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![Efficiency of Solar Collectors
Rate of heat loss:
UL collector overall heat loss coefficient [W/m/K]
A area, m²
TC collector average temperature [°C]
Ta ambient temperature [°C]
21](https://image.slidesharecdn.com/week7solar-thermal-240313014137-89b9303a/85/Solar-Thermal-in-power-generation-for-cleaner-18-320.jpg)
![Case Study:
Crescent Dune
• Bloomberg: "A $1 Billion Solar
Plant Was Obsolete Before
It Ever Went Online"
• ten thousand mirrors form a
spiral almost 2 miles wide
(Nevada – USA)
• designed to generate enough
power night and day to supply
a population of 100,000
• its energy costs about $135/MWh, compared with less than
$30/MWh today at a new Nevada photovoltaic solar farm
[BloombergNEF]
https://www.bloomberg.com/news/articles/2020-01-06/a-1-billion-solar-plant-was-obsolete-before-it-ever-went-online](https://image.slidesharecdn.com/week7solar-thermal-240313014137-89b9303a/85/Solar-Thermal-in-power-generation-for-cleaner-52-320.jpg)
Solar Thermal in power generation for cleaner
- 1. Solar Thermal B59ES EnergyStudies 1
- 2. Overview 1. What issolar thermal energy conversion 2. Heat 1. Flat plate collector 2. Evacuated tube collector 3. Power 1. Parabolic trough collector 2. Linear Fresnel reflector 3. Fresnel tower 4. Parabolic dish 5. Storage 4. Installed systems 2
- 3. Solar Energy toPower Generation Solar Photovoltaics Solar Thermal Two technologies come-to-mind when we think about solar energy 3
- 4. Solar Thermal EnergyConversion STEC Heat Flat Plate Collector Evacuated Collector Power Parabolic Trough Parabolic Dish Linear Fresnel Reflector Power Tower 4
- 5. What is SolarThermal ? Solar Thermal Energy is a technology for harnessing Solar Energy in the form of heat 5
- 6.
- 7. Solar heat: industrialprocesses Lataria-Engiadinaisa-Dairy, Switzerland https://www.iea-shc.org/Data/Sites/1/publications/Solar-Heat-Worldwide-2021.pdf
- 8. Global Solar Resources •3,850,000 Exajoule (EJ) of solar energy received by Earth per year • Worldwide primary energy consumptions ~500 EJ • 6 hours of Solar Energy at deserts could meet annual global energy requirement 8
- 9. Types of SolarThermal System Passive solar thermal system Does not use a pump or fan - relies on natural forces like convection… • Shading to keep cool in the summer • Large window for ‘solar gain’ in the winter 12
- 10. Types of SolarThermal System Passive solar thermal system Does not use a pump or fan - relies on natural forces like convection… Specific solar air heaters also exist Space heating 13
- 11. Types of SolarThermal System Active solar thermal system Uses a pump, fan, or other powered device. Uses solar collector More sophisticated system Insulation 14
- 12. Overview 1. What issolar thermal energy conversion 2. Heat 1. Flat plate collector 2. Evacuated tube collector 3. Power 1. Parabolic trough collector 2. Linear Fresnel reflector 3. Fresnel tower 4. Parabolic dish 5. Storage 4. Installed systems 15
- 13. Development of SolarCollectors a. Open-container on ground b. Open trough off ground c. Black closed container d. Black tank insulated underneath e. Sheltered black tank f. Metal tube and plate collector g. Double glazed flat plate h. Selective surface collector i. Evacuated tube collector
- 14. Solar Collectors Flat PlateCollector Evacuated Tube Collector 17 Dark Surface with High Absorptance Gathers Full Spectrum of Solar Radiation. Glass and/or Selective Surface Used to Minimize Conduction and Re-radiation Losses. Efficiency Dependent on Collector Design and Working Temperature.
- 15.
- 16. Flat Plate Collector CrossSection of a Basic Flat-Plate Solar Collector 19
- 17. Flat Plate Collector Absorberplate Glass cover Pipe Collector box Insulation Cross Section of a Basic Flat-Plate Solar Collector Radiation 20
- 18. Efficiency of SolarCollectors Rate of heat loss: UL collector overall heat loss coefficient [W/m/K] A area, m² TC collector average temperature [°C] Ta ambient temperature [°C] 21
- 19. Amount of solarirradiation: Amount of solar power collected by the absorber plate: 22 Solar collector efficiency: energy input
- 20. Solar collector efficiency •Useful heat gain Qi = input heat from the sun (as radiation) Qo = heat lost back to the environment (in all forms) • Note that Qu will be used to heat a working fluid entering the collector at temperature Ti and exiting at To: Note: all Q’s should have a dot over, as they are heat flows 23 𝑄𝑢 = 𝑄𝑖 − 𝑄𝑜 𝑄𝑢 = 𝑚𝑐𝑝 𝑇𝑜 − 𝑇𝑖
- 21. Solar collector efficiency:heat removed • Hottel-Whillier-Bliss equation where the design factors are: • FR → heat removal factor • → effective transmittance-absorptance product • UL → heat loss coefficient • A → gross collector area Operating parameters are I, Ti and Ta 24 C. C. Smith and T. A. Weiss, ‘Design application of the Hottel-Whillier-Bliss equation’, Solar Energy, vol. 19, no. 2, pp. 109–113, Jan. 1977, doi: 10.1016/0038-092X(77)90047-0.
- 22. Solar collector efficiency •We can now define the efficiency (η) as: which is therefore equal to: 25
- 23. Notes on solarcollector efficiency • is about 5% larger than the product of transmittance of cover (τ) and absorptance (α) of absorber • FR essentially measure the effectiveness of the working fluid in removing heat from the absorber (depends on fluid, flow rate, etc.) • UL includes all heat losses, in all forms: conduction to external structure, radiative loss through cover, etc. 26
- 24. Collector Performance: Ambienttemperature Efficiency increases with ambient air temperature 28 so, it’s A
- 25. Collector Performance: Inletwater temperature 30 Better efficiency with cooler inlet water so, it’s A
- 26. Collector Performance: SolarRadiation 31 Which curve for higher fluid inlet temperature? A B
- 27. Collector Performance: SolarRadiation 32 Which curve for higher fluid inlet temperature?
- 28. 33 Solar Collectors Evacuated TubeCollector
- 29. Solid metal surfacegets hot and the liquid (alcohol/ water) absorbs heat Turns into vapour Rises up heat pipe to cold surface and condenses back into liquid – releasing latent heat Utilises high heat transfer coefficient for condensation so gives excellent thermal conductivity through the tube 34
- 30. Why Evacuated? To reduceconvection and conduction losses Evacuated Tube Collector Cross Section of an evacuated tube Solar Collector 35 Vacuum Absorber Heat Pipe Glass Cover Clip Heat Transfer Fin
- 31. Distribution of Stationarycollectors installed (2020) 36 https://www.iea-shc.org/Data/Sites/1/publications/Solar-Heat-Worldwide-2021.pdf ← World Europe →
- 32. Distribution of solarthermal by application type Source: Solar Heat World wide Report , IEA, 2015 37
- 33. Overview 1. What issolar thermal energy conversion 2. Heat 1. Flat plate collector 2. Evacuated tube collector 3. Power 1. Parabolic trough collector 2. Linear Fresnel reflector 3. Fresnel tower 4. Parabolic dish 5. Storage 4. Installed systems 38
- 34.
- 35. Solar Thermal EnergyConversion 40
- 36. Solar Thermal PowerPlant Heat Exchanger Turbine Generator Storage system Thermo-oil circulation pipes Solarfield
- 37.
- 38. Concentrated Solar Power(CSP) Uses large area of mirrors or lenses to focus the sunlight to smaller absorber Concentrate sunlight: 50-3000x concentration Track sun position: daily/seasonally Store Heat Energy Covert Heat to Power: Turbine and Stirling Engines 43
- 39. Solar Thermal PowerPlant https://www.youtube.com/watch?v=rO5rUqeCFY4 After watching the video, try to sketch the heat flow of a solar thermal power plant to produce electricity by including - Solar field/Receiver - Hot and Cold fluid - Heat Exchanger - steam and water - Turbine/Generator 44
- 40. Concentrating Collectors A concentratingcollector comprises a receiver, where the solar radiation is absorbed and a concentrator which is an optical device that directs beam radiation onto the receiver. Concentration Ratio: For circular concentrators maximum possible CR =45000 For linear concentrators maximum possible CR=212 Source: R. Nicolas and J. Duran, „Theoretical maximum concentration factors for solar concentrators” J. Opt. Soc. Am. 1(11), 1100 (1984) 46 Area Receiver Area Aperture CR
- 41. Different Concentrator Geometry (a)Tubular absorbers with diffuse back reflector (b) tubular absorber with specular cusp reflectors (c) plane receiver with plane reflectors (d) parabolic reflector (e) Fresnel reflector (f) array of heliostats with central receiver 47
- 42.
- 43. Focus: Line Line -tracks thesun on single axis -focus irradiance on a linear receiver -temperature will be lower <500oC 49
- 44. Parabolic Trough Collector •Curved, mirrored trough • Reflects solar radiation onto glass tube containing a fluid (oil, water or molten salt) 50
- 45. Linear Fresnel Reflector •An array of flat, long, narrow mirrors at slightly different angles • Light reflected to a single line receiver, as opposed to multiple for trough collector 51
- 46. Focus: Point Point trackthe sun along two axes focus irradiance at a single point receiver permit good receiver efficiency at higher temperature, able to reach 1000oC 52
- 47. Fresnel Tower • Again,use an array of flat mirrors at slightly different angles • This time the radiation is focussed on a receiver at the top of a tower • Receiver contains molten salt • When heated this flows into a storage tank and can be used to create steam to drive a turbine using Rankine cycle • Can also be used on non-flat terrain 53
- 48. Parabolic Dish Collector •Like a TV satellite receiver • Heat used for steam engine or, more commonly, Stirling engine • Kinetic energy used to drive an electricity generator 54
- 49. The 100 MWShams 1 concentrated solar power plant has begun operation in the west of Abu Dhabi. 55
- 50. World’s largest ConcentratedSolar Power (CSP) project at Mohammed bin Rashid Al Maktoum Solar Park to generate clean energy at the rate of 700 MW 56 Project at a glance: Dubai is building the world’s most ambitious CSP project To deliver 700 MWe (troughs+tower) 15 hours storage Include the world’s tallest solar tower, standing 260 metres tall DEWA says the project will achieve the lowest cost price of energy, at 73 $/MWh
- 51. Case Study: Andasol,Spain Area: Site: 3×200 ha = 6 km² Collectors: 0.51 km² Solar irradiance: 2,200 kWh/m2/yr Nominal: 3×50MW Energy generation: 3×165 GWh/yr Capacity factor ~38% Conversion efficiency ~4% (radiation on ALL the facility) £500M total cost, 25yr lifetime Electricity costs 20p/kWh (UK price cap 2023: 67p/kWh*) * https://www.ofgem.gov.uk/publications/latest-energy-price-cap-announced-ofgem
- 52. Case Study: Crescent Dune •Bloomberg: "A $1 Billion Solar Plant Was Obsolete Before It Ever Went Online" • ten thousand mirrors form a spiral almost 2 miles wide (Nevada – USA) • designed to generate enough power night and day to supply a population of 100,000 • its energy costs about $135/MWh, compared with less than $30/MWh today at a new Nevada photovoltaic solar farm [BloombergNEF] https://www.bloomberg.com/news/articles/2020-01-06/a-1-billion-solar-plant-was-obsolete-before-it-ever-went-online
- 53. Thermal Storage • Theconcept : throughout the day, excess heat is diverted to a storage material (e.g. molten salts). • When production is required after sunset, the stored heat is released into the steam cycle and the plant continues to produce electricity. Hot Oil Molten salt Cold Oil Steam Water 59
- 54. Molten Salt Storage– Andasol, Spain Solid salts heated until they melt • Day time: Stored in insulated tanks • Night time: pumped to release heat • Heat storage capacity ~2GWh • 1400 t of nitrate salts (60% sodium nitrate + 40% potassium nitrate) • 2 tanks 61
- 55. Molten Salt Storage– Andasol, Spain Conventional steam turbine Collector field Molten salt storage H2O NaNO3-KNO3 Syn. Oil 62
- 56. Solid Media ConcreteStorage • Storage system with regenerative heat transfer • Low cost and low maintenance • Flexible to large number of sites and construction materials 63
- 57. Back-up and hybridisation Back up: for when the solar resource is low and to guarantee an alternative thermal source (compensate night thermal losses, prevent freezing and assure a faster start-up in the early morning). Full hybrids: constant use of fuel (usually a fossil fuel) or another source of heat together with solar energy. the Shams-1 (100 MW) in the United Arab Emirates combines hybridisation and backup, using natural gas and two separate burners. The plant burns natural gas continuously during sunshine hours to raise the steam temperature (from 380°C to 540°C) for optimal turbine operation.
- 58.
- 59. Summary 1. What issolar thermal energy conversion 2. Heat 1. Flat plate collector 2. Evacuated tube collector 3. Power 1. Parabolic trough collector 2. Linear Fresnel reflector 3. Fresnel tower 4. Parabolic dish 5. Storage 4. Installed systems 68