04.11.2025 10:30 bis 04.11.2025 15:00

The power of the Sun

Swiss International School Basel

Looking at the Sun and its Significance for Our Planet
The sun is vital for life on Earth. Without it, our planet would be dark, frozen, and lifeless.
It is a gigantic ball of hot plasma. Inside, nuclear fusion processes take place: two atomic nuclei merge to form a new nucleus. When hydrogen fuses into helium, an enormous amount of energy is released. The more helium that is produced, the brighter and warmer the Sun shines.

Compared to Earth, our Sun is huge – but in relation to other stars, it is actually rather small. If it were hollow, about one million Earths could fit inside. With a mass of 1,989,000,000,000,000,000,000,000,000,000 kg, it accounts for 99.86% of the total mass of our solar system. To visualize this in class, we use a blue push pin to represent Earth and a yellow foam ball to represent the Sun. The to-scale distance between them would be about ten meters in the classroom.

The Sun moves around the center of the Milky Way, while the Earth orbits the Sun. The Earth’s rotation and the tilt of its axis cause day and night, as well as the seasons. Sunlight takes 8 minutes and 20 seconds to reach us. Heat, however, cannot be transferred directly across this distance – it is only generated on Earth when light is absorbed and converted into thermal energy.

The Sun as the Source of Almost All Energy 
Virtually all forms of energy on our planet originate from the Sun: Without the Sun, there would be no photosynthesis, no plant growth, no biomass, no wood, no coal, no oil, and no natural gas. Even wind and hydropower exist thanks to solar energy: without sunlight, there would be no evaporation, no water cycle, and no air movement.

Warm air rises (creating thermals and low pressure), while cool air sinks (heating up and forming high pressure). The uneven heating of different – such as rock, water, or forest – and their varying heat capacities cause air currents, including sea and land breezes.

Experiments and Discoveries
What happens on Earth when the Sun shines? Using a tree trunk with annual rings, we explore the concept of photosynthesis. We model the water cycle with a transparent bag containing a little water, warmed by sunlight. We demonstrate the formation of wind with a tealight and a small pinwheel. Afterwards, we transfer these three phenomena onto a worksheet and match them with their corresponding energy sources.

The Sun’s power is impressive: In Switzerland, solar radiation at noon under direct sunlight reaches about 1,000 W/m². Over a year, the Sun provides roughly as much energy per square meter as 100 kg of heating oil. Overall, the amount of energy the Sun emits to Earth is more than 5,000 times greater than humanity’s total energy demand. It is therefore up to us to make better use of this energy.

Using Google Earth, we explore large solar power plants and how they look. On a swisstopo map, we discover that our school roof is rated “very suitable” for a photovoltaic installation, with an estimated annual yield of around CHF 17,240. After comparing the output of large photovoltaic systems in Basel (Grosspeter Tower, Messe Basel, St. Jakob Park, and Multiterminal 4 in the Rhine Port) with that of the run-of-river power plants at Riehenteich and Birsfelden, we build our own small PV device. The miniature airplane we construct can already fly in circles under diffuse light – meaning it works even without direct sunlight.We then learn about the structure and function of a solar cell: what materials it is made of, where the raw materials come from, and how electrical energy is generated through photovoltaics (from the Greek phōs = light and volt = unit of electrical voltage).

The Power of the Sun in Action
In the afternoon, lessons take place outdoors. Fortunately, the sky is almost cloudless, because solar thermal energy, unlike photovoltaics, requires direct sunlight. With magnifying glasses and a parabolic mirror, we focus sunlight until a newspaper catches fire. Equipped with hand mirrors, the whole class again imitates Planta Solar 20, making a balloon pop using nothing but sunlight. A real solar-thermal power plant works much like a conventional steam power plant – except that concentrated sunlight replaces fossil fuels. At the top of the tower, temperatures can exceed 1,000°C. Molten salts act as heat carriers, storing energy and allowing operation even after sunset. Parabolic trough power plants reach slightly lower temperatures. Curved mirrors focus incoming sunlight along a focal line. We even mounted such a tube collector with mirror onto an e-bike as a mobile hotdog steamer! To finish, everyone enjoys a warm sausage or vegetarian option in a bun – of course, heated by the power of the Sun.