Rooftop solar potential and how homes are heated

Many roofs, few residents

The rooftop potential indicator estimates how much electricity the roofs of a municipality could generate in a year. Divided by the number of residents, it shows how much roof each person has to share. Montagny-près-Yverdon has the highest potential per inhabitant at 40,810 kWh/inh., followed by Ried bei Kerzers at 39,502 kWh/inh., while the median municipality stands at 9,356 kWh/inh., far below both.

In absolute terms the largest cities lead the table. Zürich could generate 1,133 GWh/year, Bern 561.0 GWh/year and Basel 545.6 GWh/year, simply because they have so many roofs. Shared among their residents the same roofs give little: Bern has only 4,049 kWh/inh. for each of its residents.

The bottom of the table is dominated by dense urban municipalities. Geneva has only 1,990 kWh/inh., Zürich has 2,571 kWh/inh. and Basel has 3,030 kWh/inh., each well below the median. Apartment blocks put many people under each roof: single-family houses make up just 11.3% of residential buildings in Geneva and 26.7% in Zürich. Villages of detached houses such as Amlikon-Bissegg reach 19,571 kWh/inh., far above the figure for Zürich.

At the top the picture is rural and often alpine. Rougemont is ranked 3 of 1,810, Rheinwald ranked 4 of 1,810 and Obergoms ranked 5 of 1,810, and holiday homes make up 61.1%, 64.5% and 79.1% of their dwellings. Roofs of holiday homes count in the potential while their owners are not counted as residents, so the figure per resident is high where many homes are used only part of the year.

Panels do not follow the roofs

Installed capacity tells what has been built. Installed photovoltaic capacity per 1,000 inhabitants has a median of 1,134 kW across municipalities, and the leaders are far above it: Liesberg reaches 6,678 kW, Neuendorf reaches 5,492 kW and Amlikon-Bissegg reaches 5,240 kW.

The municipalities with the most roof per resident are not always those with the most panels. Montagny-près-Yverdon is ranked 28 of 1,806 on installed capacity, a strong position, in line with its high potential, and Ried bei Kerzers is ranked 10 of 1,806. Three alpine municipalities break the link: Rougemont is ranked 824 of 1,806, Rheinwald is ranked 1,435 of 1,806 and Obergoms is ranked 1,713 of 1,806, although each of them has a potential per inhabitant far above the median.

Cities lag on both counts. On installed capacity Zürich has 224.2 kW, Bern has 331.9 kW, and Geneva has only 85.3 kW, far below the median. Mid-sized rural municipalities show the other end of the scale: Liesberg has 6,678 kW, Neuendorf has 5,492 kW and Amlikon-Bissegg has 5,240 kW. Across the country the two rankings are only partly related, so a high place in one table is no promise of a high place in the other.

Where heat pumps lead

Among residential buildings, the median municipality has 13.7% heated mainly by a heat pump. The top of the national table is almost a map of one canton: Lufingen has 63.4%, Aesch (ZH) has 59.3%, and Niederweningen and Winkel are close behind. All of the five highest shares are found in the canton of Zurich.

Large cities split into two groups. Two lakeside cities show how rare heat pumps can be: Geneva has 1.4% and Lausanne has 2.9%. Winterthur reaches 19.0% and St. Gallen reaches 20.1%, more than either of them. In Geneva, 88.8% of residential buildings have an oil or gas heating system.

The median municipality has 53.5% of its residential buildings on an oil or gas system, and the range is wide. Lavizzara has 5.4%, while St. Moritz has 96.7%. Between these two sit mountain villages with wood stoves and boilers, lowland towns with heat pumps and a few places served by district heating.

Wood, district heat and altitude

Wood is the fuel of the hills. Trub has 82.2% of its residential buildings heated with wood, with Trachselwald at 77.1% and Ochlenberg at 75.0%. All three lie in the canton of Bern. The median municipality stands at 12.4%.

Altitude alone does not decide. St. Moritz has an average altitude of 2,292 m, yet it has 96.7% of residential buildings on oil or gas, the highest share of any municipality, and only 0.5% on wood. Bregaglia, with an average altitude of 2,217 m, has 13.1% on oil or gas and 43.8% on wood.

District heating is rare in most municipalities, with a median of 1.4%, but a few rely on it for most buildings: Aire-la-Ville reaches 78.6%, Würenlingen reaches 78.2% and Böttstein reaches 65.1%. Big cities sit in the upper part of the table, with Basel ranked 14 of 1,806 and Zürich ranked 131 of 1,806.

How to read these figures

Each indicator answers a different question. Rooftop potential describes what the roofs could produce, not what is planned. Installed capacity is the registered output of plants relative to the number of inhabitants, so a municipality with many holiday homes and few residents can look low even when its roofs are well used. Heating shares count residential buildings, not households, and show the main system of each building.

No figure reflects the quality of a single roof or boiler, and they should be read as portraits of whole municipalities. A town with a modest ranking on one of them can still lead on another.