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Solar PV Calculator

Enter monthly or daily energy consumption, sun hours, coverage, and panel specs to estimate system size, panel count, generation, roof area, and savings.

Tool statusRuns in your browser
Preview
prontouso://home/solar-sizing
LOCAL● LIVE UPDATE

Project data

Adjust the assumptions. Results recalculate immediately.

01 / INPUT
Consumption profile
kWh/month
%
$/kWh
Lower offset100% of consumptionHigher production
Solar conditions
h/day
%
Modules & installation
Wp
m²
Preliminary estimate. Shading, orientation, tilt, regulations, inverter, structure, and local conditions should be assessed by a professional.

Sizing summary

A quick read of the system needed to meet the target you entered.

02 / OUTPUT
Suggested installed power2.75 kWp5 panels of 550 Wp to produce approximately 330 kWh per month.
Minimum power2.50 kWpneeded before rounding up to whole panels
Modules5panels needed for this configuration
Daily generation11.0 kWhaverage estimated output per day
Monthly generation330 kWhaverage output over a 30-day month
Roof area11.5 m²footprint of the panels, excluding walkways
Estimated savings$285approximate monthly amount offset

Energy balance

Target
300
System
330

The rounded configuration produces about 10% above the target.

How the estimate was built

Daily consumption considered
10.00 kWh
Output per kWp/day
4.00 kWh
Calculated power
2.50 kWp
Estimated annual generation
4,015 kWh
Processed locally in your browser

How it works

  1. Enter your input

    Fill in the values, paste your text, or upload the file this tool works with.

  2. See results instantly

    Most tools update live as you type; a few use a single button. Either way, the result appears right on this page.

  3. Use your results

    Copy, download, or share what the tool produces — you're always in control of the output.

Privacy and processing — Runs locally in your browser. This tool does not upload your input.

What is Solar PV Calculator?

The Solar PV Calculator is a tool for sizing a system from your energy consumption, estimating panel count, daily, monthly, and annual generation, the roof area needed, and approximate monthly savings.

UNDERSTAND THE TOOL

How to size a solar PV system

Enter your monthly or daily consumption, the coverage you want to reach, peak sun hours, and your panel specs to see the suggested power, panel count, and estimated savings — all recalculated instantly.

Monthly or daily consumption, and desired coverage

Switch between "Monthly consumption" and "Daily consumption" — the tool converts the value automatically assuming a 30-day month, so use whichever matches your utility bill. "Desired coverage" ranges from 10% to 150%: 100% sizes the system to offset your entire stated consumption, a lower value sizes a partial system, and anything above 100% leaves room for future growth or lower-generation months.

How the system size is calculated

The calculated minimum power is rounded up to whole panels, so the final installed power is always at or above the target — never short of it.

Formula
power_kW = (monthly_kWh × coverage% / 30) / (peak_sun_hours × efficiency)

What "peak sun hours" means

It's not daylight hours — it's the equivalent number of hours per day the sun would need to shine at its peak intensity (1000 W/m²) to deliver the same total energy your location actually receives. Typical values range from about 3–4 in cloudier northern regions to 5–6 in sunnier ones; check a solar irradiance map for your specific location.

Use the Low sun (3.5h), Balanced (5h), or High sun (6.5h) shortcuts as a starting point, or type the value from a solar irradiance map for your location.

Panels, roof area, and tariff

Panel power (with 450, 550, and 610 W shortcuts) and the approximate area per panel determine how many modules fit on the roof and how much space they take up. The energy tariff doesn't affect sizing — it's only used to estimate monthly savings, calculated on the generated energy capped at your stated consumption, even if the chosen coverage goes above 100%.

Worked example

300 kWh/month, 100% coverage, 5h sun, 80% efficiency, 550 W panels

Minimum power is 2.5 kWp; rounding up to whole panels gives 5 modules and 2.75 kWp installed, generating about 330 kWh per month — 10% above target.

300 × 100% / 30 = 10 kWh/day; 10 / (5 × 0.8) = 2.5 kWp; ceil(2500 / 550) = 5

Solar sizing note

Every field, the calculation, and the summary you copy or download run locally in your browser — nothing is sent to a server. It's still a preliminary estimate: shading, orientation, roof tilt, inverter, structure, local codes, and your utility company all need a professional review before finalizing a design.

Frequently Asked Questions

What system efficiency should I use?

75–85% is a reasonable range for a typical grid-tied inverter system once wiring, temperature derating, and inverter conversion losses are accounted for.

Does this account for seasonal variation?

No — it uses a single average peak-sun-hours figure. Real generation is higher in summer and lower in winter; use a conservative (lower) figure if you want the estimate to hold up through winter months.

Can I use this instead of a professional design?

Use it for a ballpark estimate only. A real installation also depends on roof orientation, shading, local regulations, and your utility's interconnection rules — get a site assessment before buying equipment.

Why is panel count rounded up?

Panels are whole items. Rounding up keeps the installed array from being smaller than the required system size.

Why doesn't the estimated savings go up when I raise coverage above 100%?

Because savings are calculated on the energy you actually use, capped at your stated consumption — generating more than you consume in a month doesn't increase savings in this estimate, even if the chosen coverage is above 100%. In that case, the extra coverage acts as margin for lower-generation days or future consumption growth, not additional savings.

What's the difference between entering monthly or daily consumption?

None in the result — it's just convenience. Switching between the two converts the value automatically assuming a 30-day month; use whichever is easier to check against your utility bill.

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