass thermal power station will supply both electrical energy and district heat. Geothermal Power: There are two types of geothermal power generation, both take the heat from the earth to generate steam or vapor and use this to drive a turbine -generator. One method uses hot water or steam from volcanic active areas and uses this either directly or through heat exchangers to generate steam that drives a turbine. Typical examples are found in Island and New Zealand. The other method uses hot rock to boil water or other liquids and use the steam or vapor generated to drive directly or indirectly via a heat exchanger a turbine that drives a generator. This is a relatively recent development and a test plant is under construction in Australia. These methods have challenges like the steam or vapor conditions, which require heat exchangers for protecting the turbine from build up of dirt (residues in the steam or vapor) or corrosion. Maintenance is high because the heat exchangers are subject to the conditions the turbines otherwise would endure. Nuclear Power: (Relative Clean Technology with relation to CO2 Emission during operational life time) Nuclear power stations operate much the same as fossil power stations: A steam turbine drives a generator. The steam is generated in a heat exchanger, which receives its heat from water or another liquid that is heated up in reactor by a nuclear reaction. The process of using several heat exchangers is to separate the radioactive primary hot liquid or water cycle from the non radioactive secondary water and steam cycle. For safety reasons the reactor is contained in a steel vessel and concrete building. The efficiency is around 33%, therefore lower than fossil power stations. But there is no emission during operation. The main issue is the disposal of the radioactive waste and the risk that spent fuel can be used for the manufacturing of nuclear weapons. When properly operated, and when high-quality design and systems are used, then nuclear power stations are safer than fossil power stations. However, if they are not designed properly, if they are not operated and maintained properly, then the damage to the environment in the case of an accident can be enormous. The Three-Mile-Island incident, where a fault in the cooling system for the reactor caused overheating of the reactor and consequent damage and a small amount of radio active emission, was a very close call, and then there was the Chernobyl disaster, where a test with the cooling system of the reactor lead to overheating and melt down (China Syndrome - an US reactor core could melt through the bottom of a reactor towards China), which goes to show just how dangerous and risky nuclear power generation can be. In perspective the number of incidents in nuclear reactors is very small, the consequences can be very big. The energy use and impact on the environment during the construction and disposal of a nuclear power station is higher than that of equivalent sized fossil power stations. Sweden is the first country in the world to have solved the issue of long term storage of its nuclear waste, and does not re-use its spent fuel, which removes the option of making nuclear weapons. There is also a considerable amount of energy used for mining, processing, transporting and storing the radioactive ore. This could be clean nuclear power, but is typically oil and electricity from coal. To fuel a 1,300 MW nuclear power station requires around 35 t per year of nuclear fuel. To make this 35 t of fuel requires around 120,000 t of ore that is then refined through processes (centrifuges and other processes) using electricity. Typically 1 kg of enriched nuclear fuel replaces 18 t (18,000 kg) of black coal or 12 t (11,000 liters) of oil. This can be increased by recycling the spent fuel to 26 t coal or 19 t of oil with the byproduct of Plutonium - as used for nuclear weapons. At 2004 the cost of electricity from nuclear power (Germany) were approximately 10% for the ore, 30% for enrichment and related actions and 60% for disposal, transportation and so on. In Germany is at this stage no permanent storage solution of waste. All nuclear power stations in Germany will be phased out after their useful life, no new nuclear stations will be built. Sweden built nuclear power plants 30 to 40 years ago with the clear commitment, that this would be a temporary solution and no new nuclear plants have been built and will be build. In many fast growing economies nuclear power plants are part of the energy mix to satisfy the growing demand for electricity.
Nuclear Energy – Permanent Waste Disposal After decades of research Sweden has is the first country in the world to depose highly radioactive waste from their 10 nuclear power stations in permanent storage. The storage are tunnels drilled in 450 m deep granite formations, which have been geologically stable for the last 900 million years. Having had foresight and political will to solve this problem the nuclear power was taxed with 0.01 SEK (Swedish Kronor, approximately 0.0015 USD) per kWh and put into a fund for this purpose. The amount saved into this fund is 35 billion SEK (5 billion USD) and has being used for research and now for the building of the storage and the storage itself. The spent fuel rods will be enclosed into pure copper containers, these are enclosed in a special clay material to prevent water contamination and corrosion and these are stored and backfilled in the granite caves. Eventually these caves will be sealed and permanently closed. The storage is expected to be safe for the next 100,000 years, long enough to reduce the radioactivity to safe levels. The location is expected to withstand all natural events like another ice age. Sweden has chosen not to recycle the spent fuel avoiding use and manufacture of nuclear weapons. VDI 8 – 23.2.2007
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Last modified: 04/05/08 |
50 kW 
14,750 MW
24 x 10 MW 
32 kW
5
MW 
15
x 2 MW 
11 MW 
2.3 MW
8,230 MW 
5,900 MW