Solar Water Heating

By Thembi Borras

Why Solar Water Heating?
Whatever your reasons for wanting to reduce your energy consumption, you will want to know what to do first. Conservation yields the largest reduction in exchange for your precious time and money.

Conservation includes:

• Use a clothesline instead of a dryer
• Wear warm clothes and turn the thermostat down
• Turn off lights not needed
• Close and open windows and cover them to employ the sun and wind for heating and cooling
• Take shorter showers
• Wash clothes in cold water

Energy conservation also involves making the most of the energy you use by:

• Replacing incandescent bulbs with compact fluorescents
• Eliminating phantom loads
• Upgrading appliances to energy star or better rated appliances
• Tightening the building envelope (e.g. filling gaps)
• Upgrading windows
• Adding insulation
• Installing a low flow shower head (e.g. 2.5 gpm showerhead)
• Wrapping hot water heaters with insulation
• Insulating hot water pipes running through unconditioned space
• Lowering the thermostat on your hot water heater to 120°F
• Replacing a top loader with a horizontal axis washing machine
  
  

After understanding the highest priority is energy conservation, the next biggest bang for your buck comes from directly heating your water with the sun. Installing a properly sized solar water heating system, can save 60% to 90% of the energy used to heat hot water per year, which makes up about 15% to 20% of a typical household’s energy outlay. Bringing up the rear, in terms of return on your investment is generating electricity from a grid connected photovoltaic (PV) system. Further, it makes sense to do everything you feasibly can to reduce your electricity use before you size your PV system.

Sizing
Alternative Energy Technology provides the following way to estimate the size of a residential system.

• Determine Delta T (DT), which is the difference between the desired water temperature (usually 140° F for residential) and groundwater supply temperature (for the Ellensburg area a rough estimate is 47°F), the difference is 93°F.
• Determine the size of the storage reservoir by estimating 20 gallons of hot water usage per day for the initial resident and 15 gallons per day for each additional occupant. Consider maximum potential occupancy and round figures up for available tank sizes. The result for a family of 5 is 80 gallons. Note: Solar water storage tanks are available in 80 and 120 gallons. Solar water storage tanks are typically larger and better insulated than average hot water tanks, and generally they have four ports instead of two. However, an average home hot water tank can be retrofitted to work as a solar water storage tank.
• Multiply DT by the weight of water in pounds per gallon (8.34#/gallon) by the solar water storage tank size (in gallons) to determine desired Btu output. The calculation is 93*8.34*80=62,050 Btu per day needed
• Estimate that an AET flat plate collector will produce 1,000 Btu per day per square foot, actually slightly less for the Northwest.
• Size accordingly. Two 4’x8’ collectors offer 64 sq. ft. of area, and will therefore produce roughly 64,000 Btu per day.

Tom Lane, author of the book Solar Hot Water Systems Lessons Learned 1977 to Today provides a rule of thumb for sizing. He suggests first estimating the size of the storage reservoir by estimating 20 gallons for the first two people and 15 gallons for each additional person. If the estimated water use exceeds 80 gallons, use a 120 gallon tank. Then base the collector area on the actual tank size chosen. East of the Cascades, 1.5 to 1.75 gallons of water storage to 1 square foot of collector area may be an appropriate ratio. For example, a family of 5 requires 85 gallons, next size up to the next largest available tank size, which is 120 gallons, then divide 120 by 1.5 because there should be 1.5 times more storage capacity than square feet of collector area. The result is 80 square feet of collector area, which can be provided by two 4’ by 10’ flat plate collectors.

Siting and Orienting
Similar siting and orientation considerations apply whether you are installing collectors to heat water or whether you are installing collectors to produce power. The University of Oregon’s Solar Radiation Monitoring Laboratory provides a paper entitled “Evaluating a Site’s Solar Potential”, for evaluating a site for PV collectors, at http://solardat.uoregon.edu/download/Papers/Evaluating_a_Site_Solar_Potential.pdf
However, if you have a south facing surface, with plenty of room, that is not encumbered by shading and is close to your point of use, then you don’t need to do much evaluation. If your site is partially shaded, I suggest using the Energy Trust Shade Effect Evaluation Form for a 45.68 degree latitude sun chart made for Pendleton, OR available at http://www.energytrust.org/TA/solar/charts/pendleton.html. From what I am able to surmise it is the most applicable available sun chart for the Ellensburg area. On this page, you will need to select both azimuth and tilt. For your information, the optimal orientation for year round performance for PV collectors in Pendleton, OR is 35 degree tilt and 177 degree azimuth. Go to:
http://www.energytrust.org/TA/solar/charts/How_to_use.html for instructions on how use the Energy Trust Shade Effect Evaluation Form.

For example, our house only offers one small south facing roof close to our primary hot water heater and it is shaded sometimes by several evergreen blue spruce trees and a deciduous birch tree. Using a Shade Effect Evaluation Form, we determined the current and future shading is less than 10%. If shading is less than 25% then the site is worth further consideration.

Keep in mind; shading does not preclude the effectiveness of a solar water heating system. Obstacles on the horizon lower than 10° will have a negligible effect. According to Tom Lane, in the summer shading before 8am and after 4pm and in the winter shading before 9am and after 3pm will have almost no effect. He suggests that the site should be unshaded for at least four hours between 8:30am and 4pm.

The performance of a solar water heating system is also a function of the tilt of the collectors. According to Tom Lane, a tilt of 10° more than the latitude will maximize collection during the winter months, which is important because cold winter air temperatures drop collector efficiency and the water to be heated (especially from wells) is often colder in the winter. The latitude of Ellensburg is 47°, so the recommended tilt is 57°. The recommended tilt for a PV array (35°east of the Cascades and 30°west of the Cascades), to maximize year-round performance, is different. The reason is timing, you don’t care when, during the year, your PV array produces the most electricity because it is connected to the grid and you draw your power from the grid. On the other hand, a solar water heating system is independent, so you care very much when the days are short and cold that the performance of your collectors are maximized.

Note: The latitude of Ellensburg is 47.00° North and the longitude is 120.55° West. The elevation is between 1520’ and 1755’.

Note: To get local weather data for the City of Ellensburg, go to the Bonneville Environmental Foundation website (http://www.b-e-f.org/), click on Renewable Energy Programs scroll down to Community Renewable Energy Projects and click on Ellensburg Community Solar Project (Ellensburg, WA).

Type of System
According to Tom Lane, “only two types of active systems can survive in climates that experience freezes every year and/or have extremely hard scaling or acidic water: closed-loop drainback systems and closed-loop anti-freeze systems with well thought out heat exchange… systems...” More specifically, his favorite system is a double-pumped drainback system with a heat exchanger in the drainback reservoir. The main components of this system are the flat plate collectors, the drainback tank with internal heat exchanger, solar water storage tank, differential controller, high head AC pump to pump the water from the drainback tank to the collectors and a low head AC pump to circulate the water between the drainback tank and the solar water storage tank. The benefits of this type of system are: they are relatively simple, offer reliable freeze protection, and if a pump should fail it does not damage the collector or component parts because there is no water in the collectors. Further, a drainback system is more efficient than a pressurized glycol antifreeze system because water is a more efficient heat exchange fluid than glycol. And drainback systems last longer than pressurized glycol antifreeze systems because the glycol in a pressurized system can break down at high stagnation temperatures shortening the collector absorber plate life and requiring higher maintenance. The main limiting factor of this type of system is the installation must be right. The pipes must be sloped so that the collectors and pipes to the collectors will adequately drainback into the drainback reservoir. This system can be viewed at http://store.altenergystore.com/mmsolar/others/Drainback_DX_System_Schematic.pdf.

If you want to compare thermal collectors, the performance of different flat plate collectors and evacuated tubes is listed in the February and March 2008 issue of Home Power magazine, “SHW buyer’s guide”. Tom Lane also compares evacuated tubes to flat plate collectors on page 2a of his book.

Note: A concern we had at our house was that because we shower in the evenings, we will not be getting as much benefit from the system because the water heated by the sun in the day will be replaced by cold water that will then need to be heated by electricity. However, this is no longer a concern. We learned that water in the tank is stratified and because the bottom element of the hot water heater is disconnected, it will not heat the cold water in the bottom of the tank. The water at the top of the tank will still be hot because we will likely only use a portion of the hot water to take our showers in the evenings. The only time the upper element would turn on is if we used all the hot water accumulated from the collectors and the cold water from the well moved to the top of the tank.

Note: If you do laundry and run the dishwasher during the day when the collectors are heating water, you will get more benefit from the system.

Payback
The following scenario is provided as an example to show how quickly it will take a system to pay for itself (payback).

An existing electric hot water heater uses 5,846 kWh/year and the current cost of electricity is .075/kWh, when you multiply the two together you get $438/year. It is estimated that you can save 75% of the energy used to heat domestic hot water per family per year by installing a solar water heating system. Therefore $329/year is the savings that can be expected by installing a solar water heating system. The total cost of the solar water heating system is $5,747, after deducting the $2,000 federal personal tax credit. Therefore, it will take 17 years for the system to pay for itself, and given that the system is estimated to last a minimum of 30 years, the sun will be heating 75% of your water for free for 13 years.

Incentives
At this time, the only incentive available to Kittitas County homeowners who install a solar water heating system is a 30% of the cost of the system federal personal tax credit (see http://www.dsireusa.org/library/includes/incentive2.cfm?Incentive_Code=US37F&State=federal&currentpageid=1&ee=1&re=1), and it is set to expire on 12/31/2016. To view state incentives for renewables and efficiency go to the Database of State Incentives for Renewables and Efficiency at http://www.dsireusa.org/library/includes/map2.cfm?CurrentPageID=1&State=WA&RE=1&EE=1

Permits
Kittitas County provided this response when I requested a permit for our project: “At this time, Kittitas County does not regulate, permit, or otherwise oversee the use, installation, or maintenance of solar water heating systems (with the exception of new construction plumbing). Therefore, the system that you propose does not require a permit through our office.”

Credit
The majority of this article was gleaned from the book Solar Hot Water Systems Lessons Learned 1977 to Today by Tom Lane. In addition, portions of this article were gleaned from the article in Mother Earth News entitled “Simple Energy Saving Strategies” by Dan Chiras, from communication with Doug Livingston and Michael Hackleman of the Renewable Energy Hour on KZYX and Z, from the article in Mother Earth News entitled “Go Solar for Free Hot Water” by Bob Ramlow, from communication with an employee at the Alternative Energy Store, from communication with Frank Vignola of the Solar Radiation Monitoring Laboratory and from the Seattle City Light webpage on water heating conservation at http://www.ci.seattle.wa.us/light/conserve/resident/cv5_wh0.htm#efficience#efficience.


Resources
The Alternative Energy StoreTel: 877-878-4060 or 978-562-5858
http://www.AltEnergyStore.com/
http://store.altenergystore.com/mmsolar/others/Drainback_DX_System_Schematic.pdf
http://store.altenergystore.com/mmsolar/others/Strut_Calculator.xls
http://store.altenergystore.com/Solar-Water-Heating/Collectors-Mounts-and-System-Components/AET-Individual-Collectors/4X8-Msc-Series-Crystal-Clear-Collector/p177/
http://store.altenergystore.com/Solar-Water-Heating/Collectors-Mounts-and-System-Components/AET-Individual-Collectors/Aet-Racks-Mounts/Standard-Mount-for-Msc-Series/p180/

Alternative Energy Technologies
Jacksonville, FL 32254
800-874-2190 or 904-781-8306
http://www.aetsolar.com/

Bonneville Environmental Foundation
http://www.b-e-f.org/
local weather data for Ellensburg

Bright Way (E web)
541-484-1125 or 541-344-6311
http://www.eweb.org/home/energy/solar/index.htm
Solar water heating program in Eugene, OR

Brooks Solar, Inc.
Randy Brooks
Chelan, WA 98816
509-682-9646
info@brookssolar.com
http://www.brookssolar.com/
Installer. Distributor of AET solar water heating systems.

Database of State Incentives for Renewables and Efficiency
To view current federal and state incentives for renewables and efficiency, go to the Database of State Incentives for Renewables and Efficiency at http://www.dsireusa.org/

Dynamic Fasteners
Kansas City, MO 64133
800-821-5448
http://www.dynamicfastener.com/
$10.95 per S-5 U clamp. Can be used to attach collectors onto standing seam metal roofs without making penetrations.

Energy Conservation Services of North Florida, Inc.
Tom Lane
Gainesville, FL 32608
352-377-8866
tom@ecs-solar.com
http://www.ecs-solar.com/
Author of Solar Hot Water Systems Lessons Learned 1977 to Today, a very valuable resource for people serious about delving into solar hot water heating systems.

Energy Trust of Oregon
Go to http://www.energytrust.org/TA/solar/charts/pendleton.html for an Energy Trust Shade Effect Evaluation Form for a 45.68 degree latitude sun chart made for Pendleton, OR which is, from what I was able to surmise, the most applicable available sun chart available for the Ellensburg area.
Go to http://www.energytrust.org/TA/solar/charts/How_to_use.html for instructions on how use the Energy Trust Shade Effect Evaluation Form.

Seattle City Light webpage on Water Heating Conservation
http://www.ci.seattle.wa.us/light/conserve/resident/cv5_wh0.htm#efficience#efficience

University of Oregon, Solar Radiation Monitoring Laboratory
Contact: Frank Vignola (fev@uoregon.edu)
Eugene, OR 97403
541-346-4745
To create your own sun chart go to: http://solardat.uoregon.edu/SunChartProgram.html
or to learn about sun charts go to: http://solardat.uoregon.edu/AboutSunCharts.html
For solar radiation data go to: http://solardat.uoregon.edu/