A NOVEL TECHNOLOGY FOR SOLAR APPLICATIONS Cristoforo BENVENUTI SEEC 2009 Trento 8-9 October 2009
Alternative route to high temperature : Decrease thermal losses! Very low thermal losses may be achieved thanks to: Vacuum It is generally assumed that: A selective coating on the light absorbers Flat panels collectors are only adequate for low temperature application High temperatures may be obtained only by light focusing In this way 300 C are at reach without mirrors The flat plate evacuated solar collector Also the diffuse light is collected, which cannot be focused The diffuse component of solar light amounts to about 30% in the best solar areas, and exceeds 50% in Central Europe 2
The flat plate evacuated solar collector Mean monthly diffuse radiation as percentage of mean monthly global radiation for four UK stations for each month 3
Direct and diffuse light components in Geneva (CH) The flat plate evacuated solar collector 4
Total and direct component of solar light at different locations The flat plate evacuated solar collector 5
Issues Vacuum => 10 tons per m 2 of glass window, the glass must be properly supported The joint between the metal frame and the glass must be vacuum tight All materials inside the panels must fulfill UHV specifications (low degassing, cleanliness) The flat plate evacuated solar collector A built-in pump is needed to maintain the vacuum for 20 years This pump must preferably be powered by sun 6
Is vacuum really useful? The flat plate evacuated solar collector Variations of the absorber temperature as a function of the panel pressure 7
Selectivity: High absorption (α) of solar (visible) light Low emission (ε) of infrared radiation For α values of 0.9 and ε values of 0.07 (at 300 C), temperatures of the order of 300 C may be obtained for absorbers blackened on both sides, and of the order of 350 C for single side blackening How important is the absorber selectivity? Calculated variation of the peak stagnation temperature as a function of the α/(ε1+ε2) ratio The flat plate evacuated solar collector 8
History On the ground of these considerations evacuated flat plate solar panels were built and testes in the 70s. 9The flat plate evacuated solar collector
Global view of the 1 st panel 3 2 The flat plate evacuated solar collector 1. Frame with spacers 2. Absorbers with coating pipes 3. Glass window 1 10
The flat plate evacuated solar collector 11
The flat plate evacuated solar collector 12
These prototypes were exposed to real environment conditions on the roof of a CERN building for about 9 years. Results The flat plate evacuated solar collector Stagnation temperatures of the best and worse absorbers of a panel prototype 13
Global view of 3m panel 3 2 1 The flat plate evacuated solar collector 1. Frame with spacers 2. Absorbers with coating pipes 3. Glass windows 3 14
In spite of the good thermal performance of the panels, the addition of mirrors helps gaining on cost effectiveness and increasing the useful operating temperature, so as to cover, with the same panel, all the possible solar applications Mirors Config.1 - Bare panel Stagnation temperature ~ 320 C Config.2 - Panel with cylindrical mirrors Concentration factor 1.9 Stagnation temperature ~400 C Config.3 - Panel with cylindrical mirrors and lateral mirrors Concentration factor 3 Stagnation temperature >450 C The flat plate evacuated solar collector Different panel configurations 15
Thermal efficiencies of the 3 possible panel configurations The flat plate evacuated solar collector These figures represent the performance which could be obtained by implementing certified improvements. The estimate is carried out for an incident power of 1000W/m 2 and a glass temperature of 30 C. 16
Thermal efficiency [%] 80 70 60 50 40 30 20 Thermal efficiencies as function of the temperature Two sides blackening of the absorber Bare panel One side blackening of the absorber The flat plate evacuated solar collector 10 0 50 100 150 200 250 300 350 Temperature [ o C] 17
Thermal efficiency [%] 80 70 60 50 40 30 Thermal efficiencies as function of the temperature Panel with cylindrical mirrors The flat plate evacuated solar collector 20 10 0 50 100 150 200 250 300 350 Temperature [ o C] 18
Thermal efficiency [%] 80 70 60 50 40 30 Thermal efficiencies as function of the temperature Panel with cylindrical and lateral mirrors The flat plate evacuated solar collector 20 10 0 50 100 150 200 250 300 350 Temperature [ o C] 19
Vacuum performances After evacuation the pressure inside the panel is in the low 10-7 Torr range. Due to the progressive decrease of the surface outgassing, the pressure decreases with time to the 10-8 Torr range, and increases to the 10-6 Torr when the absorbers are heated by sun to 300 C The flat plate evacuated solar collector The temperature dependance and its evolution over about 6 months for a recent panel prototype is illustrated in fig. 20
The flat plate evacuated solar collector 21
Applications The unique feature of the SRB solar panel is that it may be used for all the Solar Energy applications, a field now covered by products of different design The SRB panel is particularly suited for applications in the temperature range 150-250 C (for instance for industrial heat production and cooling / air conditioning) for which the panel performance is outstanding. For the production of electricity the SRB panel efficiency is similar to that offered by parabolic through solar fields, but the mirror geometry is much less critical and the maintenance for cleaning much reduced For low temperature applications (<100 C, domestic water heating) the SRB panel provides higher efficiencies than the existing flat panels in regions as Central Europe, where the available solar energy is reduced. The flat plate evacuated solar collector 22
Solar power repartition The flat plate evacuated solar collector 23
400 300 200 100 0-100 -200 TWh a Potential for thermal electricity 0 0.5 1.0 % LAND USE SPAIN FRANCE GREECE ITALY PORTUAL UK FRG Potential solar thermal electricity generation vs. present electricity demand as a function of land use The flat plate evacuated solar collector 24
Solar Energy Input KWh(th)/m 2.year 2300 and above 1200 to 2200 1000 to 1100 Key general information Typical Options and outputs Electric power generation and/or hydrogen production Electric power generation ; Industrial process heat; Heating and cooling Water and/or air heating for resindential buildings and low grade process heat Estimates of Attainable Systems Efficiencies Thermal Electric 0.60 0.20 0.40 to 0.55 0.30 to 0.40 0.10 to 0.18 0.08 to 0.10 Typical Regions Desert regions of North Africa, Southwest USA, Australia, etc. Moderate regions of North and South America, Asia, Australia, and primary regions of Southern Europe, etc. Secondary regions of Europe, Asia, Africa, North and South America, etc. The flat plate evacuated solar collector 25
Facilities in Spain 26
General view of the plant Facilities in Spain 27
Frame welding Facilities in Spain 28
Glass metallization Plasma gun Facilities in Spain Global view 29
Glass soldering Facilities in Spain 30
Glass washing machine Facilities in Spain 31
Frame chemical treatment Facilities in Spain 32
Chemical plant for absorber treatment Facilities in Spain 33
Assembly line Facilities in Spain 34
Assembly process Software Facilities in Spain General view 35
Tubes welding Bellows welding Facilities in Spain Sleeves welding 36
Absorbers Facilities in Spain Absorber cutting 37
Laser welding Facilities in Spain 38
Roll to roll system for Getter Facilities in Spain 39
Baking system prototype Facilities in Spain 40
Vacuum testing bench Facilities in Spain 41
Vacuum Facilities in Spain 42
Panel of 3m Facilities in Spain 43
Sun tracker for the homologation Facilities in Spain 44
Sun tracker Facilities in Spain 45
c/o CERN CH-1211 Genève 23 Tel. +41 22 767 89 77 Fax. +41 22 767 17 80 geneva@srbenergy.com www.srbenergy.com
References 1. Evacuable Flat Panel Solar Collector PCT / EP 2004 / 000503 (18.08.2005) Inventor: C. Benvenuti Applicant: CERN CH-1211 Geneva 23 2. Protective device for a solar collector PCT / EP 2006 / 006142 (26.06.2006) Inventor: C. Benvenuti Applicants: SRB ENERGY RESEARCH SARL rue de Candolle,9 CH-1205 Geneva CERN CH-1211 Geneva 23 The flat plate evacuated solar collector 3. Solar panel collector with cooling conduits comprising thermal expansion means PCT / EP 2006 / 001141 (26.06.2006) Inventor: C. Benvenuti Applicants: SRB ENERGY RESEARCH SARL CERN 47
References 4. Device for vacuum tight soldering an evacuated flat panel solar collector PCT / EP 2006 / 006140 (26.06.2006) Inventor: C. Benvenuti Applicants: SRB ENERGY RESEARCH SARL CERN 5. High efficiency evacuated solar panel PCT / EP 2008 / 057286 (11.06.2008) Inventor: C. Benvenuti Applicants: SRB ENERGY RESEARCH SARL CERN 6. Evacuated solar panel with a non evaporable getter pump PCT / EP 2008 / 057281 (11.06.2008) Inventor: C. Benvenuti Applicants: SRB ENERGY RESEARCH SARL CERN The flat plate evacuated solar collector 7. Sealing mechanism for an evacuated solar panel PCT / EP 2008 / 057283 (11.06.2008) Inventor: C. Benvenuti Applicants: SRB ENERGY RESEARCH SARL CERN 48