Solar Energy

1. Solar Water Heater

Solar water heaters capture the sun's heat via thermal absorbers, often placed on roofs, which heat a heat transfer fluid. This fluid then transfers the heat to water stored in an insulated tank for hot water and heating. There are two main types of solar water heaters. Thermosiphon systems operate without a pump using natural convection; they are simple and reliable but require good sun exposure. Forced circulation systems are more efficient in cold climates as they use a pump to circulate the heat transfer fluid. Both systems are autonomous, durable, and require little maintenance. They offer reliable performance over many years.

2. Concentrated Solar Power Plant

Like a gas or coal power plant, a concentrated solar power plant feeds a steam turbine to produce electricity, but using sunlight as a heat source. Proven technologies include parabolic trough collectors, tower power plants, and linear Fresnel systems. Following the principle of burning mirrors, they can heat water to high temperatures. These technologies address short-term intermittency. Electricity generation can indeed be extended for several hours after solar radiation disappears, as the heated fluid has thermal inertia. Dynamic heat storage systems can also be integrated into the installations. Another advantage is the possibility of cogeneration, i.e., using also the generated heat. Concentrated solar power plants require a lot of maintenance and water, especially for mirror washing, and are only profitable in high irradiance parts of the world, such as deserts.

3. Photovoltaic

When photons from sunlight hit solar cells, they release electrons which, when evacuated, create a DC current. The electric current generated can be consumed locally by a device (such as a satellite) often coupled with a battery system. Electricity generated by photovoltaic installations can also be fed into the grid via an inverter that converts DC into AC current.

Photovoltaic Cells

1. Crystalline Silicon

Crystalline silicon photovoltaic cells are the most common cells in the solar panel industry today due to their efficiency and relatively low cost. They accounted for 98% of PV module production in 2023. Silicon is an abundant semiconductor material made from sand. Cells can be monocrystalline (20-25% efficiency), made from a single silicon crystal, or polycrystalline, made from multiple crystals. The latter were used in large-scale installations because, despite lower efficiency (18-21%), they were cheaper to produce. Recent innovations in monocrystalline cell production, durability, and efficiency have led to the near-total abandonment of polycrystalline cell manufacturing.

2. Thin Films

Unlike crystalline silicon photovoltaic cells, which use thick slices of silicon (cut from a block), thin films are made by depositing very thin materials layers (a few micrometres) on flexible or rigid substrates. This technology offers several advantages, including increased flexibility and reduced weight, allowing integration into various applications, including less resistant roofs and portable electronic devices. The main types of thin films include cadmium telluride (CdTe), copper indium gallium selenide (CIGS), and amorphous silicon (a-Si).

3. Organic Photovoltaic Cells and Dye-sensitised Solar Cells

Organic photovoltaic cells (OPV) use organic semiconductor materials, such as polymers or small molecules, to convert sunlight into electricity. They are lightweight, flexible, sometimes transparent, and can be manufactured at low cost using large-scale printing techniques, making them particularly suitable for applications where flexibility and low cost are crucial: smart textiles, photovoltaic windows, and portable electronic devices. OPVs currently have lower conversion efficiencies than established photovoltaic technologies, typically around 10-15%, but show promise in indirect light. Intensive research is underway to improve their efficiency and stability due to the degradation of organic materials. Dye-sensitised solar cells use a porous layer of semiconductor material (typically titanium dioxide, TiO₂) combined with a dye molecule that absorbs light.

4. Multi-junction Cells

Multi-junction cells use several junctions stacked on top of each other: a p-type material, doped with impurities that add positive charge carriers, and an n-type material, doped with impurities that add negative charge carriers. Each junction is optimised for a different wavelength band to absorb a specific part of the solar spectrum, maximizing light absorption and improving overall efficiency. Multi-junction cells are often used in space applications or concentrator photovoltaic systems (lenses or mirrors). Their efficiency can exceed 40%, making them one of the most efficient photovoltaic technologies, and research is still ongoing.

5. Tandem Cells

Tandem cells are a specific type of multi-junction cells. They combine two semiconductor materials with different absorption windows to capture a broader range of the solar spectrum. By stacking these materials, each layer absorbs part of the light, increasing the cell's overall efficiency. For example, a tandem cell can combine a layer of crystalline silicon with a layer of perovskite (a semiconductor combining organic and inorganic materials). Over 30% efficiency is achieved.

Photovoltaic Systems

1. Pico Photovoltaic Systems

Solar home systems (SHS) or pico photovoltaic systems (pico PV) combine the use of adapted lights (mostly LEDs) with charge controllers or batteries. A photovoltaic panel of just a few watts can provide essential services such as lighting, phone charging, or powering a small computer. These systems are primarily used for basic off-grid electrification, especially in developing countries. Expandable versions of pico PV systems are available on the market to integrate additional loads into the initial kit.

2. VIPV

To reduce greenhouse gas emissions in the mobility sector, there has been significant technological progress in integrating solar cells into vehicles (VIPV) or installing modules on the body to meet both aesthetic expectations and technical requirements, such as lightness and load resistance.

3. BAPV and BIPV

Building-Applied Photovoltaics (BAPV) are photovoltaic systems added to an existing building, while Building-Integrated Photovoltaics (BIPV) replace conventional building materials as roofing or facade elements. BIPV are thus building components, serving as both photovoltaic modules and building materials. They come in various forms, colours, and sizes, often in a glass sandwich composition. They typically replace conventional building envelope solutions.

4. Photovoltaics Integrated into Infrastructure (IIPV)

This system involves integrating photovoltaic panels into infrastructures such as noise barriers, dam walls, pavements, roads, etc. New applications are regularly demonstrated. For example, the Swiss Federal Office of Transport has authorised the installation of solar panels between the rails of swiss railway. A first trial is expected to take place in Buttes (canton of Neuchâtel).

5. Agrivoltaics

Agrivoltaics combines agricultural and energy production on the same site. It can be a static tool added to pastures or crops or a dynamic tool to facilitate agricultural production. Sharing light between these two systems allows for higher yield, depending on the climate and crop variety, and can even be beneficial in some cases, as the water evaporating from crops helps to reduce the operating temperature of photovoltaic modules. When combined with pastures, the shade they provide can improve grass quality, while reducing the maintenance costs of the photovoltaic system. The political stakes are significant as electron cultivation appears to be more profitable than plant cultivation or livestock farming, while the permitted occupancy rates are debated in many countries.

6. Floating Photovoltaics

Floating photovoltaic systems are mounted on structures at water level and often benefit from existing grid connections, for example near a hydroelectric dam. Their development in artificial aquatic zones can be a response to land scarcity in high-density population areas. Floating photovoltaic systems also offer other advantages: reduced evaporation rates in dry climates and better module cooling in hot climates. They have also been installed at sea.

7. Solar Farms

Centralised photovoltaic systems function like power plants: they supply electricity in bulk. Ground-mounted solar farms often raise controversy related to land use and landscape protection, them being in competition with agriculture or industry while also facing the issue of conservation of natural spaces and landscapes.

With already 1 GW installed, the over 100-hectare solar power plant located in Datong (China) is connected to the grid and has been producing electricity since the summer of 2016. With a target of 3 GW, it has the potential to be the world's largest solar power plant once completed.

A solar panel on a traditional Kenyan home.

The first solar-powered all-terrain vehicle, developed in 2023 by Eindhoven University of Technology (Netherlands)

The world’s first Alpine Solar Park installed on Lac des Toules at an altitude of 1,810 metres, in the commune of Bourg-St-Pierre (Switzerland).

A project to cover a cycle track in the Netherlands with solar panels to protect cyclists from the rain.

An addition of solar panels (BAPV) on the roof of an alpine chalet.

Related exhibition

Soleil·s

Solar Biennale 2

21.03 → 05.10.2025

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Solar Energy

Photo­vol­taic Cells

Photo­vol­taic Systems

With already 1 GW installed, the over 100-hectare solar power plant located in Datong (China) is connected to the grid and has been producing electricity since the summer of 2016. With a target of 3 GW, it has the potential to be the world's largest solar power plant once completed.

A solar panel on a traditional Kenyan home.

The first solar-powered all-terrain vehicle, developed in 2023 by Eindhoven University of Technology (Netherlands)

The world’s first Alpine Solar Park installed on Lac des Toules at an altitude of 1,810 metres, in the commune of Bourg-St-Pierre (Switzerland).

A project to cover a cycle track in the Netherlands with solar panels to protect cyclists from the rain.

An addition of solar panels (BAPV) on the roof of an alpine chalet.

Related exhibition

Soleil·s

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Solar Energy

Photovoltaic Cells

Photovoltaic Systems