Solar Panel Calculator Widget

Add a solar panel sizing calculator to your website. Visitors enter their monthly or daily electricity use, their location's peak sun hours, the panel wattage and an allowance for losses, and see how many panels and what system size would cover it, with the expected yearly generation.

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<iframe src="https://a2z.tools/embed/w/solar-panel-calculator" title="Solar Panel Calculator by A2Z Tools" width="100%" height="730" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>

A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.

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How it works

The widget uses the solar engine of the A2Z Solar Panel Output Calculator. A panel's rating is its output at the standard 1,000 W/m2 irradiance, so a site that receives 5 kWh/m2 of sunlight a day has 5 'peak sun hours' and each panel is expected to produce its rating x the peak sun hours x (1 - losses) per day. A monthly bill figure is first turned into a daily average (x 12 / 365); the daily need is divided by one panel's output and rounded up to whole panels, and the resulting system is then run forward to give daily, monthly and yearly generation. Peak sun hours are the visitor's own figure for their site - the widget does not look up weather or location data - so the result is only as good as that number: a yearly average suits a year-round estimate, the worst month's figure sizes a system for winter. The single losses figure has to stand in for everything NREL's PVWatts model treats separately - soiling, shading, wiring, mismatch, availability, inverter efficiency and cell temperature.

Calculation method

  • Daily need = monthly kWh x 12 / 365 (or the daily figure entered)
  • Energy per panel per day (kWh) = panel W / 1000 x peak sun hours (kWh/m2/day) x (1 - losses)
  • Panels = ceil(daily need / energy per panel); system kWp = panels x panel W / 1000
  • Generation = kWp x peak sun hours x (1 - losses) per day; x 365 per year; x 365/12 per month; kWh to 2 decimals, yearly to whole kWh

Worked examples

Household using 600 kWh a month

Inputs: 600 kWh/month, 5 peak sun hours, 400 W panels, 20% losses

Result: 13 x 400 W panels, 5.2 kWp (minimum 4.93 kWp); 20.8 kWh a day, about 633 kWh a month and 7,592 kWh a year

600 x 12 / 365 = 19.73 kWh/day; one panel gives 0.4 x 5 x 0.8 = 1.6 kWh, so 12.33 rounds up to 13.

Daily figure with PVWatts-style losses

Inputs: 10 kWh/day, 4 peak sun hours, 450 W panels, 14% losses

Result: 7 x 450 W panels, 3.15 kWp; 10.84 kWh a day, 3,955 kWh a year

0.45 x 4 x 0.86 = 1.548 kWh per panel; 10 / 1.548 = 6.46, rounded up to 7.

A planning estimate from the figures entered, not a quote or a design. Roof orientation, tilt, shading and local regulations can change the result; get a site survey from a qualified installer.

Limitations

  • Does not look up location, weather, tilt, orientation or shading: peak sun hours are the visitor's entry, and a wrong figure scales the answer directly.
  • Uses one flat losses percentage; seasonal variation, temperature derating in hot climates, inverter clipping and panel degradation over the years are not modelled separately.
  • Sizes panels to cover average energy only - not roof area, string voltages, inverter sizing, export limits or batteries.
  • Assumes all generation is used or credited; self-consumption and tariff rules decide how much of the bill it actually offsets.

Where publishers use it

  • Solar installers giving visitors a first estimate before a site survey
  • Sustainability and home-energy blogs
  • Off-grid cabin and farm websites
  • Energy courses explaining peak sun hours

Questions

What are peak sun hours?

The daily solar energy at your site expressed as hours of full 1,000 W/m2 sunshine - numerically the same as kWh/m2 per day. Solar resource maps such as NREL's or the Global Solar Atlas publish it for any location; use the value for your panels' tilt if the map offers it.

What losses should I allow?

NREL's PVWatts uses a default of 14% for soiling, shading, snow, mismatch, wiring, connections, light-induced degradation, nameplate rating, age and availability, and models the inverter and panel temperature on top of that. This widget folds all of them into one number, so a figure around 20% is a reasonable planning value.

Will the system cover my bill every month?

Not necessarily. Generation is higher in summer and lower in winter; the widget works with the average you enter.

Does it include batteries?

No, it sizes the panels only. Use the battery or inverter backup calculators for storage.

What does kWp mean?

Kilowatt-peak: the combined nameplate rating of the panels, measured by the maker under standard test conditions of 1,000 W/m2 irradiance and 25 C cell temperature. Real output is usually below it because cells run hotter than 25 C in sunshine.

Sources

  1. PVWatts Version 5 Manual (Dobos), NREL/TP-6A20-62641 - National Renewable Energy Laboratory, 2014 . Standard irradiance, default 14% system losses and the separate inverter and temperature models
  2. Global Solar Atlas - World Bank Group / Solargis . Source of site peak sun hours (global horizontal and tilted irradiation, kWh/m2/day)

Cite or recommend this tool

If you reference this tool in an article, course or documentation, these formats are ready to copy. They are optional - nothing is added to your site unless you paste it.

A2Z Tools Solar Panel Calculator
https://a2z.tools/solar-panel-output-calculator

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