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Solar Thermal TECHNOLOGY EB

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					 Solar Thermal
  TECHNOLOGY



Eric Buchanan
Renewable Energy Scientist
West Central Research and Outreach Center
Wcroc.cfans.umn.edu
           Solar Energy History
Solar Thermal
•   700 BC – Chinese use burning mirrors
•   1760 – Saussure uses solar hot box
•   1891 – First DHW patent
•   1909 – Separate panel & storage
     – 4000 sold in 10 yrs (CA) until nat. gas discovered in 20’s
     – Used in 1/2 of houses in FL (1941) until cheap electricity
• Boom & bust cycle repeats itself in Japan, Israel
  and Australia due to cheap fossil fuels
           Sunlight to Heat
Solar thermal systems heat air or a fluid to
provide space conditioning or domestic hot
water (DHW)
• Active systems use a pump or fan to move fluids,
  passive systems use gravity and convection

• Direct systems heat the fluid that is consumed,
  indirect systems heat a working fluid and use a
  heat exchanger
            Sunlight to Heat
Active, indirect systems are typically used in
a cold climate – 2 types of freeze protection
  • Antifreeze
     – 50% Propylene glycol (food grade) & water
            o Freezes at -29 deg F, boils at 222 deg F
            o Limited life ~ 5 years, annual pH check

                          • Drain back
                               – When pump stops, fluid drains
                               from panels into a storage tank
                                    o Allows use of plain water
                                    o Can also prevent overheating
             Sunlight to Heat
Solar thermal panels
  • Flat plate panels
     – Simple, proven design
     – Very robust
     – More effective at lower
     fluid temperatures


      • Evacuated tube panels
           – Elegant design
           – Passive tracking
           – More efficient at higher fluid
           temperatures
                   Sunlight to Heat
Collector efficiency
                                                    • Unglazed collectors are
       unglazed flat plate collector
                                                    used for pool heating

                                                    • Efficiency calculations are
                                                    based on collector gross area
                                                          – Penalizes evacuated
                                                          tubes because of spaces
                                                          between tubes

                                                    • The SRCC provides test
                                                    data for thermal panels
                                                          www.solar-rating.org

   More sunlight                Less sunlight
   Lower fluid temp             Higher fluid temp
   Higher air temp              Lower air temp
            Sunlight to Heat
   Domestic Hot Water (DHW) systems

One                                   Or
Tank…                                 Two?
           Sunlight to Heat
Domestic Hot Water (DHW) systems
• Can provide 50% to 75% of hot water needs
                      • A back up system is needed
                         – Can’t be 100% solar
                      • Must deal with excess heat
                         – Heat dump or drain back
                           system
                      • A boiler can be added to
                        provide solar space heating
              Sunlight to Heat
Heating air
• Fan turns on when panel temperature is higher than
  room temperature




                                         www.RReal.org
            Sunlight to Heat
Solar fraction is the percentage of load
provided by solar energy
• It is not practical to have a 100% solar fraction
   – A back-up system is required
               • Doubling the system size does NOT
               double the solar fraction (24% to 37%)
                    – Must deal with excess summer heat
                         o Heat dump or drain back system
                         o Increase summer load
                               • Swimming pool
                               • Seasonal storage
                               • Air conditioning??
              www.caleffi.us
        Solar Thermal History
Solar cooling
• 1858 – Absorption cooling invented by F. Carre
• 1878 – Auguste Mouchout makes ice at the
  Universal Exhibition in Paris
• 1929 – First Icy Ball patent
• 1930 – Einstein refrigerator (Electrolux)
• Absorption cooling has been used commercially
  since the early 20th century
   – Used in RV’s and tractor trailers
        Solar Thermal Basics
Solar air conditioning
• Absorption chillers           • Adsorption chillers
   – water and salt (LiBr) or      – water and silica gel or
     ammonia and water               zeolite
         Solar Thermal Basics
Peak air conditioning loads typically occur
when solar resources are high
• High water temps needed (190 deg F)
   – Evacuated tube collectors
• Need cooling tower for heat rejection
   – Requires chemical water treatment
• Residential sizes (<5 ton) are rare
   – Chillers are more efficient in larger size
       WCROC System Details
LEED silver office building addition/remodel
completed in 2010
• Honeywell control and monitoring system
• Primary HVAC system is 15 ground source heat pumps
• Horizontal and vertical closed loop system

                                   • Addition space is
                                     4,700 ft2 (434 m2)
                                   • HVAC design loads:
                                   10 tons (35 kW) cooling
                                   15 tons (53 kW) heating
           WCROC System Details
  Solar thermal system
      3 heating/cooling coils inserted ahead of heat pumps
      About 2100 ft2 (200 m2) of evacuated tube collector area


                                                   40 Solar Panels Plus,
                                                   SPP-30 panels



 Heat transfer fluid is 50/50 mix of water and
  propylene glycol
 System volume is 600 gallons (2270 liters)
  including 300 gallons (1135 liters) of storage
 Slant fin tubing for heat dissipation
                 Heating Mode
 Solar heated water is directed through a
 mixing valve to the fan coils and/or the
 storage tank
• Mixing valve is
  controlled by
  temperature drop
  across coils
• When coil load is
  low, hot water is
  directed to storage
  tank
          Heating Mode
Results
                      SRCC Comparison
                    Insolation = 793 Btu/ft2 /day
                               = 2.50 kWh/m2/day
                      (Cloudy Day = 1000 Btu/ft2 /day)

                    Ave fluid temp = 150°F (66°C)
                     Outdoor temp = 45°F (7°C)

                          Evacuated Tubes:
                   Panel output = 12.8 kBtu (13.5 MJ)
                   SRCC table* ≈ 8.8 kBtu (9.3 MJ)


                   *Extrapolated
                    Cooling Mode
   Solar heated water is directed to an
   absorption chiller
• Chilled water is directed
  through a mixing valve to
  the fan coils and/or storage
• Mixing valve is controlled by
  coil exit temperature
• When coil load is low,
  chilled water is directed to
  the storage tank
          Cooling Mode
Results
                       SRCC Comparison
                     Insolation = 1049 Btu/ft2 /day
                                = 3.32 kWh/m2/day
                       (Cloudy Day = 1000 Btu/ft2 /day)

                     Ave fluid temp = 180°F (82°C)
                      Outdoor temp = 45°F (7°C)
                    Chilled water temp = 46°F (8°C)

                           Evacuated Tubes:
                    Panel output = 17.2 kBtu (18.1 MJ)
                    SRCC table ≈ 11.2 kBtu (11.8 MJ)
                          Cooling Mode
       Solar air conditioning equipment
                   Yazaki SH-10 absorption chiller
                      •   Refrigerant is water, absorbent is lithium bromide
                      •   Operating range: 158°F (70°C) to 203°F (95°C)
                      •   Nominal input: 190°F (88°C) at 38 gpm (144 lpm)
                      •   Chiller can be reversed to operate in heating mode

                   Amcot ST-50 cooling tower
                      •   Requires chemical treatment of
                          water

 Variable Frequency Drive (VFD) for solar pump
   •    Helps low light heat collection
U.S. Air Conditioning
                      A/C Conclusions
   Is solar air conditioning the future?
    • Only about 1000 units in operation worldwide
    • Planners and installers have little experience
    • Small, unstable market creates tough business plan
    On the plus side…
     • Technology works!
     • Improvements are in the works
     • Solar A/C decreases grid load at peak times
Source: IEA SHC Task 38 - October 2011
Germany had 6 times as much solar in 2011 as in 2007
  • Peak electricity price dropped 40% - EVERYBODY pays less!!




          2008                          2012
         The Solar Thermal Industry
                                      • China and Europe account for more
                                      than 90% of the world SHW market!
                                         • It is mostly residential




                                                  Total collectors in use as of 2009
                                                   Total collectors sold in 2009

                                           China is driving the collector market
                                            towards evacuated tubes
Source: International Energy Agency
What is China doing?
            UMM RFC Pool
32 Solar Skies flat plate collectors
• Solar heated water is pumped through a heat
  exchanger
• Pool pump sends pool water through the same
  heat exchanger http://146.57.12.91/db/UM_Morris_Web_Sup/Graphics/PE_Center/Solar_Hx
UMM RFC Pool - JUN 2012
 Solar Thermal
  TECHNOLOGY



Eric Buchanan
Renewable Energy Scientist
West Central Research and Outreach Center
Wcroc.cfans.umn.edu

				
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