Solar Hot Water Heating Systems

Home , Concentrated solar power, Electric heating, Solar water heating, Water heating

Courtesy of DOE/NREL

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

Pete Shoemaker PG&E Pacific Energy Center (415) 973973--88508850 [email protected]

with assistance from G. Paul Menyharth of the American Solar Institute and Josh Plaisted of Kineo Design and PVT Solar Agenda

• Industry overview • Essential physics • Terms and concepts • Collector and System types • Site evaluation and design The Full Energy Picture

PG&E Portfolio Solution

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

Light energy Photovoltaic (PV) Electricity produced directly from light

Heat energy Concen tra te d S ol ar P ower (CSP) Electricity produced by steam

Solar Pool Heating Hot water for pools

Solar Water Heating (SWH - Solar Thermal) Hot water for domestic use (DHW) All courtesy of DOE/NREL Solar Pool Heating Swimming pool water heating 80 - 85 degrees from May to October

Courtesy of DOE/NREL

Mat ure i nd us try with mai n mar ke ts i n Ca liforn ia an d Flor ida. Overview

Courtesy CCSE Overview

Courtesy CCSE SHW Industry Overview: World

1890 to 1930’s: Beginnings in California

1930 to 1973: Growth in Florida

1973 to 1986: Oil Embargo and Carter Tax Credits

1986 to 2003: Removal of Tax Credits and Decline

2003 – present: Revival of Incentives and Climate Action Industry Overview: U.S. Favorable regulatory environment

Federal Tax Credit: • Extended through 2016 • 30%f30% for bthboth commerc ilial and resid idtilential • MACRS depreciation for commercial

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

State rebate program: AB1470

• Applications accepted 5/1/10 (residential) and TBD (commercial). • Systems installed after 7/15/09 eligible. • Allocation is 40% residential, 60% commercial and multi-family. Essential Physics

Courtesy ofNASA It all starts with the sun. Electromagnetic Spectrum

10 -3 10 -7 heat light

Courtesy of Wikipedia Continuum of energy. Greenhouse Effect

Ozone layer

light Short waves get through

Long wa ves are trapped heat Earth Greenhouse Effect

Glass

light Short waves get through

Heat absorber Long wa ves are trapped heat SWH collector Color Absorption

Dark colors absorb a lot, reflect little

Light col ors ab sorb littl e, refl ect a l ot 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 •Liggppht enters but heat trapped • Color absorption • Dark colors absorb and light colors reflect • Metal conductivity • Copper conducts more than others • WtWater b bhehavi or • 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)

Thermosi ph on: NtNatura l process o fhtf hot wa ter r iiising (in a tb)tube). Stratification: Separation of hot and cold water (in a tank). HtHeat exc hanger: DiDevice thttthat trans fers h htfeat from one medi um to another. Climate zones: Areas of distinct seasonal temperatures. Hard freeze: A freeze in which seasonal vegetation is destroyyged, ground is frozen solid, and heav y ice is formed. Stagnation: Condition when collectors are not used and become overheated. 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: Design

Cover 100% in summer. Will result in 30 – 50% in winter.

Average year-round coverage of 60 – 70% in PG&E territory. Will ALWAYS need a backup heating source (gas or electric). Change in perspective

Solar Electric: Solar Thermal:

Selling / maintaining Selling / maintaining “solar” “total hot water system” (solar + backup)

Courtesy of DOE/NREL Change in perspective

One overall system

solar + backup

One overall cost One overall maintenance One overall effi ci ency One overall lif espan Collector and System Types

Courtesy ofNASA Standard Water Heaters

Typical gas heater:

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

Courtesy PG&E Standard Water Heaters

Improved model:

Same basic technology, better insulation. Efficiency around 70 – 80%.

Source: Energy Star 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

New model:

Heat pump. Like refrigerator in reverse. Electric powered, no gas burning. Best to replace electric water heater.

Source: Energy Star Standard Water Heaters

Tankless

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

Source: Energy Star System Overview

Five main aspects of solar systems: 1. Heat collection 2. Heat transfer 3. Heat storage 4. Heat backup 5. Extreme temperature protection (freezi ng /st agnati on) System Overview

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 Solar electric glycol panel Storage heater tank System Overview

Two types of heat transfer systems:

1O1. Open Loop 2. Closed Loop (Direct) (Indirect)

water glycol

Uses just the water Uses heat-transfer fluid from the main. in “closed” system. “Open” t o out sid e Needs heat exchanger. elements. Collector and System Types

Two types of heat transfer systems:

1O1. Open Loop 2. Closed Loop (Direct) (Indirect)

one fluid Heat HX Potable loop water water glycol

Uses just the water Uses heat-transfer fluid from the main. in “closed” system. “Open” t o out sid e Needs heat exchanger. elements. System Overview

Further categorized by “pumping” source:

1P1. Pass ive 2. Active (electric (natural) pump)

Thermosiphon Must have electric process. source. TkTank must tbhih be higher Tank can be anywhere. than collector. Collector Types

ICS (Batch) Flat Plate Evacuated Tube

Figure courtesy NREL ICS: Integral Collector Storage

Heat Heat CllCollect ion Storage

Solar panel Storage tank ICS: Integral Collector Storage

Courtesy energybychoice.com ICS: Integral Collector Storage

Hot water Roof out tilt

Cold water in Holds 20 to 40 gallons of water ICS: Integral Collector Storage

Courtesy NREL Flat Plate Collector

Headers Risers

Figure courtesy SunEarth Flat Plate Collector

“Fin” for heat absorption

Souce: PG&E Flat Plate Collector

Header HtHot wa ter out

RfRoof tilt Risers

Header

CldCold water in Holds about one gallon of fluid Evacuated Tubes

Photo courtesy Industrial Solar Technology Photo courtesy William Lord

Figure courtesy Edwards Hot Water

Courtesy of DOE/NREL Evacuated Tubes

Copper rod: may be solid or hollow.

Heat m ov es up to bulb.

Double glass wall with vacuum between.

Souce: PG&E Evacuated Tubes

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

5 6. Collector return (hot) 7. Collector supply (cold) 8. Heat exchanger 9. Shock absorber Evacuated Tubes

HdHeader

Cold water in Hot water out

Roof tilt

Holds little or no fluid Evacuated Tubes

HdHeader

Cold water in Hot water out

Roof tilt

Holds little or no fluid Plumbing Different Collectors

Flat Plate Evacuated tube

Photo courtesy Industrial Solar Technology

Return Supply Return

SlSupply ICS: Integral Collector Storage 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 Courtesy of EERE Simple system with ICS Heated water moves to top

Hot water is drawn into tank

120 degree water goes into house

Additional heating element boosts temperature as necessary Water comes in from main System Characteristics

FtilICStFor 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

Photo courtesy NREL Thermosiphon Passive Systems

Courtesy CCSE Thermosiphon Passive Systems

TkTank—potbltable wat er

Heat-exchange loop—”closed” to outside elements

Separation between water in tank and heat-exchange fluid

Figure courtesy SunEarth Inc Thermosiphon Passive Systems Additional heating element boosts tttemperature as necessary

120 degggree water goes WtWater comes i n 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

FtiltkFor typical tank-on-rooftf 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

P Active Systems Can be Open- or Closed-loop Benefits • Highest thermal performance • Freeze protection to –60 F • Lightweight low roof profile Disadvantages • Some active components Figure courtesy SunEarth Inc • More expense and maintenance

Courtesy of DOE/NREL Active Systems

Courtesy University of Central Florida Active Systems

Courtesy University of Central Florida System Characteristics

FtilfltltFor typical flat plate or evacuat tdtbed tube syst ems:

Active • Uses pumps and other active elements

Open Loop • Potable water itself is heated or Closed Loop • Glycol is heated and heat-exchanger is used

Figure courtesy NREL Freeze Protection

Six different methods (can be combined): 1. Thermal mass (ICS) 2. Antifreeze (closed loop glycol) 3. Auxiliary heater (electric element) 4. Drip valves (moving water won’t freeze) 5. Forced circulation of hot water (DFC) 6. Draining (removing water from collector)

Figure courtesy NREL Thermal Mass

20 to 40 gallons of water will only freeze under extreme conditions.

ICS systems are freeze-protected in mild (coastal) climate zones. Antifreeze

• Closed-loop (indirect) systems • Uses food-grade glycol, specific mixture depending on climate zone. • Must be serviced every 5 – 15 years. • The hotter the glycol is run, the more it breaks down and the sooner it needs to be replaced. • Freeze protection up to 40 degrees below zero. Auxiliary Heater

• Electric resistance (strip) heater on pipes, collectors. • Like a heating pad. • Triggered at specific temperature. • Vulnerable to power outages. Drip Valves

Membrane in valve retracts at around 40 degrees, permitting water to drip out onto the roof.

Courtesy University of Central Florida

Drip valves are good backup protection against mild freezes, but are vulnerable to failure, particularly in hard-water areas. Direct Forced Circulation (DFC)

Freeze drain valve Always combined with drip valve(s).

Courtesy University of Central Florida Direct Forced Circulation (DFC)

In freeze conditions, Freeze drain valve reverse flow gives up heat to protect the system.

Hot water

Courtesy University of Central Florida Drain-back System (closed loop)

Collectors are always empty when s ystem (pump) is not running.

Courtesy University of Central Florida Drain-back System (closed loop)

Start up: Collectors are filled and heating cycle begins.

Courtesy University of Central Florida Drain-back System (closed loop)

Shut down: Collectors automatically drain and heating cycle ends.

Courtesy University of Central Florida Drainback System

• Closed loop • Can use water or ggylycol in heat-collection loop • Fluid is drained from collectors whenever system is not running • Needs large pump to push water into collectors • Pipes must be sloped properly for drainage

Figure courtesy NREL Site Evaluation and System Design

Courtesy ofNASA Site Evaluation and Design

Criteria: • Solar resource • AilblAvailable space and ori ittientation • Climate zone (temperature range, freezes) • Hot water usage amount and patterns • Economics

Courtesy of DOE/NREL Solar Resource

Peak SunSun--hourshours Measured in kWh/m2/day

Source: DOE National Renewable Energy Laboratory (NREL) Resource Assessment Program http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/serve.cgi Shading

• SWH panels not as sensitive to shading as solar electric (PV) panels • Shade measurements and tools similar to that of PV • Major difference: the SWH rebate program onlidhdif103ly considers shading from 10 to 3. Sunset Sunrise Solar Window “Shade-free from 10 to 3” Tilt and Orientation

Tilt = angl e f rom th e h ori zon. Orientation = Azimuth = direction north-south in which the panels are facing.

tilt Ex. 30º angleº axis From Horizon Tilt Azimuth Surface Orientation Factor (SOF)

San Francisco, CA 90

SOF 0.40-0.50 60 0500600.50-0.60 0.60-0.70 Tilt 0.70-0.80 0800900.80-0.90 30 0.90-1.00

0 -90 -60 -30 0 30 60 90 East Azimuth West Chart courtesy NREL Rough Home Estimate

• Do you have 60 to 80 square feet o f roo f (or ground) space that is unshaded from 10 to 3? • Is it on a non-North facing slope (flat is OK)?

If you pass this first screening then the next step is to solicit bids from contractors. They can determine the appropriate system and give a financial assessment. Solar Pathfinder

Used to gain a quick and approximate understanding of solar access and objects on the horizon that shade a given location.

• Latitude specific sun path diagram is placed in the pathfinder. • The transparent , convex plastic dome reflects objects on the horizon, enabling the user to see the relationship between these o bjec ts an d the pa th o f the sun. • Obstructions can be traced onto sunppgath diagram. Solmetric SunEyeTM

• Handheld measurement didevice th thtat accurately measures solar access and shadingg( (about $1400)

Courtesy: Solmetric, Corp. Mounting Mounting Usage

How much energy are you using to heat water?

Usually it’s not easy to determine, since water heating bills can include sppgace heating and cookin g as well.

Three ways: 1. Direct measurement 2. Bill ana lys is 3. Estimation from industry standards Industry Standards / Surveys

Average hot water usage per home per day: •20 gall on s f or th e fir st per son • 15 gallons for the second • 10 each for all others

4 person household = 20 + 15 + 10 + 10 = 60 gallons per day

These assumptions are used in the CSI Thermal online ca lcu la tor. Industry Standards / Surveys

Averages for typical 4-person home in PG&E territory:

Natural Gas Water Heating Yearly usage: 200 therms Yearly cost: about $300 (current prices) Typical solar fraction: 65 - 70% Typical solar savings: about $200 per year.

Electric Water Heating Yearly usage: 3,500 kWh Yearlyy$(p) cost: about $700 (current prices) Typical solar fraction: 65 - 70% Typical solar savings: about $500 per year.

Electric heating is 2 to 3 times as expensive as gas. State Rebate Program: AB 1470 Modeled after the very successful solar electric program (CSI) to lower costs and raise product and contractor quality. Uses online entry/calculation program:

• Only allows approved systems. • Makes sure system is sized appropriately. • Ensures proper freeze protection for climate zone. • Gives conservative estimate of production. • Determines rebate. State Rebate Program: AB 1470 In addition … All contractors or self-installers who want to participate in the rebate program must attend a one-day workshop given by the Program Administrators. After attendinggy they will receive a uni que ID number to use in the online entry program. The URL for the CSI Thermal site is: www.csithermal.com

For a list of registered contractors go to http://www.gosolarcalifornia.ca.gov/solarwater/contractors.php Rebate Program: AB 1470 Systems must be SRCC certified: www. solar-rating.org

OG-300 System ratings

OG-100 Panel ratings Sample Costing

Savings: • Average yearly usage 210 therms • Solar saves 70% of that, or 147 therms • Average cost per therm $1.37 • Yearly savings about $200 (first year)

Cost: • Total installed price $7000 • State rebate $1875 (147 * $12.82 up to max) • Tax credit ((7000-1875) * .3) = $1537 • Net cost = (7000 – 1875 – 1537) = $3588 Sample Costing Glycol: • Will need to be recharged every 5 – 10 years • Best to be professionally done • Estimate of $250 per visit • Total about $750 Pump(s): • At least one replacement • Es timat e of $500 - $1000, use $750 Tank + heat exchanger • At least one replacement • Estimate $1000 Estimated total = $750 + $750 + $1000 = $2500 Sample Costing Natural Gas: • Typical heater costs $500 • Labor costs can be another $300 - $500 • Lifespan is 7 – 10 years • Electric heaters may be somewhat less

Conservative total approx. $2500 Similar to solar maintenance

What’s a reasonable assessment? Sample Costing

Solar needs to maintain both systems (solar + backup), but backup works 70% less. Can we assume 70% less maintenance costs for backup? If so, backup costs with solar would be about $2500 * .3 = $750. Maintenance with solar (25 yrs.)

MiMaintenance costs wi ihth sol ar: $2500 (solar) + $750 (backup) = $3250

Maintenance costs without solar: $2500 Difference: $3250 - $2500 = $750 Conclusion: solar maintenance costs are about $750 extra than before, and this should be added in to the overall cost of a solar system. Works out to about $30/year, or about 0.5% of the purchase price per year. Sample Costing

Payback: • First cost: $3, 600 • Maintenance adder: $750 • Tot al lif ecycl e cost : $4350 • Savings first year: $200 • Straight payback (no inflation factor) = 4350 / 209 = 21 years • With inflation factor of 5.5%, payback shortens to about 15 years. Economics It’s recommended that you get at least three bids from reputable contractors. The bids should all contain the following, clearly specified:

• Full price, including tax, permit, and any additional charges. • Estimated maintenance costs and maintenance schedule. • Estimated production, based on the CSI Thermal calculator output. • Estimated first year and system lifetime savings, based on reasonable assumptions of utility costs and inflation. • Warranties for all products and labor, clearly written. Solar Water Heating Benefits

• Saves money • Lowers greenhouse gas emissions (local and national goals) • Qualifies for state and federal incentives • Promotes energy independence • Keeps money in local economy Thank you for participating! PG&E P acifi c E nergy C ent er

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