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The Solar Collectors Heat Storage Supplemental Heat Sources Managing the systems - The Control Unit The Solar Water Heater System Summary and some Frequently Asked questions

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    The Buttons to the left will take you on a tour of the system. Each provides a direct link to the designated stop, or you can continue from here by reading each page and simply click the "Next Stop" button found at the bottom for the complete tour.

    The tour begins HERE with the Summary Report and an Overview of the system.

    The Sub Systems described are:

    • Collectors - Heat recovery system and its operation
    • Storage - System which saves excess heat for use at a later time
    • Aux Heat - Supplemental electric furnace and woodburning fireplace
    • Controls - The computer system which coordinates operation of all systems
    • Water Heater - The Solar domestic water heater system
    • More Information - Frequently Asked Questions about the Solar Heat System

    System Overview - Goals and Conclusions

    Most articles dealing with topics of this nature provide "how to" instructions, give details on a "just completed" project, or maybe the latest technological innovations. What is not usually found is a critical look at a system which has been in operation for a number of years and an evaluation of how it has performed. Did it meet its original goals? Has it been cost-effective? Any unforeseen problems encountered? Is it still viable today? This page will attempt to answer some of these questions and maybe pose some new ones.

    photo of collector array
    Photo of the back of the Solar House. The collector array for space heating is
    located on the roof. The smaller unit on the ground is the solar water heater.

    Background and Design Criteria

    Before we can determine whether the system has performed as expected, we need to look back at conditions in the mid 1970s when the system was conceived. Oil shortages had drastically increased the price of fossil fuels. Electric rates were increasing rapidly. Inflation was in the double digits and was expected to continue this way for some time. Society had also begun to recognize environmental concerns. Commercially available active solar heat systems could cost as much as 20 - 30 thousand dollars installed. Passive systems could be done for somewhat less, but they required continued interaction by the user for optimum performance.

    Needing a house and with these factors in mind, I designed one specifically for solar heating. (fig 1, above) Next, I went to work on the design of a low cost solar heating system which could be home built. In order to keep cost at a minimum, I chose a slightly less efficient single glazed forced air collector array. The lower efficiency was offset by an increase in the surface area of the collectors. A reflective surface below the collectors also increased their heat gathering abilities.

    A second requirement was minimal user intervention which is why the active system was chosen. I did not want to be involved with operating the system once the temperature requirements were set. I like the idea of programmed temperature and time settings. Just let the system take care of itself. Because of my background in electronics, I was able to design and build a microprocessor based special application controller to do this at minimal cost.

    Finally, at the time the house was built, the Alternate Energy Tax Credit was in effect. This helped to offset some of the initial costs involved in setting up the system.

    The Solar Heat System

    block diagram
    Block Diagram of the Heating System

    Fig. 2 provides a basic diagram of the system as it went into operation in 1980. The collectors are located on the roof above the ledge. A blower in the attic circulates air through the collectors where it is heated and into the storage unit in the basement. The heat is transferred into the storage mass and the air returns to the blower.

    Heat is circulated to the house by the furnace blower. This heat may be either taken from storage or provided by the back up electric furnace. The air handler sets the return air path based on heat availability. Air returns directly to the furnace if no solar heat is available or through the storage unit when solar heat is present. A more complete description is provided in the Tour of the System.

    Now that you are somewhat familiar with the system basics and what it was designed to do, the question is,"How has it done?" The answer to this is it has met its goal of providing 50 percent of the heat needed for the house, but...

    Initially payback was estimated to be 5 - 6 years based on the data available in the 1970s. However due to the fact that energy costs stabilized in the 1980s, this payback did not occur until the tenth year. Had costs continued to spiral as they did in the late 1970s, the 5 year estimate would have been on target. From an environmental point of view the system did succeed in cutting the use of non-renewable energy for heating in half.

    The FRP (fiberglass reinforced plastic) panels used as glazing have a life expectancy of 15 - 20 years. As I write this in 2015, they have exceeded this time period and show definite signs of degradation. As they age, they become slightly less efficient at allowing sunlight to enter. Current estimate is a loss of about 15 percent. The present cost to replace them is about 900 dollars U.S. This would be recovered in about 4 years at today's energy costs. Replacement is underway this year which should extend their life expectancy through 2035.

    Since 1980, one panel has experienced damage. It's glazing was partially torn loose due to high winds in 1984. Repairs were made and no other modifications deemed necessary. Similar winds have not caused any damage since.

    A modification was required to the storage assembly. The original design used a rock pile for thermal mass. This was found to have a problem with mildew when the storage was not used during the summer. In 1982 the rock was replaced with approximately 3000 water filled and sealed glass jars. (These were obtained at minimal cost - they were re-cycled!) The mildew problem was eliminated.

    The system continued to operate with minimal intervention aside from normal maintenance until 2010. At that time a support failed in the storage unit allowing the jars to shift. A few were broken when they fell. Support shelves were strengthened and reinstalled, along with a complete cleaning of the accumulated dust which had settled in the compartment. Jars were inspected and most found to have maintained their integrity. Those needing refilled were topped off and reinstalled in the storage unit. Operation was restored to the level it was before this incident.


    As I stated earlier, the system has met the design criteria, but... After analysis of the data, in the climate here in Southwest Pennsylvania, a solar heat system is feasible and cost effective if the owner is able to do most of the construction and installation himself. If I would have spent the 20 thousand dollars to have had a commercial system installed, most likely it would have still not reached its payback point.

    Regarding maintenance costs, after over 30 years of operation there have been no major expenses encountered. The glazing replacement is the first major expense to be considered, however this was anticipated back when the system was initially installed. Replacement is considered normal maintenance, not a system failure. There have been two component failures in the electric furnace, neither directly related to the solar heat system. A contactor failed whch resulted in one heat bank becoming inoperative until the relay was replaced. Also a circuit breaker in the furnace developed a high resistance contact which resulted in it repeatedly tripping out. It was replaced, both of these items together cost less than $40 to purchase and replace. Even with all these costs factored in, operating expenses remain well below the estimated costs of the electric the system has offset.

    It is difficult to estimate an exact dollar amount the system has saved since the fireplace is also utilized at times. It would be possible to offset virtually all of the electric heat if this option was used regularly. However as I stated earlier I don't use it that often, and then only for short periods when the mood strikes. So the electric furnace is the main backup for the system as it was originally intended. Overall I can estimate that the solar is providing about 40% of the heat, the electric furnace also about 40% with the fireplace picking up the remaining 20% as I am currently utilizing them.

    Finally, regarding the Digital Controller some expenses have been encountered. However these were related to experimentation and upgrades related to research on the system. These would not be expected in a similar system installed strictly to provide heat. There have been two cases of electronics related failure since the current controller went on line in 1985. The first occurred in 1993 and was the result of a nearby lightning strike. A voltage regulator and output latch chip were replaced. The second failure occurred in 1997 when an EPROM failed. Repair costs in each case were under 20 dollars in parts.

    What's Next?

    Even though the system is performing well, upgrades have been made and more are planned. This includes the replacement of the FRP panels on all collectors in 2015.

    First, while not a part of the Solar Space Heating System, the water heater collectors used the same type FRP panels for glazing. They reached the end of their life expectancy sooner than the main heating collectors because they operated at a much higher temperature. They have been replaced with double glazed tempered glass panels. (Since 1980, when I built the original collectors, I have found a source for these on the salvage market. I am using recycled patio glass door panels.) These were placed on the water heater collectors since they will benefit most from the increased operating temperatures expected.

    In 2015 I noticed the glass panes were showing signs of fogging at times. One also had a crack in the lower pane. Possibly this was caused by heat expansion as a fastener was located directly beside one end of the crack. This was not deemed an issue since the outer pane was intact and protected it from the weather. I decided to evaluate how well the collector was working after 15 years. Upon inspection it was found that the integrity of the seals in the double pane glass panels was compromised, likely due to the high temperatures encountered. This does not appear to be an issue though as the collectors are still working properly. It appears that the efficiency has not been affected much, if at all.

    Also in 2015 the FRP panels on the main collectors were replaced. Visibly they showed considerable deterioration due to sunlight and weathering. The manufacturer gives a life expectancy of about 20 years; these had gone almost 30. Efficiency was down about 15% on the collector array. In the course of replacing the panels I also inspected the absorber plates and integrity of the collectors themselves. All appeared good, a slight amount of dust had built up in the ducts, but the interior components and frame of the collectors was still in good shape. I cleaned what I could easily reach and reassembled everything. The collectors should be good for another 20 years or more. The cost of this repair was about $950, doing the work myself.

    Another digital controller upgrade has eliminated the need for a separate controller for the solar water heater. The upgraded space heating controller now performs and monitors these functions as well as all space heating requirements. The upgrade consisted mainly of programming changes with minor hardware modifications.

© J.Brown - AUG - 2015