Skip to content
OneKitly
Sign up · Sign in

Solar panel calculator

Estimate how many solar panels you need from your daily energy use.

Related tools

All Energy & power tools →
Solar battery size calculatorEstimate the battery capacity you need from daily energy use and days of autonomy.Appliance running cost calculatorEstimate what an appliance costs to run per day, month and year.Heat pump savings calculatorWhat a heat pump costs to run against your current boiler, from your own fuel bill: the heat you actually need, the electricity a given SCOP would draw, the yearly difference and the payback. Plus the one number that decides it — the electricity price above which the heat pump stops being cheaper.kWh to CO₂ calculatorEstimate the CO₂ emissions from electricity use and a grid emission factor.Battery life calculatorEstimate how long a battery lasts from its capacity and the load current.Heating BTU CalculatorEstimate the heating power in watts and BTU needed to heat a room based on its area and climate.Voltage drop calculatorEstimate the voltage drop in a copper cable from its length, current and cross-section.Amperage CalculatorConvert a load in watts and a supply voltage into the current drawn in amps.

The Solar panel calculator turns Daily energy use (kWh), Panel power (W), Peak sun hours/day into Panels needed, System size (kWp), instantly and for free. For instance, with Daily energy use (kWh) = 10, Panel power (W) = 400 and Peak sun hours/day = 4 it returns Panels needed = 9 and System size (kWp) = 3.6.

How to use it

  1. Enter your values: Daily energy use (kWh), Panel power (W), Peak sun hours/day.
  2. Read the result instantly: Panels needed, System size (kWp).

Frequently asked questions

What does the Solar panel calculator actually compute?

It takes Daily energy use (kWh), Panel power (W) and Peak sun hours/day and derives Panels needed and System size (kWp) from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

3 values: Daily energy use (kWh), Panel power (W) and Peak sun hours/day. Nothing else is required — no account, no file upload.

Can you show a worked example?

With Daily energy use (kWh) = 10, Panel power (W) = 400 and Peak sun hours/day = 4, the calculator returns Panels needed = 9 and System size (kWp) = 3.6. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What happens if I enter larger values?

It moves a lot. Using Daily energy use (kWh) = 20, Panel power (W) = 800 and Peak sun hours/day = 8 instead, Panels needed goes from 9 to 5 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Daily energy use (kWh) = 5, Panel power (W) = 200 and Peak sun hours/day = 2, Panels needed comes out at 17. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Putting a number on a bill: what an appliance costs to run, whether a solar array covers the load, and how much heating a room actually needs.

What is the most common mistake?

Confusing power with energy. A kilowatt is a rate and a kilowatt-hour is a quantity; a 2 kW heater on for half an hour uses 1 kWh, and only the second figure appears on a bill.

How accurate is it, and what are the limits?

Estimate — actual yield varies with location, shading and season.

What is the difference between the Solar panel calculator and the Solar battery size calculator?

This one returns Panels needed and System size (kWp); the Solar battery size calculator returns Battery capacity (kWh). That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Appliance running cost calculator is the closest one after this: Estimate what an appliance costs to run per day, month and year.

Further reading

All guides →
How-toHow Many Solar Panels Do I Need? A Simple Sizing MethodSize a solar array from your annual electricity use, panel wattage, and local sun hours — plus a quick payback estimate in dollars.ComparisonSolar Panels: the Self-Consumption Rate Decides the PaybackSince June 2026 a French rooftop is paid 1.1 cents for an exported kilowatt-hour and avoids 25.61 cents by consuming the same one. That ratio of 23 to 1 makes the self-consumption rate — the variable almost every quote omits — worth more than the amount of sun falling on the roof.How-toWhat Size Solar Battery Do I Need? Sizing by Daily UseSize a solar battery from your daily energy use, the days of autonomy you want, and the battery's usable depth of discharge.How-toHow to Convert kWh to CO₂: Grid Emission Factors ExplainedConvert electricity in kWh into CO₂ emissions using your grid's emission factor — and understand why that factor differs so much by country and time.How-toHow Far Apart to Plant? Spacing and Plants per AreaTurn a plant-spacing figure into how many plants you need for a bed or row — including the difference between square and triangular layouts.How-toHow Much Grass Seed Do I Need? Seed Rate by Lawn AreaWork out how much grass seed to buy from your lawn area and the seed rate — with different rates for a new lawn versus overseeding.