Produced in Association with


SERIES 24 / Module 02 Solar Thermal Systems


heat into the system’s primary working fluid – typically water or a water-glycol solution. The condensed working fluid then returns by gravity to the base of the heat pipe to repeat the cycle. With each tube functioning independently, damage to one tube does not compromise the performance of the array, and individual tubes can be replaced without draining the system. The advantages of evacuated tube


collectors include their maintenance of high collection efficiency across a wide range of ambient temperatures and irradiance conditions and their ability to reach temperatures exceeding 200°C, which along with their modular architecture suits both domestic and large commercial installations. These characteristics explain why evacuated tube collectors now dominate the markets for small-scale systems in northern Europe, China and the UK, and why they are increasingly specified for industrial process heat applications where reliable year-round performance is required.


Concentrating solar power Concentrating solar power systems


operate on a fundamentally different scale and with a distinct strategic purpose. Rather than heating water for building services, CSP installations use arrays of mirrors or lenses to focus sunlight onto a small receiver area, achieving temperatures that can range from 300°C in parabolic trough systems to over 1,000°C at the focus of a solar tower. This intense thermal energy is used to generate steam, which drives a conventional turbine-generator set to produce electricity. Europe hosts several landmark CSP


installations, most notably in Spain, where the combination of high direct normal irradiance and supportive policy frameworks enabled a substantial programme of commercial deployment in the late 2000s up to 2013. The Gemasolar plant near Seville


– a 19.9 MW solar tower facility – incorporates a molten-salt thermal storage system capable of sustaining full-load operation for up to 15 hours after sunset, demonstrating that CSP can provide genuinely despatchable renewable electricity rather than merely intermittent generation. The Andasol series of parabolic trough plants, also in Andalusia, similarly uses molten- salt storage to extend generation into evening peak demand periods. These installations illustrate both the technical maturity of CSP and its fundamental geographical constraint: CSP is commercially viable only in regions with sustained high direct normal irradiance, which limits its commercial deployment in the UK.


Produced in Association with Solar thermal water collectors 2010-2023 (m2)


Solar thermal capacity installed (kWth per 1000 inhabitants)


Images copyright International Energy Agency, Solar Heating & Cooling Programme, Solar Heat World Wide Edition 2024


Global context Solar thermal is one of the most widely


deployed renewable heat technologies in the world, with a level of installed capacity that is often underappreciated in UK policy discussions that focus primarily on electricity generation. According to data compiled by the International Energy Agency and the Solar Heat Worldwide report series, global installed capacity now exceeds 530 GWth, representing a substantial stock of operating collector area. China accounts for more than 70% of


this total, reflecting a combination of low- cost domestic manufacturing, supportive building standards that mandate solar hot water in many residential developments, and a large population with high baseline hot water demand. The number of Chinese deployments is dominated by evacuated tube collectors, which are produced at industrial scale by a large number of domestic manufacturers and have become standard equipment in millions of urban and rural households. Beyond China, the global picture is


varied but consistently demonstrates that solar thermal is a proven technology capable of delivering reliable performance across a wide range of climatic and cultural contexts. Turkey has one of the world’s highest per-capita densities of solar thermal installations, with flat- plate and evacuated tube collectors a standard feature of residential buildings across the Aegean and Mediterranean coastal regions. In Brazil, solar thermal programmes have been deployed specifically to reduce the very high electricity demand associated with electric resistance shower heaters, which historically placed enormous peak loads on the national grid. India is increasingly adopting solar thermal for industrial process heat, with installations in the textile, dairy, food processing, and pharmaceutical sectors demonstrating


the technology’s relevance beyond the domestic market. Notable large-scale evacuated tube


installations include the solar hot water system serving the Beijing Olympic Village, which used more than 6,000 m² of collector area to provide reliable hot water for thousands of athletes and support staff, and residential tower developments in São Paulo where solar thermal has been integrated as a standard utility infrastructure component.


European market Europe has a long and technically


accomplished history of solar thermal deployment, with more than 36 GWth installed across the continent and a well- developed supply chain encompassing collectors, controls, storage vessels, and installation services. The market is geographically polarised, with southern European countries – Greece, Cyprus, Portugal, Spain and Italy – achieving high levels of penetration in the domestic hot water sector, driven by abundant direct solar radiation, supportive building regulations, and strong consumer awareness of the technology’s long-term cost benefits. Greece in particular has one of the highest per-capita rates of solar thermal installation in the world, and solar collectors are a visible and unremarkable feature of residential roofscapes across the country. Northern Europe presents a more


complex picture. Germany and Austria have strong manufacturing sectors and well-established domestic markets, but system costs are higher and payback periods are longer than in the south. The response to this challenge has been twofold: a shift towards larger and more technically sophisticated systems, and a growing interest in solar thermal as a component of district heating networks. Denmark is the global leader in large- scale solar district heating, having


developed a distinctive model in which very large collector fields – sometimes exceeding 50,000 m² of aperture area – are connected to municipal heating networks through thermal storage systems ranging from buffer tanks to pit storage and aquifer storage. The Silkeborg Solar District Heating Plant, one of the largest solar thermal installations in the world, uses more than 156,000m² of collectors to meet approximately 20% of the city’s annual heat demand. This approach to short term thermal storage transforms the diurnal mismatch between peak solar availability and peak heat demand from a constraint into an engineering design problem that is tractable with current technology. Solar thermal is also extensively


used across southern Europe in tourist accommodation, where hotels, resorts, and holiday apartments rely on the technology to meet high and predictable hot water loads while reducing dependence on diesel boilers and improving sustainability credentials for environmentally conscious travellers.


UK market The United Kingdom solar thermal market


is considerably smaller than those of comparable European economies, reflecting a combination of historical policy discontinuities, competition from alternative technologies, and persistent public scepticism about the adequacy of the UK solar resource. Approximately 500,000 solar thermal installations are operational in the UK, the large majority of which are domestic evacuated tube systems installed between 2000 and 2015, many under the Renewable Heat Incentive or its predecessor programmes. The predominance of evacuated tube


collectors over flat-plate collectors in the UK market is a reflection of their superior performance under the diffuse, low-angle irradiance conditions that characterise


20


EIBI | JULY � AUGUST 2026


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