Solar Thermal Evacuated Tube Absorber Coating 2026
Solar Thermal Evacuated Tube Absorber Coating
Selective surface coatings determine evacuated tube collector efficiency by maximising solar absorptance (α) while minimising thermal emittance (ε). This dataset spans patents and literature from 1979 to 2026, mapping cermet multilayers, liquid metal inks, and functional nanocoatings.
Spectrally Selective Absorber Coatings: Architecture and Performance
Evacuated tube solar collectors rely on spectrally selective absorber coatings that maximise absorption of incoming solar radiation in the 0.3–2.5 µm wavelength range while suppressing thermal re-emission above 2 µm. The dominant architecture across retrieved patents is the multilayer thin-film stack: a metallic infrared-reflective base, one or more cermet absorbing layers, and a dielectric anti-reflection cap.
Cermet compositions documented in this dataset include AlN-Al, AlN-SS-Cu, SS-C-Cu, AlN-Ti, Cr₃C₂/Si₃N₄, and Ni-Mo or W-Co ceramic composites. Siemens Aktiengesellschaft’s US patent targets solar absorptivity α ≥ 0.98 and thermal emissivity ε ≤ 0.05 at 500°C as ideal parameters, with practical medium-temperature targets of α > 0.85 and ε < 0.15 at 400°C.
Magnetron sputtering is the primary industrial deposition technique referenced in Chinese patents, while electron beam evaporation is used for precise layer thickness control in Jiangsu Jingzhan Energy Technology Co., Ltd.’s Cr₃C₂/Si₃N₄ system. A lower-cost alternative — liquid metal ink applied under ambient conditions — is documented by Zhonglv Space Liquid Metal Technology (Jiangsu) Co., Ltd. in two active filings.
In this dataset, China (CN jurisdiction) accounts for approximately 28 patents, reflecting the country’s position as the largest single-country contributor in retrieved records. Innovation is concentrated among Chinese industrial manufacturers for mass-market cermet coatings, while a small set of Western firms and universities lead functional and advanced-architecture innovations.
Innovation Periods and Coating Technology Distribution
The retrieved patent dataset spans four identifiable innovation periods from 1979 to 2026, with Chinese industrial scale-up concentrated in 2010–2016 and the most recent filings emphasising nano-functionalization and system integration.
Patent Filings by Technology Cluster (Dataset Snapshot)
In this dataset, multilayer cermet thin-film coatings account for the largest share of retrieved filings, followed by functional coatings and liquid metal ink deposition approaches.
↗ Click bars to exploreInnovation Timeline: Patent Filings by Period (Dataset Snapshot)
In this dataset, the 2010–2016 Chinese industrial scale-up period contains the highest concentration of retrieved filings, followed by the 2013–2020 performance and process innovation period.
↗ Click bars to exploreWhere Evacuated Tube Absorber Coatings Are Deployed
Absorber coatings in evacuated tubes serve a range of thermal applications from domestic hot water in Jinan, China to parabolic trough solar power plants requiring stability above 400°C. Each domain imposes distinct coating performance requirements.
Jinan, China Rural Heating
A 2019 literature study demonstrated field implementation of evacuated tube collectors with selective absorber coatings for indoor heating in Jinan, China. The system was evaluated alongside an auxiliary electric heater and confirmed adequate thermal performance for rural heating loads. Techno-economic analyses from 2018 literature confirmed life cycle savings dependent on coating-driven collector efficiency.
Domestic Hot WaterIndustrial Process Heat 80–140°C
A 2014 study on a static low-concentration evacuated tube collector demonstrated instantaneous thermal efficiency above 30% at operating temperatures of 80–140°C. This range is relevant to industrial process heat, seawater desalination, refrigeration, and thermal power generation. Siemens Aktiengesellschaft’s US patents explicitly target absorber layers stable at 400–500°C in air for linear concentrating solar thermal power plants.
Industrial Process HeatConcentrating Solar Power Plants
Siemens Aktiengesellschaft (2012/US) and Bharat Heavy Electricals Limited (2016/IN) filed patents on absorber layers for parabolic trough collectors, with Co-Cr-Al-Y alloy selective coatings applied to central metal tubes at high solar flux. A 2022 literature review on selective absorber coatings for parabolic trough collectors identified thermal stability, corrosion resistance, and qualification testing as key unresolved gaps. Ideal coating parameters target α ≥ 0.98 and ε ≤ 0.05 at 500°C.
Solar Thermal PowerAgricultural Drying and Air Heating
A 2021 study on evacuated glass-thermal absorber tube collectors (EGATC) examined air-type collectors for air heating applications. Chinese patents from Huangming Solar Energy Co., Ltd. (2013 and 2015/CN) and Shandong Yijiia Solar Energy Co., Ltd. (2014/CN) describe evacuated tube air collectors with SS-AlNx/Cu selective absorber coatings specifically designed for air heating circuits used in space heating and agricultural drying.
Air HeatingLeading Assignees in Evacuated Tube Absorber Coatings — Dataset Snapshot
In this dataset, Chinese industrial assignees account for the highest concentration of retrieved filings, with Jiangsu Jingzhan Energy Technology Co., Ltd. filing three patents in 2019 alone on Cr₃C₂/Si₃N₄ cermet systems. No single assignee leads across all technical dimensions in retrieved records.
Top Assignees by Filing Count — Evacuated Tube Absorber Coatings (Dataset Snapshot)
↗ Click bars to exploreJiangsu Jingzhan Energy Technology
Jiangsu Jingzhan Energy Technology Co., Ltd. filed three patents in 2019 (CN jurisdiction) on Cr₃C₂/Si₃N₄ cermet absorber coatings for solar vacuum tubes. The patents document a Cu-Cr infrared reflective base layer, Cr₃C₂/Si₃N₄ cermet absorber, and Si₃N₄ anti-reflection cap prepared by electron beam evaporation. All three retrieved filings are from 2019 and are included as active-status CN patents in this dataset.
China — CNTIGI Ltd
TIGI Ltd. (Israel) holds two active filings in this dataset: a 2013 WO patent and a 2020 EP patent on a radiation-based overheat prevention coating with deliberately elevated IR emissivity (ε > 0.25 above 2 µm) for evacuated tube solar thermal collectors. The 2020 EP patent extends the earlier WO filing and remains active, covering passive stagnation temperature control without mechanical relief valves. Both filings target thermosiphon systems and building-integrated collector configurations.
Israel — EP/WONext-Generation Coating Signals in Retrieved Records
Among the most recently dated records in this dataset (2019–2026), three directional signals are identifiable: self-cleaning nanocoatings on outer glass surfaces, ambient-condition liquid metal ink deposition, and passive overheat-prevention via spectrally engineered high-emissivity coatings.
Self-Cleaning Nanocoatings on Outer Glass Surfaces
The 2026 pending Indian patent from R.M.K. College of Engineering and Technology targets efficiency losses caused by dust accumulation in arid and high-pollution environments. The coating combines hydrophobic, superhydrophobic, and photocatalytic mechanisms — likely TiO₂-based — to enable autonomous surface cleaning. This represents a shift from treating the selective absorber alone to treating the entire optical system as a coated assembly.
Liquid Metal Ink for Ambient-Condition Coating Deposition
Two active patents from Zhonglv Space Liquid Metal Technology (Jiangsu) Co., Ltd. (filed 2014, updated 2016) document the use of oxidised liquid metals mixed with solar selective absorbing materials to form a printable ink applied under ambient conditions. This eliminates capital-intensive vacuum sputter deposition equipment. The 2019 literature study on CuO nano-structured coatings prepared via chemical oxidation reports α/ε ratios of approximately 0.90/0.11, a low-cost deposition route with efficiency comparable to sputtered cermets.
Cermet Multilayer (Magnetron Sputtering) vs. Liquid Metal Ink Deposition
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| Dimension | Cermet Multilayer (Magnetron Sputtering) | Liquid Metal Ink (Ambient Deposition) |
|---|---|---|
| Representative Assignee | Jiangsu Jingzhan Energy Technology; Dezhou Xuneng Vacuum Tube; Shandong Guangpu Solar Energy | Zhonglv Space Liquid Metal Technology (Jiangsu) Co., Ltd. |
| Typical Coating Structure | IR-reflective base (Cu, Ti) + cermet absorber (AlN-Ti, Cr₃C₂/Si₃N₄) + dielectric AR cap (Al₂O₃, AlN) | Oxidised liquid metal + solar selective absorbing material mixed into printable ink; applied to inner tube outer surface |
| Deposition Process | Magnetron sputtering (primary); electron beam evaporation (Jiangsu Jingzhan) | Ambient-condition application — no vacuum deposition equipment required |
| Target Optical Performance | α ≥ 0.98, ε ≤ 0.05 at 500°C (ideal per Siemens); α > 0.85, ε < 0.15 at 400°C (medium-temperature target) | Not explicitly quantified in retrieved filings; cost reduction is the primary stated objective |
| Capital Equipment Requirement | High — requires vacuum sputter deposition chambers | Low — designed to eliminate vacuum deposition equipment |
| Patent Activity Period | 2010–2019 (dense CN cluster); most CN filings now inactive | 2014–2016 (two active CN filings as of dataset snapshot) |
| Jurisdiction | China (CN), United States (US), Germany (DE via Siemens) | China (CN) |
| Technology Maturity | Mature — widely adopted in mass-market Chinese evacuated tube production | Earlier stage — active patents suggest approaching commercial validation as of 2026 |
FAQ: Evacuated Tube Solar Thermal Absorber Coating Patents
The dominant architecture across retrieved patents is the multilayer thin-film stack, comprising a metallic infrared-reflective base layer (e.g., Cu or Ti), one or more cermet absorbing layers (ceramic-metal composites), and a dielectric anti-reflection cap (e.g., Al₂O₃, Si₃N₄, or AlN). Magnetron sputtering is the primary deposition technique referenced in Chinese industrial patents.
Siemens Aktiengesellschaft’s US patent targets solar absorptivity α ≥ 0.98 and thermal emissivity ε ≤ 0.05 at 500°C as ideal parameters. Practical medium-temperature targets are α > 0.85 and ε < 0.15 at 400°C. The CuO nano-structured coating described in 2019 literature achieved α/ε ratios of approximately 0.90/0.11 via chemical oxidation.
Zhonglv Space Liquid Metal Technology (Jiangsu) Co., Ltd.’s approach oxidises liquid metals and mixes them with solar selective absorbing materials to form a printable ink applied under ambient conditions. This eliminates the need for capital-intensive vacuum deposition equipment. By contrast, magnetron sputtering requires vacuum chambers and is the established mass-production route used by Chinese industrial manufacturers.
TIGI Ltd.’s coating uses a deliberately elevated IR emissivity (ε > 0.25 above 2 µm) and a critical wavelength ≥ 3 µm to dissipate excess heat radiatively under stagnation conditions. This prevents system damage without mechanical relief valves or electronic intervention, applicable to thermosiphon systems and building-integrated collectors. The approach inverts the usual low-emissivity optimisation target.
China (CN jurisdiction) accounts for the largest single-country share with approximately 28 patents identified in this dataset, reflecting its position as the dominant manufacturer of all-glass evacuated tube collectors. The United States contributes the second-largest cluster, covering a historical range of 1979–2016 with concentration in foundational and CSP-oriented patents. Europe (EP/WO) contributions include TIGI Ltd. (Israel), Abengoa Solar (Spain), and Heliocaminus AB (Sweden). Australia hosts early foundational work from University of Sydney and Rhem Australia Limited (1987–1992).
Documented cermet compositions include AlN-Al, AlN-SS-Cu, SS-C-Cu (stainless steel/carbon/copper), AlN-Ti, Cr₃C₂/Si₃N₄, and Ni-Mo or W-Co ceramic composites. Specific layered systems include Dezhou Xuneng’s five-layer AlN-Al/Cu/AlN-Ti/AlN-Ti/AlN stack, Jiangsu Jingzhan’s Cu-Cr/Cr₃C₂/Si₃N₄/Si₃N₄ stack, and Shandong Guangpu’s Ti/Cu bilayer reflector with dual-layer H-Al₂O₃:TiO₂AlN absorber system.
Data and insights on this page are based on a limited patent and literature dataset and are for reference only. Figures may not represent the complete technology landscape.