Building the Solar Behemoth- a slideshow chronology

We’re very pleased that our solar heating project is getting so much attention- thousands of hits on our construction blog tells me that the interest in renewable energy is there!  One of the goals of the project was to demonstrate the feasibility and performance of do-it-yourself solar heating projects in extreme climates like northern Minnesota.  Here are the details of the project, along with a slideshow chronology of the build.

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As part of our commitment to energy conservation, a large solar water and space heating system was fabricated on-site and installed in the winter of 2010/2011.  This system experiments with the low-cost, low-tech method of sand bed solar heat storage which is well suited to our cold climate location in Northern Minnesota.

System details:

  • (9) 4X8 fin-tube solar collectors, site built and vertically-mounted to a 40′ steel storage container
  • 50 Gal. domestic hot water (DHW) preheat tank
  • Slab-on-grade foundation with 50 ton concrete/gravel “thermal battery”

How it works:
Whenever solar energy is available, a pump circulates a heated glycol solution from the outdoor solar collector panels into the home through an underground insulated pipe.  Once inside, the heated fluid passes first through a DHW preheating tank then to pex tubing within the concrete slab of the building. The high mass of the concrete slab/underslab compacted gravel bed acts as a ’thermal battery’- slowly warming during the day, then releasing the stored heat to the building during the night.   When excess heat is produced (spring, summer, fall periods), a diverter valve redirects the fluid to a shunt loop after passing through the DHW preheat tank.
Benefits (over conventional systems that use large water tanks to store the heat) are that solar energy is utilized at the lowest possible temperature resulting in the highest possible collector efficiencies. Overall cost, complexity and footprint is reduced by using the existing building foundation as the heat storage system.

Materials Cost:

  • (9) Collectors @ $250ea =    $2250
  • Mounting hardware     =    $  300
  • Plumbing & Controls     =    $  800

Total system cost      =    $3350

Performance Data:

This solar heating system was put into use mid-January 2011.

The 9-collector solar array produces approx. 43,000BTU/hour during full sun.

Runtime and energy use was monitored during the months of February and March, 2011.  The solar heating system provided 51% of the building’s total heat requirement in February and 73% in March, resulting in an energy cost savings of $176 for this 2-month period.

Backup heating during this period was provided by the home’s  7KW electric micro boiler, also tied into the in-slab heating system.  Total backup electric heating cost during this period (at full electric utility rate, as we are not on ‘off-peak’ service yet)  was $79 in February and $36 in March.

Additional information:

The Domestic Hot Water (DHW) ‘preheat’ tank has not been installed yet, as we’re still catching up on the gazillion other projects around here!  Therefore, all of the energy produced by the solar collector array is being used for space heating.  During the Spring and Fall ‘swing season’ of 2011, we found that the building slab was able to absorb and release the large amount of heat being produced without overheating the home.  During the summer period, when no space heating was required, the system was covered with shade cloth and shut down.

Future plans involve 1) installing the DHW preheat tank, which will allow us to better utilize the heat during the spring, summer and fall when space heating is not a priority, and 2) complete the ‘dump’ loop to shunt excess heat to other needs.  These include raised bed gardens/greenhouse heating as well as an outdoor summer shower facility for us and our guests at Green Gate Guest House.

Resources: 

A great deal of time was spent on ‘research & development’ leading up to the start of this project.  Two indispensible resources were Gary Reysa’s Build It Solar website and the “Simply Solar” Yahoo Group– without their generous amount of help and advice, we likely would not have undertaken this adventure!

Stay tuned for more progress on this ongoing project!

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