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Solar Hot-Water Collector and Storage Sizing

Calculate water-heating load, whole collector count and a storage/recovery window from actual volumes, temperatures, useful yield and candidate equipment.

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Inputs that matter
Water volume unit, Daily delivered hot-water volume, Incoming water temperature (°C), Delivered-water temperature (°C), and 10 more
Output to expect
Hot-water load and collector area, Hot-water storage and recovery window
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Hot-water load and collector area

Calculate a daily sensible-heating load from actual draw volume and temperatures, then estimate collector area for an entered solar contribution and net useful yield. Compare whole identical collectors using their actual aperture area.

Water heat = litres × 4.186 × temperature rise / 3600 kWh; target solar heat = load × target fraction; aperture area = target heat / (collector-plane irradiation × net useful efficiency).

Hot-water storage and recovery window

Estimate the storage volume needed for a stated draw window after concurrent useful recovery, using actual tank temperature and a usable-volume allowance. Compare one candidate tank on the same energy basis.

Required stored heat = max(draw heating load − useful recovery,0); nominal volume = required heat / [water heat capacity × (tank temperature − incoming temperature) × usable-volume fraction].

Updated: September 2026

Example Scenarios

Try this example to see the calculation, then enter actual documented values and preserve the measurement conditions. A failed or unresolved comparison is part of the record.

→ 2 whole collectors

Try this example to see the calculation, then enter actual documented values and preserve the measurement conditions. A failed or unresolved comparison is part of the record.

→ 118.888358 L nominal storage

FAQ

Calculate a daily sensible-heating load from actual draw volume and temperatures, then estimate collector area for an entered solar contribution and net useful yield. Compare whole identical collectors using their actual aperture area. Estimate the storage volume needed for a stated draw window after concurrent useful recovery, using actual tank temperature and a usable-volume allowance. Compare one candidate tank on the same energy basis.

Use the exact equipment data, measurement point, operating conditions and units described in the selected mode. Record source documents, dates and unresolved conditions in Sources and assumptions. Built-in examples illustrate arithmetic; they are not manufacturer ratings or approved designs.

Use Save planning case for an explicit local history entry. Copy MD keeps current inputs and notes; Download CSV exports the result breakdown. Export portable copies before clearing storage and save a separate case after changing equipment, conditions or measurements.

About Solar Hot-Water Collector and Storage Sizing

Calculate a daily sensible-heating load from actual draw volume and temperatures, then estimate collector area for an entered solar contribution and net useful yield. Compare whole identical collectors using their actual aperture area. Estimate the storage volume needed for a stated draw window after concurrent useful recovery, using actual tank temperature and a usable-volume allowance. Compare one candidate tank on the same energy basis.