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					Solar Hot Water Heating Systems




 Courtesy of DOE/NREL




                                       PG&E
                        Pacific Energy Center, San Francisco
                         Energy Training Center, Stockton
              Instructor


        Pete Shoemaker
       PG&E Pacific Energy Center
              (415) 973-8850
             pjsy@pge.com




              with assistance from
Paul Menyhearth of The American Solar Institute
 Josh Plaisted of Kineo Design and PVT Solar
Courtesy of NASA
The Full Energy Picture
                      PG&E Portfolio Solution

1) Reduce consumption as
much as possible.                Reduce
                                 Energy
                                  Use                     2) Get the
                                                          “greenest”
                                                          power you
                                Partnership
 3) Offset any                                            can.
 remaining                      Education
 carbon                          Outreach
                                              Renewable
 emissions.      ClimateSmart                   Power
                                               Supply
Agenda

  • Industry overview
  • Essential physics
  • Terms and concepts
  • Collector and System types
  • Site evaluation and design
  • Economics
Industry Overview
Two Types:
1. Solar pool heating
   • Recreational use
   • Typically unglazed panels (no glass)
   • Temperature around 80 degrees
   • Works seasonally
2. Solar water heating (SWH)
   • Essential use
   • Glazed panels
   • Temperature around 120 degrees
   • Works year-round
   • Heats domestic hot water (DHW)
                            Solar Pool Heating
                           Swimming pool water heating
                       80 - 85 degrees from May to October




                                                             Source: Fafco




Courtesy of DOE/NREL




  Mature industry with main markets in California and Florida.
Overview




           Courtesy CCSE
Overview




           Courtesy CCSE
Overview




           Courtesy CCSE
Overview




           Courtesy CCSE
Industry Overview: U.S.
 Favorable regulatory environment
 Federal Tax Credit:
 • Extended through 2016
 • 30% for both commercial and residential
 • MACRS depreciation for commercial



 Other state and local rebate programs exist or
 are in the planning stages.
Industry Overview: California
Upcoming state rebate program: AB1470


 • Applications accepted 5/1/10 (residential) and 6/1/10
   (commercial).
 • Systems installed after 7/15/09 eligible.
 • Allocation is 40% residential, 60% commercial and
   multi-family.
 • Handbook and online calculator to be developed
   soon.
 • Public meetings held at the CPUC on Van Ness.
Essential Physics




                                    Courtesy ofNASA



          It all starts with the sun.
Greenhouse Effect

          Ozone layer


           light     Short waves get through



                         Long waves are trapped
              heat
  Earth
Greenhouse Effect

                 Glass


            light       Short waves get through


 Heat
 absorber                   Long waves are trapped
                 heat

     SWH
     collector
Metal Conductivity

   Some metals transfer more heat than others.




           Fluid                        Fluid




                   Pipe cross-section

         Copper                         Iron
Water Behavior


  Water expands both when heated and frozen.



           Steam             Ice




         Moving water will NOT freeze.
Water Behavior

    Warm water will rise, cold water will sink.
Water Behavior

 Water contains dissolved minerals, which can
 cause unwanted buildup and clogging.

 • “Hard” water contains more minerals, “soft” water less.
 • Most common minerals are calcium and magnesium.
 • The buildup of minerals is called “calcification” or “scaling”.
Essential Physics: Summary

    • Greenhouse effect
       • Light enters but heat trapped
    • Color absorption
       • Dark colors absorb and light colors reflect
    • Metal conductivity
       • Copper conducts more than others
    • Water behavior
       • Expands when heated and frozen
       • Moving water will not freeze
       • Warm water rises, cold water sinks
       • Water contains dissolved minerals
Which leads to …

   Glass-covered collectors,
   dark-colored, with copper or
   aluminum piping…

   Systems designed to take
   advantage of the movement
   of heated water …

   With protection against
   freezing, overheating, and
   mineral buildup.
Terms and Concepts




                     Courtesy ofNASA
Terms and Concepts

 BTU: British Thermal Unit. Amount of heat needed to raise
  one lb. of water one degree F.
 Watt-hour: 3.4 BTU          Kilowatt-hour: 3,413 BTU
 Therm: 100,000 BTU (29.3 kWh)


 Vacuum (evacuated) tube: Tube with no air.
 Thermosiphon: Natural process of hot water rising (in a tube).
 Stratification: Separation of hot and cold water (in a tank).
 Heat exchanger: Device that transfers heat from one medium
  to another.
    T (Delta T): Change in temperature.
Terms and Concepts

 System design: Storage is the key.


 Solar Electric:                Solar Thermal:




    Tied to the grid.                 No grid--you’re on
    Every kWh is used,                your own.
    no waste.                         Potential for waste.
                                                       Courtesy of DOE/NREL
Terms and Concepts
Solar Fraction: Percentage of building’s hot water requirements
 that can be met by solar—at optimum economics (no waste).

 Example:
 Design to cover 100% of usage year-round, including winter.
 Minimal sun in winter, so need many collectors (expensive).




  But in summer sun, these collectors produce far more hot water
  than you use, and you can’t store it or sell it.
  Wasted energy, wasted money.
Solar Fraction: U.S.




    Simulated Solar Fraction Using a “Base” (Current
    Technology) Residential SWH System
                                               Source: NREL report 2007
Collector and System Types




                             Courtesy ofNASA
Standard Water Heaters

 Typical gas heater:


 Direct flue.
 Much heat loss “up
 the chimney”.
 Low efficiency.
 (50 – 70%)




                         Courtesy PG&E
Standard Water Heaters

 More improved model:

 Condensing heater.
 Extended flue which
 releases much of its heat
 to the water before
 venting.
 Vent gases are cool
 enough to condense.
 Efficiency around 80 –
 90+%
                             Source: Energy Star
Standard Water Heaters

 Tankless

 Gas or electric.
 Can require special
 hookup service.
 Effectiveness related to
 usage patterns.




                            Source: Energy Star
Collector and System Types

   Five main aspects of solar systems:
    1. Heat collection
    2. Heat transfer
    3. Heat storage
    4. Heat backup
    5. Extreme temperature protection
       (freezing/stagnation)
Collector and System Types

  Five main aspects of solar thermal systems:

   1. Heat      2. Heat    3. Heat   4. Heat     5. Extreme
   Collection   Transfer   Storage   Backup      Temperature
                                                 Protection


                                                  Special
                                                  valves,
                                                  pumps,
                                                  processes,
                                      Gas or      etc.
                Water or              electric
      Solar
                glycol                heater
      panel                Storage
                           tank
Collector and System Types

  Two types of heat transfer systems:

     1. Open Loop                2. Closed Loop
        (Direct)                    (Indirect)




         water                       glycol



    Uses just the water      Uses heat-transfer fluid
    from the main.           in “closed” system.
    “Open” to outside        Needs heat exchanger.
    elements.
Collector and System Types

  Further categorized by “pumping” source:

     1. Passive                2. Active (electric
         (natural)                 pump)




    Thermosiphon
                              Must have electric
    process.
                              source.
    Tank must be higher
                              Tank can be anywhere.
    than collector.
ICS: Integral Collector Storage


       1. Heat        3. Heat
       Collection     Storage




          Solar
          panel        Storage
                       tank

                     Combined
ICS: Integral Collector Storage: 50% SF




                                 Courtesy energybychoice.com
ICS: Integral Collector Storage: 50% SF
The Simplest Form of Solar

                                             Benefits
                                             • Low first cost
                                             • No moving parts
                                             • Inherent overheat protection
                                             • Moderate freeze protection


                                             Disadvantages
                                             • Sensitive to ambient temperatures
                                             • Weight
  Figure courtesy SunEarth



                             Sample specifications




                                                                    Figure courtesy NREL
Simple system with ICS
System Characteristics
 For typical ICS system:

  Passive
  • No pumps, nothing requiring outside power

 Open Loop
 • New fluid (water) is constantly entering—system is “open”
   to outside elements




                                                      Figure courtesy NREL
Flat Plate Collectors
The Industry Workhorse




                                                 Figure courtesy SunEarth




                         Sample specifications




                                                                            Figure courtesy NREL
Thermosiphon Passive Systems: 65% SF

                                Benefits
                                • High thermal performance
                                • Not sensitive to ambient temp
                                • No moving parts
                                • Array is freeze protected




 Figure courtesy SunEarth Inc
                                Disadvantages
                                • Can’t you get that tank off my roof!
                                • Supply & return lines not freeze
                                  protected
Thermosiphon Passive Systems: 65% SF




                             Photo courtesy NREL
Thermosiphon Passive Systems: 65% SF
  Additional heating element
  boosts temperature as necessary



                                                           120 degree water goes
Water comes in                                             into house
to tank from main



                                                         Heated fluid rises

       Heat is transferred to
       water in tank

                                    Cooled fluid sinks



                                      Solar fluid circulates
                                      through collector
                                                                        Figure courtesy SunEarth Inc
System Characteristics
 For typical tank-on-roof systems:

  Passive
  • No pumps, nothing requiring outside power

 Closed Loop
 • Heat-exchange loop is closed to new elements

 Also can be:

 Open Loop
 • New fluid (water) is constantly entering—system is open
   to new elements

                                                     Figure courtesy NREL
Active Systems
Low-Profile Active System

                                                          Benefits
                                                          • Highest thermal performance
                                                          • Freeze protection to –60 F
                                                          • Lightweight low roof profile

                                                          Disadvantages
                  Figure courtesy SunEarth Inc
                                                          • Some active components
                                                          • More expense and maintenance




                                                 Courtesy of DOE/NREL
Active Systems




  Needs pump(s)
  to operate.
                  P
Evacuated Tubes

 Photo courtesy Industrial Solar Technology
                                              Photo courtesy William Lord




 Figure courtesy Edwards Hot Water




                                                    Courtesy of DOE/NREL
Evacuated Tubes
Lower Losses for Colder Climates
                                                             Figures courtesy Thermomax


                                               6
     1.   Vacuum tube                                                                     7
     2.   Heat pipe
                                           1                   8
     3.   Cold liquid                                         9
                                       2
     4.   Hot vapor                3
                               4
     5.   Absorber

                                                     5
                                                   6. Collector return
                                                       (hot)
                                                   7. Collector supply
                                                       (cold)
                                                   8. Heat exchanger
                                                   9. Shock absorber
System Characteristics
 For typical flat plate or evacuated tube systems:

  Active
  • Uses pumps and other active elements

 Closed Loop
 • Heat-exchange loop is closed to new elements

 Also can be:

 Low or High Pressure
 • Different pressures for different system requirements


                                                       Figure courtesy NREL
Freeze Protection

 Five different methods:

    1.   Thermal mass (ICS)
    2.   Auxiliary heater (electric element)
    3.   Antifreeze (closed loop)
    4.   Water flow (moving water won’t freeze)
    5.   Draining (removing water from collector)




                                                    Figure courtesy NREL
Drain-down and Drain-back Systems
Drain-down:
    • Drain “down & out”
    • Open loop
    • Removes water from collector and completely
      out of system onto ground or roof

 Drain-back:
     • Drain “back in later”
     • Closed loop
     • Removes HX fluid from collector into tank, to be
       put back after freeze passes
                                               Figure courtesy NREL
Drain-down System (open loop)




                          Courtesy University of Central Florida
Site Evaluation and Design




                             Courtesy ofNASA
Climate Zones




 California climate zones




http://www.energy.ca.gov/maps/building_climate_zones.html
Usage
Usage




 This is baseline rate. Second tier rate is approx. 20% more, on avg.
 High is $1.91 (July 2008), low is $.81 (May 2009).
 Average is $1.16
Usage




    Avg. statewide annual use (2004): 431 therms
    44% of that = 189 therms.
    In the study, avg. house size = 1,500 sf., avg. # people = 3
Orientation
 Proper Orientation Does not Require Perfect Orientation
             • Collectors needn’t be racked due South at latitude plus 15°
             • Typical penalty is less than 10-20%
             • Always possible to augment collector area

              San Francisco, CA
                                                                                90

 SOF
 0.40-0.50
                                                                                60
 0.50-0.60
 0.60-0.70                                                                           Tilt
 0.70-0.80
 0.80-0.90                                                                      30
 0.90-1.00


                                                                                0
         -90                 -60   -30        0          30          60       90
        East                                                                 West
             Chart courtesy NREL
                                          Azimuth
Mounting
Mounting
Rebate Program: AB 1470


 • Applications accepted 5/1/10 (residential) and 6/1/10
   (commercial).
 • Systems installed after 7/15/09 eligible.
 • Allocation is 40% residential, 60% commercial and
   multi-family.
 • Handbook and online calculator to be developed
   soon.
 • Public meetings held at the CPUC on Van Ness.
Rebate Program: AB 1470


 Residential rebate amounts:

      Step     Incentive per       Maximum          Funding Amount
             therm displaced    Incentive Single
                               Family Residential
                                    Projects
        1             $12.82              $1,875        $20,000,000
        2             $10.26              $1,500        $18,000,000
        3              $7.69              $1,125        $18,000,000
        4              $4.70                $680        $16,000,000
Design Exercise: Residential

  Considerations:
  •   Usage
  •   Geography—climate zone
  •   Space and collector location
  •   Type of system
  •   Size of collector(s)
  •   Size of storage tank
  •   Mounting
  •   Financials
Design Exercise: Residential
  Standard Assumptions (California):
  • 20 gallons of hot water per person per day
  • 1 sq. ft. of collector will produce 1.5 gallons of
    hot water per day
  • Tank size should hold one full day’s usage


  Typical residence (4 people):
  • 80 gallons of hot water daily usage
  • 80/1.5 = about 60 sq. ft. of collector area
  • 80 gallon storage tank
Design Exercise: Residential

    Our system:
    • Active, closed-loop for freeze protection
    • Two 8’ x 4’ flat plate collectors
    • 80 gallon storage tank
    • Standard flush roof mount
    • 70% solar fraction
Design Exercise: Residential
    Cost:
    • Total installed price $6500
    • State rebate $1875 (147 * $12.82 up to max)
    • Tax credit ((6500-1875) * .3) = $1388
    • Net cost = (6500 – 1875 – 1388) = $3237

    Savings:
    • Average yearly usage 210 therms
    • Solar saves 70% of that, or 147 therms
    • Average cost per therm $1.25
    • Yearly savings about $185 (first year)
Design Exercise: Residential

 Payback:
 • Add $500 maintenance cost over lifetime
 • Total cost about $3,800
 • Straight payback (no inflation factor) =
  3800 / 185 = 20 years
 • With inflation factor of 5%, payback shortens
   to about 17 years.
Case Study: Residential
Case Study: Residential
Case Study: Residential
Case Study: Residential
Commercial System Issues




                           Courtesy ofNASA
              Instructor


        Pete Shoemaker
       PG&E Pacific Energy Center
              (415) 973-8850
             pjsy@pge.com




              with assistance from
Paul Menyhearth of The American Solar Institute
 Josh Plaisted of Kineo Design and PVT Solar

				
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