A review of solar collectors and thermal energy storage in solar thermal applications
Highlights
► The latest developments in solar thermal applications are reviewed. ► Various types of solar collectors are summarised. ► Thermal energy storage approaches and systems are discussed. ► The current status of existing solar power stations is reviewed.
Introduction
CO2-induced global warming has become a pressing issue, and needs to be tackled. Efficient utilisation of renewable energy resources, especially solar energy, is increasingly being considered as a promising solution to global warming and a means of achieving a sustainable development for human beings. The Sun releases an enormous amount of radiation energy to its surroundings: 174 PW (1 PW = 1015 W) at the upper atmosphere of the Earth [1]. When the energy arrives at the surface of the Earth, it has been attenuated twice by both the atmosphere (6% by reflection and 16% by absorption [1]) and the clouds (20% by reflection and 3% by absorption [1]), as shown in Fig. 1 [2]. Another 51% (89 PW) of the total incoming solar radiation reaches the land and the oceans [1]. It is evident that, despite the attenuation, the total amount of solar energy available on the Earth is still of an enormous amount, but because it is of low-density and intermittency, it needs to be collected and stored efficiently.
Solar collectors and thermal energy storage components are the two kernel subsystems in solar thermal applications. Solar collectors need to have good optical performance (absorbing as much heat as possible) [3], whilst the thermal storage subsystems require high thermal storage density (small volume and low construction cost), excellent heat transfer rate (absorb and release heat at the required speed) and good long-term durability [4], [5]. In 2004, Kalogirou [6] reviewed several different types of solar thermal collectors that were in common use, and provided relative thermal analyses and practical applications of each type. However, the technologies involved in solar collectors have been much improved since that review was published, so that some of the latest collectors, such as PVT (Photovoltaic-Thermal) collectors, were not available in time for inclusion in [6]. These latest technologies are described in Section 2 of the present paper. In addition, most of existing review-type literature on thermal energy storage has been mainly restricted to low-temperature applications [4], [5], [7], [8], [9]. There are only a few papers addressing high-temperature thermal energy storage applications. These include Kenisarin [10], who reviewed a group of potential phase change materials (PCMs) used from 120 °C to 1000 °C, and provided their thermal properties and Gil et al. [11], who reviewed the high-temperature thermal storage systems especially for power generation; they also listed desirable materials and thermal models that can be used. Updates of the latest developments in high-temperature thermal storage technologies are given in Section 3 of the present paper.
This paper provides a review of various solar collectors and thermal storage methods, and is organised as follows:
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Solar collectors: non-concentrating collectors; concentrating collectors.
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High-temperature thermal energy storage: design criteria; materials, heat transfer enhancement technologies.
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An overview of existing and future solar power stations.
Section snippets
Solar collectors
A solar collector, the special energy exchanger, converts solar irradiation energy either to the thermal energy of the working fluid in solar thermal applications, or to the electric energy directly in PV (Photovoltaic) applications. For solar thermal applications, solar irradiation is absorbed by a solar collector as heat which is then transferred to its working fluid (air, water or oil). The heat carried by the working fluid can be used to either provide domestic hot water/heating, or to
Solar thermal energy storage
After the thermal energy is collected by solar collectors, it needs to be efficiently stored when later needed for a release. Thus, it becomes of great importance to design an efficient energy storage system. Section 3 of the present paper focuses on the solar thermal energy storage, discussing its design criteria, desirable materials and emerging technologies for heat transfer enhancement.
Existing solar power stations
Spain has the most solar thermal power installations in the World, with the U.S. ranked the second. As shown in Table 7, most of existing solar power stations (71.0%) use parabolic troughs to harvest solar energy, as it is a relatively mature technology compared to other technologies discussed in Section 2.2, such as central solar towers (12.9%), parabolic dishes (3.2%) and Fresnel reflectors (12.9%). The installed capacity for each power station ranges from 0.25 MW to 354 MW, and the overall
Conclusions
This paper has reviewed the state of the art on solar thermal applications, with the focus on the two core subsystems: solar collectors and thermal energy storage subsystems.
A variety of solar collectors have been discussed, including non-concentrating types and concentrating types. Among non-concentrating collectors, the PVT solar collectors show the best overall performance. Sun-tracking concentrating solar collectors have also been examined, in terms of optical optimisation, heat loss
Acknowledgments
This work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC Grant No: EP/F061439/1), National Basic Research Programme of China (973 Project: 2013CB228303) and the National Natural Science Foundation of China (NSFC Grant No: 51176110). The authors also gratefully acknowledge the valuable support by Professor Keith Richard Godfrey from University of Warwick in United Kingdom.
References (161)
- et al.
Review on thermal energy storage with phase change: materials, heat transfer analysis and applications
Appl Therm Eng
(2003) - et al.
Review on thermal energy storage with phase change materials and applications
Renew Sust Energy Rev
(2009) Solar thermal collectors and applications
Prog Energy Combust
(2004)- et al.
A review on phase change energy storage: materials and applications
Energy Convers Manage
(2004) - et al.
Solar energy storage using phase change materials
Renew Sust Energy Rev
(2007) - et al.
Review on phase change materials (PCMs) for cold thermal energy storage applications
Appl Energy
(2012) High-temperature phase change materials for thermal energy storage
Renew Sust Energy Rev
(2010)- et al.
State of the art on high temperature thermal energy storage for power generation. Part 1—concepts, materials and modellization
Renew Sust Energy Rev
(2010) - et al.
Theoretical approach of a flat plate solar collector with clear and low-iron glass covers taking into account the spectral absorption and emission within glass covers layer
Renew Energy
(2005) - et al.
The impact of optical and thermal properties on the performance of flat plate solar collectors
Renew Energy
(2003)
Mechanically manufactured selective solar absorber surfaces
Sol Energy Mat Sol C
Solar collector overheating protection
Sol Energy
Enhanced heat transfer using oscillatory flows in solar collectors
Sol Energy
Heat-transfer enhancement in double-pass flat-plate solar air heaters with recycle
Energy
Evaluation of thermal efficiency of double-pass solar collector with porous–nonporous media
Renew Energy
CFD modeling of a polymer solar collector
Renew Energy
A numerical investigation of heat transfer in phase change materials (PCMs) embedded in porous metals
Energy
Heat transfer enhancement for thermal energy storage using metal foams embedded within phase change materials (PCMs)
Sol Energy
Thermodynamic optimization of solar flat-plate collector
Renew Energy
Exergetic optimization of flat plate solar collectors
Renew Energy
Validation of CFD simulation for flat plate solar energy collector
Renew Energy
Design, development and performance monitoring of a photovoltaic-thermal (PVT) air collector
Renew Energy
Model calculations on a flat-plate solar heat collector with integrated solar cells
Sol Energy
Use of TRNSYS for modelling and simulation of a hybrid PV-thermal solar system for Cyprus
Renew Energy
Transient analysis of a photovoltaic thermal solar collector for co-generation of electricity and hot air water
Energy Convers Manage
Study of a photovoltaic thermal system––thermosyphonic solar water heater combined with solar cells
Energy Convers Manage
Improved PV/T solar collectors with heat extraction by forced or natural air circulation
Renew Energy
Comparative study of the performances of four photovoltaic/thermal solar air collectors
Energy Convers Manage
Conventional hybrid photovoltaic/thermal (PV/T) air heating collectors: steady-state simulation
Renew Energy
Annual exergy evaluation on photovoltaic–thermal hybrid collector
Sol Energy Mat Sol C
Performance evaluation of solar photovoltaic/thermal systems
Sol Energy
The thermal and electrical yield of a PV-thermal collector
Sol Energy
Energy and exergy efficiencies of a hybrid photovoltaic–thermal (PV/T) air collector
Renew Energy
Optical and thermal behavior of submerged photovoltaic solar panel: SP2
Energy
Photovoltaic/thermal solar hybrid system with bifacial PV module and transparent plane collector
Sol Energy Mat Sol C
A new method for the design of the heliostat field layout for solar tower power plant
Renew Energy
State of the art on high-temperature thermal energy storage for power generation. Part 2—Case studies
Renew Sust Energy Rev
Simulation, construction and testing of a two-cylinder solar Stirling engine powered by a flat-plate solar collector without regenerator
Renew Energy
Optimum performance characteristics of an irreversible solar-driven Brayton heat engine at the maximum overall efficiency
Renew Energy
Design and construction of a two-axis Sun tracking system for parabolic trough collector (PTC) efficiency improvement
Renew Energy
The effect of using sun tracking systems on the voltage–current characteristics and power generation of flat plate photovoltaics
Energy Convers Manage
Determining optimum tilt angles and orientations of photovoltaic panels in Sanliurfa, Turkey
Renew Energy
The impact of array inclination and orientation on the performance of a grid-connected photovoltaic system
Renew Energy
Thermal property characterization of a low melting-temperature ternary nitrate salt mixture for thermal energy storage systems
Sol Energy Mat Sol C
Novel low melting point quaternary eutectic system for solar thermal energy storage
Appl Energy
Design aspects of solar thermochemical engineering – a case study: two-step water splitting cycle using Fe3O4/FeO re-dox system
Sol Energy
Thermal conductivity enhancement in a Latent Heat Storage System
Sol Energy
An experimental study of enhanced heat transfer in rectangular PCM thermal storage
Int J Heat Mass Trans
Paraffin/porous-graphite-matrix composite as a high and constant power thermal storage material
Int J Heat Mass Trans
Extension of heat transfer area using carbon fiber cloths in latent heat thermal energy storage tanks
Chem Eng Process: Process Intensif
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