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Solar thermal hot water Calculator
Compare potential collector yield with annual hot-water demand. This free solar thermal hot water calculator shows the calculation and its assumptions so you can compare your own figures.
Your results
Compare potential collector yield with annual hot-water demand.
Calculated outcomes
- Annual Demand KWh
- 2,864.79 kWh
- Usable Solar KWh
- 1,200 kWh
- Supplied Solar KWh
- 1,200 kWh
Assumptions and estimates
- Method: Demand uses water heat capacity. Usable solar yield = area × specific yield × usability; contribution is capped at annual demand.
- Annual energy matching does not model seasonal storage or daily mismatches. The usability input should account for excess summer yield, storage and system losses.
Useful next steps
- Use Compare options to test an alternative side by side.
- Copy, print or download a record of this calculation when you need one.
Reports open your email app addressed to s@s1.ie with the public page address only. Your inputs are never added.
How the solar thermal hot water calculation works
Demand uses water heat capacity. Usable solar yield = area × specific yield × usability; contribution is capped at annual demand.
Annual energy matching does not model seasonal storage or daily mismatches. The usability input should account for excess summer yield, storage and system losses.
Using this calculator
- Enter your own figures in the labelled inputs. Keep the currencies, units and time periods consistent.
- Choose any applicable rate profile, pattern or assumption shown for this tool. Open additional inputs when relevant.
- Review solar fraction percent and annual fuel saving, then read the stated assumptions and eligibility conditions before using the result.
Worked example
This is a static example using illustrative inputs, not facts about you or today’s date. The displayed eligibility selections and assumptions apply only to this example.
See example inputs
- Collector area (m²)
- 4
- Annual collector yield (kWh/m²)
- 400
- Usable fraction of yield (%)
- 75
- Daily hot-water demand (litres)
- 150
- Temperature increase (°C)
- 45
- Days per year
- 365
- Backup heater efficiency (%)
- 90
- Backup input energy price (€/kWh)
- 0.1
- Solar Fraction Percent
- 41.89%
- Annual Fuel Saving
- €133.33