This is part II of how to make your own solar thermal collector to help offset heating costs this winter.  You will need a good south facing wall to mount this collector on.  In order to be most effective, the wall should be unshaded between 9 am to 3 pm daily.  Some defused sunlight shining through the branches of a deciduous tree is fine.

Preferably this collector will be mounted adjacent to a large reflective surface.  A snow field would be perfect, however, dry sand, concrete and water will also work.  The quality of the reflective surface is called Albedo, which in Latin refers to its “whiteness.”

Here are some albedo figures for some common reflective surfaces:

Also, the lower the sun angle, the larger the reflective surface should be.  This is for two reasons; first, the law of reflection states:

1. The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.
2. The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.

Therefore, the lower the angle of the sun the further away the reflection point will be from the collector.

Secondly, the lower sun angle also means that the energy density of the sun light is much less.  A larger reflective area will aid in gathering more energy.

Solar Collector parts list:

*Not required for a passive system
**Quantities doubled for a passive system

Total, active system: $447.16
Total, passive system: $355.74

All parts except snap disk switch, PV panel, and DC fan were priced and purchased at the Home Depot.

Therefore, a passive collector needs to offset $355.74 in the first year’s use, an active collector needs to offset $447.16.  According to NYSERDA, the cost of home heating oil is currently $3.823 a gallon.  I need to save 117 gallons of fuel oil to offset the $447.16 collector cost.  Each gallon of home heating oil has 139,000 BTU. My boiler is 86 percent efficient, therefore, I get 119,540 BTU per gallon.

My solar collector needs to generate 13,986,000 BTU to save 117 gallons.

I expect the active solar collector I build to generate about 45,000 BTU per day.  The heating season lasts from October through April, or 212 days.  I expect 30 percent of those days to be too cloudy to generate significant heat from the collector.  I have 148 days of good solar resource, so 6,660,000 BTU can be expected.  That makes the payback approximately two years vs the one year original design goal.

Solar collector tools:

Ridgid MS1065LZ 10 inch miter saw

Makita 6213D 3/8 inch cordless drill

Ridgid R84001 3/8 inch cordless drill

Bosch 1587A Jig Saw

DeWalt D28110 rotary grinder

Construction details to follow in Part III

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