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USDA solar by ToddCostello


									                                                                                           REV 1           2009

                                                                                Solar Thermal
TERMS & DEFINITIONS                                  TERMS & DEFINITIONS (CONT.)                                  ANNUAL SUN POSITION
Active System: Uses a mechanical device (e.g.        Magnetic Declination: Difference in degrees
pump) to move the transport medium and               from magnetic north and true north. Adjustment
operate any end-use heat exchange.                   needed to estimated energy generation potential
Azimuth Angle: the angle clockwise from true         of thermal collector.
north of the direction that the PV array faces.      MW: megawatt. Unit of turbine capacity.
Due south = 180 .
                                                     MWh: Megawatt-hour. Unit of energy.
Bypass Valves: Solar bypass is a series of
three valves that allow you to bypass the existing   Minimum Temperature Controllers: Trigger the
water heater to manually force the solar system      supplementary heating whenever the water tank
to do all of the work. Used with solar batch         temperature drops below a minimum pre-defined
heaters. (See figures next page)                     temperature.

BOS: Balance of System—typically denoting all        OG-100—SRCC Document #OG-100 is the
components other than the solar themal               "Operating Guidelines for Certifying Solar                   SUNCHART
collectors. (e.g. controllers, tank, piping)         Collectors." Often panel performance is depicted
Closed Loop System: A heat transfer fluid is         as OG-100 Certified.
circulated through a heat exchanger in line with     Open Loop System: Water from the storage tank
the storage tank to heat the storage water.          is circulated through the solar collector and
These systems are preferable in areas prone to       heated directly.
frost and freezing.
                                                     Orientation: Position of SHW panels with
Controllers: Automatically regulate the              respect to true south. Differs by state/location.
temperature of the water in the storage tank.
There are two main types—time trigger                Passive System: Relies on thermal gradients to
controllers and minimum temperature                  move energy.
controllers. Newer controllers are set up to         Peak Irradiance: Standard peak sunlight
incorporate both functions.                          condition (1000 W/m )
Evacuated Tube Collector: This collector             Peak Sun Hours: 9am – 3pm
typically includes a heat exchanger at it’s higher
end and a transfer fluid, which rises in thetubes    Pressure Temperature Relief Valve (PTRV):
and heats the water in theheat exchanger.            Installed at the hot water outlet of batch heater
Highest efficiency collectors but also come at       systems in case temperatures or pressures
higher cost.                                         become excessive.

Flat Plate Collector: Consists of a flat sheet       Solar Collector: An element that absorbs solar
absorber or envelope of specially blackened          energy and transmits it to a medium that can be
material which absorbs the sunlight and transfers    used to convey the energy to where it is used.
the heat produced into the water, or transfer        There are two main types—flat plate collector
fluid, flowing through the collector.                panels and evacuated tubes.

Frost Protection: Solar collectors in colder         SRCC: Solar Rating & Certification Corporation—
climates need freeze protection to avoid damage      Housed at FSEC, providing independent
in cold weather. Protection is achieved in a         certification of solar water heating collectors &
number of ways:                                      systems.
x Closed Loop Systems—heat transfer fluid in         SHW: Acronym used for Solar Hot Water system.
  the panels, such as glycol, has anti-freeze
                                                     Standard Test Conditions (STC): the standard
                                                     reference environment for PV cell operation is an
x Open Loop Systems—Temperature sensors                                       2
                                                     environment of 1000 W/m irradiance, 1.5 air
  turn the pump on to run water from the bottom                                      o
                                                     mass, and cell temperature of 20 C.
  of the storage tank through the panel before it
  freezes. Frost valves can also be installed to     Storage: A means of smoothing out fluctuations
  let water flow through the panel when the          in solar supply (e.g. insulated water tank.
  temperature is close to freezing.
                                                     Tilt Angle: The tilt angle is the angle from                 THERMOMAX EVACUATED TUBE
x Frost Tubes--Frost tubes may also enable the       horizontal of the inclination of the PV array (0° =
  water in the panels to freeze without damaging                                                                  COLLECTOR
                                                     horizontal, 90° = vertical).
                                                     Time Trigger Controllers: Used to keep the
FSEC: Florida Solar Energy Center, the leading       booster heating turned off during the day, to
US solar equipment testing and technical             ensure you’re not paying for electricity or gas to
installation training center.                        heat your water when the sun could be doing the
Insolation: Radiant solar energy reaching an         job for free. The timer can be set to turn on the
area (kWh/m /day)                                    supplementary heating before periods of high
                                                     water use. Both features increase the system’s
Irradiance: Radiant power per unit area from the     efficiency.
sun (Watts/m )
                                                     Transport Medium: A fluid or gas that transfers
kW: kilowatt. Unit of turbine capacity.              the heat from the solar collector to the end use
kWh: kilowatt-hour. Unit of energy.                  site (e.g. hot water heater).
 System Overviews & Rules of Thumb for System Design
SOLAR ELECTRIC SYSTEM OVERVIEW                                                  RULES OF THUMB
Solar Thermal Collector Output—Depends on four main criteria:
x Size, type, and construction materials of the collector;                      Energy Replacement—Standard systems can replace 75% of a
x Solar energy available at the site;                                           households water heating demand in summer and 25-45% in the
x Difference between the collector inlet temperature (Ti) and the ambient air   winter. Similar rations exist for properly sized commercial systems.
  temperature (Ta);                                                             Systems sized to supply 100% of the annual load will produce over-
x The application of the collector.                                             heated water in summer which is unnecessary & potentially
SYSTEM LAYOUTS                                                                  Efficiency First—Before installing a SWH system, insulate pipes
                                                                                and tanks, install efficient faucets & showerheads, lower water
                                                                                heater thermostat.
                                                                                Roof Structural Loading—Roof loading is typically not an issue.
                                                                                Panels weight about 100# each. Passive systems with roof storage
                                                                                tanks may require additional structural bracing. Architectural signoff
                                                                                required for these systems.
                                                                                Materials Selection:
                                                                                x Don’t use dissimilar materials
                                                                                x Use only sunlight resistant materials
                                                                                x Structural materials:
                                                                                  o Corrosion resistant aluminum 6061 or 6063
                                                                                  o Hot dip galvanized steel per ASTM A123
                                                                                  o Stainless steel
                                                                                Waterproofing—Require builder/roofer signoff on mounting for roof
                                                                                mounted systems to prevent leaking at connection points.
                                                                                Solar Collector Output Decreases As:
                                                                                x (Ti - Ta) the collector temperature delta grows
                                                                                x The available solar energy decreases
                                                                                Sizing Estimates:
                                                                                Rough estimates for 100% of summer demand and 40% of year
                                                                                round demand.
                                                                                x In the Sunbelt—1 square foot of collector per 2 gallons of tank
                                                                                  capacity (daily hot water demand)
                                                                                x In the SE & Mountain States—1 square foot of collector per 1.5
                                                                                  gallons of tank capacity.
                                                                                x In the Midwest & Atlantic States—1 square foot of collector per 1
                                                                                  gallon of tank capacity.
                                                                                x In New England & the NW—1 square foot of collector per 0.75
                                                                                  gallon of tank capacity.
                                                                                Freeze Protection—Systems which use liquites as heat-transfer
                                                                                fluids need protection from freezing in climates where temperatures
                                                                                fall below 42 F.
                                                                                Factors Affecting Well Designed SWH Systems—The major
                                                                                factors affecting the performance of properly sited and installed
                                                                                SWH systems are scaling (in liquid or hydronic-based systems) and
                                                                                corrosion (in hydronic and air systems).
                                                                                x Avoid scaling by using water softeners or by circulating a mild
                                                                                  acidic solution (e.g. vinegar) through the system every 3-5 years,
                                                                                  and cleaning in-tank heat exchanges w/ sandpaper.
                                                                                x Avoid corrosion by avoiding dissimilar metals and by using the
                                                                                  proper materials for components to prevent rust in an open loop
                                                                                  system due to oxygen.

                                                                                SYSTEM LAYOUTS (CONT.)
 Calculations/Engineering Review

LOAD & COLLECTOR SIZING CALCULATIONS                                                  ENGINEERING REVIEW
1. Calculate daily water heating load—Measuring water temperature and                 REVIEW STEPS
   timing the length of use will allow you to calculate energy consumed. For          x Check commercial availability of key system components (vendor
                                          o                    o
   example, a 10-minute shower at 110 F (heated from a 50 F supply) with a              specification sheets must be supplied)
   flow rate of 1.5 gpm in Des Moines, Iowa, would result in an energy                x Verify total system generation capacity (gallons/day)
   consumption of:                                                                    x Confirm solar radiation value based upon location, tilt & orientation
   Volume (gallons) X Temperature Rise(oF) X 8.33 Btu/gal (specific heat) = Btu         (kWh/m /day). Use NREL data.
   1.5 gpm X 10 min X 60 F X 8.33     = 7,497 Btu for the 10 minutes                  x Check shading correction factor
                                      = 44, 982 Btu/hr                                x Verify the system design contains all key components and that
                                      = 13.2 Watts                                      they are adequately sized for the hot water demand (Solar
                                                                                        collectors/panels, storage tanks, components like pumps and
2. Determine sites average daily insulation and equivalent SRCC “Sky
                                                        2           2                   controllers to circulate the heated water through the system and
   Type—Use NREL data (PVWatts) and convert the kWh/m /day to Btu/ft /day
                                                                                        control the backup system, safety signage)
               2                   2                      2
   4.83 kWh/m /day X 317.1 Btu/ft /day = 1,531.6 Btu/ft /day                          x Verify energy demand & hot water production calculations.
   This available solar resource most closely matches the SRCC’s “Mildly              x Review system installation and mounting methods.
   Cloudy” (1,500 Btu/ft /day) sky-type category                                      x Confirm adequacy of O&M and decommissioning procedures.
3. Categorize your climate—For all but the coldest locations in the US, using         x Confirm system installed cost ($/m ) is within a reasonable range.
   the “C” category will give you a reasonable estimate                               x Calculate simple payback using stated utility rate, system costs
                                                                                        minus any stated incentives/tax rebates, and calculated energy
                                                                                      CONVERSION VALUES
                                                                                      1 Watt                     =    3.412 Btu/hr
                                                                                      Specific Heat of Water     =    8.33 Btu/gallon
                                                                                               2                                  2
                                                                                      1 kWh/m /day               =    317.1 Btu/ft /day

                                                                                      PV WATTS
                                                                                      Performance calculator to determine site W/m .

4. Obtain collector performance output data from the SRCC Web Site—Use                MAGNETIC DECLINATION
   SRCC ratings for location & equipment manufacturer. (See reference section
   for web link.)
                                                                                      SRCC COLLECTOR PERFORMANCE RATINGS
5. Size system (no. of collectors) according to demand—50-70% of load                 Solar radiation data for panel & evacuated tube collectors and
   covered by SWH                                                                     systems compiled by SRCC, organized by manufacturer and by
DESIGN CONSIDERATIONS                                                                 state.
Backup Heating: Systems require a backup water heating method (e.g. standard
water heater or instantaneous water heating) to “boost” the water temperature         SUNRISE & SUNSET TIMES
when there isn’t enough solar energy to heat the water.                               You can obtain the times of sunrise, sunset at:
System Sizing—Systems are usually sized to provide enough hot water to      
supply the average daily demand. In the USA 30 gallon/person/day is
reasonable for design. Typical household (family of four) use is 120 gal/day.         Costs/Financials
Systems will produce twice as much in summer as winter.
                                                                                      COSTBREAKDOWN                            LIFE CYCLE
Storage Tanks                                                                         Installation   =   30% of cost           20-30 years
x Sizing dependant upon no. of collectors and climate at the site.                    Panels         =   50% of cost
x Generally, larger storage = lower collector operating temp = higher                 BOS            =   15% of cost
  performance                                                                         Engineering    =   5% of cost
x Storage tank for solar should be separate from the backup system storage.           O&M            =   5-10% of system cost every 3-5 years. Electrical
x Backup system storage should accommodate 100% if load.                                                 component replacement each 10 years.
Closed Loop vs. Open Loop—Closed loop systems are preferable in areas                 SYSTEM COST RANGE
prone to frost and freezing.                                                                                               2
                                                                                      Flat Plate collector systems--$6-8/ ft
Orientation Factor: Combined affects of SWH panel’s tilt & orientation from true      Evacuated tube systems--$8-12/ ft
south. SHW systems oriented within 45 east or west of true south will not see
significant decreases in performance. A tilt equal to the local Latitude is ideal     SIMPLE PAYBACK
                                                                                                 (Total Installed System cost + Lifetime O&M)
Shading: Use of a suncharting tool is critical to estimating shading impacts to            (Annual SWH System kWh savings) X (Utility Rate $/kWh)
system performance. Both manual and software versions are available for use.
See Reference section for suncharting tool links.
Collector Rating—Manufacturer ratings are in Btu/ft /day energy saved. Will
need converted to W/m .                                                               CRITICAL FACTORS
Solar Resource—Usable solar radiation = average value from solar insulation           Verification of shading, energy demand & supply calculations.
table X 96%. Approximately 4% of annual solar energy is not captured due to low       ENVIRONMENTAL ISSUES
irradiance conditions.                                                                No adverse environmental issues.
Maximizing Efficiency—Heat losses typically occur through the plumbing and            MARKET STATUS
the storage tank walls. Properly insulation can reduce these losses to less than
                                                                                      Commercially available solar thermal panel or tube assembly
5% per day. Use ¾” thick closed cell foam pipe insulation and wrap tanks with
                                                                                      systems. Refer to the Florida Solar Energy Center’s website for a
insulating blankets. Select solar storage tanks with insulation levels greater than   list of certified panels
R-15, or with more than 2’ of foam insulation.
                                                                                                                                          Solar Electric

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