Swiss solar calculator.

Start with the right data

The address provides context, but it alone does not describe the roof. Check usable area, orientation, slope, chimneys, skylights, trees, neighboring buildings and condition of roofing. An aerial view may miss an obstacle or interpret an annex as a main roof. The calculation should indicate which data is measured, which is estimated and which areas have been excluded.

On the consumption side, an annual bill is a first benchmark. Monthly data shows seasonality; hourly or quarter-hourly data show whether the household consumes during production. Heating, hot water, heat pump, charging station, swimming pool and teleworking are significantly changing self-consumption. If your profile is going to change, calculate a current scenario and a future scenario instead of silently replacing a data point with a national average.

• Retain the date and source of each data entered.
• Separate observed consumption, forecast consumption and growth hypothesis.
• Note shadows and non-installable parts of the roof before comparing prices.

Production: look at the curve, not just one number

An estimate of annual production is useful for a first framing, but it can hide a weak winter, a loss of shade or an east-west orientation. Ask for production per month and the main losses: temperature, dirt, cables, inverter, shadows and availability. A lower but explained estimate is better than a high number without assumptions. Always compare the number of modules, their power, the surface area and the simulated production.

The reference weather is not a guarantee for the following year. A very sunny year does not prove that the system will always produce the maximum, and a weak year does not necessarily mean a fault. The calculator must therefore provide a range or at least a conservative scenario. When requesting a quote, convey the same assumption to each installer to compare their technical differences rather than different weather bases.

Self-consumption and injection

Self-consumption is the portion of solar electricity consumed on site. It depends on the time, the power of the devices and the ability to move certain loads. Self-sufficiency is another measure: it indicates how much of your total consumption is covered by your solar. The two percentages should not be confused. A house can self-consume a large part of its production while still needing the network in the mornings and evenings.

The remuneration of the surplus depends on the network operator and the applicable rules. In the calculation, separate the value of a kilowatt hour consumed on site from the value of a kilowatt hour injected. Add the price of energy, the network components that remain due and any metering costs. If a rate changes, you will be able to adjust a cell without redoing the entire simulation. This transparency makes the result more sustainable.

Net cost, aid and financing

A calculator must present the gross cost before displaying assistance. The gross cost includes modules, structure, inverter, cabling, protections, electrical work, roof access, connection and commissioning. Optional items such as the battery, terminal or roof renovation must remain separate. An estimate that mixes them makes it difficult to compare with an actual quote.

Pronovo, cantonal programs, municipalities and taxation do not have the same rules or the same timetable. Possible help should be shown as a guess until confirmed for address and project type. Likewise, a tax benefit depends on your situation and should not be presented as a guaranteed refund. Calculate the return with confirmed help, then separately show a favorable scenario.

Compare scenarios without moving the goalposts

To compare two offers, keep the same roof, the same consumption profile, the same price and the same period. Change one variable at a time: number of modules, orientation, battery, control or price. If an offer shows a better return, check if it assumes greater self-consumption, a different take-back price or no replacement cost. The table should show the hypotheses and not just the conclusion.

Calculate at least one minimal variant, one balanced variant, and one evolving variant. The minimum variant shows the entry cost; the balanced variant meets your use; the scalable variant retains a possibility for the battery, the terminal or the heat pump. This approach avoids choosing an oversized facility for fear of missing a future opportunity, while also avoiding closing a reasonable expansion.

Questions to ask after the result

After a simulation, ask the installer what elements he would confirm on site. He must be able to explain the condition of the roof, distances, shadows, chains, inverter, monthly production, protection, connection and deadline. Also ask what happens if production is lower, if the trade-in price changes or if part of the roof is excluded. A useful estimate produces a checklist, not a false sense of precision.

Keep the file or scenario capture with the date. When you receive an offer, compare its assumptions to those of the calculator. Deviations are not necessarily an error: they can come from a more precise roof measurement, a different orientation or a stricter shading model. The important thing is that the discrepancy is explained and you know which assumption to use for your decision.

Data, confidentiality and limits

If a map or solar potential tool uses an external service, check what data is sent and when. An address, roof position and consumption profile can be sensitive. The calculator must explain what is stored, what remains in the browser and what is transmitted to a map or data provider. This information is a condition of trust, especially when the result then suggests a commercial contact.

Finally, no simulation replaces an electrical, structural or administrative control. It does not guarantee an invoice amount, a return period, a price or a subsidy. Use it to raise the right questions, then have the project confirmed by a detailed offer and by the competent organizations. The best calculator is the one that makes its limits visible and improves the quality of the conversation with the installer.