High Temperature, High Efficiency PV-Thermal Solar System
Lead Research Organisation:
Imperial College London
Department Name: Physics
Abstract
Solar energy can be used to generate both heat and electrical power. Most solar panels are designed for only one of these purposes, so an electrical photovoltaic panel is typically no more than 20% efficient and will become hot when exposed to sunlight. If the panel is actively cooled by passing a fluid through the rear of the panel, it is possible to generate both heat and electrical power. This combined solar heat and power system is known as a hybrid Photovoltaic-Thermal (PV-T) collector and offers some advantages when space is at a premium and there is demand for both heat and power. By 2050 solar power is projected to deliver the majority of the world's electricity and will require much more efficient use of the premium, unshaded space that exists in the built environment. PV-T collectors are a highly efficient technology, capable of achieving system efficiencies (electrical + thermal) of over 70%.
In response to this medium term opportunity, this research proposal develops optical nanostructured surfaces that enable an industrially manufacturable solar cell to become the ideal PV-T absorber. This is achieved by ensuring visible and near-infrared sunlight light is scattered internally within the solar cell, longer wavelength sunlight is absorbed and very long wavelength thermal emission is suppressed. The research employs state of the art computer simulation to design the nanostructured surface, followed by large area nanofabrication that can be performed using low-cost effective nanoimprint methods (the technique used to manufacture DVDs). The the suppression of thermal radiation is achieved using a low-emissivity surface which is also a low-cost process, similar to the 'heat reflecting' coatings that are applied to low-E glass used in energy efficient windows.
The solar cell architecture employed is the Heterojunction Interface (HIT) solar cell pioneered by Sanyo and that recently set the world record for the highest efficiency silicon solar cell ever demonstrated. Remarkably, this solar cell can be manufactured at low cost and lends itself to structured coating owing to the unique heterojunction design. Importantly, this solar cell retains it's characteristically high electrical efficiency at high temperature making it ideal for PV-T applications.
Prototype PV-T collectors that contain this optimised solar cell will be fabricated in this project and subjected to both indoor and outdoor testing. A predictive computer model will be established that reproduces the electrical and thermal output of the collector under both indoor and outdoor conditions. The model will be used as a basis to assess the applicability of the technology in various applications, especially those that demand relatively high temperature heat (100 degC) for which the system will be particularly well suited.
The research will be disseminated in the scientific literature and conferences and also to a broader audience at workshops held at Imperial College and trade shows.
In response to this medium term opportunity, this research proposal develops optical nanostructured surfaces that enable an industrially manufacturable solar cell to become the ideal PV-T absorber. This is achieved by ensuring visible and near-infrared sunlight light is scattered internally within the solar cell, longer wavelength sunlight is absorbed and very long wavelength thermal emission is suppressed. The research employs state of the art computer simulation to design the nanostructured surface, followed by large area nanofabrication that can be performed using low-cost effective nanoimprint methods (the technique used to manufacture DVDs). The the suppression of thermal radiation is achieved using a low-emissivity surface which is also a low-cost process, similar to the 'heat reflecting' coatings that are applied to low-E glass used in energy efficient windows.
The solar cell architecture employed is the Heterojunction Interface (HIT) solar cell pioneered by Sanyo and that recently set the world record for the highest efficiency silicon solar cell ever demonstrated. Remarkably, this solar cell can be manufactured at low cost and lends itself to structured coating owing to the unique heterojunction design. Importantly, this solar cell retains it's characteristically high electrical efficiency at high temperature making it ideal for PV-T applications.
Prototype PV-T collectors that contain this optimised solar cell will be fabricated in this project and subjected to both indoor and outdoor testing. A predictive computer model will be established that reproduces the electrical and thermal output of the collector under both indoor and outdoor conditions. The model will be used as a basis to assess the applicability of the technology in various applications, especially those that demand relatively high temperature heat (100 degC) for which the system will be particularly well suited.
The research will be disseminated in the scientific literature and conferences and also to a broader audience at workshops held at Imperial College and trade shows.
Planned Impact
Improving the efficiency and operating temperature of a hybrid PV-T collector will accelerate the integration of solar technology in the built environment. This project delivers improvements in both electrical efficiency and collector temperature addressing a wider range of applications than conventional PV-T collectors.
The provision of electrical power is universally useful but cannot be easily stored, so one important impact PV-T system enables the electrical output to be switched to thermal generation at will. The applications therefore depend upon the temperature of the heat produced by the collector. Low to moderate heat output are well suited for use in commercial buildings, for example supermarkets, hotels and leisure centres and large residential buildings, for example social housing where district heating is used. The collector developed in this proposal is unique since it both delivers high electrical efficiency at high temperature, which opens up additional applications, specifically in the industrial sector in industries such as food processing, breweries, textiles, copper mining as well as thermal processing and absorption refrigeration.
The research therefore has impact at many levels of the solar technology supply chain. Firstly it significantly improves the performance of an innovative PV-T collector developed and patented by a British Company, Naked Energy. Secondly, it establishes a predictive computer modelling capability that enables rapid design and prototyping of PV-T systems by end users. Thirdly it marks the scientific milestone for the application of nanoscale optical structures into cost effective solar collectors.
The provision of electrical power is universally useful but cannot be easily stored, so one important impact PV-T system enables the electrical output to be switched to thermal generation at will. The applications therefore depend upon the temperature of the heat produced by the collector. Low to moderate heat output are well suited for use in commercial buildings, for example supermarkets, hotels and leisure centres and large residential buildings, for example social housing where district heating is used. The collector developed in this proposal is unique since it both delivers high electrical efficiency at high temperature, which opens up additional applications, specifically in the industrial sector in industries such as food processing, breweries, textiles, copper mining as well as thermal processing and absorption refrigeration.
The research therefore has impact at many levels of the solar technology supply chain. Firstly it significantly improves the performance of an innovative PV-T collector developed and patented by a British Company, Naked Energy. Secondly, it establishes a predictive computer modelling capability that enables rapid design and prototyping of PV-T systems by end users. Thirdly it marks the scientific milestone for the application of nanoscale optical structures into cost effective solar collectors.
Publications
Alonso-Álvarez D
(2019)
Assessing the operating temperature of multi-junction solar cells with novel rear side layer stack and local electrical contacts
in Solar Energy Materials and Solar Cells
Alonso-Álvarez D
(2019)
Thermal emissivity of silicon heterojunction solar cells
in Solar Energy Materials and Solar Cells
Alonso-Álvarez D
(2017)
ITO and AZO films for low emissivity coatings in hybrid photovoltaic-thermal applications
in Solar Energy
Alonso-Álvarez D
(2017)
Comparative Study of Annealed and High Temperature Grown ITO and AZO Films for Solar Energy Applications
in MRS Advances
Freeman J
(2017)
A small-scale solar organic Rankine cycle combined heat and power system with integrated thermal energy storage
in Applied Thermal Engineering
Georgiou S
(2018)
A generic tool for quantifying the energy requirements of glasshouse food production
in Journal of Cleaner Production
Guarracino I
(2016)
Dynamic coupled thermal-and-electrical modelling of sheet-and-tube hybrid photovoltaic/thermal (PVT) collectors
in Applied Thermal Engineering
Guarracino I
(2019)
Systematic testing of hybrid PV-thermal (PVT) solar collectors in steady-state and dynamic outdoor conditions
in Applied Energy
Harraz A
(2019)
Diffusion-absorption refrigeration cycle simulations in gPROMS using SAFT-? Mie
in Energy Procedia
Herrando M
(2019)
Solar combined cooling, heating and power systems based on hybrid PVT, PV or solar-thermal collectors for building applications
in Renewable Energy
Herrando M
(2018)
Technoeconomic modelling and optimisation of solar combined heat and power systems based on flat-box PVT collectors for domestic applications
in Energy Conversion and Management
Hu Y
(2018)
Identifying and controlling phase purity in 2D hybrid perovskite thin films
in Journal of Materials Chemistry A
Huang G
(2020)
Challenges and opportunities for nanomaterials in spectral splitting for high-performance hybrid solar photovoltaic-thermal applications: A review
in Nano Materials Science
Huang G
(2021)
On the performance of concentrating fluid-based spectral-splitting hybrid PV-thermal (PV-T) solar collectors
in Renewable Energy
Huang G
(2021)
Spectral-splitting hybrid PV-thermal (PV-T) solar collectors employing semi-transparent solar cells as optical filters
in Energy Conversion and Management
Huang G
(2021)
Efficiency limits of concentrating spectral-splitting hybrid photovoltaic-thermal (PV-T) solar collectors and systems
in Light: Science & Applications
Li Q
(2023)
A ternary system exploiting the full solar spectrum to generate renewable hydrogen from a waste biomass feedstock
in Energy & Environmental Science
Madurai Elavarasan R
(2022)
Pathways toward high-efficiency solar photovoltaic thermal management for electrical, thermal and combined generation applications: A critical review
in Energy Conversion and Management
Mariaud A
(2017)
Integrated optimisation of photovoltaic and battery storage systems for UK commercial buildings
in Applied Energy
Markides C
(2015)
Low-Concentration Solar-Power Systems Based on Organic Rankine Cycles for Distributed-Scale Applications: Overview and Further Developments
in Frontiers in Energy Research
Mellor A
(2017)
Interstitial light-trapping design for multi-junction solar cells
in Solar Energy Materials and Solar Cells
Mellor A
(2018)
Roadmap for the next-generation of hybrid photovoltaic-thermal solar energy collectors
in Solar Energy
Najjaran A
(2019)
Experimental investigation of an ammonia-water-hydrogen diffusion absorption refrigerator
in Applied Energy
Obalanlege M
(2022)
Techno-economic analysis of a hybrid photovoltaic-thermal solar-assisted heat pump system for domestic hot water and power generation
in Renewable Energy
Peacock J
(2022)
Techno-economic assessment of integrated spectral-beam-splitting photovoltaic-thermal (PV-T) and organic Rankine cycle (ORC) systems
in Energy Conversion and Management
Ramos A
(2018)
Optimisation of a high-efficiency solar-driven organic Rankine cycle for applications in the built environment
in Applied Energy
Ramos A
(2017)
Hybrid photovoltaic-thermal solar systems for combined heating, cooling and power provision in the urban environment
in Energy Conversion and Management
Riverola A
(2018)
Mid-infrared emissivity of crystalline silicon solar cells
in Solar Energy Materials and Solar Cells
Wang K
(2020)
Spectral-splitting hybrid PV-thermal (PVT) systems for combined heat and power provision to dairy farms
in Renewable Energy
Wang K
(2019)
Thermoeconomic assessment of a PV/T combined heating and power system for University Sport Centre of Bari
in Energy Procedia
| Description | We have determined for the first time, the origin of thermal emissivity from a silicon solar cell. This property determines the temperature which a solar cell will reach and was not previously known. A set of specially modified solar cells were produced and used in a new prototype collector that achieved a 10% increase in thermal efficiency. A predictive computer simulation was configured to confirm the observed behaviour. |
| Exploitation Route | The passive control of solar panel module temperature is fast becoming a very active topic with solar panel manufacturers now scrambling to better understand the thermal behaviour of their product. Our work provides the fundamental understanding required for this activity. |
| Sectors | Energy |
| Description | Findings from this research were presented at an industrial engagement workshop held in August 2016. |
| First Year Of Impact | 2016 |
| Sector | Energy |
| Impact Types | Economic |
| Description | Held a PV-Thermal technical workshop |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | National |
| Primary Audience | Industry/Business |
| Results and Impact | The workshop brought together industrial parties around our EPSRC project with the purpose to explore the barriers to deploying PV thermal technology widely. Issues such as standardisation and professional training were identified to be critical to achieving both low cost and high reliability. |
| Year(s) Of Engagement Activity | 2016 |
| Description | Held an event and published a public briefing paper on "Solar-thermal and hybrid photovoltaic-thermal systems for renewable heating" |
| Form Of Engagement Activity | Participation in an activity, workshop or similar |
| Part Of Official Scheme? | No |
| Geographic Reach | Regional |
| Primary Audience | Industry/Business |
| Results and Impact | Our team wrote a briefing paper entitled "Solar-thermal and hybrid photovoltaic-thermal systems for renewable heating" and held a launch event at Imperial College London on the 24th July 2016 |
| Year(s) Of Engagement Activity | 2017 |
| URL | https://www.imperial.ac.uk/grantham/publications/solar-thermal-and-hybrid-photovoltaic-thermal-syste... |