CHAPTER 5 RENEWABLE ENERGY SYSTEMS. SOLAR ENERGY

Transcription

1 CHAPTER 5 RENEWABLE ENERGY SYSTEMS. SOLAR ENERGY

2 Introduction Renewable energy is generally defined as energy that comes from resources which are naturally replenished on a human timescale such as sunlight, wind, rain, waves and geothermal heat. Wind, solar, and biomass are three emerging renewable sources of energy. Renewable energy can basically be classified in three categories: renewables for transport, renewables for electricity and renewables for heat. In international public opinion surveys there is strong support for promoting renewable sources such as solar power and wind power. At the national level, at least 30 nations around the world already have renewable energy contributing more than 20 percent of energy supply.* *REN21, the Renewable Energy Policy Network for the 21st Century: "Renewables global futures report

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4 Solar Energy Solar power has a long historyasenergysourcefor humans. For example, solar power was used for heating of water in the Roman empire. A steam engine based on solar power was constructed by Auguste Mouchout in 1861, but was found to be far too expensive to have a commercial value. 4

5 The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. 5

6 The Sun and Radiation The sun 1.4 million km in diameter 3.8 x MW of radiated electromagnetic energy Energy from the sun in the form of ultra violet, visible and infra red electromagnetic radiation is known as solar radiation. Insolation (from Latin insolare, to expose to the sun) is the total amount of solar radiation energy received on a given surface area during a given time. It is also called solar irradiation and expressed as "hourly irradiation" if recorded during an hour or "daily irradiation" if recorded during a day. Practitioners in the business of solar energy may use the unit watthour per square meter (Wh/m2). If this energy is divided by the recording time in hours, it is then a density of power called irradiance, expressed in watts per square meter (W/m2). The intensity of energy arriving from the sun in space just outside the earth s atmosphere is approximately 1367 W/m2, called the solar constant. Although it is termed a constant, it varies over time. 6

7 Average insolation, or solar energy reaching a given location on earth, will be lower than the amount available outside the atmosphere due to absorption and diffraction of sunlight in the atmosphere, changing weather, loss of sunlight at night, and so on. Worldwide average values for some representative cities, taking all these factors into account, range between 100 W/m2 for Glasgow, Scotland, and 280 W/m2 for Cairo, Egypt. 7

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10 Solar Insolation I 0 I 0 depends on distance between earth and sun and on intensity of the sun. Ignoring sunspots, I0 can be written as I 0 360n SC cos (W/m ) SC = solar constant = kw/m2 n=daynumber(january1isday1;december31isday365). n is also called the Julian date, from the Julian calendar 10

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12 Solar Declination Solar declination δ the angle formed between the plane of the equator and the line from the center of the sun to the center of the earth δ varies between +/ Assuming a sinusoidal relationship, a365dayyear,andn=81isthe spring equinox, the approximation of δ for any day n can be found from: sin n 12

13 Altitude Angle and Azimuth Angle Altitude Angle Azimuth Angle of sunlight/azimuth angle 13

14 Solar Basic Processes Three processes have been implemented in practice to transform the solar radiations into energy: Solar photovoltaics (PV), passive solar power (PSP) and concentrated solar power (CSP). 14

15 Solar photovoltaics (PV) Solar Cells Background 1839 French physicist A. E. Becquerel first recognized the photovoltaic effect. Photo+voltaic = convert light to electricity 1883 first solar cell built, by Charles Fritts, coated semiconductor selenium with an extremely thin layer of gold Bell Laboratories, experimenting with semiconductors, accidentally found that silicon doped with certain impurities was very sensitive to light. Daryl Chapin, Calvin Fuller and Gerald Pearson, invented the first practical device for converting sunlight into useful electrical power. Resulted in the production of the first practical solar cells with a sunlight energy conversion efficiency of around 6% First spacecraft to use solar panels was US satellite Vanguard 15

16 Bell System Solar Battery Converts Sun s Rays into Electricity, Advertisement from Look Magazine, 1956.

17 The solar cells in the early 1950s were about 0.5 % efficient. Today a module is about 20 % efficient. A 1 kw system: In 1950 = 2,400 square feet In 2005 = 80 Square feet 17

18 Annual output of world PV manufacturing and average cost per rated watt of panels, 1975 to 2003.

19 Global Cumulative PV Power

20 Cumulative installed solar electric power by st Germany 3.8 GW 2 nd Japan 1.9 GW 3 rd US 814 MW 4 th Spain 632 MW

21 World's largest photovoltaic (PV) power plants (12 MW or larger) Name of PV power plant Country DC Peak Power (MW) GW h /year Notes Olmedilla Photovoltaic Park Spain Completed September 2008 Puertollano Photovoltaic Park Spain Moura photovoltaic power station Portugal Completed December 2008 Waldpolenz Solar Park Germany ,000 First Solar thin-film CdTe modules. Completed Dec 2008 Arnedo Solar Plant Spain 34 Completed October 2008 Merida/Don Alvaro Solar Park Spain 30 Completed September more 2 more Spain Korea Avg 20 Avg 20 Koethen Germany ,000 First Solar thin-film CdTe modules. Completed Dec 2008 Nellis Solar Power Plant USA ,000 solar panels Planta Solar de Salamanca 6 more Spain, 1 US, 1 Germany Spain 13.8 Avg 12 n.a. 70,000 Kyocera panels

22 Germany 10,000 companies, including installers work in solar PV 80 companies are cell and module makers 42,000 employees Sales were $5.7 B including $2.5 B in exports The feed in tariff 2008 German utilities pay $0.47 to $0.68/kWh depending on type and size of system for new solar systems Solar Generation V Report Sep 2008

23 Waldpolenz Solar Park The Waldpolenz Solar Park is built on a surface area equivalent to 200 soccer fields, the solar park will be capable of feeding 40 megawatts into the power grid when fully operational in

24 Waldpolenz Solar Park

25 The Major PV Cell/Module Manufacturers

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27 Photovoltaic (PV) Hierarchy Cell < Module < Panel < Array

28 Overview of PV Function How PV cells work: A photovoltaic cell can convert sunlight into DC current. The working principle of photovoltaic cell is largely depending on the characteristic of a semiconductor. A semiconductor consists of two types of materials which are p type silicon and n type silicon these two made up the internal circuit. Due to this characteristic, light of specific wavelength will be able to ionize the atom in the silicon. This causes the electron to move freely and is pulled towards the n type semiconductor and the holes produced will move to the p type semiconductor this is called photovoltaic effect. The electricity will flow normally when the outside circuit is closed.

29 Overview of PV Function 29

30 Available Cell Technologies Single crystal or Mono crystalline Silicon Polycrystalline or Multi crystalline Silicon Thin film Ex. Amorphous silicon or Cadmium Telluride

31 Effect of Material Choice on Efficiency Basic Si Types Monocrystalline: <25% (but expensive) Multicrystalline: <20% (lower cost offsets lower efficiency) Amorphous: <13% (increased from 4% in 1978) Other emerging materials: Gallium Arsenide, Cadmium Telluride, Copper Indium Diselenide

32 Monocrystalline Silicon Modules Most efficient commercially available module (11% 14%) Most expensive to produce Circular (square round) cell creates wasted space on module

33 Polycrystalline Silicon Modules Less expensive to make than single crystalline modules Cells slightly less efficient than a single crystalline (10% 12%) Square shape cells fit into module efficiently using the entire space

34 Amorphous Thin Film Most inexpensive technology to produce Metal grid replaced with transparent oxides Efficiency = 6 8 % Can be deposited on flexible substrates Less susceptible to shading problems Better performance in low light conditions that with crystalline modules

35 Selecting the Correct Module Practical Criteria Size Voltage Availability Warranty Mounting Characteristics Cost (per watt)

36 Problems by solar cells Effects of Temperature Effects of Temperature As the PV cell temperature increases above 25º C, the module V mp decreases by approximately 0.5% per degree C. Shading on Modules Depends on orientation of internal module circuitry relative to the orientation of the shading. SHADING can half or even completely eliminate the output of a solar array!

37 PV System 37

38 PV System A photovoltaic system, also photovoltaic power system, solar PV system, PV system or casually solar array, is a power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and directly convert sunlight into electricity, a solar inverter to change the electrical current from DC to AC, as well as mounting, cabling and other electrical accessories to set up a working system. It may also use a solar tracking system to improve the system's overall performance or include an integrated battery solution. 38

39 Off Grid 39

40 Grid off solar energy power generating Main used in the area where is no electricity supply or the telecommunication station which is faraway from the electricity net or the wireless places. Key components: solar panel battery intelligent controller inverter and electricity distribution. (electricity distribution is close to the active load). Advantages: offer the independent electricity net which will not restricted by the local public electricity net. Disadvantages:much waste of the energy resources or can controller the use of the solar energy resources. the electricity use is high restricted by the weather condition, the low efficiency of use and high investment( large solar batteries and a battery bank). 40

41 On Grid 41

42 On Grid PV System Main use in the place where the city electricity distribution net. It is the lead direction of New energy from home and all over the world. Key components: solar panel grid on inverter electricity distribution. Advantages:high efficient use of the system,long life span;the investment cost is some lower Disadvantages: Homes must be located close to power lines, as grid tied power systems require connection with the local utility. Grid tied system installations require large roof surface areas in sunny locations. 42

43 Solar Power Plants Therearetwowayswecanproduceelectricityfromthe sun: Photovoltaic Electricity This method uses photovoltaic cells that absorb the direct. Solar Thermal Electricity This also uses a solar collector: it has a mirrored surface that reflects the sunlight onto a receiver that heats up a liquid. This heated liquid is used to make steam that produces electricity. 43

44 Photovoltaic Electricity: PV Power Plants (station) A photovoltaic power station, also known as a solar park, is a large scale photovoltaic system (PV system) designed for the supply of merchant power into the electricity grid. They are differentiated from most building mounted and other solar power applications because they supply power at the utility level, rather than to a local user or users. The power conversion source is via photovoltaic modules that convert light directly to electricity. should not be confused with concentrated solar power, the other large scale solar generation technology, which uses heat to drive a variety of conventional generator systems. Both approaches have their own advantages and disadvantages, but to date, for a variety of reasons, photovoltaic technology has seen much wider use in the field. As of 2013, PV systems outnumber concentrators by about 40 to 1. 44

45 Technology: Most Solar parks are ground mounted PV systems, also known as free field solar power plants. They can either be fixed tilt or use a single axis or dual axis solar tracker While tracking improves the overall performance, it also increases the system's installation and maintenance cost. A solar inverter converts the array's power output from DC to AC, and connection to the utility grid is made through a high voltage, three phase step up transformer of typically 10 kv and above. Solar panels produce direct current (DC) electricity, so solar parks need conversion equipment. to convert this to alternating current (AC), which is the form transmitted by the electricity grid. This conversion is done by inverters. 45

46 Construction of on grid PV power plants 46

47 Topaz Solar Farm is a 550 megawatt (MW) photovoltaic power station in San Luis, California. Construction on the project began in November 2011 and ended in November It is the world s largest solar farm. Topaz Solar Farm from space. Earth Observatory image,

48 Solar thermal electricity: Concentrated Solar Power (CSP) CSP is a technique to increase the conversion efficiency by increasing the incoming flux to the medium to be heated. By constructing mirrors which focus all the incoming radiation towards a small concentrated spot containing the fluid, the conversion efficiency per mirror area can be made almost proportional to the constant c1 in Eq. (4.2). The radiation energy, often of the order of 50 % is lost in the mirror system. The temperature of the working fluid is nevertheless easily brought to many hundred degrees. This much higher fluid temperature can be combined with a turbine or engine system to produce electricity. By assuming 100 % efficiency of the fluid to absorb the radiation, the efficiency of the electricity production process then depends in general on two factors: The efficiency of the mirrors and the efficiency of the engine which converts heat to electricity. The three main types of concentrating solar power systems are: linear concentrator, power tower systems and dish/engine. 48

49 Linear concentrator systems* Linear concentrator systems capture the sun's energy with large mirrors that reflect and focus the sunlight onto a linear receiver tube. The receiver contains a fluid that is heated by the sunlight and then used to create steam that spins a turbine generator to produce electricity. Alternatively, steam can be generated directly in the solar field, eliminating the need for costly heat exchangers. Currently, individual systems can generate about 80 megawatts of electricity. *Source: The U.S. Energy Information Administration (EIA) 49

50 Power Tower System Power tower systems consist of numerous large, flat, sun-tracking mirrors, known as heliostats that focus sunlight onto a receiver at the top of a tower. The heated fluid in the receiver is used to generate steam, which powers a turbine and a generator to produce electricity. Some power towers use water/steam as the heat-transfer fluid. Individual commercial plants can be sized to produce up to 200 megawatts of electricity. 50

51 Dish/engine systems Dish/engine systems use parabolic dishes of mirrors to direct and concentrate sunlight onto a central engine (Stirling engine) that produces electricity. The dish/engine system produces relatively small amounts of electricity compared to other CSP technologies typically in the range of 3 to 25 kilowatts. 51

52 Media

53 Presentation 8: PV solar economic analysis Presentation 9: Solar Energy in Palestine 53