Solar Thermal System Sizing Calculator

1. Enter annual heat demand

Use delivered thermal energy required over one full year.

2. Choose a solar contribution

Set the share of that demand the solar system should supply annually.

3. Enter collector-plane irradiation

Use a typical-year value for the planned tilt and orientation.

4. Set annual useful efficiency

Represent delivered heat after collector and system losses.

5. Add collector area

Use the applicable area per module to obtain an integer collector estimate.

6. Review feasibility

Check the resulting field against seasonal load, storage, and available installation area.

Core formula

Target solar heat = Annual thermal demand × Target solar fraction

Required collector area (m²) = Target solar heat ÷ [Annual irradiation × Useful-heat efficiency]

Collector count = Round up(Required area ÷ Area per collector)

Variables

• Annual thermal demand: yearly useful-heat requirement in kWhₜₕ
• Target solar fraction: desired annual solar contribution as a decimal
• Annual irradiation: collector-plane solar energy per square meter
• Useful-heat efficiency: annual delivered-heat fraction

Assumptions

Demand, irradiation, and efficiency represent a typical year. Annual production can match a target while still occurring at the wrong season or hour, so storage and auxiliary heat are not sized here.

What the result means

The area is the annual-energy collector requirement under the entered resource and efficiency. The rounded collector count may provide slightly more area.

A detailed design should simulate monthly or hourly demand, supply temperature, storage, stagnation risk, auxiliary heat, and layout constraints.

Given

• Annual thermal demand: 500,000 kWhₜₕ
• Target solar fraction: 55% = 0.55
• Annual irradiation: 1,700 kWh/m²-year
• Useful efficiency: 45% = 0.45
• Collector area: 2.5 m² each

Calculation

Target solar heat = 500,000 × 0.55 = 275,000 kWhₜₕ/year

Useful yield = 1,700 × 0.45 = 765 kWhₜₕ/m²-year

Required area = 275,000 ÷ 765 = 359.477... m²

Collector count = round up(359.477 ÷ 2.5) = 144 collectors

Result

Required collector area: 359.48 m²

Using 144 collectors of 2.5 m² provides 360 m² before layout and piping adjustments.

What does the Solar Thermal System Sizing result represent?

The area is the annual-energy collector requirement under the entered resource and efficiency. The rounded collector count may provide slightly more area.

Which assumption most affects this solar thermal system sizing estimate?

Use a site- and system-specific value for the resource, efficiency, production, price, or load input that drives this calculation. Keep its time period and unit consistent with the other entries.

Which real-world effects are outside the Solar Thermal System Sizing model?

A detailed design should simulate monthly or hourly demand, supply temperature, storage, stagnation risk, auxiliary heat, and layout constraints.

Why can an input be rejected in calculator 1120?

A required denominator or physical quantity must be greater than zero, while percentage inputs must stay within their displayed limits. Reset restores the worked-example values.

What should I verify before relying on the Solar Thermal System Sizing estimate?

Confirm site data, equipment specifications, system boundaries, applicable codes, and the time basis of every input. Use a detailed model and qualified professional review for final engineering or investment approval.