Last year I built prototype solar panels and summarized the preliminary data gathered in some test runs (see this project’s archive here). Here I will outline the plans drawn up to get a building permit from our local municipality.
These show the basic operation of the system. It is a schematic and not to scale.
The heart of the system are two 4-×-16-ft and one 4-×-8-ft collection panels. Each one has 1/2-in copper riser tubes with aluminum fins connected to a 3/4-in manifold at top and bottom. As the sun hits the fins, it warms the water-glycol solar fluid mix circulating through the tubing. The heated fluid enters into the house and warms water in a 500-gal water tank system in the basement through a series of coiled-copper-tube heat exchangers.
Domestic hot water is produced by routing incoming water through another series of coiled-copper-tube heat exchangers in the hottest part of the reservoir. During the winter, domestic hot water is precharged in the solar system and then sent to the existing electric water heater, which keeps it warm but doesn’t have to work to warm cold water, thus saving energy. In the summer, when we have an excess of solar heat, domestic hot water is produced solely by the solar system. A series of ball valves control this configuration.
The home will get supplemental heat from a hydronic radiator system. Hot water from the reservoir will be drawn out of the tanks by a circulating pump. The water will pass through a series of radiators in the house before coming back to the reservoir to be heated by the solar system again. Individual radiators will be controlled by room-specific regulators.
To get a building permit, we had to submit to-scale structural drawings.
Outside the house, the three panels will be spaced at 12-ft intervals (not 8 ft as shown here). They are connected by an underground copper pipes encased in a PVC shroud. The panels are supported and secured by 2-ft-deep, 8-in-diameter cement footings with belled bottoms to help avoid frost heave. The panels are supported on triangular supports secured to the footings. The plumbing line is below the frost line, although this is not technically necessary as the system will be pressurized, food-safe antifreeze.
The panels are essentially wooden boxes built of 2-×-6-in lumber on the perimeter with 2-×-4-in studs at 24 in on center. The back is 3/8-in plywood for lateral stability. Between the studs are batts of mineral wool insulation. The insulation is covered by 1/4-in plywood layer onto which is attached an aluminum-flashing backing. The sweat-soldered copper grid of risers and manifolds is then placed over the aluminum backing and attached with 6-in strips of flashing bent around the risers for maximum heat transference. All surfaces are painted matt black with high-heat paint. The panel is covered with a double-layered poly glazing. The outer surfaces are painted and covered in flashing to prevent water damage.
The reservoir is built of dimensional lumber and plywood enclosing a base of sand and insulated with batts of insulation around the perimeter and packed loose insulation around ten 55-gal drums filled with 50 gal of water each. The drums will be connected by top-loaded heat exchangers and siphons to run the solar fluid loop, domestic hot water, and hydronic systems, described above.
The panels will be arrayed on the south face of our house, allowing for space between them to allow the sun to fully strike each panel. We will put walkways around the panels with a herb garden beds along the south side of each panel.
“Lab Notes” are a series of posts chronicling the daily progress our research projects. Research Project No. 1 is the testing and installation of a solar heating system for domestic water and space heating. These notes may be useful for anyone interested in building such a system at home. Others might prefer the more succinct guide to solar heating, videos, and other formal publications that will result from this research project and be posted to the website as they are available.