Cu stp 04_fundamentals
0 likes490 views
This document discusses solar thermal concentrating systems which collect solar radiation and convert it to thermal energy. It describes how these systems work, including defining the geometrical concentration ratio and discussing optical efficiency. The document outlines the ideal concentrating system and how increasing the concentration ratio leads to higher optimum temperatures and global efficiency. It also discusses concentration limits based on the sun being a disk rather than a point source, and types of concentrating systems like parabolic troughs and central receivers.
Cu stp 04_fundamentals
- 1. SOLAR THERMAL POWER! GEEN 4830 – ECEN 5007! 4. Fundamentals of solar thermal concentrating systems! Manuel A. Silva Pérez ! silva@esi.us.es !
- 2. Solar Thermal Concentrating Systems Systems that make use of solar energy by first concentrating solar radiation and then converting it to thermal energy } Uses: } Electricity (Solar Thermal Power) } Industrial Process Heat } Absorption cooling } Chemical processes } … 1 GEEN 4830 – ECEN 5007 07/07/11
- 3. Solar energy } Abundant } High-quality energy } Variable (on time) } Unevenly distributed (on space) } Low density 2 GEEN 4830 – ECEN 5007 07/07/11
- 4. Why high temperature? 3 GEEN 4830 – ECEN 5007 07/07/11
- 5. The sun as a heat source 4 GEEN 4830 – ECEN 5007 07/07/11
- 6. Why concentrate solar radiation? 5 GEEN 4830 – ECEN 5007 07/07/11
- 7. Ideal concentrating system } The receiver (or absorber) converts concentrated solar radiation to thermal energy (heat) } An ideal receiver may be characterized as a blackbody, which has only radiative losses 6 GEEN 4830 – ECEN 5007 07/07/11
- 8. Geometrical concentration ratio } The geometrical concentration ratio, Cg, is defined as A Concentrator Cg = C Aabs Where Aabs is the receiver (or Collec'on absorber) area area Absorp'on and Ac is the area collection area. 7 GEEN 4830 – ECEN 5007 07/07/11
- 9. Optical efficiency of the receiver 8 GEEN 4830 – ECEN 5007 07/07/11
- 10. Ideal concentrator } The maximum theoretical optical efficiency (when Tabs≥TSky) is the effective absorptivity of the receiver. } The higher the concentrated solar flux (C*I), the better the optical efficiency. } The higher the absorber temperature, the higher the radiative loss and, therefore, optical efficiency is lower. } The higher the effective emissivity, ε, the lower the optical efficiency. 9 GEEN 4830 – ECEN 5007 07/07/11
- 11. Global efficiency of the ideal concentrating system 10 GEEN 4830 – ECEN 5007 07/07/11
- 12. Ideal concentrating system } For each value of the geometrical concentration ratio, there is an optimum temperature. } The higher the geometrical concentration ratio, the higher the optimum temperature and the global efficiency. 11 GEEN 4830 – ECEN 5007 07/07/11
- 13. Concentration limits } The Sun is not a point light source. Seen From the Earth, is a disk of apparent diameter θS ≈ 32’. } The maximum concentration ratio is given by 32’ n′2 C max,3D = 2 2 n sen θ S 32’ Focus Where n and n’ are the refractive indices of the media that the light crosses before and after the reflection on the concentrator surface 12 GEEN 4830 – ECEN 5007 07/07/11
- 14. Types of concentrating systems } Line focus (2D) } Parabolic troughs; CLFR Cmáx,2 D = 1/ sin θ S } Point focus (3D) } Central receiver systems, parabolic concentrators (dishes) Cmáx ,3D = 1 / sin θ S 2 13 GEEN 4830 – ECEN 5007 07/07/11
- 15. Real concentrating systems Theoretical 3D: < 46200 2D: < 215 14 GEEN 4830 – ECEN 5007 07/07/11