Solar Hot Water Heating Systems

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. 3) Offset any remaining carbon emissions. ClimateSmart Reduce Energy Use Partnership Education Outreach Renewable Power Supply 2) Get the greenest power you can.

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

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 Earth heat Long waves are trapped

Greenhouse Effect Glass light Short waves get through Heat absorber heat Long waves are trapped SWH collector

Metal Conductivity Some metals transfer more heat than others. Fluid Fluid Copper Pipe cross-section 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 Therm: 100,000 BTU (29.3 kwh) Kilowatt-hour: 3,413 BTU 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. Every kwh is used, no waste. No grid--you re on your own. 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 Collection 2. Heat Transfer 3. Heat Storage 4. Heat Backup 5. Extreme Temperature Protection Solar panel Water or glycol Storage tank Gas or electric heater Special valves, pumps, processes, etc.

Collector and System Types Two types of heat transfer systems: 1. Open Loop (Direct) 2. Closed Loop (Indirect) water glycol Uses just the water from the main. Open to outside elements. Uses heat-transfer fluid in closed system. Needs heat exchanger.

Collector and System Types Further categorized by pumping source: 1. Passive (natural) 2. Active (electric pump) Thermosiphon process. Tank must be higher than collector. Must have electric source. Tank can be anywhere.

ICS: Integral Collector Storage 1. Heat Collection 3. Heat 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 Water comes in to tank from main 120 degree water goes into house 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 Figure courtesy SunEarth Inc Benefits Highest thermal performance Freeze protection to 60 F Lightweight low roof profile Disadvantages 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 1. Vacuum tube 6 Figures courtesy Thermomax 7 2. Heat pipe 3. Cold liquid 4. Hot vapor 5. Absorber 4 3 2 1 8 9 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 0.50-0.60 0.60-0.70 0.70-0.80 0.80-0.90 0.90-1.00 60 30 Tilt 0-90 -60-30 0 30 60 90 East West Chart courtesy NREL Azimuth

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 therm displaced Maximum Incentive Single Family Residential Projects Funding Amount 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

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