Sizing a solar collector

Sizing the Collector

Usually, the bigger the collector, the better. The reasons for this are:

• Most outbuildings suffer high heat losses due to high infiltration rates and a lack of adequate
insulation. The heat a large collector generates can be put to good use.

• With this collector design, overheating is usually not a problem. Upper vents can be easily closed off or thermal mass, such as water containers or PVC pipes mounted on the ceiling near collector exit vents, can be incorporated. This has the added benefit of reducing nighttime interior temperature swings.

• More collector area provides some allowance for partly cloudy and thinly overcast days.

• The added time and material cost to build a collector that uses the full wall versus part of the wall is small.

Exceptions to using the full south wall for the collector include locations with mild climates, well-insulated and well-sealed buildings, or buildings that are much longer along their eastwest axis than their north-south axis. If the full south wall is not available, using a portion of the wall still pays off.

Hot Air Collector Pros & Cons

Pros:
• Simple (not much to go wrong or watch over)

• Easy to build

• Long life and little maintenance (so far)

• Low initial cost (one-tenth the cost of most commercial panels)

• Good economic return on the initial investment

• Operation produces no greenhouse gases

• Output can be adjusted by opening and closing vents—summer output can be made zero

• Does not impact use of building (I can still pile stuff against the interior wall, but now it’s not junk—it’s thermal mass)

• Does not require changes to the building structure

• My wife doesn’t think it’s ugly (or at least not too ugly!)

Cons:

• It hurts a bit to cut holes in the wall (but you get over it)

• The building might require additional thermal mass and insulation to keep inside

temperatures from dropping too much at night