U N I V E R S I T Y O F A L A S K A FA I R B A N K S

Alaska Center for Energy and Power

Solar Thermal Energyfor Alaska

Harnessing the energy

potential of Alaska’s

natural resources.

Oil

Gas

Geothermal

Wind

Water

Biofuels

Solar thermal technology (or active solar water heating) transforms radiation from the sun into usable heat, while solar photovoltaic technology uses traditional solar panels to create electricity.

Fairbanks

Kotzebue

Flat-panel collectors in Fairbanks draw in power. Notice the PV power panel for the pump on the solar system. You can hear it running quietly from indoors. Cooperative Extension Service photo

The University of Alaska Fairbanks is accredited by the Northwest Commission on Colleges and Universities. UAF is an affirmative action/equal opportunity employer and educational institution.

U N I V E R S I T Y O F

A L A S K AF A I R B A N K S

Modern solar thermal technology has been in use for well over 100 years in hot, arid climates around the world, including the American Southwest, Australia and Israel. Innovations in solar thermal systems have allowed the technology to expand across nearly every latitude below the Arctic Circle. In addition, recent tax credits have also added to the economic appeal of solar water heating in the United States. Despite low levels of light during some parts of the year, rising heating oil prices, tax incentives and new innovations in technology have now made solar thermal energy a viable technology for use in arctic communities.

One of the challenges with using photovoltaic solar collectors in northern climates, especially high latitudes, is that the peak energy use comes during the cold, dark winters, when solar energy is relatively unavailable. However, the summer months in arctic Alaska bring 24 hours of sunlight, warm temperatures and mild weather. This is an optimal environment for solar thermal technologies. Heat derived from these systems can be used to meet domestic hot water demands, which remain fairly constant throughout the year, or supplement low-grade heating requirements sometimes necessary during arctic summers.

Will solar thermal work for me?

Solar thermal technology can be viable if it can be designed and installed appropriately. New computer simulation programs allow designers to inexpensively evaluate various design options quickly. To determine if a solar thermal system is right for you, a number of factors need to be considered.

Does it make financial sense? If economics are an important factor in your decision to use solar thermal or any alternative energy, your financial investment should be considered. Because of cold weather and limited sunlight during parts of the year, a solar thermal system will not completely

displace the need for heating oil, but it can provide nearly 100% of the hot water needs of a house during optimal conditions.

Payback period

One way to analyze the economics of a system is to determine your payback period, which is the number of years it takes for your cost savings to pay for the expenses of running your system. To estimate your payback, identify your current heating costs, then define the amount of that bill you can realistically expect to offset with your system. This can be estimated best with a professional assessment of your annual available light, location of your collectors and the efficiency of your chosen system. The resulting number is your annual fuel savings. Subtract the annual additional costs to operate and maintain your solar thermal system for your annual system savings. Next, identify the initial cost to design, purchase and install your system. Divide this number by your annual system savings for your payback period.

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Assessing the Evacuated Tube Collector for Domestic Hot Water (DHW) HeatingSince the last revision of this manual, evacuated tube type collector arrays have come on the market and are now in use in Alaska. Figure 3-7 is an example of a system installed off the deck of a house in the Nome area of Alaska.

To assess their performance in Alaska, several test runs using the evacuated

tube module from F-chart are given in

used for the performance is that obtained from the Beijing Sunda company’s model Seido 2-16, and is taken from company literature. This is the same company that made the collectors shown in Figure 3-7 (below).

To assess the performance of evacu-

ft2 of effective tube area and the Sunda

Anchorage, Mer-rill Field data, as shown in Table AC-41. The col-lector and sys-tem details used for that Anchor-age run, and all the subsequent evacuated tube runs, are shown in Tables AC-41a and AC-41b. A tabular perfor-mance report similar to the previous f lat plate collector reports is then given for the lo-cations of Fair-banks, Homer, Kodiak, Palmer,

and Talkeetna. This is done to give a fairly good perspective on how these collectors will perform in the major population areas of Alaska. Since perfor-

performance for these locations, similar extrapolations are reasonable for rural Alaska locations. The Comparative Notes at the bottom of each of the tables are used to give more precise and important detailed assessment and interpretations of the results of these runs.

Figure 3-7. The Sunda evacuated tube collector system at Matt Erickson’s home in Nome shown on a grand solar day in

of bright snow, no doubt enhancing the performance of this array.

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Figure 3-8. Collector tilt angle in relation to the ground surface and the solar elevation angle. Collector tilt is optimum when the sum of the collector tilt angle and the solar elevation angle (at noon) equals 90°, indicating the maximum solar intensity possible at noon on the collector surface. This optimum tilt changes daily, so an annual optimum tilt must be selected if collectors are not movable.

Figure 3-9. An illustration of what is meant by the azimuth of a collector. Any nonsouth orientation will reduce the total daily solar radiation gain in proportion to the azimuth angle. The largest theoretical sum of total daily radiation will fall on a surface that faces due south.

For more information about solar thermal systems in Alaska, please refer to the A Solar Design Manual for Alaska by UAF Cooperative

Extension Service Community Sustainability Coordinator Richard Seifert. To order, call Extension at 1-877-520-5211.

Collector tilt is optimum when the sum of the collector tilt angle and the solar elevation angle (at noon) equals 90°, indicating the maximum solar inten-sity possible at noon on the collector surface. This optimum tilt changes daily, so an annual optimum tilt must be selected if collectors are not movable.

The Sunda evacuated tube collector system at Matt Erickson’s home in Nome shown on a grand solar day in April 2008. Cooperative Extension Service photo

Collector Tilt Angle

Solar Elevation Angle

Collector Tilt

Angle

Initial system cost

Annual fuel savings = Current heating costs minus estimated cost of fuel offset with solar thermal system

Annual system savings= Payback

Factors that impact your payback

Tax incentives — Current tax breaks offset the capital costs of installing solar thermal systems. Preliminary studies using 2011 tax credits indicate these savings should always reduce the payback to less than 10 years.

Plumbing — In addition to the cost of the collectors, there is the cost of installing either a solar water heater or a new double-coil hot water tank. Specialized plumbing and controllers are also necessary and will affect the cost of installation depending on how easy it is to integrate them into your existing plumbing system.

Durability — These systems have proven durable even in rural Alaska. Once they are installed, little or no maintenance is required under typical circumstances. However, care must be taken to ensure that potential damage is mitigated.

Your heating “load” — Since solar thermal energy will only be available during a portion of the year due to the lack of sunlight or bad weather, it is wise to estimate your heating requirements for those months to determine if the technology will meet enough of your heating needs to justify the costs.

F o r m o r e i n f o r m a t i o n : w w w . u a f . e d u / a c e p A l a s k a C e n t e r f o r E n e r g y a n d P o w e r : F o s t e r i n g d e v e l o p m e n t o f i n n o v a t i v e s o l u t i o n s t o A l a s k a ’ s e n e r g y c h a l l e n g e s t h r o u g h a p p l i e d e n e r g y r e s e a r c h a t t h e U n i v e r s i t y o f A l a s k a

An Alaska Case Study: Kotzebue

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Figure 3-6. Schematic of a typical active solar domestic water heating system.

Current estimates for Alaska indicate that solar energy can provide 40 to 60% of the hot water load on an annual basis. A number of successful solar thermal systems have been installed in Anchorage and the Kenai Peninsula. Systems farther north in Denali, Fairbanks, Nome and Kotzebue have been recently installed with encouraging results.

How is solar thermal energy collected?

Currently there are two primary ways to directly gather and store usable energy from the sun: solar thermal panels and solar photovoltaic panels. Photovoltaic solar panels transform radiation into electricity. Solar thermal panels transfer the energy into a fluid, from which it is then extracted for heating purposes.

Solar thermal systems can most easily be used to provide energy for use in meeting hot water needs. Since a significant amount of home energy is used to heat hot water, solar thermal systems are an attractive option for many homeowners. Systems can also be designed to utilize any additional heat generated to supplement space-heating requirements.

Two types of solar collectors may be installed, a flat-panel solar collector (also called “flat plate”) and an evacuated-tube solar collector. Both collectors have

advantages and disadvantages for installation in Alaska that should be considered before purchasing.

Flat panel (plate) — These collectors are easy to install, will melt snow off the face of the panel and can be independently powered by a photovoltaic pump so if there is a power outage, the collector will not overheat the solar fluid. Installers in rural or remote Alaska also report that the flat panel (plate) is easier to transport without breaking, even by snowmachine, and is easier to fix if it breaks or has leaks.

Evacuated tube — While these collectors are more complex and more difficult to install, they have advantages over flat-panel collectors. Transport to remote locations can result in breakage. However, since the evacuated tubes are connected in series, the collector can continue working even if some of the tubes are broken. One of the biggest disadvantages of installing an evacuated-tube collector in Alaska is that snow will not melt off the collector because it does not release heat back into the atmosphere. Therefore, these collectors require constant maintenance and should be installed in a location that is easy to access. An easy solution to this issue is to install evacuated tubes vertically or under an eave to prevent being covered by snow. This is important for all collectors in Alaska situations.

The annual sum of solar energy collected from a flat-plate system and an evacuated-tube system of very similar size is nearly the same. While the flat-plate system is not as good at collecting solar energy in the

colder parts of winter, it does well in summer, so that the difference is not significant. With both systems, it is crucial to install collectors vertically (90 degrees). This also mitigates the snow buildup issue.

There are two primary types of systems and configurations:

• Indirect systems — Instead of domestic hot water directly heated by the solar panel, a fluid flows through the solar panels and the heat is transferred to the domestic hot water through a heat exchanger. These systems can use either flat panels or evacuated tubes. Indirect systems are typically considered the most beneficial to an

Alaska homeowner because the heat-exchanging fluid allows the system to generate usable heat at lower temperatures and, therefore, operate at a higher efficiency.

• Direct systems — Water is heated directly by solar radiation and then transported to where it will be used. This type of system is strongly discouraged in Alaska, where the recommendation is to never circulate liquid water outside of the heated shell of the building. See pages 22-23 of the Cooperative Extension A Solar Design Manual for Alaska for more details.

Schematic of a typical active solar domestic water heating system

Kotzebue’s location above the Arctic Circle would typically be considered a challenging environment for a solar thermal system. However, with $6-a-gallon heating oil, nearly 24 hours of sunlight during the summer months and recent advancements in solar thermal technology, opportunity for solar thermal systems in the Arctic is growing.

In December 2010, Kotzebue Electric Association, working with ABS Alaska and Susitna Energy Systems, installed six solar thermal systems in volunteer houses around Kotzebue. Both evacuated-tube and flat-panel collectors were installed in various configurations to allow for a rigorous assessment of performance. This project, funded through the Denali Commission Emerging Energy Technology Grant program, seeks to investigate the effectiveness of solar thermal technology in arctic conditions. The Alaska Center for Energy and Power is providing technical assistance for data collection and analysis.

It is believed that the systems will prove to be an economical, environmentally friendly way to displace heating oil in the community. All systems began registering BTUs as of March 2011. The systems are still relatively new, but in the first four months, the six volunteer houses are enjoying hot water heated by the sun with minimal maintenance on the collectors.

This project will run through September 2012 and will be followed by a technical and economic analysis.

An engineer checks on a nearly complete solar hot water installation. Cooperative Extension Service photo

A flat-panel collector in Kotzebue tests the feasibility of solar in the Arctic.

Solar Radiation

SolarCollector

HeatExchanger

Storage Tank

Auxiliary Heater

To Load

Water FromMain at 400 F