Solar thermal energy

Energy is at the heart of the climate challenge – and the first solution. Fossil fuels, such as coal, oil and gas, are by far the biggest contributors to climate change, accounting for over 75% of global greenhouse gas emissions. To halve emissions by 2030, we must collectively end our dependence on fossil fuels and invest in alternative energy sources that are clean, accessible, affordable, sustainable and reliable. (1)

Solar thermal energy is a low-carbon renewable energy source. Its use emits few greenhouse gases compared with fossil fuels. Producing heat from solar thermal panels emits a similar proportion of CO2 to producing electricity from photovoltaic panels: around 44 gCO2e/kWh (Compared with 418 gCO2e/kWh for a gas-fired power plant). (2)

Moreover, solar energy has virtually unlimited potential since it is available everywhere. In contrast, fossil fuels such as oil, gas and coal are running out and are only produced by a handful of countries that hold the key to global energy supply and stability.

Like photovoltaic solar energy, solar thermal energy is set to grow significantly in the coming years. (3) Solar energy projects are on the increase, attracting the attention of both public and private funding bodies, who are showing increasing interest in financing them.

Solar thermal energy can be used to heat water or air. It is an alternative to gas or oil heating, or any other heating system that uses carbon-based electricity.

Composition & Operation of the Solar Thermal System

A solar thermal energy production system converts the sun’s rays into heat. Using a thermal collector (thermal solar panels), the sun’s rays are captured by a highly inert material (copper in particular). The heat is then transferred to a heat-transfer fluid, which then transports the heat to a storage tank, for example, or to a central heating circuit. (7)

There are different types of thermal collectors/panels:

• Flat plate glazed collectors: These are the most used. A black metal plate enables them to absorb the sun’s rays by being in direct contact with the heat transfer fluid.
• Evacuated glass tube collectors: These consist of glass tubes placed side by side. The sun’s rays are absorbed by a black plate. They are called “evacuated” glass tubes because the residual air is then removed from the tubes to create better insulation and limit heat loss. They are more efficient, but also more expensive.
• Unglazed collectors: Water-filled tubes made of black plastic or metal allow the collectors to absorb heat. This system is less efficient and deteriorates more quickly. (8)

Solar thermal energy has great potential and can be used in a wide variety of ways, whether in private households, the service sector or industry. (9)

Skills & Technical Expertise 

The design, installation and operation of solar systems requires a certain level of technical expertise, which can be brought in-house or outsourced depending on the size, needs and financial resources of the organisation. The equipment chosen must be robust and, as far as possible, repairable locally or regionally.

Internalising expertise within an organisation requires substantial, long-term financial resources (design, training, operation, maintenance). By limiting the number of intermediaries in this way, it is often easier to monitor the progress of projects, guarantee appropriate training for operators and ensure that installations are operating and maintained correctly.

Outsourcing expertise means relying on partners and subcontractors, from project design through to equipment end-of-life management. To ensure the success of projects, it is important to choose experienced and reliable service providers from the outset, to draw up long-term contracts providing for regular maintenance and servicing of facilities, and to ensure that there are sufficient funds to cover all costs over the lifetime of the facilities.

All energy production has a cost. Even if the source of energy – the Sun – is infinite and free, the production of heat from this source has a cost, limits and risks. The production of solar thermal panels requires metals and rare earth elements that are not accessible everywhere. These materials are often imported and transporting them has a significant environmental impact. Furthermore, the exploitation of the raw materials needed to manufacture lithium batteries is highly controversial in terms of respect for human rights (child labour) and the local pollution caused (Congo). Furthermore, all these devices have a limited lifespan, and special attention needs to be paid to their end-of-life, particularly in the case of electronic waste.

The installation of solar panels only becomes environmentally profitable if the installation has a long lifespan, in other words if the panels continue to produce energy for at least 10 years after their installation. If, due to lack of maintenance, the solar panels no longer produce much energy or stop working after just a few years, then the environmental and climatic impact of the solar installation is likely to be greater than simply connecting them to the local electricity grid. Therefore, installing solar panels should not be done lightly. (10)

Nuclear → 6 g CO2-eq / kWh

Hydroelectric power → 12 g CO2-eq / kWh

Wind energy → 15 g CO2-eq / kWh

Solar energy PV and thermal → 44 g CO2-eq / kWh

Natural gas → 418g CO2-eq / kWh

Fuel oil → 730g CO2-eq / kWh

Coal → 1058g CO2-eq / kWh

(11)

(1) United Nations, Reinforcing the ambition of renewable energies. – Read here

(2) Climate Selectra, what are the CO2 emissions by energy source, 2023 – Read here (in French)

(3) Inis iaea, Solar thermal energy around the world, 2012 – Read here (in French)

(4) Climate selectra, CO2 emissions by energy source, 2023 – Read here (in French)

(5) Nouvelr energie, Factors determining the performance of solar thermal panels,2023 – Read here (in French)

(6) Choisir, Is solar energy profitable, 2020 – Read here (in French)

(7) Engie, How thermal solar panels work, 2023 – Read here (in French)

(8) Engie, The different types of solar thermal panels, 2023 – Read here (in French)

(9) Swiss Federal Office of Energy, Solar energy, 2023. Read here

(10) Solar service, The importance of maintaining solar thermal panels. Read here 

(11) Trajectoires media, Decarbonised energies, 2023 – Read here (in French)

(12) Solar services, The importance of maintaining solar thermal panels. Read here

(13) Gironde, Bordeaux University Hospital goes solar, 2021 – Read here (in French)

(14) Andrianos, Solar thermal installation at Kalamata Hospital – Read here (in French)

(15) Balk green energy news, A Romanian high school on the way to a net-zero building, 2022. Read here

(16) Sunoptimo, Chemin du mouille galant in Geneva, 2018 – Read here (in French)