An integrated desalination system with a combination of electrical heating by power supply and solar heating by Fresnel lens with sun tracking system was investigated in this study. The experiments were carried out under the climatic conditions of Kaohsiung City (22°36’58” N, 120°18’47” E), Taiwan. With only solar heating by Fresnel lens, the temperature of the seawater is strongly dependent on the position of the seawater tray and climatic conditions, and seawater evaporation is not stable. To maintain the uniform evaporation of seawater, an electrical heating plate was also used to provide energy for the desalination process. The results indicate that there are two desalination processes: evaporation on the surface of the seawater and boiling inside the seawater. The production of distilled water is greatly improved with this solar/electrical desalination system, especially at boiling temperature. The results indicate that the energy efficiency and recovery efficiency of this desalination system increase rapidly as electrical power increases. In this study, the commercial energy efficiency of the system can reach 85%, and the recovery efficiency can approach 56.52%. Additionally, a higher annual productivity (6036 L) is obtained, and the cost per liter of distilled water is about 0.152 (US$/L).

In this paper, thermal-fluid modeling of nonporous/porous thermal coil filled by alumina nanofluid is discussed considering constant/variable solar heat fluxes. The fluxes are calculated for a parabolic concentrator at the solar paths for the city with a longitude of 59.20 deg and latitude of 32.87 deg in the clear sky at spring season. The governing equations are included as continuity, momentum, and energy conservations with considering variable solar flux by shadow effects of the coil on the parabolic concentrator. The numerical model is based on the finite element method by LU algorithm using the mumps solver. The results show that, in a porous medium, that the normalized temperature of the presented model has an acceptable agreement with experimental data with maximum errors of 3%. The existence of porosity significantly increases heat transfer parameters that improve transferred solar heat from the wall of the coil to nanofluid. The variable solar heat flux increases the temperature in the length of the coil rather than constant heat fluxes because of increasing exchanged heat to nanofluid.

Using solar energy for space heating is an efficient and simply way to satisfy the energy demands of buildings. In this study, a typical office building is selected as a case model to obtain indoor air temperature characteristics with dual heat storage devices. By analyzing our solar heating system, a mathematical model of the system working process is set up. Using the software matlab / simulink for simulation, the indoor air temperature characteristics in 1 day are obtained. Simulation and experimental results show good consistency. And using the mathematical model, the storage tank size is optimized to search for the minimum size for the fixed building. Based on our analysis, the optimum ratio of storage tank A volume and collector field area is 0.11 m. This research can be a good reference for the design of the solar heating system.

A scheme to streamline the electric power generation profile of concentrating solar power (CSP) plants of the parabolic trough collector (PTC) type is suggested. The scheme seeks to even out heat transfer rates from the solar field (SF) to the power block (PB) by splitting the typical heat transfer fluid (HTF) loop into two loops using an extra vessel and an extra pump. In the first loop, cold HTF is pumped by the cold pump from the cold vessel to the SF to collect heat before accumulating in the newly introduced hot vessel. In the second loop, hot HTF is pumped by the hot pump from the hot vessel to a heat exchanger train (HXT) to supply the PB with its heat load before accumulating in the cold vessel. The new scheme moderately decouples heat supply from heat sink allowing for more control of heat delivery rates thereby evening out power generation.

A solar radiation model is applied to a low temperature water-in-glass evacuated tubes solar collector to predict its performance via computational fluid dynamics (CFD) numerical simulations. This approach allows obtaining the transmitted, reflected, and absorbed solar radiation flux and the solar heat flux on the surface of the evacuated tubes according to the geographical location, the date, and the hour of a day. Different environmental and operational conditions were used to obtain the outlet temperature of the solar collector; these results were validated against four experimental tests based on an Official Mexican Standard resulting in relative errors between 0.8% and 2.6%. Once the model is validated, two cases for the solar collector were studied: (i) different mass flow rates under a constant solar radiation and (ii) different solar radiation (due to the hour of the day) under a constant mass flow rate to predict its performance and efficiency. For the first case, it was found that the outlet temperature decreases as the mass flow rate increases reaching a steady value for a mass flow rate of 0.1 kg/s (6 l/min), while for the second case, the results showed a corresponding outlet temperature behavior to the solar radiation intensity reaching to a maximum temperature of 36.5 °C at 14:00 h. The CFD numerical study using a solar radiation model is more realistic than the previous reported works leading to overcome a gap in the knowledge of the low temperature evacuated tube solar collectors.

This paper presents a comparison of air conditioners using the conventional heating, ventilation, and air conditioning heat pumps and the one using solar heat stored underground, also known as shallow geothermal air conditioning. The proposed air conditioner with solar heat stored underground reunites practical data from an implementation of the heuristic perturb-and-observe (P&O) control and a heat management technique. The aim is to find out the best possible heat exchange between the room ambient and the underground soil heat to reduce its overall consumption without any heat pump. Comparative tests were conducted in two similar rooms, each one equipped with one of the two types of air conditioning. The room temperature with the conventional air conditioning was maintained as close as possible to the temperature of the test room with shallow geothermal conditioning to allow an acceptable data validation. The experiments made both in the winter of 2014 and in the summer of 2015 in Santa Maria, South Brazil, demonstrated that the conventional air conditioner consumed 19.08 kWh and the shallow geothermal conditioner (SGC) consumed only 4.65 kWh, therefore, representing a reduction of energy consumption of approximately 75%.

This paper describes a perturb-and-observe (P&O) control aiming to increase the heat exchange between solar heat stored underground and the ambient of a single conditioned room without any heat pump. This P&O control increases or decreases the water flow rate through an underground hosepipe heat exchanger. With this purpose, two power converters were used to activate, respectively, a low power water pump and a fan coil so as to keep the room within the limits of a reference temperature range (between 18 °C and 24 °C). Outside these limits, the P&O control searches for the best heat exchange between the ambient room and the underground soil and, when inside these limits, the water pump and fan coil are turned off. Two identical experimental rooms, referred in this study as “reference” and “test” rooms, had their temperatures measured every 1-min during winter and summer. For comparison purposes, the reference room was left at its natural conditions without any air conditioning. The experimental results show a remarkable improvement in the heat exchange and a considerable reduction in power demand when using the P&O control. As a result, it was obtained an energy saving of approximately 45% in one summer day and 22% in one winter day. It is important to point out that this paper refers, strictly, to the description of a P&O control for heat exchange systems involving solar heat stored underground in a single room.

In this study, the parabolic trough collector's (PTC) performance is analyzed. In order to achieve this goal, the adopted procedure comprises two main steps. In the first step, the concentrated solar heat flux densities in the solar concentrator focal zone are calculated by soltrace software. In the second step, computational fluid dynamics (CFD) simulations are carried out to analyze and to optimize the thermal performance of the tube receiver. The calculated heat flux densities by soltrace software are used as wall heat flux boundary conditions for the receiver tube. The effect of the receiver tube diameter variation on the PTC thermal performance is studied. A new type of receiver tube is tested. This latter is covered with a metallic thickness. The performance of tube receiver covered with a metallic layer for different diameters is compared to those of the same diameters without the addition of metallic thickness. It has been found that increasing tube metallic thickness enhances the performance of PTC system comparing to the tubes of the same diameter and crossed by the same flow rates.

An experimental study was carried out to investigate the thermal performance of solar heat pipe collector at outdoor test condition. The thermal performance of wickless heat pipe solar collector was investigated by using CNT–water nanofluid. Carbon nanotubes (CNT) nanoparticles with diameter 10–12 nm and 0.1–10 μm length were used in the present experimental investigation. The effects of various filling ratio (F.R.) (50%, 60%, and 70%) and coolant flow rate on thermal performance were discussed in this study.

In this paper, energy and exergy analyses of a new solar-driven triple-staged refrigeration cycle using Duratherm 600 oil as the heat transfer fluid are performed. The proposed cycle is an integration of absorption refrigeration cycle (ARC), ejector (EJE) refrigeration cycle (ERC), and ejector expansion Joule–Thomson (EJT) refrigeration cryogenic cycles which could produce refrigeration output of different magnitude at different temperature simultaneously. Both exergy destruction and losses in each component and hence in the overall system are determined to identify the causes and locations of the thermodynamic imperfection. Several design parameters, including the hot oil outlet temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ERC and EJT cycle are also tested to evaluate their effects on energy and exergy performance. It is observed that largest contribution to cycle irreversibility comes from the central receiver and heliostat field with the heat recovery vapor generator (HRVG), condenser, and ejector of ERC itself also contributing considerably. The exergy efficiency of the solar-driven triple-staged refrigeration cycle is 4% which is much lower than its energy efficiency of 10%, respectively. The results clearly reveal that thermodynamic investigations based on energy analysis alone cannot legitimately be complete unless the exergy concept becomes a part of the analysis.

In a solar hybrid system, the intermittent solar radiation seriously effects the solar-to-electricity conversion. In this paper, the energy-level mechanism between the concentrated solar heat and the thermal cycle was discussed. The system analysis was taken on a 200 MW coal-fired power plant hybridized with solar heat at approximately 300 °C, where the middle-temperature solar thermal energy was used to preheat the feed water before entering the boiler. With changing solar radiation in typical days, the solar share, the work output and the net solar-to-electricity efficiency of this solar hybrid system were evaluated. The net solar-to-electricity efficiency would be increased by 3–7% points compared to that in a solar-only power plant. An off-design parallel configuration of this hybrid system was proposed, achieving the net annual solar-to-electricity efficiency of 18%. It would expected to be an attractive approach to develop the scale-up mid-temperature solar thermal power technology in the short and midterm.

Current heat transfer fluids for concentrated solar power applications are limited by their high temperature stability. Other fluids that are capable of operating at high temperatures have very high melting points. The present work is aimed at characterizing potential solar heat transfer fluid candidates that are likely to be thermally stable (up to 500 °C) with a lower melting point (∼100 °C). Binary and ternary mixtures of nitrates have the potential for being such heat transfer fluids. To characterize such eutectic media, both experimental measurements and analytical methods resulting in phase diagrams and other properties of the fluids are essential. Solidus and liquidus data have been determined using a differential scanning calorimeter over the range the compositions for each salt system and mathematical models have been derived using Gibbs Energy minimization. The Gibbs models presented in this paper sufficiently fit the experimental results as well as providing accurate predictions of the eutectic compositions and temperatures for each system. The methods developed here are expected to have broader implications in the identification of optimizing new heat transfer fluids for a wide range of applications, including solar thermal power systems.

This study investigates annual performance of the hybrid energy system with geothermal and solar heat sources for hot water, heating and cooling of a residential house in South Korea. A small-scale hybrid-renewable energy system (H-RES) consists of a geothermal heat pump for heating and cooling, solar collectors for hot water, a gas fired backup boiler, and incidental facilities. All pipelines are designed for heat flow between the modules such as storage tank, heat production units, and radiators. Also, all systems automatically operated by the integrated sensing and control system. The average coefficient of performance of geothermal module during cooling and heating seasons is evaluated as about 4.1 and 3.5, respectively. Solar fraction for hot water is calculated as over 54%. And annual energy consumption of the H-RES is estimated as much as about 40% of conventional energy systems.

Experimental simulations of a sustainable desalination process have been carried out using a pilot unit. Experiments were conducted at analogous conditions to simplify design evaluation but with different values of the controlling variables to enhance analysis and modeling. The proposed desalination process, which employs solar heating and passive vacuum generation, has been theoretically simulated in earlier work. It entails flowing seawater through a condenser to preheat it and then through a heater before flashing it in a vacuumed evaporator connected to the condenser where the flashed hot vapor is condensed by the incoming cold seawater forming fresh water. All experiments were run for the same period of time starting at the same initial vacuum. Experiments were carried out at different seawater flow rates and different flash temperatures. In addition, each experiment was duplicated three times to validate its outcome. Flashing seawater at higher temperatures increases vaporization and fresh water production rate. In addition, the accumulating noncondensable gases that are slowly eroding the vacuum will decrease the overall vaporization with time, which reduces the production rate of fresh water.

Scale formation in risers and header of direct solar hot water systems is a problem in places where hard water is being used. In this paper, the effect of scaling on energy efficiency indices such as instantaneous efficiency, mass flow rate, and overall heat loss coefficient are quantified by Hottel–Whillier–Bliss equation in the case of thermosiphon and forced circulation systems. The effect of scaling on mass flow and heat transfer rate for both the systems are quantified with experimental validation. Experimentally found mass flow rate is 50% of the analytical mass flow rate for a clean riser and agrees 99% for the case of riser with 3.75 mm scale thickness. This is due to the extreme change in pressure gain in the narrow region. Scale mapping is done for the entire solar hot water system to study the nature of scale growth. The complete footer and nine risers for the length of 150 mm from footer are free from scaling in axial and radial direction. This is due to the low water temperature in the region. The major portion of header and risers for the length 180 mm from the header are completely blocked due to maximum temperature of water in that region. A scale prediction model is brought out based on the experimentally observed scaled water heaters in the field. It reveals that the major parameters to be considered for the correlation are water total hardness and calcium hardness. It is seen in the thermosiphon system that the mass flow rate decreased by scaling affects energy efficiency more than that caused by the heat transfer rate. The scaling effect is more predominant in thermosiphon systems than in forced circulation systems. The analytical study reveals a drop in instantaneous efficiency of 39.5% in thermosiphon system and 7.0% in the case of forced circulation system for the scale thickness of 3.75 mm. The difference between mass flow rate in scaled and unscaled condition is less in forced circulation but much higher in thermosiphon system.

The reactive ceramics suitable for the rotary-type solar reactor (proposed by Tokyo Institute of Technology, Tokyo) with two-step water-splitting reaction were developed. It is confirmed that O 2 gas is evolved in the two-step water-splitting reaction with the reactive ceramics vigorously by rapid heating ( α -O 2 -releasing reaction). The α -O 2 -releasing reaction is due to the formation of interstitial defect and the conversion of lattice oxygen into O 2 gas at a nonequilibrium state. Reactive ceramics ( NiFe 2 O 4 and yttria stabilized zirconia (YSZ)-NiFe 2 O 4 solid solution) can absorb solar thermal energy and convert thermal energy into chemical energy under high O 2 partial pressure atmosphere in the α -O 2 -releasing reaction. Repetitive evolutions of O 2 gas were observed in the two-step water-splitting reaction with YSZ-Fe 3 O 4 solid solution and cerium based metal oxides ( CeO 2 – NiO , CeO 2 – ZrO 2 , and CeO 2 – Ta 2 O 5 ) at high O 2 partial pressure. The CeO 2 – Ta 2 O 5 ( Ce : Ta = 90 : 10 ) released a large amount of O 2 gas ( 3.95 cm 3 / g ) in the α -O 2 releasing reaction in the flow of air.

Pyrometers are commonly used for high temperature measurement, but their accuracy is often limited by uncertainty in the surface emissivity. Radiation heating introduces additional errors due to the extra light reflected off the measured surface. While many types of specialized equipment have been developed for these measurements, this work presents a method for measuring high temperatures using single color pyrometers when the surface emissivity is unknown. It is particularly useful for correcting errors due to reflected light in solar heating applications. The method requires two pyrometers and is most helpful for improving measurement accuracy of low cost commercial instruments. The temperature measurements of two pyrometers operating at different wavelengths are analyzed across a range of sample temperatures to find the surface emissivity values at each wavelength that minimize the difference in temperature measurements between pyrometers. These are taken as the surface emissivity values, and the initial temperature measurements are corrected using the calculated emissivity values to obtain improved estimates of the surface temperature. When applied to temperature data from a solar furnace, the method significantly decreased the difference in the temperature measurements of two single color pyrometers. Simulated temperature data with both random noise and systematic errors are used to demonstrate that the method successfully converges to surface emissivity values and reduces temperature measurement errors even when subjected to significant errors in the model inputs. This method provides a potential low cost solution for pyrometric temperature measurement of solar-heated objects. It is also useful for temperature measurement of objects with unknown emissivity.

Proton exchange membrane fuel cells (PEMFCs) are good candidates for portable energy sources with a fast response to load changes, while being compact as a result of their capability to provide a high power density. Hydrogen constitutes the fuel for the PEMFC and can be obtained in situ to avoid transportation and safety problems. An efficient method to produce hydrogen is by methanol steam reforming in a microreactor, an endothermic reaction for which the highest efficiency occurs between 250 ° C and 300 ° C . Different methods have been used to reach and maintain these temperatures including electrical heaters and exothermic reactions. We propose to use solar energy to increase the efficiency of the microreactor while taking advantage of a free renewable energy source. The microchannels, where the water-methanol mixture flows, are insulated from the surroundings by a thin vacuum layer coated with a selective material. This coating has a high absorptance for short wavelength incoming radiation and low emittance for infrared radiation, reducing the heat losses. By using these coated insulation layers, the fluid temperature in the microchannels is predicted to be higher than 250 ° C . Hence, it is expected that the solar-powered microreactor will produce hydrogen with a higher overall efficiency than the present reactors by taking advantage of the solar radiation.

Water vapor sorption in salt hydrates is one of the most promising means for compact, low loss, and long-term storage of solar heat in the built environment. One of the most interesting salt hydrates for compact seasonal heat storage is magnesium sulfate heptahydrate ( MgSO 4 ⋅ 7 H 2 O ) . This paper describes the characterization of MgSO 4 ⋅ 7 H 2 O to examine its suitability for application in a seasonal heat storage system for the built environment. Both charging (dehydration) and discharging (hydration) behaviors of the material were studied using thermogravimetric differential scanning calorimetry, X-ray diffraction, particle distribution measurements, and scanning electron microscope. The experimental results show that MgSO 4 ⋅ 7 H 2 O can be dehydrated at temperatures below 150 ° C , which can be reached by a medium temperature (vacuum tube) collector. Additionally, the material was able to store 2.2 GJ / m 3 , almost nine times more energy than can be stored in water as sensible heat. On the other hand, the experimental results indicate that the release of the stored heat is more difficult. The amount of water taken up and the energy released by the material turned out to be strongly dependent on the water vapor pressure, temperature, and the total system pressure. The results of this study indicate that the application of MgSO 4 ⋅ 7 H 2 O at atmospheric pressure is problematic for a heat storage system where heat is released above 40 ° C using a water vapor pressure of 1.3 kPa. However, first experiments performed in a closed system at low pressure indicate that a small amount of heat can be released at 50 ° C and a water vapor pressure of 1.3 kPa. If a heat storage system has to operate at atmospheric pressure, then the application of MgSO 4 ⋅ 7 H 2 O for seasonal heat storage is possible for space heating operating at 25 ° C and a water vapor pressure of 2.1 kPa.