Agricultural Applications of Solar Heat Jorge Facão jorge.facao@lneg.pt XVIII SIMPÓSIO LUSO-ALEMÃO DE ENERGIA 3rd July 2018 ENERGIA FOTOVOLTAICA E BIOENERGIA PARA O SETOR AGRÍCOLA
National Laboratory of Energy and Geology (LNEG) 1. LNEG is a State Laboratory of the Ministry of Economy. 2. R&D oriented to the needs of society and enterprises. 3. Sustainable research in areas of Energy and Geology. Energy Units located in Lisbon. 4. LNEG develops R&D activities in the following domains: Energy Production Systems; Energy Efficiency; Energy Analysis; Innovative Strategic Technologies; Endogenous Resources; Geological Hazards and Environment; Geology for the Territorial Enhancement.
LNEG UNITS National Laboratory of Energy and Geology Laboratory of Energy Laboratory of Geology and Mines Renewable Energies and Energy Systems Integration Unit Bioenergy Unit Laboratory of Solar Energy (LES) Laboratory of Materials and Coatings (LMR) Laboratory of Biofuels and Biomass (LBB)
Solar Energy Laboratory (LES) Accredited test laboratory: Testing of solar thermal collectors (EN ISO 9806:2013) Testing of factory made systems (EN 12976-2:2006) Testing of custom built systems (EN 12977-2:2012) (*) Testing of stores (EN 12977-3:2012) and combi-stores (EN 12977-4:2012) (*) out of acreditation scope Test laboratory recognized by: - CERTIF - DIN CERTCO Solar Keymark Optical characterization of absorbers and reflectors (collector components) (*) (*) out of acreditation scope
Processing temperatures for industrial sectors
Process temperatures for industrial sectors (low to medium temperatures)
Classification of solar collectors
Solar resources Direct and difuse radiation Nontracking collectors Flat-Plate Direct radiation Tracking collectors Linear Evacuated tubes with CPC refletor Pontual Solar Payback Project (https://www.solar-payback.com/)
Nonconvecting Solar Ponds The solar pond should be located close to a cheap source of salt and adequate source of water. Application: industrial processes and drive organic Rankine power cycle.
Flat-Plate absorber
Evacuated tube Direct-Flow vacuum tube Heat pipe vacuum tube Vacuum tubes Sydney with CPC
Parabolic trough
Moving line-axis Fresnel reflectors
Two recent agriculture, forestry and fishing solar powered projects ZACATECAS TERMOSOLAR DRYING PLANT 125 m 2 FLATE PLATE Carretera Zacatecas - Fresnillo KILOMETRO 21.5, 98050, FRESNILLO, ZACATECAS Mexico Operation start: 2017 Woltow, 440 m 2 Parabolic trough power plant for a fish farm 17179 Walkendorf Germany Operation start: 2008
Re-design of dairy industry for sustainable milk processing t Grant Agreement 613589 Call FP7-KBBE.2013.2.5-02 Instrument: Collaborative Project Start date: Nov 1, 2013 Duration: 36 months
Design methodologies Empirical correlations, e.g. F-chart method Semi-analytical simulations Stochastic simulation Detailed hour-by-hour simulations, e.g. TRNSYS
Earliest use of solar energy in agricultural Drying of food (vegetables, fruits, fish, meat) to reduce moisture content Drying is dual process: heat transfer to product from heating source and mass transfer from the product to air.
Solar Dryer Types
Practical issues in the use of solar dryers Direct solar radiation enhances the proper color of greenish fruits during dehydration. Some varieties of grapes and dates exposure to sunlight is considered essential during drying for the development of the required color. A period of exposure to sunlight of Arabica coffee is thought to give full flavor in roasted bean. However insolation entering a process chamber can overheating and shorten the durability of internal components due to ultraviolet. In some fruits, exposure to sun reduces the vitamin content. Some greenhouse dryers have employed PV to power the fan and control systems.
Greenhouses Short-wave insolation transmitted through a greenhouse cover is absorbed by internal surfaces. These surfaces reemit longer wavelength radiation, to cover (glass is opaque). The rate of heat loss from polyethylene-covered is 10-15% higher than glass greenhouse. Radiation trapping typically contributes only 10-25% of the total greenhouse effect, rather it is the suppression of convection losses. Most greenhouses use supplementary heating. Heat storage is less used, but solar air collector could be coupled with rockpile to provide a sensible heat store. In temperate and hot climates greenhouse cooling is provided by ventilation and evaporative cooling (directly wetting the air inside, wetting the ground surface or external cover).
Solar cooking
Solar desalination 79% of water available on earth is salty, 20% is brackish and only 1% is fresh. Conventional distillation plants are intensive users of fossil fuel energy. Arid regions have underground brackish water resources or are close to seawater and have high annual levels of insolation. Common solar desalination systems: 1. Basin solar still 2. Multistage flash evaporation
Solar refrigeration Solar cooling in remote rural communities (cool vaccine stores, ice making for commercial food storage) ST cooling such as absorption or adsorption chillers, which can be single or double effect LiBr-H2O water cooled or H2O-NH3 air cooled. The requested temperatures are respectively around 90ºC (flat plate) for the simple effect and 160ºC (evacuated tube collectors at a fixed tilt or parabolic trough collectors with a tracking system) for the double-effect chiller. PV modules with compression chillers.
Jorge Facão jorge.facao@lneg.pt www.lneg.pt