The contribution of renewable energies towards the global production of electric heat and power has been on the increase for years; its proportion, relative to primary energy consumption, is currently around 13%. Studies by renowned institutions have reasoned that this proportion can be increased to 25% by 2030 and to 50% by 2050.
Looking at the capacities of the individual energy sources, there have been high, double-digit growth rates in the last few years. For example, in photovoltaics the figure was more than 40%; and in wind power, 25% per year. According to statistics global investment in renewable energies had already passed the 100 billion dollar mark (2007).
In any system for producing renewable energy, pressure and temperature monitoring play an important role. Wika’s precise and economical solutions contribute to the reliability and longevity of such systems.
Wind Power
The conversion of wind power into electrical energy is an immensely sensitive task – even for experts. In principle, a rotor (wind turbine) is set in motion by an air flow and a connected generator, driven by the kinetic power, produces electric current. Since, however, wind speeds are never constant; a control system which works precisely must enable the system to be tuned for both high and low wind velocities. Modern plants use a pitch control for this, which optimally adjusts the rotor blades to changes in the force acting on them – and (in extreme cases, eg, storms) can also introduce braking.
So a wind power generation plant can operate even when there is relatively weak air movement and always runs at a high degree of efficiency. Or it can, if needed in the particular circumstances, be static.
Pressure measurement
Examples of where pressure measurement is needed are in the hydraulic and lubrication systems. In addition brake control and transmission cooling oil need reliable monitoring.
The measuring systems must be particularly reliable and to ensure that the plant operates efficiently and safely.
Hydropower
Hydropower is the most significant form of renewable energy in the world. Its use is based on its large availability and technology matured over the past 100 years. The plants in operation, such as running water, reservoir and pump-fed power stations, achieve high efficiencies: They can convert up to 90% of their energy source into electricity.
Application example – wave energy converter
For the operating sequence of the wave energy converter, the monitoring and control of the hydraulic pressure is central. The major task here is the adjustment of the movement to the current wave strength and length, in order to obtain the optimum energy output and to minimise the mechanical load on the structure. In addition, the pressure generation, in terms of both speed and strength, is monitored and then evaluated by the intelligent control unit.
The measurement technology used must be as reliable as it must be strong, due to the extreme operating conditions.
Both the optimisation of the energy yield and – with heavy storms – the survival of the generators, depend upon the uninterrupted precision of the pressure measurement.
Solar thermal energy
On each square metre of the earth‘s surface, the sun’s radiation produces on average a thermal output which corresponds to one small heater, ie, nearly 1,4 kW. If one could use this energy at the same time everywhere, the global heat requirement would be covered at least 6000 times over.
There are various techniques to convert solar power into usable heat. In principle a solar collector absorbs the heating energy from the sun’s radiation and passes it to a heat exchanger. There water is warmed – for example for bathing or to support a heating system.
In the design of the solar collectors, one essentially differentiates between panel collectors, vacuum tube collectors and parabolic trough collectors. The latter have a particularly high efficiency, working at temperatures well over 200°C in parts, and therefore use oil as a heat transfer medium.
Application example – collector and water heating tank
With the classical solar collector for households, the temperatures of the collector and hot water tank must be permanently monitored. If the difference between these values is larger than a preset value, the solar heating circuit increases the temperature of the reservoir.
On the other hand, if not enough solar heating is available, the control must provide for water heating via a conventional boiler. Only continuous, reliable measurement of the temperatures at the solar heat collector and within the lower and upper zone of the reservoir water heater ensures that the solar power is used optimally. At the same time, the residents of the house enjoy optimal warm water comfort.
Photovoltaics
In the first half of the 19th century, it had already been discovered that when a beam of light falls on the surface of particular metals, an electrical current is generated – the photoelectric effect.
Application example – mover
A ‘mover’ supports solar fields of up to 100 m², which are adjusted by a hydraulic system and so can follow the sun. The most important of the measuring tasks is pressure measurement whereby a pressure transmitter is normally used for permanently monitoring the X- and Y-directions.
Photovoltaic plants are generally exposed to harsh ambient conditions. Instruments used for safe and continuous pressure monitoring must therefore be particularly robust and measure precisely even under extreme variations in temperature.
Biogas
Biogas is a natural product of decomposition, which is produced from the fermentation of organic materials. The production of energy from biogas is particularly environmentally friendly, since it causes no additional emissions of the greenhouse gas CO2, and reduces the quantity of methane output into the atmosphere. Biogas is storable and thus can be used for both base and peak loads.
As a source material for biogas facilities, almost all organic matter is suitable such as manure, sewage, bio wastes and specifically grown biofuels. These are pumped into heated and thermally-insulated tanks, where they ferment under air-tight conditions between 37 and 40°C.
Bacteria decompose the biomass and produce a methane-rich gas. With this biogas, either cogeneration plants (combined heat and power – CHP) are operated which produce electricity and heating, or the gas is processed to natural gas quality and fed into the gas network. The electricity is fed to the local grid and the residual matter into a reservoir. This can then be converted into compost and liquid fertiliser.
Not all the waste heat of the CHP is used. This energy surplus can be used meaningfully eg, for heating homes or drying grain. In addition, biogas (compressed to 200 to 300 bar) can be used as an almost CO2 neutral fuel in car engines.
Application example – fermenter
Level and density in the gas reservoirs of the fermenters are controlled by pressure measurement. In order to produce the optimal fermenting climate for the maximum gas yield, a measuring system with suitable sensor technology and high precision is needed.
Geothermal energy
The potential of the earth‘s heat has only recently been explored. World-wide, more and more geothermal heating and power stations are being constructed. They get their energy from depths of between 1500 and 6000 metres. The use of terrestrial heat from close to the surface as heating energy has developed rapidly. The basis for this is a plant with a heat pump. In Germany alone, some ten thousand buildings are supplied in this way, from single family houses to larger residential complexes.
Application example – heat pump
For the measurement and control of a heat pump temperature measuring instruments are the most important. They continuously monitor the inlet temperature of the working fluid in the heat pump, the temperature of compressed and condensed steam, as well as the inlet and return temperatures and the temperature in the buffer tank.
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