Begin with daily hot water demand
Count occupants and estimate realistic daily hot water use. Adjust for the building type, fixtures, schedules, and known high demand activities. A generic per person allowance can start the discussion, but a contractor should replace it with better project information when available.
Choose an appropriate solar contribution
Solar fraction describes the portion of the hot water energy load supplied by solar energy. Designing for an extreme fraction can create excessive summer production or storage problems. The target should reflect climate, demand consistency, system cost, available roof area, and the role of backup heat.
Match collector area and storage
Collector performance depends on operating temperature, ambient conditions, irradiance, orientation, tilt, and system losses. Storage has to absorb useful production and support the draw pattern. Collector area and tank volume should be evaluated together rather than chosen independently.
Collector information
Use traceable product dimensions and performance data. Keep certified, manufacturer supplied, and dealer entered data clearly identified.
Storage
Check usable tank volume, heat exchanger configuration, temperature limits, backup element or heater, and space at the site.
Loop type
Open loop, drainback, and glycol closed loop systems have different equipment and site requirements. Local freeze risk comes from the site, not simply the country name.
Roof and piping
Verify orientation, shading, array fit, pipe length, lift, insulation, penetrations, and a practical route between collectors and mechanical equipment.
Present the assumptions with the result
A proposal should state the demand basis, equipment, estimated contribution, backup energy, and limitations. The goal is a design the contractor can explain and the customer can understand.
See how SunProjeX connects these decisions in its solar hot water design workflow.