Solar Requirement For Building Calculator

Work out solar requirement for building instantly with clear inputs, formula shown and shareable results.

About Solar Requirement For Building Calculator

Building codes increasingly mandate rooftop solar as a percentage of connected load. The capacity follows directly, panel count is capacity divided by module rating, and daily generation applies peak sun hours with a performance ratio of about 0.8 for inverter, temperature and soiling losses. Roughly eight square metres of roof are needed per kilowatt peak.

Formulas

Required capacity

kWp = connected load x mandated share

Generation

Daily kWh = kWp x peak sun hours x 0.8 performance ratio

Worked example

With the default values below, Solar Requirement For Building Calculator returns Solar capacity required of 10.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Connected electrical loadminimum 0.1 kW: 200 kW
Mandated solar share of loadaccepts 0.1–100 %: 5 %
Peak sun hoursminimum 0.5 h/day: 4.5 h/day
Panel ratingminimum 50 W: 540 W

Results

Solar capacity required: 10.00 kWp
Panels required: 19
Daily generation: 36.0 kWh
Roof area required: 80.0 m²

Step by step

1Values used
2Required capacity
3Generation
4Solar capacity required= 10.00 kWp
5Panels required= 19
6Daily generation= 36.0 kWh
7Roof area required= 80.0 m²

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Mandated solar provision, structural roof capacity and grid connection terms must be confirmed with the authority and a qualified engineer.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Mandated solar provision, structural roof capacity and grid connection terms must be confirmed with the authority and a qualified engineer.

Frequently Asked Questions

How is the Solar Requirement For Building figure worked out?

kWp = connected load x mandated share. Building codes increasingly mandate rooftop solar as a percentage of connected load.

Why a performance ratio of 0.8?

Panels are rated at 25 °C and 1000 W/m². Real modules run hotter, get dirty, and inverters lose a few percent, so 75-85 percent of nameplate is what is actually delivered.

What values do I need to enter?

This calculator takes 4 inputs: Connected electrical load, Mandated solar share of load, Peak sun hours, Panel rating. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.