Definition

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Solar energy or solar power refers to the energy of solar radiation, which can mainly be utilised technically in the form of electricity and heat. Solar radiation is the electromagnetic radiation that is generated on the surface of the sun due to its extremely high temperature of approx. 5500 °C and reaches the earth's surface with an intensity of approx. 1000 W/m2. Solar energy has enormous potential and can be utilised directly with solar collectors or photovoltaic systems. However, most other energy sources such as hydroelectric power stations, wind power or biomass and even fossil fuels are actually based on the indirect utilisation of solar energy.

Solar Thermal

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Solar thermal refers to technologies that convert solar radiation directly into thermal energy. Solar thermal collectors are usually used for this purpose, which absorb the solar radiation on a dark surface - the absorber - convert it into heat and transfer it to a heat transfer medium. Important collector technologies are flat plate solar collectors, evacuated tube collectors, vacuum flat plate solar collectors, parabolic trough collectors and photovoltaic-thermal collectors. The conversion efficiency of solar collectors is strongly dependent on the collector technology and the operating temperature and can reach up to 80% in ideal conditions. Due to the irregular availability of solar energy, a thermal storage is usually required. Solar thermal energy can be used directly on buildings to produce domestic hot water and/or space heating as a standard application. In the themes of DeCarbCH large scale applications for solar district heating or solar heat for industrial processes, which are still only rarely present in Switzerland, are in the focus. Swiss Research is allocated to the ongoing Tasks 64 (process heat) and Task 68 (district heating) of the international energy agency IEA.

Photovoltaics

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Photovoltaics, commonly known as solar power technology, convert sunlight directly into electricity using semiconductor materials. Photovoltaics is considered the renewable technology with the greatest potential and its expansion is strongly promoted in Switzerland and worldwide. Cost reductions and improvements in efficiency have greatly boosted the spread of this technology. Nowadays, standard modules with efficiencies of 20% are now being offered. Switzerland will have to greatly increase its productions of electricity provided by PV to become carbon neutral in 2050 [1], one of the reason is the electrification of heat (via heat pump or other technologies) and the transition from fossil fuel engine vehicle to electrical vehicle. However, as PV does not directly produce heat nor cold, its current and future development, and its general usage is out of the scope of this SWEET program.
SWEET SURE (SUstainability and Resilient Energy for Switzerland) , and also SWEET EDGE (Enabling Decentralized renewable GEneration in the Swiss cities, midlands, and the Alps) are other programs which have more focus on PV.

Tool

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SPF has made an Excel file able to help with the selection of solar collector: online tool or downoad the Excel file.

References

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[1] Walch, Alina, and Martin Rüdisüli: Strategic PV expansion and its impact on regional electricity self-sufficiency: Case study of Switzerland, Applied Energy 346 (2023): 121262.
[1 bis] EPFL Actu:Energy Strategy 2050: the potential of millions of Swiss rooftops
online, 20.02.24.