What the gap between two quotes for the same roof reveals

When several installers price the same roof, from the same file, the prices should look alike. They do not. On projects that went through the SOLARSPLIT comparison in 2026, the gap between the lowest and the highest offer for the same roof regularly exceeds 20%, and sometimes reaches 40%. Here is what those gaps reveal, on a few real cases made anonymous, and how to read them to your advantage.

Case 1: the same capacity, a 38% gap

A villa in Vaud, a roof without a home battery, three offers for exactly 23 kWp. Gross prices: 32’200, 37’000 and 44’600 francs. Same capacity, same number of panels, same roof. The gap comes from three things: the equipment, panels and inverter from different ranges with different warranties, the services included, scaffolding, connection to the electrical panel, Pronovo file and notification to the municipality charged or not, and the margin, quite simply. The most expensive offer was not the best equipped. The cheapest offer included everything.

This case is the most instructive, because it isolates what the price does not say: at equal capacity, it is the list of what is included that explains the gap, and it can only be read in detail.

Case 2: the capacity changes from one offer to the next

A house in Neuchâtel, with a home battery. Three offers: 26.6 kWp with 6.9 kWh of storage, 27.5 kWp with 18 kWh, and 18.8 kWp with 20.7 kWh. Prices from 43’500 to 51’300 francs. Here, comparing the totals makes no sense: the third offer has a third fewer panels and three times more battery than the first. Each installer sized according to their reading of the roof and the consumption, and two of them proposed a battery that the file did not call for.

This case says one thing: a quote answers the question the installer asked themselves, not necessarily yours. The first job is to bring all the offers back to the same capacity and the same equipment, or to have them redone on a common specification.

Case 3: the battery makes the price

A house in Valais, three offers around 25 kWp, all with a home battery, from 10 to 14 kWh. Prices from 34’700 to 43’800 francs. Brought back to the net kWp after one-off remuneration, they range from 1’440 to 1’930 francs. A third of the gap comes from the battery capacity, the rest from the equipment and the services. Without isolating the battery, you do not know whether you are comparing roofs or storage units.

Case 4: the same equipment, almost the same price

A house in Neuchâtel, five offers with the same 13.8 kWh battery, four of them between 13.4 and 15.7 kWp for 33’000 to 43’200 francs. Brought back to the net kWp, four offers sit between 2’650 and 2’980 francs. The fifth proposed only 7.2 kWp, with the same battery, at 28’000 francs, or 4’200 francs per kWp: a battery oversized for a small roof, and a price per kWp that says so straight away.

When the equipment is comparable and the scope the same, the offers tighten up. It is the sign that a well-framed call for tenders does half the work.

The measure that makes everything comparable

Three operations, in order:

1. Bring back to the scope. Same capacity to within 10%, same presence or absence of a battery, same services included. What is missing from one offer is added to its price, what is surplus in another is taken off.
2. Calculate the price per net kWp: gross price, less the one-off remuneration, divided by the capacity. In 2026, an added installation without a battery on a single-family house sits between 1’500 and 2’500 francs per kWp, decreasing with size. Our article on the cost of an installation gives the context.
3. Ask everyone the same questions. Make and model of the panels and the inverter, warranties and who carries them, scaffolding, connection, Pronovo file, notification to the municipality, installation lead time, payment terms. Our guide to reading a solar quote lists each line.

What the gap says about the installer

An offer clearly more expensive than the others at equal scope is not necessarily bad: it may carry top-of-the-range equipment, a long warranty, an in-house team rather than subcontractors. An offer clearly cheaper deserves a check of what is missing. In both cases, it is the justification that counts, and an installer who explains it willingly is generally the one you go with.

That is exactly what the SOLARSPLIT process does: the installers respond to the same file, the offers are brought back to the same measure and scored on the same criteria, and an adviser explains the gaps before you choose. The starting point is the free online study, which sets the specification everyone responds to.