Solar energy: Inexhaustible – including in Switzerland

How it works

Solar energy, also known as photovoltaics, is based on the ability of certain materials to convert light directly into electricity. The underlying physical principle is called the photovoltaic or photoelectric effect.

Simply put, solar energy works like this: While light falls on the solar cells, they generate direct current from it. This means that light energy is converted directly into electrical energy. The individual solar cells are interconnected to form larger solar modules. The direct current generated is converted into alternating current by the inverter and can thus be consumed directly on site or fed into the power grid.

Do you want it in more complex terms? Here you go:

So-called semiconductors are used in solar technology like they are also used in the manufacture of computer chips. They owe their name to the fact that they can act as an electrical conductor and a non­conductor. ln a solar cell, the non-conductive material becomes a conductor when the electrons are released from the non-conductive crystal compound by the absorption of a photon (sunlight consists of these countless tiny energy carriers). The kinetic energy that they absorb forms the generated current. This is direct current, which is converted into alternating current by an inverter to make it suitable for the power grid.

Our solar energy


ln the summer of 2019, Axpo acquired 100% of the French photovoltaic company Urbasolar. In doing so, Axpo

significantly strengthened its position in the solar energy sector, Urbasolar being one of the most important solar companies in France. The new Axpo subsidiary, which currently employs 160 people, is headquartered in Montpellier in the south of France. The company also has offices in Toulouse, Aix, Nantes, Bordeaux, Vichy, Paris and La Reunion.

Urbasolar's portfolio currently includes operational photovoltaic systems with a total capacity of around 250 MW. Since 2006, Urbasolar has built over 500 photovoltaic systems. ln addition, the company has a

development pipeline of more than 1000 MW and offers maintenance, repair, as well as asset management services. In the future, Urbasolar's specific know-how will benefit all the country subsidiaries in their PV projects, including Switzerland.

Urbasolar plans, builds and operates PV systems. Most of the business will be realised in France. However, individual PV projects will also be developed or built outside France, for example, in French overseas territories. Urbasolar covers the following four business areas:

  • Ground-mounted systems: The company is a pioneer in this segment and has built numerous systems that are technological showpieces. Systems are also built in old quarries, in contaminated areas, former waste dumps, or even on an old racing track.
  • Parking canopies: These facilities are not only used to generate electricity, they also provide shade over car parks. As a general contractor, Urbasolar is one of the recognised market Ieaders in this field thanks to its extensive know-how.
  • Rooftop installations: To date, Urbasolar has converted over 2 million square metres of roof space on industrial, commercial and other buildings into PV systems.
  • Photovoltaic greenhouses: With dozens of hectares of greenhouses built or under development, Urbasolar has established itself as an industry benchmark. By developing innovative and efficient instruments for agriculture, the Axpo subsidiary helps to improve the competitiveness of agricultural enterprises while taking environmental aspects into account.

ln addition to development and construction, Urbasolar's business also includes services (maintenance and repair work) and asset management services, in particular for buyers of PV systems. Customers include public sector companies (postal services), industry (Airbus), logistics (Lidl), real estate (Bouygues) and retail (Carrefour).

Solar energy from the mountains

Axpo is planning the first alpine solar power plant in Switzerland: The facility will be built on the Muttsee dam wall of the Limmern pumped storage power plant. With the megawatt pioneering project, Axpo is driving forward the expansion of renewable energies in Switzerland and intends to supply important winter electricity in the future with the plant located at an altitude of nearly 2500 metres above sea Ievel. The reasons:

  • Thanks to its existing infrastructure, orientation and altitude, the Muttsee dam wall is exceptionally well suited for photovoltaics.
  • The plant will produce electricity on an area of 12,000 square meters with its 7,000 PV modules. About half of its electricity production will be generated in the winter half-year, i.e. the time of year when more electricity is consumed than is produced in Switzerland. A comparable system in the midlands would only produce a quarter of this winter electricity volume.

Solar plants on Swiss rooftops

With its subsidiary CKW, Axpo is firmly committed to the expansion of solar installations on Swiss rooftops. CKW offers solutions for homeowners and business customers.

Find out whether a solar plant is worthwhile for you here (German only).

Solar energy from A-Z

Photovoltaics and solar energy have many different aspects. You will find a quick summary to a few important keywords below (FAQ).

Solar energy in keywords

A solar cell is about the size of the palm of your hand and consists of two layers that are two to three tenths of a millimetre thick. Today, most solar cells are made of silicon. Their basic material, quartz sand, is available in sufficient quantities on earth - and silicon is considered environmentally friendly.

There are two types of solar cells: Crystalline and amorphous. Crystalline cells account for the largest share of global production. Monocrystalline solar cells are manufactured from pure silicon, which is withdrawn from a silicon melt in a time-consuming and costly process, pressed into bars, and then cut into discs up to 12 centimetres in diameter. All atoms are aligned equally in the monocrystal. The blue to black cells, which also come in different colours if desired, harvest up to 24 per cent of the solar rays in the Iaboratory; in practice, efficiency is 16 to 20 per cent.

Multi-crystalline solar cells consist of industrially produced polysilicon, and their production is significantly less expensive than monocrystalline solar cells. They are bluish in colour and their efficiency in practice is between 11 and 14 per cent.

Amorphous solar cells are less expensive and suitable for simple applications such as a garden fountain or on large house facades. In amorphous solar cells, the electricity generating layer is steamed onto a glass plate. The atoms are no Ionger deposited in a crystal structure, but in a disorderly (amorphous) manner instead. Relatively little silicon is needed for this process, which lowers the price. ln comparison with the 0.2 to 0.3-millimetre thick crystalline cells, these so-called thin-layer cells measure only 0.01 to 0.05 millimetres. The cells are brown or anthracite and have an efficiency of 6 to 10 per cent. On gloomy days, amorphous cells deliver more electricity than others - but their efficiency drops over the years.

When the sun shines, solar panels produce electricity. Logical, isn’t it? But even on less clear days, solar cells can produce electricity, although not at full capacity. This is comparable to our skin, which reacts to solar UV rays even when it is cloudy. Around 75 percent of the electricity generated by conventional solar systems installed in the lowlands is generated from May to September. What’s more: Solar plants do not produce electricity during the night. ln contrast to base load energy from hydropower or nuclear power, photovoltaic power is therefore only moderately predictable and controllable.

By the way: The share of photovoltaics in the Swiss electricity mix in 2018 was 1944 GWh, which corresponds to around 2.9 per cent.By the way: the share of photovoltaics in Swiss electricity production in 2018 was 1944 GWh, which corresponds to around 2.9 percent.

A typical solar panel (one square metre in size) made of commercially available silicon can generate an average of 180 W on a clear, sunny day in Switzerland. That's enough to run a Iaptop computer. A solar system consisting of several panels with a size of 20 square metres produces around 3600 kWh of electricity per year. In comparison: An average Swiss household consumes between 4500-5000 kWh of electricity per year.

As a general rule, the output of solar modules essentially depends on the amount of sunlight (global radiation/geographical location), on orientation (the more precisely the photovoltaic system is positioned at the optimum inclination angle to the south, the higher the yield) or on shade (from trees, chimneys, etc.). But of course the quality of the solar cells also has a significant influence on the overall performance.

A solar park is a large number of solar modules that are installed on fields or other large surfaces and feed the generated electricity into the grid. Sometimes they are referred to as solar farms or open space solar plants. ln a solar park, the solar modules are installed on approximately 3-metre high mounting systems, which are placed into the ground like fence posts. Rows of these mounting systems would be a typical feature of a solar park. Solar parks can be of any size. About 1.6 to 2 hectares of land are required for every megawatt (MW) of installed solar modules (around 4000 modules per MW).

Studies show that up to 67 TWh of electricity could be generated on rooftops and facades in Switzerland. This corresponds to around 110 per cent of annual electricity consumption in Switzerland. If other infrastructures (car parks, reservoirs, noise barriers) and other open spaces, such as those in already developed Alpine regions, were to be covered with solar panels, there would be an additional potential of 25 per cent. The sun could therefore become a major factor in Switzerland's energy supply. However, politicians would have to create incentives for this, i.e. design the market and the framework conditions in such a way that companies are prepared to make the necessary investments - also for large-scale plants. In addition, a strong expansion of photovoltaics requires large storage facilities, which do not yet exist, as well as grid expansion and grid reinforcement, especially at the lowest Ievel.

How much does electricity produced from photovoltaics cost? Thanks to increasingly cheaper solar modules, the production costs for solar energy are continue to drop. They are between 8 and 28 centimes/kWh depending on the size of the system. For comparison, the production costs for nuclear power plants are between 4 and 7 centimes per kWh – for large-scale hydropower they range between 4 and 9 centimes per kWh.

ln addition, the costs per kWh of electricity produced also depend to a large extent on the location, i.e. the local sunshine duration/radiation. In a normal year, the sunshine duration in Lugano is around 2100 hours, while in Glarus it is only around 1200 hours. Accordingly, more or less solar energy can be produced, which naturally has an impact on costs.

A market of the future

The development of the solar industry currently knows only one direction: Up. Prices for photovoltaics, on the other hand, have dropped steadily in recent years. In addition the importance of climate­ friendly energy production has grown. This mix has given solar energy a boost. Technology is also an important growth market for Axpo.

As part of the Energy Strategy 2050, some 25 TWh, or over 40 per cent of total electricity consumption in Switzerland, must be covered from renewable sources. The expansion of photovoltaics (PV) is becoming increasingly important. Photovoltaic (PV) systems on private homes and industrial building rooftops could play an important role, as well as PV systems in high alpine regions.

As Switzerland’s largest producer of renewable energies, Axpo is strongly committed to climate-friendly, C02-free electricity production. After entering the wind power business four years ago, Axpo is now also a major player in the solar energy sector. With the acquisition of the French project developer Urbasolar (for more information, see: Our plants), Axpo is entering a new international business segment, which is considered to have great growth potential everywhere.

In a video interview, Christoph Sutter, Head of the New Energies Division at Axpo, talks about the potential of solar energy:

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