Free Online Calculators
Calculate yield, self-consumption & annual savings
This solar calculator estimates the annual yield, self-consumption, grid feed-in, savings and feed-in revenue of a photovoltaic system from system size, orientation, consumption, battery, electricity price and feed-in tariff. The specific yield is preset to 1,000 kWh per kWp and can be changed for your site. It does not ask for the system price; divide the price by the total annual benefit for a rough payback time.
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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.
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.
Before you invest in a solar photovoltaic (PV) system, you want to know how much electricity it will produce and how much of it you can use yourself. This free solar calculator estimates both from seven inputs: system size, specific yield, annual consumption, battery capacity, roof orientation, electricity price and feed-in tariff. No engineering background is needed, and the result appears as soon as you type.
The calculator does not ask for the price of the system, so it shows no payback period or ROI. For a rough payback time, divide the system price by the total benefit per year.
Enter the peak power in kilowatt-peak (kWp); residential systems are often between 4 and 12 kWp. Then choose the roof orientation and check the specific yield in kWh per kWp and year. It is preset to 1,000 kWh/kWp, a rough value for a well-tilted south roof in the UK or Central Europe. Replace it with the figure for your site from PVGIS, the free tool of the European Commission's Joint Research Centre, or from the Global Solar Atlas; sunnier regions reach considerably more. The calculator multiplies the specific yield by 0.9 for south-east or south-west, 0.85 for a flat roof and 0.75 for east or west.
Enter your annual electricity consumption in kWh from your bills and the battery capacity in kWh (0 if you have none). Without a battery the calculator assumes that you use 30 % of the yield yourself at 3,000 kWh consumption, one percentage point more or less for every 1,000 kWh above or below, and never more than 40 %. Each kWh of battery adds 5 points (30 at most); the share is capped at 85 % and can never exceed your consumption. This is a simplified model: with a large battery relative to your consumption it can show an autarky close to 100 %, which real households rarely reach.
Enter your electricity price per kWh and the feed-in or export tariff you receive for each exported kWh. Both fields and all amounts are shown in euros.
A household plans an 8 kWp system facing south and keeps the preset 1,000 kWh/kWp. It uses 4,200 kWh a year, pays €0.30 per kWh, receives €0.08 per exported kWh and has no battery.
The calculator shows an annual yield of 8,000 kWh. It estimates 2,496 kWh of self-consumption (31 % of the yield), which saves about €749 a year. The other 5,504 kWh go to the grid and earn about €440. The total benefit is about €1,189 per year; the household still buys 1,704 kWh for about €511, and the autarky rate is 59 %. If the system costs €12,000, a rough payback time is 12,000 ÷ 1,189 ≈ 10.1 years. With a 5 kWh battery the calculator raises self-consumption to the full 4,200 kWh and shows 100 % autarky, which real households do not achieve; treat battery results as an upper bound.
Every kilowatt-hour you use yourself replaces one you would otherwise buy at the retail price, which is usually much higher than the feed-in tariff. That is why self-consumption drives the savings. Incentives, tax rules and export tariffs differ from country to country and change often, so check the current conditions with your government or energy supplier.
This online solar calculator is a good starting point for comparing scenarios, for example different system sizes or with and without a battery. It helps you walk into consultations with installers already informed. For the final system design, always consult a certified installer who can assess your roof's orientation and pitch, shading from trees or chimneys, structural capacity and local grid connection requirements.
It works with simple assumptions: the specific yield you enter (preset 1,000 kWh/kWp), flat reductions for other orientations and a simplified self-consumption model. The results are rough guides, not a yield forecast. Roof pitch, shading, system losses and your daily load profile are not modelled, and for large systems the real self-consumption is often lower than the estimate. The closer the specific yield matches your site, the better the yield estimate.
Without a battery, households typically use around a third of their solar output directly; the calculator lands between roughly 30 and 40 % depending on consumption. A battery raises the share. Higher self-consumption means more savings per kWh generated, because the electricity price you avoid is usually higher than the feed-in tariff.
A battery increases self-consumption and reduces grid purchases, but it adds cost. Enter 0 and then your planned capacity and compare the total benefit per year: the difference is what the battery earns in the calculator's model. Set that against the battery's extra price, and keep in mind that the model is optimistic for large batteries.
For a first estimate, yes. The self-consumption model is built for households, though; businesses that use most of their power during the day usually reach higher self-consumption than the calculator shows. For larger commercial systems, add a professional energy assessment that covers tax treatment, demand charges and grid connection.
Most modern solar panels carry a 25-year performance warranty, typically guaranteeing around 80 % or more of the rated output after 25 years. Inverters usually need replacing once during that time. A well-maintained system can therefore keep saving money long after it has paid for itself.