Rules of Thumb - Collector

Production:  1,000 Btu's / SF / day

Usage:  20 gal / day

Cold Water Supply:  50 degrees F

Domestic Hot Water Temperature:  130 degrees F

Rules of Thumb - Storage

Solar Domestic Hot Water:  1.5 gallons / SF Collector

Space Heat:  1.0 gallons / SF Collector

Patterns of Hot Water Use

When will hot water be used?

How often will hot water used?

How much hot water will be used?

Example (Per Day)

Amount of hot water needed

4  # of people
x 20  gallons / person / day
= 80 gallons hot water / day

Amount of energy needed
80  gallons hot water / day
x 8.34   lbs / gallon
= 667.2 lbs of water
x 80 degrees F change in Temperature (50 degrees F to 130 degrees F)
=53,376 Btu's needed per day

Solar Panel Output

4 x 10 panel:  32,000 - 40,000 Btu's /day

4 x 8 panel:  25,000 - 32,000 Btu's / day

Solar Panel Selection

Requirement:  53,376 Btu's / day

2 - 4x10 panels = 64,000 - 80,000 Btu's /day (Overkill)

2 - 4x8 panels = 51,000 - 64,000 Btu's / day (Perfect)

Panel tilt rules of thumb

Year round use:  Latitude + 0 degrees (Domestic Hot Water)

Primarily Summer Use:  Latitude -15 degrees (Pool Heating)

Primarily Winter Use:  Latitude +15 degrees (Space Heating)