Free Online Calculators
Calculate yield, self-consumption & ROI
This solar calculator estimates your annual energy yield, self-consumption share, and payback period for a photovoltaic system. It uses your system size, location, electricity price, and feed-in tariff to run the numbers. Get a clear picture of when your investment pays off.
Start with your annual electricity use in kilowatt-hours, divide it by the yearly output one kilowatt of panels produces at your location, and you get the system size in kilowatts. Then adjust for roof area, shading, orientation and how much of your consumption you actually want to cover.
The 120% rule is an electrical code limit: the main breaker rating plus the solar backfeed breaker rating may not exceed 120% of the busbar rating of your service panel. If it does, you need a line-side tap, a derated main breaker or a panel upgrade.
The most useful one is whichever tool lets you enter your own consumption, electricity price, roof orientation and tilt instead of assuming an average household. Tools built on satellite roof data or local irradiation databases give more realistic yield estimates than generic rule-of-thumb calculators.
Online solar sizing calculators are free to use. If you mean the pocket calculator powered by a small solar cell, those are among the cheapest calculators sold.
Yes, a well-built solar calculator gives a solid first estimate of system size, yield and payback, because irradiation data and panel performance are well documented. It cannot replace a site survey, since shading, roof condition, wiring and local tariffs still have to be checked on site.
In most places the cost per kilowatt-hour of self-produced solar power over the system's lifetime is lower than the retail grid tariff, which is why self-consumption pays best. Whether it works out for you depends on your electricity price, installation cost, feed-in compensation and how much of the output you use yourself.
Yes, but only with a battery large enough to cover nights and a system oversized for the winter months, or with a backup generator. Grid-connected homes usually reach high self-sufficiency rather than full independence, because seasonal storage is expensive.
The common reasons are roof repairs or replacement that require removing the array, aging or underperforming equipment, unfavourable leases and loan terms taken on through aggressive sales, and changes to feed-in rules that cut the value of exported power. Panels are also removed when a system was badly sized or poorly installed.
Problems arise mainly when the system is leased or financed, since the buyer has to qualify for and take over the contract, or the seller has to pay it off. Owned, paid-off systems are usually a selling point, though buyers may still ask about roof penetrations, warranties and system age.
Investing in a solar photovoltaic (PV) system is one of the smartest financial decisions a homeowner or business can make today. But how do you know if it's truly worth it for your specific situation? Our free solar calculator gives you instant, data-driven answers — no engineering background required. Simply enter a few key figures and discover your expected energy yield, savings, and payback period in seconds.
Our PV calculator is designed to give you a comprehensive financial and technical overview of a planned or existing solar installation. Here's what it calculates:
Getting accurate results is straightforward. Follow these steps to get the most out of the tool:
Input your planned solar system's peak power in kilowatt-peak (kWp). A typical residential system ranges from 4 to 12 kWp. Next, select your location or enter the average annual solar irradiance (kWh/m²) for your region. Southern Europe enjoys around 1,400–1,800 kWh/m², while Northern Europe averages 900–1,100 kWh/m². This figure is crucial because solar irradiance directly determines how much electricity your panels produce.
Enter your annual household electricity consumption in kWh. The average UK household uses around 3,500 kWh per year, while a US household averages approximately 10,500 kWh. The calculator uses this to determine your self-consumption rate — the share of solar power you use on-site rather than exporting to the grid. Without a battery, this typically ranges from 25–35%; with storage, it can rise to 60–80%.
Enter the total system cost including installation and inverter. Current prices range from roughly £800–£1,200 per kWp in the UK. Also input your electricity rate and any applicable feed-in tariff or net metering rate from your utility provider.
The Johnsons are planning a 8 kWp rooftop solar system in Southern England. Their annual consumption is 4,200 kWh and their electricity rate is £0.29/kWh. Total installation cost: £9,500. The local Smart Export Guarantee (SEG) tariff is £0.05/kWh.
The solar calculator returns: an estimated annual yield of 7,200 kWh. With a 30% self-consumption rate, they use 2,160 kWh directly, saving approximately £627 per year on electricity bills. The remaining 5,040 kWh is exported, earning £252. Total annual benefit: £879. The system pays for itself in approximately 10–11 years, with around 15–19 years of profit thereafter.
Electricity prices have risen dramatically in recent years and experts predict continued increases. A solar PV system locks in a large portion of your energy costs and shields you from market volatility. Combined with generous government incentives available in many countries — including tax credits, rebates, and feed-in programs — the economics have never been better.
Our online solar calculator is an excellent starting point for financial planning and comparing scenarios. It empowers you to walk into consultations with solar installers already informed. However, for final system design, always consult a certified installer who can assess your roof's orientation, shading from trees or chimneys, structural capacity, and local grid connection requirements.
The calculator uses industry-standard performance ratios and irradiance data. Results are reliable estimates within a ±10–15% margin. Actual output depends on roof pitch, shading, panel quality, and inverter efficiency — factors best assessed on-site by a professional.
A self-consumption rate of 30–40% is typical for a household without battery storage. With a home battery system, rates of 70–80% are achievable. Higher self-consumption means greater savings per kWh generated, since avoided electricity costs are usually higher than feed-in tariff rates.
A battery storage system increases self-consumption significantly and reduces grid dependence. However, it adds upfront cost. Our calculator lets you compare scenarios with and without storage so you can determine the most cost-effective configuration for your home.
Yes, the tool works for both residential and small commercial installations. For large commercial or industrial systems exceeding 50 kWp, we recommend supplementing this calculation with a detailed professional energy audit, as depreciation, tax treatment, and demand tariffs play important roles.
Most modern solar panels carry a 25–30 year performance warranty, guaranteeing at least 80% of rated output after 25 years. The actual lifespan is often longer. This makes solar one of the few investments that continues generating returns well beyond the payback period.