Solar heating and cooling: key trends and challenges

In 2020, the solar thermal energy yield amounted to 407 TWh, which correlates to savings of 43.8 million tons of oil and 141.3 million tons of CO2. Although still only a niche market, solar cooling has an enormous  potential. 

The 2021 report "Solar Heat Worldwide”, prepared by the IEA’s Solar Heating & Cooling Programme (1), gives an overview of the general trends in the global solar thermal market, including solar cooling. 


Solar thermal market development and trends 


The cumulative solar thermal capacity in operation at the end of 2020 was 501 GWth, corresponding to 715 million square metres of collector area. The annual solar thermal energy yield amounted to 407 TWh, which correlates to savings of 43.8 million tons of oil and 141.3 million tons of CO2


The worldwide solar thermal market shrank by 4 % in 2020 compared to 2019. This is mainly due to the decline in the Chinese market, which is by far the largest market worldwide. 


The top 10 countries in terms of total installed collector area at the end of 2019 were China, Turkey, the United States, Germany, Brazil, India, Australia, Austria, Greece and Israel. However, the picture is clearly different when comparing per capita data. The top 10 countries per 1,000 inhabitants are Barbados, Cyprus, Austria, Israel, Greece, the Palestinian Territories, Australia, China, Denmark and Turkey. 


The market for Photovoltaic Thermal Collectors (PVT) and systems saw significant global growth by 9% in 2020. At least 2,052 new PVT systems were commissioned in 2020. In 2020, the total installed PVT collector area was 1,275,431 m², with the vast majority installed in Europe (732,955 m²), in particular in France (500,992 m²). 


Regarding solar thermal collector technology, the global share of evacuated tube collectors – the dominant technology in China – decreased from about 82 % in 2011 to 61.9 % in 2019, and at the same time, flat plate collectors increased their share from 14.7 % to 32.5 %. 


In terms of applications, interest in megawatt-scale solar district heating systems and solar heating and cooling applications in the commercial and industrial sectors continues.  


In economic terms, the number of jobs in the production, installation and maintenance of solar thermal systems was estimated at 400,000 worldwide in 2019. The estimated worldwide turnover of the solar thermal industry in 2019 was EUR 13.4 billion (USD 16.1 billion). 


Solar cooling 


Solar thermal cooling is still a niche market, with about 2,000 systems deployed globally as of 2020. However, there is enormous potential for cooling systems that use solar energy, both solar thermal and PV driven solar cooling systems. This potential is particularly important in air-conditioning applications since, by 2050, 37 % of the growth in total electricity demand growth will be due to air-conditioning electricity demand.   


A major argument for using solar thermally driven systems is that they consume less conventional energy (up to a factor of five) and use natural working fluids, such as water and ammonia. Another driver of solar cooling technology is its potential to reduce peak electricity demand, particularly in countries where cooling demand is high and national electric grids require protection against overloads, such as the US and India. 


Of the small and medium capacity (< 350 kW) solar cooling systems worldwide, 70% are installed in Europe, but only a small number of new systems were installed in 2018, mainly in Italy and Germany.  


Solar cooling using thermal absorption chillers with a cooling capacity over 350kW improved significantly in performance and, at the same time, decreased in terms of costs. This makes solar cooling applications cost-competitive for large office buildings, hotels, hospitals and commercial / industrial applications. Thus, the electrical demand for solar air conditioning in a building is cut by more than 80% compared to conventional equipment.  


Even though the technical and economic conditions for solar cooling and air conditioning have improved significantly in recent years, it remains a challenging market, as evidenced by the comparatively small number of solar cooling systems built in recent years. 


The world’s largest solar cooling application is located in Arizona, USA and was commissioned in May 2014. The installation covers a roof-mounted solar thermal collector field with a capacity of 3.4 MWth (4,865 m²) that supplies heat to a single-effect lithium bromide absorption chiller with a cooling capacity of 1.75 MW. 


The authors of the report conclude that the focus on potential markets for solar cooling technologies is becomingincreasingly important to break out of a niche market. Therefore, the know-how capitalised in OECD countries (Europe, USA, Australia, etc.) on solar cooling, both thermal and PV, needs to be adapted and transferred to countries with good insolation in Africa, MENA region and Asia, which are all dynamic emerging economies. 


For more information on the subject, see the IIR Informatory Note on Solar Cooling.