Solar panels: how much they produce in your municipality

A solar system is described by two numbers that are often confused. kW (more precisely kWp, kilowatt peak) tells you how big it is: 3 kW is a small home system, about 15 square metres of panels. kWh tells you how much energy it produces in a year, and that is the number that matters for your bills. Between the two lies the local sunshine: the same 3 kW system produces more in Cagliari than in Bolzano, and more on a south-facing roof slope than on an east-facing one.

To measure the sun at a precise point, the reference tool in Europe is PVGIS, from the European Commission's Joint Research Centre. Version 5.3 uses satellite solar radiation data from 2005 to 2023 and takes the mountains on the horizon into account. Every figure in this guide comes from it.

Output of 1 kW in ten cities

We asked PVGIS 5.3 for the output of 1 kW of crystalline silicon panels, with the best tilt and orientation, 14% system losses and calculated horizon, in the centre of ten cities. These are the same assumptions our report uses for its starting estimate.

From Bolzano to Florence the cities sit between 1,340 and 1,380 kWh. From Rome southwards the figure rises above 1,480, and Cagliari reaches almost 1,600: about 18% more than Rimini. The gap is widest in winter: in December one kW produces 93 kWh in Cagliari and 55 in Bolzano. In summer the cities come much closer together.

Within the same municipality the numbers can vary a lot. In an Alpine valley the mountains cut hours of winter sun, and PVGIS sees them. The city centre used here is only a reference point.

Three systems, two cities

Multiplying by the size gives the output of the system. Here are Milan and Palermo, with panels in the best position:

Month by month the curve differs a great deal between summer and winter. A 3 kW system in Milan produces about 470 kWh in July and 200 in December; in Palermo 500 and 255. For comparison, the typical household that the Italian energy regulator ARERA uses for its price comparisons consumes 2,700 kWh a year. Without a battery, though, much of the energy arrives in the middle of the day, when the house is often empty: what is not used straight away goes into the grid and is paid for at less than it costs to buy.

The roof slope matters as much as the city

The figures above are for panels at the best tilt and orientation, which on a real roof you do not get to choose: the panels follow the slope. Pitched roofs in Italy typically have a gradient of about 30%, or 17 degrees. At that pitch PVGIS gives these values for 1 kW:

In Milan an east or west-facing slope loses about a fifth compared with the best position, in Palermo about a seventh. And an east-facing slope in Palermo produces slightly more than a south-facing one in Milan. North-facing slopes yield even less, and the report leaves them out.

What PVGIS does not see

PVGIS knows the sun, the temperature and the outline of the mountains. It does not know about nearby buildings and trees: a taller block to the south or a large tree can take away much more than the estimate suggests. It does not know what the roof looks like, whether there are chimneys, dormers or skylights, or what condition the roof covering is in. The output it calculates is an average over many years: a cloudy year may fall below it, a clear one above.

Condominium rules and landscape protection

In a block of flats, article 1122-bis of the Italian civil code allows each owner to install a system serving their own flat on the flat roof, on other suitable common surfaces and on parts they own. If common parts need altering, the building manager (amministratore) must be told, and the owners' meeting can require different methods or precautions for the stability, safety and appearance of the building, and share out use of the roof among those who want to install. Before buying it is worth asking the building manager whether someone has already taken up the roof and what the condominium rules say.

If the house lies in an area with a landscape restriction or in a historic centre, ask the municipality or your surveyor whether the panels need authorisation: it depends on the type of restriction, the rules of the plan and how the panels are mounted. The report says whether the area falls within a restriction on the Ministry of Culture's map.

Running the calculation yourself on PVGIS

The tool is free, in English and Italian, at re.jrc.ec.europa.eu/pvg_tools:

1. Type the address in the box at the top left, or click on the map.
2. Check that "Calculated horizon" is ticked, so the mountains are taken into account.
3. In the grid-connected tab, enter the installed peak power in kWp and the system loss (14% is the value offered).
4. To compare the results with this guide, leave the mounting position on "Free-standing", as the report does. Then enter the slope and azimuth of the roof. Azimuth is measured in degrees from south: 0 is south, -90 east, 90 west. If you want the theoretical maximum, tick "Optimize slope and azimuth".
5. Press "Visualize results": you get the yearly output, the month-by-month chart and how much it varies from year to year.

What the report shows

Type the address on the site: you immediately see, for free, the liveability index of the area. In the full report the block "Sun and solar panels" starts from the PVGIS 5.3 estimate for 1 kW at the exact point, with the monthly output and the recommended tilt. Then it looks at the building's roof: from the building outline on open maps it works out whether the roof is gabled, hipped or flat, asks PVGIS how much each slope yields in its own direction, leaves out the north-facing ones and calculates how many kW fit, the first-year output, the cost and the years needed to recover it. Every assumption is written next to the figures, from the cost per kW (VAT included, no battery) to the share of energy used at home and the electricity price published by ARERA with the quarter it refers to.

The roof shape is derived from the outline, not measured: a site visit may find different slopes. In our sample report on a building in Rimini the roof comes out as hipped, with the two useful slopes facing south-east and south-west: about 12 kW fit, for about 14,900 kWh a year. The full method is in Sun and solar panels.

Sources

• European Commission, Joint Research Centre, PVGIS 5.3: values calculated on 26 September 2026 with PVGIS-SARAH3 data (2005-2023), crystalline silicon, 14% losses, calculated horizon, coordinates of each city centre.
• Codice civile, article 1122-bis, text on Normattiva.
• ARERA, electricity price for the typical household customer.