The Sun as a Fusion Reactor

The sun is the central point of our solar system it has probably been in existence for 5 billion years and is expected to survive for a further 5 billion Table 2.1 Important Radiant Physical Quantities and Daylight Quantities Radiant physical quantities Daylight quantities Table 2.1 Important Radiant Physical Quantities and Daylight Quantities Radiant physical quantities Daylight quantities Note W watt m metre s second sr steradian lm lumen lx lux cd candela Source DIN, 1982 ISO, 1993 Note W...

Alternating current AC

Three-phase machines work with a three-phase AC. Before three-phase machines can be explained in detail, a short introduction into AC calculations is given here. An alternating voltage dependent on time is defined as with amplitude v, zero phase angle frequency m given by The associated current i with the zero phase angle y and the amplitude t is The phase angle between current and voltage is If the phase angle is positive, the voltage is ahead of the current (leading). If the phase angle is...

Influence of surroundings and height

The wind speed is usually recorded at a height of 10 m. Changes in elevation can change the wind speed in a distance of only a few hundred meters. Hills or mountains influence the wind speed significantly. On top of a mountain or on the luff side, which is perpendicular to the wind (see Figure 5.3), the wind speed can rise to become double the uninfluenced value. In contrast, the wind speed is much lower on the lee side. Obstacles, plants or hills near a wind generator site can slow the wind...

Solar energy

By far the largest energy resource is the sun. Annually, 3.94024 J 1.084018 kWh of solar energy reaches the surface of the Earth. This is about ten thousand times more than the annual global primary energy demand and much more than all available energy reserves on earth. In other words, using one-ten-thousandth part of the incoming sunlight would cover the whole energy demand of mankind. Figure 1.9 illustrates these values with energy cubes. There is a distinction between direct and indirect...

Costs for a wind power plant

The investment costs of wind power plants have also decreased during the past few years. On one hand, costs for wind power plants with the same capacity have decreased. On the other hand, the rated power of wind turbines has grown rapidly during the same time. This reduces the incidental expenses per kilowatt. Figure 6.2 shows the sale prices and rated powers of wind turbines in two different years. However, the price conditions vary between different turbine designs. Besides the pure cost of...

Costs for a wind power plant with return on capital

Adapting the example of the 1500 kW wind power plant (A0 1,800,000 Ai 50,000 q 1.08 n 20 Ea 3.5 106 kWhel) to an interest rate of ir 8 per cent yields c0 1,800,000 + 50,000 9.82 2,291,000 a 0.1019 cE 2,291,000 0.1019 3.5-106 kWhel 0.067 kWhel A high number of privately financed wind power projects have been built in the past few years in Germany. Many projects have been realized with 30 per cent equity capital. The remainder of the investment has come from bank loans with relatively low...

Wind turbines with vertical rotor axis

Wind wheels and windmills with vertical axes are the oldest systems to exploit the wind. For more than 1000 years drag devices with vertical axes have been constructed. Today there are some modern wind generator concepts that also have vertical axes as shown in Figure 5.11. Rotor concepts with vertical axes are The Savonius rotor works similarly to the above-described cup anemometer, using the drag principle. It has two semi-cylindrical blades that are open on

Ai A f ep rr

Solar Cell Characteristics

Extended equivalent circuit one-diode model The simple equivalent circuit is sufficient for most applications. The differences between calculated and measured characteristics of real solar cells are only a few per cent. However, only extended equivalent circuits describe the electrical solar cell behaviour exactly, especially when a wide range of operating conditions is to be investigated. Charge carriers in a realistic solar cell experience a voltage drop on their way through the semiconductor...

Wind turbines with horizontal rotor axis System components

Wind Turbine Blade Azimuth Angle

Most wind turbines generating electricity today are horizontal axis machines. It is predominantly medium-sized enterprises that have pushed wind market developments. Wind power plants have reached a high technical level and Figure 5.12 Section through the Stall-controlled TW600 Wind Generator 600 kW Change-pole Asynchronous Generator, 43 m Rotor Diameter, 50-70 m Hub Height Figure 5.12 Section through the Stall-controlled TW600 Wind Generator 600 kW Change-pole Asynchronous Generator, 43 m...

Evacuated tube collectors

The high vacuum inside the closed glass tube of the evacuated tube collector is easier to maintain over a long period of time than that in an evacuated flat-plate collector. Glass tubes can resist the ambient air pressure due to their shape so that no supports are necessary between the back and front sides. A metal absorber sheet with a heat pipe in the middle is embedded inside a closed glass tube with a diameter of a few centimetres. A temperature sensitive working medium such as methanol is...

Synchronous generator with DClink converter

Modern power electronics can avoid the disadvantages of a synchronous generator that is directly coupled to the mains. The synchronous generator is connected via a DC link or frequency converter to the mains see Figure 5.38 . In this configuration, the system can operate the generator at a frequency independent of the mains frequency. Changing the generator frequency varies the generator speed. Hence it is possible to vary the speed over a wide range and to run at the optimal speed to obtain...

Speed Torque Characteristics and Typical Generator Data

Kloss Formula

The connection between torque and speed for an asynchronous generator is also interesting because the rotor speed changes with the driving torque. The intrinsic torque of the machine is used for the following calculations. It is calculated from the air-gap power Pg and the synchronous speed nS of the stator field as The internal torque Mi is also given by the mechanical torque M negative sign in generator mode and the friction torque Mf positive sign With the equation of the current for the...

Lift devices

Power Speed Wind Generator Matlab

If wind, which circulates around a body, develops higher flow speeds along the upper surface than along the lower, an overpressure emerges at the upper surface and an underpressure at the lower. The result is a buoyancy force, according to Bernoulli The buoyancy force is calculated using the lift coefficient cL, the air density p, the apparent wind speed vA and the projected body area AP. Rotor blades of modern wind generators usually make use of the buoyancy force. The projected area of a...

Figures

1.1 Prices for Water Heating 4 1.2 Energy Conversion Chain and Losses for Water Heating with a 1.3 Energy Conversion Chain and Losses for Water Heating with an Electric Cooker 6 1.4 Evolution of Annual Crude Oil Production 7 1.5 World Primary Energy Demand by Region in 2001 8 1.6 Origin of the Anthropogenic Human-induced Greenhouse Effect 11 1.7 Annual per capita Carbon Dioxide Emissions from Fuel Combustion for Different Countries in 2001 14 1.8 Nuclear Power's Share of Electricity Generation...

Irradiance gain for surface tilt or tracking

If a solar energy system tracks the sun so that the angle of incidence is virtually zero, the energy yield increases significantly. The higher direct irradiance on a surface perpendicular to the solar radiation causes the increased energy yield. During days with high direct irradiation, tracking can achieve energy gains over horizontal orientation in the order of 50 per cent in summer and up to 300 per cent in winter, depending on the latitude of the location see Figure 2.15 . However, tracking...

Integral collector storage systems

Integrated Collector Storage Ics

For integral collector storage systems ICS the hot water storage tank is integrated with the collector itself. A technically robust system is not easy to Table 3.4 Heat Transition Coefficient k and Total Energy Transition Coefficient g-value of Various Conventional Materials and Transparent Insulation Materials TIMs Conventional glass covers k in g-value W m2 K TIM between low-iron glass with air gap Conventional glass covers k in g-value W m2 K TIM between low-iron glass with air gap 2 layers...

Photovoltaic inverters

Modulwechselrichter

Photovoltaic inverters differ from inverters for other applications. This is because they must operate the photovoltaic generator at the optimal operating point to generate the maximum power. Grid-connected inverters are therefore often combined with MPP trackers, i.e. DC-DC converters, to set a voltage at the generator that differs from the grid voltage. A battery charge controller is integrated into most stand-alone inverters. Photovoltaic inverters operate at the rated power PN for only very...

Electrical description of a synchronous machine

All three phases of the stator windings produce a main field that is connected to the rotor. The useful inductance Lh and the useful reactance Xh 2nfjLh reflect this. Besides the useful field there are leakage fields that are not connected to the rotor. The leakage reactance Xa describes these leakages. The rotor field of a rotating rotor induces a voltage leak in the stator. This voltage is also called the synchronous internal voltage Vp. The rms value of the induced voltage is proportional to...

Solar thermal domestic water heating systems

Thermosiphon Flat Plate Schematic

The heating of domestic water involves much higher temperatures than for swimming pool water. The simple absorbers used for swimming pool heating are in most locations not suited to domestic hot water systems because the absorber losses due to convection, rain and snow as well as heat radiation are unacceptably high. Domestic water heating systems typically use collectors that have much lower losses at higher water temperatures. These are either flat-plate, evacuated flat-plate or evacuated...

Introduction

Solar thermal systems are an important use of solar energy. The use of solar thermal applications has a long history Archimedes is reported to have boiled water using a concave mirror as early as 214 BC thermal systems today still represent the most cost-effective use of solar energy. Solar thermal signifies the thermal use of solar energy in general. Therefore, a number of different technical applications exist. Besides building space heating, water heating or industrial processes, solar...

Solar Irradiance on the Surface of the Earth

Values measured on the surface of Earth are usually lower than the solar constant. Various influences of the atmosphere reduce the irradiance. They are reduction due to reflection by the atmosphere reduction due to absorption in the atmosphere mainly O3, H2O, O2 and CO2 reduction due to Rayleigh scattering reduction due to Mie scattering. The absorption of light by different gases in the atmosphere, such as water vapour, ozone and carbon dioxide, is highly selective and influences only some...

Wind speed ranges

Efficiency Enercon E40

The design tip speed ratio depends closely on the number of rotor blades. The maximum power coefficient of a three-bladed rotor is reached at a tip speed ratio of between 7 and 8, whereas for two-bladed rotors the figure is 10 and for a one-bladed rotor about 15. However, these values can vary depending on the system design. The optimum tip speed ratio Aopt also defines the design wind speed along with the rotor radius r and the rotational speed of the rotor n in min-1. For example, the optimum...

Photovoltaics

Photoeffect Solar Cell

The word 'photovoltaic' consists of the two words, photo and Volta. Photo stands for light Greek phos, photos light and Volta Count Volta, 1745-1827, Italian physicist is the unit of the electrical voltage. In other words, photovoltaic means the direct conversion of sunlight to electricity. The common abbreviation for photovoltaic is PV. The history of photovoltaics goes back to the year 1839, when Becquerel discovered the photo effect, but in that century the technology was not available to...

Synchronous machines Design of synchronous machines

Cylindrical Rotor Pole

A synchronous machine consists of a stator and a rotor. The stator is the stationary part of the machine with the three-phase windings to produce the rotating field as described in the previous section. The casing is made of Figure 5.23 Cross-section through a Synchronous Machine Left Cylindrical Rotor, Right Salient-pole Rotor Figure 5.23 Cross-section through a Synchronous Machine Left Cylindrical Rotor, Right Salient-pole Rotor stacked sheets containing the three-phase windings of the...

Limiting power output and storm protection

Wind Stall Effect

The power that can be taken from the wind varies with the wind speed. After reaching the nominal power, the power should remain constant for wind speeds greater than the nominal wind speed because the turbine and generator cannot handle more power. Therefore, a wind power plant must limit the power with one of the two following methods Figure 5.14 Stall Effect at Higher Wind Speeds Figure 5.14 Stall Effect at Higher Wind Speeds Stall control takes advantage of the stall effect that occurs at...

Drag devices

Drag Forces Anemometer

If an object is set up perpendicularly to the wind, the wind exerts a force FD on the object. The wind speed v, the effective object area A and the drag coefficient cD, which depends on the object shape, define the drag force Figure 5.5 shows drag coefficients for various shapes. With PD FD v, the power to counteract the force becomes If an object moves with speed u by the influence of the wind in the same direction as the wind, the drag force is l'd-0.4 dosed l gt back open Figure 5.5 Drag...

Calculation of the Solar Angle of Incidence

Solar Angles For Tilted Surface

The solar angle of incidence 0hor on a horizontal surface is a direct function of the sun height yS. This angle is also called the zenith angle dZ The calculation of the angle of incidence 0tilt on a tilted surface is more complicated. The surface azimuth angle at describes the deviation from the south. If the surface faces to the west, at is positive. The inclination angle yt describes the surface tilt or slope of the surface. If the surface is horizontal, yt is zero. Figure 2.13 visualizes...

Reserves of Fossil Energy Sources

The current energy supply depends mainly on fossil energy carriers as described in the previous section. Fossil fuels such as natural gas, petroleum, hard and brown coal needed many thousands of years to form. Organic substances i.e. animal or vegetable residues were the base materials. Hence, fossil fuels are stored biomass of the ancient past. A huge amount of these fossil fuels has already been consumed in the 20th century. However, due to the increasing exploitation of the fossil...

Irradiance on a Horizontal Plane

Diffuse Solar Radiation Kairo

As described above, solar radiation is scattered and reflected when passing through the atmosphere. Rays of extraterrestrial sunlight are virtually parallel. Terrestrial sunlight, on the other hand, consists of direct and diffuse components see Figure 2.6 . Direct solar radiation casts shadows, because it is directional, coming directly from the sun diffuse irradiation, on the other hand, has no defined direction. The total irradiance on a horizontal surface on Earth is also called global...

Wind Turbine Design

Turbine Darrieus

Figure 5.11 Rotors with Vertical Axes Figure 5.11 Rotors with Vertical Axes opposite sides. Near the axis, the blades overlap so that the redirected wind can flow from one blade to the other. The rotor blades also utilize the lift principle so that the efficiency of the Savonius rotor is little better than that of simple drag devices. However, the efficiency is much worse than that of good lift devices, reaching maximum power coefficients of the order of 0.25 Hau, 2000 . Savonius rotors have...

Wind speed distributions

Wind Speed Distribution

Wind speed distributions are commonly used to indicate the annual available wind energy. These distributions are estimated using measurements, wind maps or computer analysis. Tables or statistical functions can give the distribution. Figure 5.1 shows the relative distribution h v of wind speed v in Karlsruhe, which is located in south Germany near the Black Forest. This distribution indicates how often a certain wind speed occurs. It is immediately obvious that the wind energy potential in...

Domestic hot water storage tanks

Geothermal Hot And Cold Tank

Only annual usage simulations can estimate the exact dimensions of a hot water storage tank. The size depends on the hot water demand, solar fraction see Equation 3.59, p112 , collector performance, collector orientation, pipes and last but not least on the annual solar irradiation. For central European climates, a rough estimate can be made. Here, the storage volume should be 1.5-2 times the daily demand. Besides the storage volume for the daily demand, a standby volume of 50 per cent and a...

Equivalent circuits and circle diagrams for the stator current

Equivalent Circuit Alternator

The electrical structure of an asynchronous machine is similar to a transformer that consists of two coupled windings. The windings of an ideal transformer are coupled free of leakages. A real transformer has leakage fields and ohmic losses that can be considered by additional resistances and reactances in the equivalent circuit see Figure 5.27 . Hence, the equations for the voltages of the transformer become With the number of turns per phase w1 and w2 and I V2tr-1 R2 2 Xhas well as Xh1 become...

Optimum distance of solar energy system support structures

Tilt Angles And Shading

Photovoltaic and solar thermal systems are often installed on the ground or on flat roofs. Support racks are used to mount the solar energy systems. Usually these are tilted to get higher annual irradiances, as explained in the section on irradiance on tilted surfaces see p60 . Furthermore, horizontally installed solar energy systems have relatively high losses due to soiling, for example, through deposition of air pollutants, bird excrement or other dirt deposits on the surface of the...