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Feasibility of Solar Hot Water Systems - An Emerging Energy Technology Grant Project

  • KEA Solar Photo 3 New
  • KEA Solar Photo 2
  • KEA Solar Photo 1 New

Project Summary

This project assessed the feasibility of solar hot water heating systems on residential units in Kotzebue. Six solar-thermal heating systems, some using flat plate and some using evacuated tubes, were installed. This project was designed to determine whether technology could prove feasible above the Arctic Circle, and whether these systems could be installed in homes throughout the region and serve as a model for alternative methods to heat homes reducing the need of fossil fuels.

Project Background

Solar thermal technology converts solar energy for heating applications such as water heating, space heating and space cooling. There is a wide array of technology types and applications, but all types primarily produce heat as opposed to electricity, like PV systems.

One main component of a solar-heating system is the solar collector, which converts the sun's radiation into heat and conducts the heat to a heat transfer fluid such as water, air or ethylene glycol. Other components include storage, heat exchangers, pumps and controls. There are several common types of active solar collector systems, which rely on pumps or controls to circulate heat transfer fluid through a collector. The types used for this project are as follows:

  • A flat-plate solar collector is comprised of a flat absorbing surface that is heated by sunlight. A heat transfer fluid such as water or ethylene glycol passes through the collector in a series of tubes, and heat is transferred from the absorbing surface to the heat transfer fluid. While typically inexpensive, these types of collectors can be hindered in cold-weather applications as their performance can be strongly influenced by the ambient temperature.
  •  An evacuated-tube collector. In this system, tubes of transparent, evacuated glass are attached to piping at either end, filled with a heat transfer fluid. Metal conduction material inside the tubes conducts heat to the fluid, while the vacuum reduces heat loss to radiation and convection.

The solar resource in Alaska is significant, but utilization of solar technology has been limited. Historically, major challenges to using solar energy technology in Alaska are its seasonal variability and its dependence on weather conditions. In general, the solar resource is most abundant in the summer, when it is least needed. However, there is a reasonable resource available for seven to eight months of the year for all but the most northern areas of the state. Technological advances, particularly in solar thermal technology, could bridge this gap between availability of the resource and energy needs. There is a large amount of research currently under way focusing on bridging this gap, with aspirations of elevating solar energy to a viable Alaskan renewable resource.

Project Description

The primary objective of this project was to investigate solar thermal technology as a way to mitigate the rising costs of home heating in rural Alaska. Kotzebue Electric Association (KEA) installed solar-thermal heating systems, in six different homes, to assess the feasibility of this technology above the Arctic Circle. KEA elected to install 2 evacuated tube and 4 flat plat systems as follows:

Manufacturer

Installer

Collector Type

System Type

Viessmann

Susitna Energy Systems

1 evacuated tube

Domestic Hot Water (DHW)

Viessmann

Susitna Energy Systems

2 flat plate

DHW

Heliodyne

ABS Alaskan

1 evacuated tube

DHW and Space Heat

Heliodyne

ABS Alaskan

2 flat plate

DHW and Space Heat

 

A major goal of the project was to gather performance data for solar thermal systems operating in arctic climates. Two types of data-monitoring systems were used and installed by KEA, depending on system manufacturer. In addition, KEA attempted to collect historical fuel use records for each home serving as a demonstration location.

For analysis purposes, other cold climate solar thermal installations were investigated, including systems in Nome, Fairbanks, Denali National Park, and Greenland. When available, detailed project and performance information was collected.

Project Findings

Production data from the Nome system demonstrate that in that region the most concentrated solar radiation is received during the spring months; the highest energy production occurs in late March and early April. Large space-heating demands still exist during this spring season. Adequate storage is necessary to maximize the potential of solar thermal systems so that energy from solar radiation during spring afternoons can be stored and distributed throughout the day.

Based on the performance of the solar thermal systems reviewed during this project, it is evident that solar thermal equipment is robust enough to endure harsh arctic weather, with some exceptions. The Kotzebue systems withstood an arctic storm of unusual strength. All systems installed flush with the roof pitches were undamaged; the systems installed at steep angles had severe wind damage. This difference in outcome supports the conclusion shared by many people interviewed during this study, that collector installation should be steeply angled on south-facing walls where possible. This angle of installation not only provides additional protection from wind loading, but also eliminates the need for roof penetrations and allows snow to shed easily.

Data from the Kotzebue solar thermal systems used for space heating are not sufficient to make any generalizations about the effectiveness of solar thermal systems tied to high-temperature hydronic heating systems. Given the temperatures required for these types of heating systems, the benefits would be limited without boiler modifications that enable lower-temperature operation. The greatest solar thermal space-heating potential occurs when radiant heating systems are tied to solar thermal, since these heating systems operate at much lower temperatures.

Next Steps

Research recommendations resulting from this demonstration include the following:

  • During future analysis, it would be worthwhile to study the fuel consumption of a boiler, which might run at a lower power setting because of the addition of energy from the solar thermal system.
  • Testing of collectors at steep angles in northern climates is warranted and would help to further establish procedures for installing collectors on south-facing walls; for example, examine the production difference between a collector oriented vertically versus a collector oriented at 60° or 70°.
  • Results from a side-by-side test of evacuated tubes and flat-plate collectors in northern Alaska would provide valuable information about the performance of the two systems in northern climates and which systems perform better in various conditions.
  • An examination of the effectiveness and maintenance requirements of the steam back method of overheating protection would be valuable. No steam back systems were observed in Alaska during the course of this investigation.
  • An investigation of the marginal benefit of installing larger storage tanks in conjunction with solar thermal systems would be useful to aid in the design of future space-heating systems.
  • Photovoltaic systems are quickly decreasing in price, and there have been suggestions that a PV system tied to a heat pump water heater could yield a quicker payback than a solar thermal system (Holladay, 2012). This suggestion deserves a case study specific to Alaska.

Photos 1, 2, 3: Heliodyne Evacuated Tube System Installation by Jesse Logan, KEA.  Courtesy of Chris Pike, ACEP.