Free solar simulator: estimate your generation in 5 minutes

What is a solar simulator?

A solar simulator is a tool that calculates what a photovoltaic installation would generate at your home, and usually what that generation means in economic terms. It answers the question every household asks before investing: “Is solar worth it in my case?”

To answer precisely, a simulator needs to know two things: the sunshine at your location (how much energy your panels will generate, hour by hour) and your consumption profile (when and how much electricity you use). By cross-referencing these two curves, it determines what share of the generation you will consume directly (self-consumption) and what share will be exported to the grid.

The problem: most online simulators settle for monthly averages and generic ratios. They estimate, for example, that you will self-consume “70%” of your generation, without taking into account your hours at home, your appliances or your real profile. The result is a rough estimate, often very optimistic, which can distort your investment decision and/or lead you to believe in unrealistic results.

The calcul-solaire.fr simulator takes a different approach to the problem: it works with real weather data and a detailed consumption profile built from what you declare, before cross-referencing these data hour by hour over a full year (8,760 hours). The result is an individualised estimate, not a generality.

The 5 steps of our simulation

Here is what happens behind the scenes when you run a simulation on calcul-solaire.fr.

1. Retrieving real weather data: We query PVGIS 5.3 (European Commission) to obtain 8,760 hours of solar irradiation, temperature and wind for your exact location. These are TMY (Typical Meteorological Year) data, compiled from satellite measurements over 10 to 20 years.
2. Breaking down your consumption: Your declared annual consumption is broken down into 9 categories (heating, hot water, household appliances, electric vehicle, pool, lighting, multimedia, cooking, refrigeration) based on your answers. If you do not know the power ratings, ADEME data comes into play and produces the closest possible estimate.
3. Generating the hourly profile: Each category is turned into an hourly curve over 8,760 hours, taking into account your presence habits (working and away during the day, remote worker, retired, family), seasonality and the specific characteristics of each appliance.
4. Hour-by-hour cross-referencing: Hourly generation and hourly consumption are compared for every hour of the year. This cross-referencing is what precisely determines self-consumption, export to the grid and import from the grid.
5. Calculation or optimisation according to your goal: Two options are offered: either you choose the system size you want to test, or you opt for an automatic suggestion. The simulator then tests several system sizes (from 0.5 kWp to 12 kWp) and selects the one that best matches your goal: maximum financial return, a balance between financial return and coverage, or energy self-sufficiency.

Weather data: PVGIS, the European reference

The quality of a solar simulator depends first of all on the quality of its weather data. We use PVGIS 5.3 (Photovoltaic Geographical Information System), developed and maintained by the Joint Research Centre of the European Commission.

What exactly is PVGIS?

PVGIS is a solar irradiation database built from satellite measurements over 10 to 20 years (SARAH-2/3, NSRDB and ERA5 databases). For every geographical point in Europe (and beyond), PVGIS provides a TMY (Typical Meteorological Year): a year of 8,760 hours that represents the “typical” weather conditions of the location.

It is the source used by professional engineering consultancies and certified installers to size photovoltaic installations in Europe. This is not an estimate: these are reference data consolidated by a public institution.

What a TMY contains

For every hour of the year, PVGIS provides:

• GHI (Global Horizontal Irradiance): the total solar irradiation received on a horizontal surface, in W/m²
• DNI (Direct Normal Irradiance): the direct component of the radiation
• DHI (Diffuse Horizontal Irradiance): the diffuse component (cloudy sky, reflections)
• Air temperature: used to calculate the loss of panel efficiency caused by heat
• Wind speed and humidity

Cache and reliability

To keep the simulation fast while respecting the European Commission's servers, PVGIS data is cached with a precision of 2 decimal places (roughly 1 km resolution).

Personalised consumption profile

The second key input of the simulator is your consumption profile. Rather than using a generic ratio (“a French household uses X kWh/year”), we build an individualised hourly profile in two stages.

Stage 1: breakdown into 9 categories

Starting from your declared annual consumption and your answers (type of heating, number of people, energy performance certificate (DPE) of the home, appliances present), the simulator breaks your consumption down into distinct categories:

• Heating
• Domestic hot water (DHW)
• Electric vehicle
• Pool
• Household appliances, cooking, lighting, multimedia, refrigeration

This breakdown is essential: a kWh of heating (consumed in winter, at night) behaves nothing like a kWh for the washing machine (which can be scheduled during the day). Treating consumption as a single block would lose all the finesse of the hourly cross-referencing.

Stage 2: generating the hourly profile (8,760 h)

Each category is then turned into an hourly curve over the year, taking into account:

• Your occupancy profile: 5 types are supported: working and away during the day, partial remote working, full-time remote working, retired, family with children. Each one changes the hourly distribution of consumption.
• Seasonality: heating is concentrated in winter, the pool in summer, lighting in winter evenings.
• The specific schedules of each appliance: the water heater peaks in the morning and evening, the fridge runs 24 hours a day, the EV charges according to the chosen mode (off-peak hours, solar, mixed).

Two levels of precision for your profile

To feed this breakdown, we offer two consumption calculators to choose from, available during the simulation:

Hour-by-hour cross-referencing: the real difference

One of the central steps of our simulator, and what sets it apart from conventional tools. For each of the 8,760 hours of the year, we compare the solar generation with the household's consumption.

How does it work in practice?

For each hour h of the year:

• If generation > consumption: the excess is the surplus (exported for free, or sold at 0.011 €/kWh, or stored in a battery if there is one)
• If consumption > generation: the shortfall is imported from the grid (and therefore paid for according to your electricity contract, for example at 0.2001 €/kWh)
• The common part (generation = consumption) is the direct self-consumption: this is what generates the maximum saving

Why monthly averages get it wrong

A monthly-average simulator would say, for example: “in June, you generate 600 kWh and consume 500 kWh, so you have a surplus of 100 kWh”. In reality, a large part of those 500 kWh is consumed in the evening and at night, when generation is zero. The real surplus is much larger (and self-consumption much lower) than the average suggests.

What sets us apart from other simulators

We are not the only ones to offer a free online solar simulator. But our technical approach is significantly different from most of the tools available. Here is a factual comparison:

Why this difference matters

Two simulators can display the same figure for annual generation (it is physics, the irradiation is the same). Where the results can diverge is on self-consumption, savings and the payback period: the indicators that determine your decision to invest.

A simulator that overestimates self-consumption by 15% will lead you to believe that your savings will be 200 to 400 €/year higher than they really are, and that your payback period will be reached 2 to 4 years sooner. It is this precision, or the lack of it, that can make the difference between a well-calibrated investment and a disappointment.

Battery and advanced scenarios

The battery simulation is included free of charge. It genuinely simulates the charge/discharge cycle hour by hour, for 5 standard capacities (5, 7.5, 10, 12.5 and 15 kWh), and you can also enter a custom capacity (from 1 to 30 kWh) to test the exact model you have in mind.

How does the battery simulation work?

For every hour of the year, the battery simulation runs the following logic:

• Surplus hour (generation > consumption): the battery charges with the excess, within the limit of its remaining capacity and its charging power, with an efficiency of 95%
• Shortfall hour (consumption > generation): the battery discharges to cover the gap, within the limit of its state of charge and its maximum depth of discharge (90% DoD)

This is therefore not an empirical formula but a physical simulation that takes the real dynamics into account: on some summer days the battery fills and empties completely, on other winter days it only charges halfway.

What you get for each scenario

• Self-consumption gain: in percentage points and in extra kWh
• Additional annual saving: the euros actually saved thanks to the battery
• Annual cycles: number of complete charge/discharge cycles per year
• Financial projection table: with or without a battery, for comparison
• Battery cost incl. VAT: estimate based on market prices, adjusted to the chosen capacity

Virtual battery: the alternative with no hardware investment

Alongside the physical battery, the simulator includes a virtual battery module. The principle: your solar surplus is exported to the grid and credited to a virtual account with an operator (Urban Solar Energy, mylight150...). You get these kWh back later, in the evening or in winter, for a return fee (TURPE grid access charge + excise duty).

The simulator calculates the real financial return of this option, taking into account the subscription, the return fees and the change in tariffs over 5, 10, 15, 20 and 25 years, for each available operator. It is one of the few tools that gives you a costed comparison of a physical battery versus a virtual battery.

25-year financial projection

The payback period is not calculated by multiplying the first year's saving by 25. Two opposing phenomena interact over time, and our simulator factors them in year by year.

Panel degradation

A solar panel loses on average 0.5% of efficiency per year (NREL data on 54,000 systems). After 25 years, your installation still produces about 88% of its initial capacity. The real lifespan of panels generally exceeds 30 years.

Rise in the electricity price

The price of electricity rises by 3% per year on average over the long term. Each self-consumed kWh will therefore be worth more tomorrow than today. This is a factor that improves the financial return and that linear simulations ignore.

Cash flow year by year

Our financial projection calculates, for each year n (from 1 to 25):

Saving in year n = year 1 saving × (1 − 0.005)ⁿ⁻¹ × (1 + 0.03)ⁿ⁻¹

The first factor (degradation) reduces generation. The second (tariff inflation) increases the value of each kWh. Over 25 years, inflation wins out: your annual savings rise slightly over time, even though generation declines.

Indicators provided

• ROI (return on investment): number of years needed to pay back the installation
• Net profit over 25 years: total cumulative savings minus the investment cost
• NPV (Net Present Value): the cash flows discounted at the discount rate
• IRR (Internal Rate of Return): the real return on your investment, comparable to a financial investment

Everything is included, free of charge

The simulation first provides the optimal system size, the estimated savings, the self-consumption rate and the payback period. That is enough to know whether solar makes sense in your case.

To refine your project before contacting an installer, the advanced analysis tools are also included, with no payment and no sign-up:

Frequently asked questions about the simulator