Impact Zero Solar Thermal Calculator

1. Project & Location

Project name

Project location

Enter project locationSearch a city, address or site name. The tool can then import monthly irradiation automatically.

Latitude (degrees)

Longitude (degrees)

Irradiation data start year

Irradiation data end year

Enter the project location and click “Search location”. The tool will then fetch NASA irradiation automatically. “Use my current location” is optional and depends on browser/location permissions.

Tip: the most reliable workflow is to type the project city or address, for example “Brisbane, Australia”, then click “Search location”. If browser GPS is blocked, the tool can use an approximate time-zone city such as Brisbane and fetch NASA irradiation automatically.

Collector tilt (degrees)Recorded for reporting. Use the orientation factor below for adjustment.

Collector azimuth (° clockwise from North)North = 0°, East = 90°, South = 180°, West = 270°. Example: 45° west of north = 315°.

Manual shading / soiling factor1.00 = no additional loss. Use this for shading, soiling or manual derating. Tilt and azimuth are now calculated automatically.

2. Collector Library & Temperatures

Collector Library

Select collector profileStarter profiles are for screening only. For proposals, verify values against manufacturer datasheets, Solar Keymark or SRCC reports.

Absorber / aperture area per collector (m²)

Number of collectors / absorbers

Tubes per collector

Conversion factor η₀ / CF

Heat loss coefficient a₁W/m².K

Heat loss coefficient a₂W/m².K²

IAM / average Kd

Fixed ambient air temperature fallback (°C)Used when monthly weather data is not available.

Ambient temperature modelRecommended: synthetic hourly profile. NASA data fills monthly average, minimum and maximum temperatures automatically.

Inlet water temperature (°C)

Outlet water temperature (°C)

3. Financial & Emissions Inputs

Installed cost

Currency

Thermal energy value ($/kWh)

Emissions factor (kg CO₂-e/kWh thermal)

4. Monthly Daily Insolation

Advanced / fallback input. Horizontal solar irradiation plus monthly average/minimum/maximum ambient temperature are filled automatically when NASA data is fetched. Tilt and azimuth are then used to estimate collector-plane irradiation.

Month	Collector-plane insolation kWh/m²/day

Results Summary

Monthly Thermal Energy

Insolation vs Energy

Each visible line represents a month. Units: kWh/m² for each hourly interval.

Each visible line represents a month. Units: watts per evacuated tube.

Efficiency is calculated hourly from collector coefficients, irradiance and ΔT. Units: %.

Monthly Output Table

Scenario Comparison

Edit the core variables below. The tool recalculates each scenario against the same monthly insolation profile.

Scenario Annual Energy Comparison

Calculation Assumptions

Solar and weather dataMonthly average daily horizontal insolation can be imported using NASA POWER ALLSKY_SFC_SW_DWN data. Ambient temperature can be imported using NASA POWER T2M, T2M_MIN and T2M_MAX data. Tilt and azimuth are used to estimate collector-plane irradiation before thermal output is calculated.

Hourly distributionDaily horizontal insolation is split across 24 hourly intervals using the workbook’s sunset hour angle and hourly fraction method, with an explicit sunrise/sunset cut-off. Each hourly value is then transposed to the collector plane using tilt and azimuth.

Collector libraryThe collector library includes the uploaded workbook default plus generic starter profiles for preliminary screening. Values remain editable and should be replaced with certified datasheet, Solar Keymark or SRCC values for proposal work.

Collector efficiencyEfficiency is calculated hourly and cannot fall below zero: η₀/CF × IAM − a₁ × ΔT/G − a₂ × G × (ΔT/G)². ΔT is calculated hourly using the average water temperature minus the selected hourly ambient temperature. In synthetic mode, hourly ambient temperature is estimated from monthly min/max values with a simple diurnal curve.

Thermal outputHourly thermal output equals total collector area × hourly collector efficiency × hourly insolation.

Financial savingsAnnual savings equal annual thermal kWh multiplied by the nominated thermal energy value.

LimitationsThis is a planning calculator, not a detailed hydraulic, storage tank, shading, load-matching or compliance model.