Site Analysis and Load Analysis
What this domain tests
Site analysis asks you to quantify two things before quoting equipment: how much usable sun reaches the collector plane, and how much energy the load actually draws. Exam items typically give a house, a family size, a roof, and obstructions, and expect you to spot the flaw in the proposed design.
Reading the site
- Use a sun-path chart or shading tool to map obstructions from roughly 9 a.m. to 3 p.m. solar time - that window carries most of the useful irradiance. Note which obstructions are evergreen and which are deciduous.
- Record true azimuth (magnetic bearing corrected for declination) and roof pitch; tilted-plane insolation differs from horizontal global data.
- Note roof covering, age, rafter size and spacing, usable square footage (leave clearance for maintenance and row spacing), and the pipe route to the tank.
- Confirm where a storage tank can sit: weight, floor loading, freeze protection, and the shortest practical pipe run.
Load analysis
Domestic hot water load, Btu/day = gallons per day × 8.34 lb/gal × (setpoint − mains temperature). Use realistic draw (typically 15–25 gal per person per day), not tank size. Pool loads dwarf DHW loads and are driven by surface area and evaporation; a pool cover changes the answer more than adding collectors does.
Worked example
Four people × 20 gal = 80 gal/day. Mains 50 °F, setpoint 120 °F, ΔT = 70 °F. Load = 80 × 8.34 × 70 = 46,700 Btu/day (about 13.7 kWh/day). At a 60 % solar fraction the array must deliver roughly 28,000 Btu/day on a design day, which you convert to collector area using OG-100 output at the site's tilt and irradiance.
Traps
Quoting collector count before calculating load; using tank capacity as the daily load; ignoring the summer-to-winter irradiance swing; forgetting that a shaded 10 a.m. to 2 p.m. window can disqualify an otherwise south-facing roof.