Heat retaining integrated collector storage solar water heater with asymmetric CPC reflector

A novel integrated collector storage solar water heater (ICSSWH) was designed, optically analysed and experimentally studied. The unit was based around a heat retaining ICS vessel design consisting of two concentric cylinders mounted horizontally inside a stationary truncated asymmetric compound parabolic concentrating (CPC) reflector trough. The annulus between the cylinders was partially evacuated and contained a small amount of water, which changed phase at low temperature, producing a vapour and creating a thermal diode transfer mechanism from the outer absorbing surface to the inner storage vessel surface. The absorbing outer vessel surface covered with selective absorber film and was partially exposed to solar radiation. The remaining vessel surface area (including the vessel ends) was thermally insulated to improve heat retention during the night. Curved reflectors with a high reflectance along with high transmittance glazing were also used to improve effective operation of the ICS system. The thermal behaviour of the ICS system was compared to that of a Flat Plate Thermosiphonic Unit (FPTU). The experimental results showed that the ICS system is as effective during daily operation as it is during the night. Furthermore, the thermal loss coefficient during night gives similar values between the ICS system and FPTU.     

Performance enhancement of an integrated collector storage hot water system

Integrated collector storage (ICS) systems offer a solution to reduce the height of the conventional flat-plate thermosiphon type collectors. The initial system developed had an aperture area of 1.77 m², a receiver diameter of 200 mm, a concentration ratio of 1.47 and total water storage volume of 65 litres. The main disadvantage of the ICS systems comes from their design, i.e., because the collector absorber is also the storage cylinder it is not possible to insulate it properly and therefore there are significant losses during the night. The main cause of these losses is the convection currents created during the night, circulating around the top glass cover. Another disadvantage of the system is its draw-off characteristics. Because the water cylinder/absorber is horizontal there is very little stratification of the water in the cylinder. It is suggested that a primary 110 mm diameter cylinder is introduced at the space between the main cylinder and the glass. The cold water is introduced directly to the primary cylinder, which feeds the main cylinder. With this modification the convection currents are drastically reduced due to the obstruction created by the primary vessel, thus reducing the night thermal losses. Also as the cold water is introduced first to the primary cylinder there is no direct mixing of the two streams thus greatly improving the system draw-off characteristics. This modification creates an 8% increase in the total cost of the system, which is reasonable, if the above benefits are considered     

Performance analysis and experimental validation of a vee-corrugated absorber integrated collector storage solar water heater

This paper focuses on enhancing the energy collection efficiency of an integrated collector storage solar water heater (ICS SWH) by vee-corrugating the absorber and optimizing the design for the vee-included angle through simulation and experimental study. This paper presents an efficient algorithm for analyzing a vee-corrugated absorber ICS SWH using Engineering Equation Solver Software. For validating this algorithm, two models of ICS SWH systems have been fabricated: one with a flat absorber and the other with a 60° vee-included angle corrugated absorber with eight corrugations. The basic purpose of the fabrication of the flat absorber ICS SWH system was to approximate the absorptivity of the absorber. A typical value of 0.68 was estimated for the absorptivity of the aluminum absorber coated with nonselective black paint. After the experimental investigation of the 60° vee-included angle ICS SWH system, it was found that the real-time readings were in close agreement with the numerical model readings. For comparison with the previous work, a five-corrugation system with an approximate 90° vee-included angle with the same projected dimensions was modeled and the efficiencies of both the models for the time from 7 a.m. to 3 p.m. were calculated. The efficiency of the eight-corrugation model was 42.56%, which was better than the previous work of the five-corrugation model, with a 38.86% efficiency for the same ambient conditions. Also, it was theoretically deduced that we had an optimized system at 18 corrugations and a vee-included angle of 28.78°.     

Experimental investigation of a domestic solar water heater with solar collector coupled phase-change energy storage

Phase change materials (PCMs) have good properties such as high thermal capacity and constant phase change temperature. Their potential use in solar energy storage is promising. Tests of exposure and constant flow rate are performed to investigate the thermal performance of a domestic solar water heater with solar collector coupled phase-change energy storage (DSWHSCPHES). Due to the low thermal conductivity and high viscosity of PCM, heat transfer in the PCM module is repressed. The thermal performance of the DSWHSCPHES under exposure is inferior to that of traditional water-in-glass evacuated tube solar water heaters (TWGETSWH) with an identical collector area. DSWHSCPHES also performs more efficiently with a constant flow rate than under the condition of exposure. Radiation and initial water temperature have impacts on system performance; with the increase of proportion of diffuse to global radiation and/or initial water temperature, system performance deteriorates and vice versa.     

Performance analysis of a latent heat storage system with phase change material for new designed solar collectors in greenhouse heating

The continuous increase in the level of greenhouse gas emissions and the rise in fuel prices are the main driving forces behind the efforts for more effectively utilize various sources of renewable energy. In many parts of the world, direct solar radiation is considered to be one of the most prospective sources of energy. In this study, the thermal performance of a phase change thermal storage unit is analyzed and discussed. The storage unit is a component of ten pieced solar air collectors heating system being developed for space heating of a greenhouse and charging of PCM. CaCl₂6H₂O was used as PCM in thermal energy storage with a melting temperature of 29 °C. Hot air delivered by ten pieced solar air collector is passed through the PCM to charge the storage unit. The stored heat is utilized to heat ambient air before being admitted to a greenhouse. This study is based on experimental results of the PCM employed to analyze the transient thermal behavior of the storage unit during the charge and discharge periods. The proposed size of collectors integrated PCM provided about 18–23% of total daily thermal energy requirements of the greenhouse for 3–4 h, in comparison with the conventional heating device.     

Design and thermal performance of an ICS solar water heater based on three parabolic sections

An integrated collector storage (ICS) consisting of a single cylindrical horizontal tank placed in a reflector composed of three parabolic branches is designed and geometric characteristics are determined. The suggested design aims to cover the need of hot water of a family composed of four persons. Based on this target, its geometric characteristics: reflector geometry, aperture, reflector length, are derived.The comparison between this system and two other systems of solar water heater, composed of a storage tank with asymmetrical CPC and symmetrical CPC, shows important thermal performances despite the simplicity and the little cost of our collector. The first experimental results are given and its comparison with the theoretical results demonstrates a good agreement.     

Development of an integrated solar home system

To date, many traditional Solar Home Systems (SHS) have consisted of separate components requiring assembly by trained individuals in the field. While this cannot be secured, many SHSs in remote areas have not fulfilled their expected lifecycles or have not functioned at all. The new Integrated Solar Home System (I-SHS) offers a solution: All components such as PV module, charge controller, inverter and wiring, but also support structure and foundation, are integrated and pre-assembled by the manufacturer. This eases installation and reduces costs and failures. Additionally, through the integration of a water tank that serves as a cooling unit as well as the system foundation, a significant reduction of operating cell temperature was achieved, increasing electrical yield by 9–12%.     

Efficiency and exergy analysis of a new solar air heater

It would be misleading to consider only the cost aspect of the design of a solar collector. High service costs increase total costs during the service life of solar collector. The most effective way to save energy is by increasing the efficiency in a solar collector by the heat transfer coefficient.In our study, five solar collectors with dimensions of 0.9×0.4 m were used and the flow line increased where it had narrowed and expanded geometrically in shape. These collectors were set to four different cases with dimensions of 1×2 m. Therefore, heating fluids exit the solar collector after at least 4.5 m displacement. According to the collector geometry, turbulence occurs in fluid flow and in this way heat transfer is increased. The results of the experiments were evaluated on the days with the same radiation. The efficiencies of these four collectors were compared to conventional flat-plate collectors. It was seen that heat transfer and pressure loss increased depending on shape and numbers of the absorbers.     

Numerical and experimental analysis of convection heat transfer in passive solar heating room with greenhouse and heat storage

In this paper, heat transfer and air flow in passive solar heating room with greenhouse and heat storage are studied. Thermal insulation of solar heating room has significant effects on temperature distribution and airflow in the heating chamber of this solar system. Heat transfer and air flow in a rock bed, which is used as solar absorber and storage layer, are also studied. If porosity is kept within certain range, increasing the rock size causes an increase of the capability of thermal storage and heating effects; increasing the porosity of thermal storage materials results in an increase of the bed temperature but a decrease of the rock mass. The specific heat capacity and thermal conductivity have a remarkable effect on the average temperature of rock bed. All these factors should be taken into account when designing a solar heating system.     

Performance evaluation of a solar thermal energy storage system using nanoparticle-enhanced phase change material

This paper presents a numerical investigation on the thermal performance of a solar latent heat storage unit composed of rectangular slabs combined with a flat-plate solar collector. The rectangular slabs of the storage unit are vertically arranged and filled with phase change material (PCM: RT50) dispersed with high conductive nanoparticles (Al₂O₃). A heat transfer fluid (HTF: water) goes flow in the solar collector and receives solar thermal energy form the absorber area, then circulates between the slabs to transfer heat by forced convection to nanoparticle-enhanced phase change material (NEPCM). A numerical model based on the finite volume method and the conservation equations was developed to model the heat transfer and flow processes in the storage unit. The developed model was validated by comparing the obtained results with the experimental, numerical and theoretical results published in the literature. The thermal performance of the investigated latent heat storage unit combined with the solar collector was evaluated under the meteorological data of a representative day of the month of July in Marrakesh city, Morocco. The effect of the dispersion of high conductive nanoparticles on the thermal behavior and storage performance was also evaluated and compared with the case of base PCM without additives.     

Performance study of a solar water heater incorporating a bed of solid particulates

An investigation of a solar water heater with built-in storage is presented. The experimental apparatus consists, essentially, of a rectangular insulated tank packed with solid particulates. The packed system is examined with no net water flow. An equation based on a heat balance is used to predict the theoretical temperature history of the water. Comparisons demonstrate that the model agrees well with experimental values. Predictions are also made regarding the effect of using various packing materials.     

Thermal modeling of integrated roof air heater for passive solar space heating of a non-air-conditioned building

This communication presents the periodic heat transfer analysis for solar space heating of an unconditioned building with an integrated roof air heater. The system consists of an air duct within the roof such that the air is continuously or intermittently forced to circulate the cooler room air through the inlet of the air duct. Time dependence of the air flow is represented by a step function of time for daily operation and, hence, has been expressed as a Fourier series in time. The analysis takes into account air ventilation, ground heat conduction and furnishings. The effects of depth of the air duct from the outer surface of the roof and the magnitude and duration of air flow rate on indoor air temperature have been studied for a typical cold winter day in Delhi. It is seen that a time dependent air flow through the duct is desirable from the point of view of increasing the indoor air temperature in the case of a bare roof. However, in the case of a blackened and glazed roof, continuous air flow is needed for increasing the room air temperature. The results are desirable from the point of view of efficient space heating of solar passive buildings.     

Integrated solar collector–storage tank system with thermal diode

Water heating by utilizing solar energy for domestic use is a well established technique. However, most systems consist of the solar collector and storage tank as separate units and require piping and extra thermal insulation for both. This work considers an integrated system, which is easy to manufacture or to modify the storage tank to operate as a solar collector as well as a storage tank. The system contains a thermal diode to prevent reverse circulation at night-time. A prototype is constructed and a mathematical model is developed to study the thermal performance of the integrated system. It is found that the thermal efficiency of the suggested system is comparable with conventional systems. Also, simulation indicated that the thermal diode significantly reduces heat losses at night-time.     

Electrolytic hydrogen based renewable energy system with oxygen recovery and re-utilization

The Hydrogen Research Institute (HRI) has developed a stand-alone renewable energy (RE) system based on energy storage in the form of hydrogen. When the input devices (wind generator and photovoltaic array) produce more energy than is required by the load, the excess energy is converted by an electrolyzer to electrolytic hydrogen, which is then stored after stages of compression, purification and filtration. Conversely, during a time of input energy deficit, this process is reversed and the hydrogen produced earlier is reconverted to electrical energy through a fuel cell. The oxygen which has been produced by the electrolyzer during the hydrogen production is also stored at high pressure, after having gone through a purification and drying process. This stored oxygen can be re-utilized as oxidant in place of compressed air in the fuel cell. The modifications of the electrolyzer for oxygen storage and re-utilization of it as oxidant for the fuel cell are presented. Furthermore, the HRI has designed and developed the control system with power conditioning devices for effective energy management and automatic operation of the RE system. The experimental results show that a reliable autonomous RE system can be realized for such seasonal energy sources, using stored hydrogen as the long-term energy buffer, and that utilizing the electrolyzer oxygen by-product as oxidant in the fuel cell increases system performance significantly.     

A critical review on integrated system design of solar thermochemical water-splitting cycle for hydrogen production

The development of clean hydrogen production methods is important for large-scale hydrogen production applications. The solar thermochemical water-splitting cycle is a promising method that uses the heat provided by solar collectors for clean, efficient, and large-scale hydrogen production. This review summarizes state-of-the-art concentrated solar thermal, thermal storage, and thermochemical water-splitting cycle technologies that can be used for system integration from the perspective of integrated design. Possible schemes for combining these three technologies are also presented. The key issues of the solar copper-chlorine (Cu–Cl) and sulfur-iodine (S–I) cycles, which are the most-studied cycles, have been summarized from system composition, operation strategy, thermal and economic performance, and multi-scenario applications. Moreover, existing design ideas, schemes, and performances of solar thermochemical water-splitting cycles are summarized. The energy efficiency of the solar thermochemical water-splitting cycle is 15–30%. The costs of the solar Cu–Cl and S–I hydrogen production systems are 1.63–9.47 $/kg H₂ and 5.41–10.40 $/kg H₂, respectively. This work also discusses the future challenges for system integration and offers an essential reference and guidance for building a clean, efficient, and large-scale hydrogen production system.     

Thermal performance of PCM thermal storage unit for a roof integrated solar heating system

The thermal performance of a phase change thermal storage unit is analysed and discussed. The storage unit is a component of a roof integrated solar heating system being developed for space heating of a home. The unit consists of several layers of phase change material (PCM) slabs with a melting temperature of 29 °C. Warm air delivered by a roof integrated collector is passed through the spaces between the PCM layers to charge the storage unit. The stored heat is utilised to heat ambient air before being admitted to a living space. The study is based on both experimental results and a theoretical two dimensional mathematical model of the PCM employed to analyse the transient thermal behaviour of the storage unit during the charge and discharge periods. The analysis takes into account the effects of sensible heat which exists when the initial temperature of the PCM is well below or above the melting point during melting or freezing. The significance of natural convection occurring inside the PCM on the heat transfer rate during melting which was previously suspected as the cause of faster melting process in one of the experiments is discussed. The results are compared with a previous analysis based on a one dimensional model which neglected the effect of sensible heat. A comparison with experimental results for a specific geometry is also made.     

Life cycle environmental impact of a thermosyphonic domestic solar hot water system in comparison with electrical and gas water heating

A methodology for the environmental impact evaluation over the life span of a Domestic Solar Hot Water System (DSHWS) is presented. The results are compared to the environmental consequences of the conventional energy form substituted and the total environmental gain is calculated. For the purposes of this analysis, the “Eco-indicator ’99” Life Cycle Impact Assessment methodology was adopted and the materials and procedures of the DSHWS production and utilization are evaluated.     

Thermal energy storage in building integrated thermal systems: A review. Part 1. active storage systems

Energy consumed by heating, ventilation and air conditioning systems (HVAC) in buildings represents an important part of the global energy consumed in Europe. Thermal energy storage is considered as a promising technology to improve the energy efficiency of these systems, and if incorporated in the building envelope the energy demand can be reduced. Many studies are on applications of thermal energy storage in buildings, but few consider their integration in the building. The inclusion of thermal storage in a functional and constructive way could promote these systems in the commercial and residential building sector, as well as providing user-friendly tools to architects and engineers to help implementation at the design stage. The aim of this paper is to review and identify thermal storage building integrated systems and to classify them depending on the location of the thermal storage system.     

Thermal performance of a solar cooker integrated vacuum-tube collector with heat pipes containing different refrigerants

A solar cooking system using vacuum-tube collectors with heat pipes containing a refrigerant as working fluid has been fabricated, and its performance has been analysed experimentally. The experiments were conducted during clear days in July and August of 2002 in Elazı , Turkey under similar meteorological conditions for three refrigerants and water. Detailed temperature distributions and their time dependences were measured. The maximum temperature obtained in a pot containing 7 l of edible oil was 175 °C. Also, the cooker was successfully used to cook several foods. The cooking processes were performed with the cooker in 27–70 min periods.