Switzerland has a great deal of potential in solar energy, a potential it has failed to exploit to date. This is beginning to change as its nuclear reactor fleet ages and it is approaching the limits of its hydropower. Building-integrated PV and solarthermal heating systems offer very good potential.

Rooftop PV in Switzerland

Swiss photovoltaic generation per person 2016

In 2016, Switzerland reached 8th place in European ranking by electricity generation capacity from photovoltaics per person. Although ahead of solar-rich Spain, it produces less than half per capita compared to Germany, Italy and Greece.

Top ten photovoltaic electricity generators in Europe /kWh per person (2016):

1. Germany 465
2. Italy 372
3. Greece 364
4. Belgium 260
5. Malta 237
6. Czech Republic 202
7. Bulgaria 180
8. Switzerland 174
9. Spain 171
10. Luxembourg 170

Rooftop photovoltaic potential in Switzerland

Switzerland in 2016 generated 174 kWh per capita from solar panels. This is equivalent to less than one square metre of photovoltaic panel per person. If Switzerland used around 4% of suitable rooftops for photovoltaic installations, it could replace all non-hydroelectric power for household requirements for the future.

The average Swiss household consumes around 5.2 MWh of electricity per year. PV installations in Switzerland can produce about 1.2 MWh of electricity per square meter per year. This means that the average household needs 4.3 m² of rooftop solar panels to cover its electricity needs at current consumption rates. Since 60% of power is covered by hydropower, Swiss households actually only need 1.7 m² (c. 4% of available surface area) per household to replace nuclear power and obviate the need for fossil fuel power generation in household electricity consumption.

• Total Swiss household electricity consumption (2016): 19 TWh (32.8% of all electricity)
• Final consumption per capita: 7.0 MWh
• Final consumption per household: 5.17 MWh
• Final consumption per household per capita: 2.3 MWh
• Average PV generation at 15% efficiency: 3.3 kWh/m²/day or 1.2MWh/m² p.a.

Solar power generation in Switzerland is, after hydropower, the most adopted renewable energy form.

Swiss Solar Farms

In Switzerland, 174 kWh of solar power and 13 kWh of wind power were produced per capita in 2016, which is very small compared to the other European countries, ranking Switzerland at a poor 25th out of 29 for overall solar and wind renewable electricity generation. The frontrunner, Denmark, produces 12 times as much per head.

Solar insolation at any point of the Earth's surface has a maximum of about 1025 W/m², measured on one square metre perpendicular to sunrays. Since the Earth's surface is curved, the further a location is from the equator, the more surface area is required to achieve this irradiation - to be more precise, 1025 W is received by a surface area 1m x 1/(cosine of the latitude). The geometry of a curved surface is more complicated, but for the purposes of our calculation this is accurate enough. Switzerland lies at between 45.8° and 47.7°, or on average 46.75° (approximately at the level of Berne, which is at 46.5° North). The surface area equivalent (SA_eq) is on average for Switzerland: 1.0m x 1/(cos46.75) = 1.46m², meaning that each 1.46m² surface area parallel to the ground in full sunlight receives 1025 W/m² as a yearly average. Throughout the year, any point on the Earth's surface changes its orientation towards the sun, which gives rise to the seasons. Since the Earth's axial tilt is 23.4°, Berne's angle of inclination to incoming sunrays varies from 23.1° to 69.9°. This then suggests that Berne's SA_eq varies from 1.09m² in mid-summer to 2.9m² in mid-winter. In Palermo (38° north), the average SA_eq = 1.27m². In Berlin (52.3° north), SA_eq = 1.64m².

Given that Switzerland has a surface area of 41,285km² (41.29 x 10⁹m²), the total average irradiation is (41.29 x 10⁹) x cos(46.75°) x 1025 W/m² = 29.0 x 10¹² Watts = 29.0 TW. This means that the average total solar irradiation at noon on a cloudless day is 29 million megawatts. But how does this translate into total energy that is available over a year?

Intensity of solar radiation varies by season, cloud cover, and time of day. We can ignore the seasonal variation, because 29.14 TW is the average over the year. The number of hours of sunlight over Berne is around 42% of the 4380 daylight hours, or 1840 hours of sunshine per year (long-term average). Since the Sun moves across the sky during the day, its intensity on any surface area ranges from zero to full, or a rough average of about 50% of the maximum daily average. This means that we can count 920 full-insolation equivalent hours over a year.

Assuming Berne's insolation is the average for Switzerland, and a full-insolation hour in Switzerland provides 29.0 x 10¹² Wh over the whole country, then 920 hours provides 920 x 29.0 x 10¹² = 2.7 x 10¹⁶Wh in a year, or 27,000 TWh. By comparison, Switzerland consumed 58.24 TWh of electricity from all sources in 2016 (total generation was 61.6 TWh, and the excess was grid losses and trade imbalance). Solar insolation is 460 times electricity consumption. Obviously, not all of solar insolation can be converted to electricity, but if Switzerland can tap and effectively convert 0.22% of it, it would not need any other power source, and just 0.08% would replace all nuclear power.

The efficiency of the newest generation of silicon-crystalline solar cells is about 18%. This means that 18% of radiation is converted to electricity by a new, clean solar panel. Panels typically lose 20% of their efficiency over their 20 year lifespan, and are not always maintained optimally, so we can use 15% as an approximate average efficiency. This means that 27,000 TWh of solar insolation could be converted to about 4000 TWh of electricity, which is 69 times consumption. Incidently, this ignores that fact that there are more efficient ways of utilising solar energy, such as solar thermal (using the thermal energy directly for heating), and fuel generation.