Integrated Collector Storage Solar Water Heater Research Articles

An advanced Photovoltaic Thermal Collector Storage Solar Water Heating based on planar liquid vapour thermal diode: Model-based design approach for the optimal energy performance assessment

The building sector is responsible for the highest portion of energy consumption and carbon dioxide emissions. To partly address this issue, the scientific community is placing greater emphasis on the utilization of Building Integrated Solar Systems (BISS) as a means of improving building thermophysics and decreasing primary energy demand. Within this framework, Integrated Collector Storage Solar Water Heaters (ICSSWH) have the potential to significantly decrease the costs associated with the installation and maintenance of building-integrated solar systems (BISS), all while optimizing the utilization of solar power. Nevertheless, ICSSWHs exhibit certain limitations in their capacity to retain thermal energy, particularly during nocturnal periods. One potential approach for enhancing the efficiency of ICSSWH collectors involves the integration of Thermal Diodes (TD), which have the capability to optimize heat absorption while minimizing heat retention. In this context, to advance the state-of-the-art in the field, this paper presents a novel dynamic simulation tool conceived to assess the performance of an innovative Hybrid Photovoltaic Thermal ICSSWH (the HyPVT), incorporating a cutting-edge Planar Liquid Vapour Thermal Diode (PLVTD), and purposely designed to be integrated into buildings’ envelope. By using the developed simulation tool, the performance of the proposed HyPVT collector concept is investigated with the aim of assessing its collection and retention efficiencies under different boundary and operating conditions. Furthermore, to show the effect of the Planar Liquid Vapour Thermal Diode (PLVTD) adoption, a comparative analysis is conducted between the proposed ICSSWH and a conventional one (without a thermal diode). Finally, the developed tool will be utilized in forthcoming research to determine the optimal device configuration through the utilization of a model-based design methodology.

Dynamic testing of a new integrated collector storage solar water heater (ICSSWH) according to standard ISO 9459‐5: Use of a numerical approach for long‐term prediction in different climatic conditions

AbstractThis work analyzes the performance of a new Integrated Collector Storage Solar Water Heater (ICSSWH) by using Dynamic System Testing (DST) method according to Standard ISO 9459‐5. The long‐term performance study of the system in different climatic conditions has been achieved by a coupling model between DST results and a numerical approach based on the system transient behavior. Results of the experimental dynamic system evaluation showed that the total store heat capacity Cs, the useful collector surface Ac* and the storage tank heat losses coefficient Us are, respectively, 0.87 MJ/K, 1.21 m2 and 10 W/K. In Tunisian climatic conditions, the ICSSWH system allows covering until 79.3% from a typical family need for a daily consumption of 170 L. The results found allow optimizing the energy gain of the ICSSWH as well as selecting a specific load volume according to the location. Especially, investigations showed that in Stockholm and Riadh climatic conditions, the ICSSWH's solar fraction reached 27% and 83%, respectively, for a daily load volume of 250 L. More importantly, the experimental effort of DST identification can be minimized by coupling DST data with a robust numerical approach.

Multi-objective optimization for comparative energy and economic analyses of a novel evacuated solar collector prototype (ICSSWH) under different weather conditions

This paper aims at optimizing the energy performance of an innovative integrated collector-storage solar water heater (ICSSWH) prototype. The system incorporates a high-vacuum gap, which significantly reduces convective thermal losses, and a serpentine absorber system coated with a low-E layer to minimize radiative thermal losses.The methodology is based on a detailed dynamic simulation model, implemented in the MatLab environment, suitable conceived to accurately predict the energy performance and economic profitability of the ICSSWH under various weather conditions and energy market prices. This approach aims to initially identify the most influential geometrical, thermophysical and optical parameters that impact the energy performance of the system through the assessment of different objective functions. After identifying the most influential parameters, the range of existence with the interval step for each variable is defined, and the optimization procedure is conducted to determine the optimal set of variables that maximize/minimize the selected objective functions.To demonstrate the effectiveness of the proposed methodology, a proof of concept was conducted to optimize the energy performance of novel ICSSWH by considering nineteen parameters with the aim of maximizing/minimizing three different objective functions. The results of this analysis yielded various sets of optimised parameters for the ICSSWH. Therefore, by implementing the set of optimised parameters into the dynamic simulation model, the energy performance of the optimised and non-optimised ICSSWH collectors was evaluated in 42 different weather zones and compared to a reference case scenario.

Effect of Phase Change Materials Integration on the Thermal Performance of a Parabolic Trough Collector

AbstractIn this paper, a parabolic trough collector (PTC) is studied, and its thermal performance is compared to that of an integrated collector storage solar water heater (ICSSWH). The effect of t...

BIPV/T facades – A new opportunity for integrated collector-storage solar water heaters? Part 1: State-of-the-art, theory and potential

Building Integrated Photovoltaic Thermal (BIPV/T) systems are promising solutions for serving local electricity and heat demands in Net Zero Energy Buildings (NZEB). Despite BIPV/T offering clear energetic and space saving advantages compared to separate BIPV and solar thermal, overheating occurs when no thermal demand exists, resulting in reduced yields, stagnation damage, and excessive fluid pressures. Whilst continuous fluid flows mitigate overheating, corresponding parasitic demands and space requirements are significant (pumps, large storage tanks or heat rejection equipment). This two-part study examines an alternative approach to BIPV/T, addressing overheating by combining BIPV and Integrated Collector-Storage Solar Water Heater (ICSSWH) concepts. Solar heating capabilities of ICSSWH collectors are well established and their overnight heat loss characteristics provide passive overheating control. BIPV-ICSSWH approaches have yet to be investigated extensively. This paper (Part 1 of 2) reviews state-of-the-art and performance benchmarks in BIPV/T and ICSSWH; proposes new performance metrics enabling fairer comparisons; and develops a heat transfer model for BIPV-ICSSWH façade elements employing Planar Liquid-Vapour Thermal Diodes (PLVTD) to regulate absorber temperatures and heat losses. Multi-day solar thermal collection, photovoltaic generation, and overnight heat retention behaviours are simulated in different climates. The modelling results (experimentally validated in Part 2 of 2) suggests BIPV-PLVTD-ICSSWHs with single transparent covers and ς ≈ 90% PLVTD diodicity achieve ηT,col ≈ 60% solar thermal efficiency at N ≈ 0.035m2K·W−1, PV/T performance ratio PRT3 ≈ 75%, and heat loss coefficient Ur,sysAsys/u ≈ 20 W·m−3K−1. The novel BIPV-PLVTD-ICSSWH approach can reduce maximum stagnation by 20 °C compared to conventional BIPV/T and therefore support NZEB realisation during global efforts to tackle the climate crisis.

Vertical Planar Liquid-Vapour Thermal Diodes (PLVTD) and their application in building façade energy systems

Buildings represent one-third of global energy consumption and corresponding CO2 emissions which can be reduced through enhanced insulation and building integrated renewables. Thermal diodes can potentially revolutionise passive heat collection/rejection devices such as Integrated Collector-Storage Solar Water Heaters (ICSSWH) and Climate-Control Building Envelopes (CCBE) employed for decarbonisation. We present novel theoretical and experimental validation work on a lumped parameter heat transfer model of Planar Liquid-Vapour Thermal Diodes (PLVTD) to support development of ICSSWH and CCBE components for building facades. This study augments our previous work on a passive horizontal PLVTD model, by introducing falling film evaporation, vapour convection in vertical rectangular enclosures, condensation on vertical plates, and a methodology for evaluating working fluid temperatures. Experimental validations are presented for vertical aluminium (Ap = 0.15 m2, x = 22 mm) and stainless steel (Ap = 0.98 m2, x = 70 mm) prototypes using two different laboratory test methodologies where temperature setpoints were controlled and measured. The model predicts measured steady state thermal conductances in reverse mode (Ur ≈ 12 W·m–2 K−1 and Ur ≈ 1.7 W·m–2 K−1 for x = 22 mm and x = 70 mm PLVTDs respectively) and forward mode (175 < Uf < 730 W m–2 K−1 and 50 < ULvL < 900 W·m–2·K−1 respectively) with reasonable accuracy across investigated ranges (15 < T2 < 65 °C condenser temperatures, 5 < –ΔT12 < 25 °C reverse mode plate-to-plate temperature differences, 50 < q/A < 1000 W·m−2 forward mode heat fluxes). Forward mode behaviour is determined by working fluid vapour mass flow driven by heat flux and influenced by temperature dependent vapour viscosity. Reverse mode behaviour is determined by vapour convection, plate-to-plate radiation, and envelope/structure conduction. Parametric design influences are theoretically examined and ς > 99% diodicity relevant to CCBE and ICSSWH applications is demonstrated experimentally. Study findings contribute towards global efforts tackling the climate crisis by enabling commercial R&D for new Net Zero Energy Building components.

BIPV/T facades – A new opportunity for integrated collector-storage solar water heaters? Part 2: Physical realisation and laboratory testing

Building Integrated Photovoltaic Thermal (BIPV/T) systems which generate electricity and heat simultaneously are promising solutions for Net Zero Energy Buildings (NZEB). Despite BIPV/T offering clear energetic and space saving advantages compared to separate PV and solar thermal, overheating problems occur when no thermal demand exists, resulting in reduced yields, stagnation damage, and excessive fluid flow pressures. This two-part study examines an alternative approach combining BIPV, Planar Liquid-Vapour Thermal Diodes (PLVTD) and Integrated Collector-Storage Solar Water Heaters (ICSSWH) to achieve BIPV/T functionality and retain heat overnight to minimises parasitic demands and reduce overheating. The introductory paper (Part 1 of 2) established novelty and rationale for BIPV-PLVTD-ICSSWH concepts, reviewed state-of-the-art and performance benchmarks, and used theoretical modelling to predict behaviour from key design and operational parameters. This paper (Part 2 of 2) describes prototype realisation and multi-day solar simulator laboratory thermal and photovoltaic testing for covered and uncovered variants exposed to different irradiance levels. Measured solar thermal efficiencies with and without transparent covers were ηT,col = 60% and 58% respectively under zero heat loss conditions whilst overnight heat loss coefficients were Ur,sysAsys/u = 23.0 and 25.4 W·m–3 K−1 respectively, showing good agreement with theoretical predictions. Photovoltaic performance reduced with increasing absorber temperature as expected, although maximum power point efficiencies (ηE,mpp = 11.4% at T1 ≈ 25 °C and 5.6% at T1 ≈ 89 °C, without cover) were lower than expected owing to partial delamination and PV cell damage. The work demonstrates practical operation of a vertical BIPV-PLVTD-ICSSWH, identifies key areas for design development, and highlights benefits of application in NZEB facades.

Experimental characterisation of different hermetically sealed horizontal, cylindrical double vessel Integrated Collector Storage Solar Water Heating (ICSSWH) prototypes

Existing Integrated Collector Storage Solar Water Heaters (ICSSWHs) are typically simple and low-cost devices that combine heat collection and storage functions in one unified vessel. However, during non-collection periods they are affected by higher heat loss characteristics when compared to standard solar collector systems. This paper introduces the design evolution of new horizontal cylindrical ICSSWH prototypes developed at Ulster University that use novel, patented double vessel, thermal diode features (to enhance heat retention during non-collection periods) achieved by incorporating a liquid–vapour phase change material (PCM) with a very low pressure annular cavity. The energy performance evaluation and characterisation of different prototype designs under solar simulated experimental conditions has been conducted and the subsequent parametric analysis presented. A balance between performance and physical/operational considerations is necessary to ensure that new and practical design solutions (in materials, fabrication and assembly) can be formulated to improve the performance of the ICSSWHs within the limits of commercial reality. The importance of augmenting heat transfer across the annulus cavity has been demonstrated with improvement of the cold-start daily collection efficiency from around (ηcol) of 20% (no HTF), to > 55% when the annulus is evacuated to remove non-condensable gases and form a liquid–vapour phase change thermal diode. Annulus thermal diode heat transfer coefficients of around (Ufr) 35 W/m2K in forward mode and 2 W/m2K in reverse mode have been demonstrated. Diurnal thermal efficiencies (ηcol24) of 22% have been measured, but values of 39% have been identified as achievable in the longer-term development of presented ICSSWH.

A method for a cradle-to-cradle life cycle assessment of integrated collector-storage solar water heaters

Solar thermal technologies are a potentially free and limitless source of energy. Due to the high demand for domestic hot water and the longer insolation periods during summer in Scotland, solar water heating (SWH) systems are a promising renewable energy technology. One of the systems within this technology is the integrated collector-storage solar water heater (ICSSWH). Existing research has predominantly focussed on the technical and economic aspects, with aims to reduce costs whilst maintaining operational performance. This begs the question, what are the true environmental costs of ICSSWH systems? Life cycle assessment (LCA) is an established methodology to evaluate the environmental performance of a product or a system across its life cycle. The aim of this paper is therefore to present an ICSSWH system from an LCA standpoint, also considering the current shift towards a more circular economy. Preliminary field data from a novel ICSSWH designed at Edinburgh Napier University will be presented. The paper will detail the data sources, impact assessment methods and software tools that will be used. Key outcomes from this research show that a holistic ICSSWH design, which considers whole-life implications, does not compromise efficiency and economic viability.

Experimental study of heat retention performance of thermal diode Integrated Collector Storage Solar Water Heater (ICSSWH) configurations

Integrated Collector Storage Solar Water Heaters (ICSSWHs) can support growing hot water demands of off-grid populations and reduce harm to human health and the environment. Despite their simple design and fewer associated components, stored thermal energy dissipates easily in foul weather. While thermal diodes are beneficial heat retention enhancement features in ICSSWHs, other simple additional strategies can enhance heat retention without significantly complicating the fabrication process. This article examines techniques of differing levels of complexity for the improvement of heat retention of a basic thermal diode ICSSWH. A basic thermal diode ICSSWH is adapted into a scalable Asymmetric Formed Reflector with Integrated Collector and Storage (AFRICaS) system and tested for heat retention performance along with other thermal insulation measures. The AFRICaS system improves heat retention efficiency and reduces heat loss coefficient to at least 35% and 1.46 W/K respectively. These results contrast with a heat retention efficiency and heat loss coefficient of 20% and 2.25 W/K respectively for a basic thermal diode ICSSWH. The AFRICaS prototype is potential launchpad for sustainable solar energy cogeneration.

Whole-life design and resource reuse of a solar water heater in the UK

Passive solar systems are often designed primarily with efficiency in mind, and research efforts are concentrated towards gaining an increase in performance. However, due to the multiple materials used, their manufacturing processes, a lifespan that is usually shorter than that of buildings that these systems are applied to and the waste generated when they have reached the end of their useful life, a more holistic approach to the design and performance of these systems should be adopted. This paper reports on the environmental impact of a unique integrated collector–storage solar water heater design, experimentally tested under Scottish weather conditions, considering circular economy and reuse potential. As such, the material flows and components used are mapped against the life-cycle stages of existing European standards while ensuring an optimal efficiency. End-of-life considerations and design for disassembly and reuse are assessed and discussed. Energy payback times of 4·5 and 4·6 years can be realised for a circular and a linear approach, respectively. Operational carbon dioxide savings, which far outstrip the embodied carbon dioxide, demonstrate carbon dioxide payback times of just 7 months, when replacing an electric system. The results show that a holistic design, which promotes circular economy principles, does not compromise efficiency and economic viability.

Performance investigation of an integrated collector–storage solar water heater based on lap-joint-type micro-heat pipe arrays

This study investigates a proposed novel integrated collector–storage solar water heater (ICSSWH) combined with lap-joint-type micro-heat pipe arrays (MHPAs) and latent heat storage. In the proposed system, the solar energy irradiated on ICSSWH is collected and stored in a phase-change material via MHPA with fins attached to the storage section inside the heat storage tank (HST). The stored thermal energy is transferred to the water supply by two multi-channel flat tubes attached to the extraction section of MHPA outside the HST. The effects of environmental conditions during the four seasons and the flowrate and inlet temperature of the water supply on the thermal response of ICSSWH are reported. The highest efficiency reached 61.5% and the average extraction power and average outlet temperature reached 1323.3 W and 42.1 °C, respectively. The thermal storage efficiency of the proposed ICSSWH is evaluated by using the “normalized mean charging efficiency” curve, the intercept and slope of which are 0.682 and 4.847 W K/m2, respectively. Furthermore, mathematical fitting is performed to obtain the function between the mean outlet temperature or extraction power and inlet temperature or volume flow rate during the thermal release process.

Optimization of melting and solidification processes of PCM: Application to integrated collector storage solar water heaters (ICSSWH)

This work presents a detailed analysis of an improved Integrated Collector Storage Solar Water Heater (ICSSWH). This type of device is well suited for rural areas of Morocco because of its low cost, simplicity and compact structure. The innovation targeted in this system lies in the integration of a latent storage system by using a layer of phase change materials (PCM) in its lower part. Indeed, this integration is likely to increase the thermal energy delivered to the user during the night. The overall performance of the system depends on external climate data, type of PCM used and its mass, and flow rate of water. N-eicosane is considered as PCM in this application while hourly weather data corresponding to the city ER-RACHIDIA is used for the analysis. A detailed 2-D transient simulation has been established to optimize the system performance by studying the effect of different design variables and operating conditions. A deep analysis was also made to understand the PCM melting and solidification processes for a better exploitation of this storage technique. Optimized results are obtained when a mass flow rate of 0.0015 kg/s is used with a PCM thickness of 0.01 m and a set temperature of 313 K.

Thermal Performance through Heat Retention in Integrated Collector-Storage Solar Water Heaters: A Review

Solar thermal systems are a long-standing technology that is receiving increased attention, in terms of research and development, due to ambitious climate change targets and the need for renewable energy solutions. Integrated collector-storage solar water heaters (ICSSWHs) are a potential contributing solution and numerous studies have focussed on the optimisation of their thermal performance and efficiency. A major drawback of these systems is the heavy heat losses experienced during non-collection periods. To combat this, various heat retention strategies have been proposed and evaluated, including baffles plates, additional insulation, multiple glazing layers, selective coatings, and phase change materials. This paper aims to bring together these studies through a systematic review of the existing literature surrounding the performance of ICSSWH systems, focusing on heat retention. This review provides a comprehensive and up-to-date point of reference on relevant research and developments for researchers in this field.

Experimental performance characterisation of a Hybrid Photovoltaic/Solar Thermal Façade module compared to a flat Integrated Collector Storage Solar Water Heater module

A modular Hybrid Photovoltaic/Solar Thermal (HyPV/T) Façade technology that utilizes Integrated Collector Storage (ICS) solar technology, providing cost effective solar PV and thermal energy collection for direct use in the building, whilst providing significant thermal insulation has been developed and evaluated experimentally at Ulster University. The HyPV/T system, based upon a patented ICS solar thermal diode concept and shaped into a flat modular profile incorporating PV cells/module can provide space heating, domestic water heating and power generation. The complete system is designed to be compatible with traditional façade structures and fenestration framing arrangements, facilitating direct integration into new and retrofit building applications.The experimental performance of HyPV/T unit has been determined and compared with a flat Integrated Collector Storage Solar Water Heater (ICSSWH) under constant indoor solar simulated conditions. The daily thermal collection efficiencies for the ‘traditional’ flat ICSSWH units performed better than the unglazed HyPV/T, by 5–10%. However, when the additional electrical power produced by the HyPV/T is included, the overall system collection efficiencies are more equal. The heat retention performance shows that's the unglazed (bare) ICS unit had a retention efficiency of 8.3% whilst the ICS unit with a single transparent cover was 23.6% and double glazed unit was 28%. The HyPV/T heat retention efficiencies were approximately 65% over the same cool-down period.

Integrated collector storage solar water heater under partial vacuum

The work focuses on the experimental study of the heat diode mechanism in an Integrated Collector Storage Solar Water Heater (ICSSWH) for domestic applications. The solar device combines a horizontal cylindrical vessel with an asymmetric reflector trough (Compound Parabolic Concentrator – CPC). The cylindrical storage tank comprises two concentric cylindrical vessels: the outer absorbing vessel and the inner storage vessel. The annulus between the cylindrical vessels is partially depressurized and contains a small amount of water serving as Phase Change Material (PCM), which changes phase (mainly at low temperatures) thus producing vapor and creating a thermal diode transfer mechanism from the outer to the inner surfaces of the vessels. Several experimental results, including uncertainty analysis, are demonstrated through diagrams depicting temperature variations, mean daily efficiency and thermal losses coefficient. Additionally results from the variation of the temperature and the total pressure inside annulus are also presented. The results clearly show that the vapor's pressure plays the most important role regarding the thermal performance of the device.

An investigation of the Performance of a Conical Solar Water Heater in the Kingdom of Bahrain

Domestic water heater corresponds to 25% of the house energy consumption and can play an important role to reduce energy house expenses. Solar energy offers a preferred renewable energy resource because of its economic and environmental advantages. It is considered the best alternative to reduce domestic water heater energy consumption cost. Converting solar energy into heat can be considered among the simplest used systems. Solar thermal conversion is more efficient than solar electrical direct conversion method. Solar water heater systems are particularly easy to use and to repair. The integrated conical solar collector water heater (ICSCWH) is so far the easiest among water heating systems. The ICSCWH converts directly and efficiently the solar flux into heat. In order to expand the utilization of ICSCWH systems, many design modifications have been examined and analyzed. This study provides an experimental investigation and mathematical simulation of an ICSCWH system equipped with a glass cover resulting in the increase of the maximum absorption. Integrating the cone-shaped heat collector with an aluminum spiral pipe flow system may enhance the efficiency of the proposed system. In order to maximize the solar radiation of the system, the solar water heater has been designed in a conical shape, which removes the need to change its orientation toward the sun to receive the maximum sun radiation during the day. In this system, the heating of water has been obtained using the spiral pipe flow without the use of the solar cells and mirrors in order to reduce the total cost. The storage water tank of this system is coupled with a conical solar collector. Based on the above design, the solar water heater has been fabricated and tested. In addition, an analytical modeling approach aiming to predict the flow rate within the conical integrated collector storage solar water heater (ICSSWH) and its efficiency, was developed. Modeling through a numerical simulation approach based on energy equations was performed. Considering the entire water amount and the total area of the cone, the amount of water (facing the sun per unit absorbing area in the two symmetrical parts of the system) is found to increase, which is expected to reach a maximum water temperature at a high performance. Our experimental findings show that the daily performance is around 32% and the highest water temperature of about 45°C is obtained in the system at 4 pm, according to seasons and weather conditions. An efficient and simple mathematical simulation approach for the new conical solar water heater is described then validates using experimental data.

Stratification enhancement for an integrated collector storage solar water heater (ICSSWH)

ICSSWH are advantageous solar thermal systems for residential buildings. Their overall efficiency can be improved by increasing stratification in the storage tank. In this paper the charge of a high aspect ratio cavity representing the storage of an ICSSWH was studied experimentally. A satisfying stratification was obtained by heating the storage tank in the middle and inserting a stratification plate. The study examined various angles of system inclination (30, 45 and 60° relative to the horizontal), heat flux imposition (1800, 2700 and 3600Wm−2) and length of the stratification plate. The experiments lasted for three hours, temperatures were measured using thermocouples and velocities were measured via particle image velocimetry. We showed that stratification was higher with a shorter stratification plate, and that it increased with greater heat flux and lower angles. Flow observations on the presented configuration showed that reverse flow was responsible for this thermal behavior. This phenomenon, however, increases with time and could result in creation a dead volume under the heated area.

Integrated collector storage solar water heaters: survey and recent developments

The direct conversion of solar to thermal energy is highly efficient, more environmental friendly and economically viable. Integrated collector storage solar water heaters (ICSSWH) converts the solar radiation directly into heat at an appreciable conversion rate and in many cases using concentrating means. These systems are compact, aesthetically attractive and reasonable in construction and can reduce the environmental impact up to 40 %. They also have high collection efficiency factor and energy saving potential. Despite of many advantages, ICS solar water heaters suffer from high thermal losses in the night/overcast sky conditions. In this article, authors discuss the recently developed new and improved ICS designs and strategies used for reducing thermal losses from such devices, especially in non-collection period. The systems have been evaluated based on a followed categorization to non-concentrating, concentrating and systems with phase change materials.

Performance comparison of four passive types of photovoltaic–thermal systems

In this paper, concept of a passive photovoltaic–thermal system (PVT) means the combination of a photovoltaic (PV) panel and an integrated collector-storage solar water heater (ICSSWH) for co-generation of heat and electricity. In this work, the four different absorber types of passive PVT systems have been simulated and compared. To compare, the aluminum with fin, the aluminum without fin, the Tedlar and the black painted glazing absorbers were selected. In the case of finned absorber, it is assumed that parallel fins have been installed longitudinally back of the absorber plate in the direction of the natural flow of the water to enhance the heat transfer rate and efficiency. Both the height (Lfin) and the numbers effects of fins on the collector performance have been studied. The simulation results show that the aluminum with fin absorber has the highest both the electrical and the thermal efficiencies from other absorber types. Fins reduce the cell temperature and increase the total efficiency (ηpvt) about 12%.