A multistage solar still with photovoltaic panels and DC water heater using a pyramid glass cover enhanced by external cooling shower and PCM

A novel multistage solar desalination system with a photovoltaic heater was manufactured. The base of the down basin of the solar still had a layer of paraffin wax with a mass of 13 kg as a phase change material. The system has been studied to evaluate the enhancement of freshwater. Saltwater was heated by solar radiation and by a direct current water heater. The surfaces of condensation vapor, such as the pyramid glass cover and lower surface of two stacked trays, were designed. This is to improve the productivity of freshwater by decreasing the resistance of condensation. The high temperature of the glass cover is modified by using a cooling water shower, especially at the highest intensity. The study includes parameters, such as cooling water shower flow rate, down basin water level, and the effect of the heater. It is observed that the novel solar desalination is proportional to solar radiation, paraffin wax, the heat input from a heater, cooling water shower flow rate, and down basin water level. The Multiple Stage Effect Photovoltaic Heater (MSEPVH) can produce 15 L/day of distilled water. The excellent flow rate of cooling water, the total freshwater, and the efficiency of MSEPVH for the optimal day were mathematically and experimentally determined.     

Exergy analysis of a passive solar still

This paper presents a steady-state and transient theoretical exergy analysis of a solar still, focused on the exergy destruction in the components of the still: collector plate, brine and glass cover. The analytical approach states an energy balance for each component resulting in three coupled equations where three parameters—solar irradiance, ambient temperature and insulation thickness—are studied. The energy balances are solved to find temperatures of each component; these temperatures are used to compute energy and exergy flows. Results in the steady-state regime show that the irreversibilities produced in the collector account for the largest exergy destruction, up to 615 W/m² for a 935 W/m² solar exergy input, whereas irreversibility rates in the brine and in the glass cover can be neglected. For the same exergy input a collector, brine and solar still exergy efficiency of 12.9%, 6% and 5% are obtained, respectively. The most influential parameter is solar irradiance. During the transient regime, irreversibility rates and still temperatures find a maximum 6 h after dawn when solar irradiance has a maximum value. However, maximum exergy brine efficiency, close to 93%, is found once T_col<T_w (dusk) and the heat capacity of the brine plays an important role in the modeling of collector–brine interaction. Nocturnal distillation is characterized by very low irreversibility rates due to reduced temperature difference between collector and an increase in exergy efficiency towards dawn due to ambient temperature decrease.     

Exergy Analysis of Solar Still with Sand Heat Energy Storage

This paper studies the experimental and exergy analysis of solar still with the sand heat energy storage system. The cumulative yield from solar still with and without energy storage material is found to be 3.3 and 1.89 kg/m², respectively for 8-h operation. Results show that the exergy efficiency of the system is higher with the least water depth of 0.02 m (m_w = 20 kg). Competitive analysis of second law efficiency shows that the exergy efficiency improves the system by 30% than conventional single slope solar still without any heat storage. The maximum exergy efficiency with energy storage material is found as 13.2% and it is less than the conventional solar still without any material inside the basin.     

Optimization of number of collectors for integrated PV/T hybrid active solar still

The aim of this paper is to optimize the number of collectors for PV/T hybrid active solar still. The number of PV/T collectors connected in series has been integrated with the basin of solar still. The optimization of number of collectors for different heat capacity of water has been carried out on the basis of energy and exergy. Expressions of inner glass, outer glass and water temperature have been derived for the hybrid active solar system. For the numerical computations data of a summer day (May 22, 2008) for Delhi climatic condition have been used. It has been observed that with increase of the mass of water in the basin increases the optimum number of collector. However the daily and exergy efficiency decreases linearly and nonlinearly with increase of water mass. It has been observed that the maximum yield occurs at N = 4 for 50 kg of water mass on the basis of exergy efficiency. The thermal model has also been experimentally validated.     

Experimental study on conventional solar still integrated with inclined solar still under different water depth

This study primarily focuses on comparative experimental analysis on standalone conventional solar still (CSS), inclined solar still (ISS), and integrated conventional and inclined solar still (CSS‐ISS) for different parameters that affect the freshwater yield. For enhancing the freshwater yield only a few studies are available on still‐still integration. The present novel study provides a greater improvement in improving the freshwater yield by integrating ISS with CSS. This experimental work mainly concentrates on the importance of water depth (d _w) and mass flow rate of water ( m _w) in the solar still. Water depth inside the conventional still varied from 0.02 to 0.06 m whereas, water is constantly flown with a mass flow rate of 8.33 kg/hour in an ISS with baffles. The experimental result shows that the accumulated freshwater yield from CSS‐ISS, ISS, and CSS were 6.2, 5.04, and 4.24 kg, respectively. CSS‐ISS and ISS produced 46.23% and 18.87% higher productivity than the CSS. From the experimental investigation, it is also identified that the water temperature is significantly improved by 20% using integration as compared with CSS without integration under the same water depth of d _w = 0.02 m. The overall improvement in yield was higher in the case of CSS‐ISS. The deviations between experimental and theoretical values of yield from the conventional and modified solar still were in the range of ±7%.     

Exergy analysis of domestic-scale solar water heaters

Solar water heater is the most popular means of solar energy utilization because of technological feasibility and economic attraction compared with other kinds of solar energy utilization. Earlier assessments of domestic-scale solar water heaters were based on the first thermodynamic law. However, this kind of assessment cannot perfectly describe the performance of solar water heaters, since the essence of energy utilization is to extract available energy as much as possible. So, it is necessary to evaluate domestic-scale solar water heaters based on the second thermodynamic law.No matter the technology process, from the property of energy utilization perspective, we can separate the technology process into three intimately related sub-procedures, namely conversion procedure, utilization procedure, and recycling procedure. An energy analysis entitled ‘Three Procedure Theory’ can be conveniently conducted as presented by Professor Hua Ben. Compared with other theories of energy analysis, three procedure theory exhibits great advantages. The utilization procedure puts forth requirement for the design of parameters in conversion procedure and sets up limits in the consideration of recycling procedure. Of course, under specific conditions, the utilization procedure also receives feedback from other procedures. Three procedure theory furnishes us a good platform to perform energy analysis.The study in this paper is based on three procedure theory. Exergy analysis is conducted with the aim of providing some methods to save cost and keep the efficiency of domestic-scale solar water heater to desired extent and at the same time figuring out related exergy losses. From this survey, it is shown that for an ordinary thermally insulated domestic-scale solar water heater, D_ju (exergy losses due to imperfectly thermal insulation in collector) and D_jR (exergy losses due to imperfectly thermal insulation in storage barrel) cannot be avoided. D_ku (exergy losses due to irreversibility in collector) is mainly caused by irreversibility of heat transfer and D_kR (exergy losses due to irreversibility in storage barrel) is dominated by the mixing of water at different temperature. D_ku acts as the driving force for the system while D_kR is of little contribution. A good design of storage barrel with little D_kR will go a long way in improving exergy efficiency. An equation for computing D_kR is presented. For the collector, which is the core of the domestic-scale solar water heater, a judicious choice of width of plate W and layer number of cover is necessary. We define collector exergy efficiency η_xc to be η_xc=E_xo/E_xu. The relation between collector exergy efficiency and width of plate together with layer number of cover is also analysed.     

Thermodynamic analysis of an oxy-hydrogen combustor supported solar and wind energy-based sustainable polygeneration system for remote locations

In this study, a solar and wind energy-based system integrated with H₂O₂ combustor is developed to produce fresh water from sea-water desalination, electricity, cooling, hydrogen, and oxygen as well as to provide food drying and domestic water heating. The main components of the proposed system contains concentrated solar power (CSP), wind turbine, Rankine cycle, multi stage flash (MSF) desalination unit, water electrolyzer, a refrigeration unit, a food drying system, oxy-hydrogen combustor, domestic water heater, as well as hydrogen and oxygen storage units. Furthermore, for continuous operation of the system during night time and in cloudy weather conditions, a thermal energy storage (TES) unit and oxy-hydrogen combustion unit are integrated to the system. Based on energy and exergy balances, performance assessment of the proposed system is conducted. Moreover, effects of various parameters such as solar irradiation, wind speed and ambient temperature on some of the outputs of the system are investigated. The results illustrate that the proposed system fulfills most of the remote community requirements in an efficient, environmentally benign and uninterrupted way. The obtained results for the reference case show that with installation of parabolic trough concentrators (PTCs) on an area of 111,728 m², the plant produces net electrical power of approximately 11.4 MW, approximately 828 m³/day of freshwater, about 36 kg/s of hot air for food drying, about 31 kg/s of heated domestic water, approximately 920 kg/day of H₂ and about 2.26 MW of cooling. The overall energy efficiency of the system is found to be 50%, while the exergy efficiency of the system is 34%. In addition, the energy and exergy efficiencies of single generation in which there is only electrical power output are approximately 15% and 16%, respectively.     

A comparative study of 3E (energy,exergy, and economy) analysis of various solar stills

In this paper, an experimental study of the conventional solar still (CSS), the conventional solar still with glass cooling (CSSGC), the conventional solar still with basin heating (CSSBH), and the conventional solar still with glass cooling and basin heating (CSSGCBH) was carried out on the basis of the distilled water production, the energy efficiency (EnE), the exergy efficiency (ExE), and economic analysis. The CSSGC and CSSBH contain Peltier modules for cooling the glass and heating the basin. The evaporative heat transfer coefficient for all the experimental stills was calculated. The values of daily distilled water production from the CSSGCBH, CSSBH, CSSGC, and CSS were 4.56, 3.79, 2.49, and 1.89 kg/m², respectively. The daily distilled yield of the CSSBH and CSSGCBH were increased by 58.55% and 50.13%, respectively, as compared with the CSS. Moreover, the daily EnE and ExE of the CSSGCBH were 27.03% and 3.5%, respectively, whereas the EnE and ExE of the CSS were 10.88% and 1.3%, respectively. Furthermore, the cost of distilled water production was found to be 0.26, 0.35, 0.53, and 0.64 $/day for the CSS, CSSGC, CSSBH, and CSSGCBH, respectively, if the selling price of the distilled water was Rs10.     

Parameters of solar collectors tested with a KMITT solar simulator

This paper reports on the experimental performances of flat plate solar collectors tested with a solar simulator under steady-state conditions, in terms of collector efficiency, η, and ratio of temperature difference and solar radiation (T_fi-T_e)/I_T. T_e was the effective heat-sink temperature of the tested collector and could be evaluated from temperatures of the collector's cover, ambient and light source panel (or infrared filter). Techniques for converting values of the collector's parameters, F_RU_Le and F_R(τα)_e, obtained from the indoor tests to match outdoor results were demonstrated. The adjusted results agreed well with those of the outdoor data in the case of a collector having a flat glass cover. For a collector having a convex plastic cover, the estimated optical efficiency was lower than that of the outdoor result.     

Design and performance of a simple single basin solar still

The lack of potable water poses a big problem in southern and south-western arid regions of Pakistan. The underground water, where exists, is usually brackish and cannot be used as it is for drinking purposes. Pakistan lies in high solar insolation band and the vast solar potential can be exploited to convert saline water to potable water. The most economical and easy way to accomplish this objective is using solar still. A simple single basin solar still was designed for 33.3° N latitude. The optimum inclination of glass cover was calculated to be 33.3^o for both summer and winter. The average daily output of solar still based on data of 8 days in July 2004 was found to be 1.7 liters/day for basin area of 0.54 m². Efficiency of the still was calculated as 30.65% with a maximum hourly output of 0.339 liters/hr at 1300 hrs. The drinking water coming from Simly dam filtration plant, Islamabad was desalinated in the solar still. The total dissolved solids (TDS), conductivity and pH of this surface water were measured as 370 ppm, 1.291 mS/cm and 6.72 before desalination and 30 ppm, 41 μS/cm and 6.5 after desalination respectively. The ground water of PIEAS colony, Islamabad was also desalinated and results obtained were 544 ppm, 1.668 mS/cm and 6.78 before desalination and 84 ppm, 31 μS/cm and 5.74 after desalination. A lab-prepared water sample was desalinated as well and results were, 17663 ppm, 85.3 mS/cm, 7.58 before desalination and 226 ppm, 88.5 μs/cm, 6.13 respectively, after desalination. The values for TDS and pH agree with the WHO guidelines for drinking water quality.     

Experimental investigation on the effect of MgO and TiO2 nanoparticles in stepped solar still

This work aims at augmenting the amount of potable water using MgO and TiO₂ in stepped solar still. Experiments were carried out for the climatic conditions of Chennai, India, with two different concentrations of nanofluids inside a stepped basin under three different cases. Results show that there is an improvement in yield of fresh water from stepped solar still by 33.18% and 41.05% using 0.1% and 0.2% volume concentration of TiO₂ nanofluid, respectively, whereas the freshwater yield from stepped still with MgO nanofluids improved by 51.7% and 61.89%. Furthermore, the economic analysis revealed that the cost of potable water from the modified solar still reduced from 0.029 to 0.016 $/kg. Similarly, the useful annual energy, yearly cost per kilogram, and annual cost per kilowatt hour are significantly profitable with the use of MgO nanofluid in the stepped basin and found as 512.46 kWh, 0.025 $/kg, and 0.026 $/kWh, respectively. It is also found that the cost of potable water from the modified still significantly increases as the amount of fresh water produced is decreased with increased fabrication cost of the solar still.     

Experimental and economic analysis of energy storage-based single-slope solar still with hollow-finned absorber basin

The paucity of drinking water is an alarming glitch across the globe. The conversion of available seawater into drinking water by utilizing renewable energy is the best way to surmount this challenge. Desalination through solar still is one of the notable, monetary, and viable processes among various desalination approaches. The current research aims to augment the potable water yield of single-slope solar still by using a hollow-finned absorber basin inserted into paraffin wax—phase change material (PCM). The effect of hollow-finned absorber basin on the yield of solar still is investigated separately, with and without PCM, and compared with the results of conventional solar still (CSS). In the first set of experiments, the CSS and solar still with a hollow-finned absorber basin without PCM (SSHF) are investigated. In the second set of experiments, the CSS and solar still with a hollow-finned absorber basin inserted into PCM (SSHFP) are investigated. The experimental results reported that the CSS is having almost the same yield on the 2 days of testing. The yield of SSHF and SSHFP is increased by 15.7% and 52.4%, respectively, when compared with CSS. The results of the economic analysis proved that the payback period and cost per liter of freshwater produced from SSHFP are comparatively better than SSHF and CSS.     

Numerical study of a passive solar still with separate condenser

A passive solar still with separate condenser has been modeled and its performance evaluated. The system has one basin (basin 1) in the evaporation chamber and two other basins (2 and 3) in the condenser chamber, with a glass cover over the evaporator basin and an opaque condensing cover over basin 3. Basins 1, 2 and 3 yield the first, second and third effects respectively. The top part of the condensing cover is shielded from solar radiation to keep the cover relatively cool. Water vapor from the first effect condenses under the glass cover while the remainder of it flows into the condenser, by purging and diffusion, and condenses under the liner of basin 2. The performance of the system is evaluated and compared with that of a conventional solar still under the same meteorological conditions. Results show that the distillate productivity of the present still is 62% higher than that of the conventional type. Purging is the most significant mode of vapor transfer from the evaporator into the condenser chamber. The first, second and third effects contribute 60, 22 and 18% of the total distillate yield respectively. It is also found that the productivity of the solar still with separate condenser is sensitive to the absorptance of the liner of basin 1, and the mass of water in basins 1 and 2. The mass of water in basin 3 and wind speed have marginal effect on distillate production. Other results are presented and discussed in detail.     

Performance analysis of solar still with cow dung cakes and blue metal stones

The aims of this paper is to investigate the effects of various materials inside the solar still on the increase of the productivity of potable water. Here, blue metal stones and cow dung cakes were used as materials. To investigate their effect, three identical solar stills with an effective area of 1 m square made from locally available materials were tested in climate conditions of Mehsana (23°50′ N 72° 23′). The first and second solar stills were filled with blue metal, stones and cow dung cakes, while the third one was taken as a reference which consisted of only blue paint at the basin. The experiments show that blue metal stones have the highest distillate output at daytime, followed by cow dung cakes solar still and reference solar still. On the other hand, the overall distillate output of blue metal stones and cow dung cakes at daytime as well as at night were 35% and 20% compared with that of reference solar still.     

Year around distilled water production,energy, and economic analysis of solar stills—A comparative study

In this paper, a year around energy efficiency (EnE) and economic analysis of single slope solar still (SSSS), the single slope solar still with glass cooling (SSSSGC), the single slope solar still with basin heating (SSSSBH), and the single slope solar still with glass cooling and basin heating (SSSSGCBH) was carried out based on the distilled water production. The annual yield production from the SSSS, SSSSGC, SSSSBH, and SSSSGCBH were 476.16, 637.44, 970.24, and 1167.36 kg, respectively. The yearly yield produced from the SSSSBH and SSSSGCBH was increased by 50.92% and 59.21%, respectively, as compared with the SSSS. Moreover, the annual EnE of the SSSSGCBH was 28.75%. However, the EnE of the SSSS was 11.73%. Also, freshwater making cost is found to be 18.9, 24.9, 37.9, and 45.6 Rs/day for the SSSS, SSSSGC, SSSSBH, and SSSSGCBH, respectively, if the buying cost of freshwater is Rs 10.     

Stand alone triple basin solar desalination system with cover cooling and parabolic dish concentrator

A stand-alone triple basin solar desalination system is experimentally tested and the results are discussed in this paper. This system mainly consists of a triple basin glass solar still (TBSS), cover cooling (CC) arrangement, parabolic dish concentrator (PDC) and photovoltaic (PV) panel. Four triangular hollow fins are attached at the bottom of the upper and middle basin in order to increase the heat transfer rate and place the energy storing materials. The performance of the system is studied by, conventional TBSS system, integrating the TBSS with CC, TBSS with PDC, and TBSS with CC and PDC. Also, each configuration is tested further by using fins without energy storing material, fins filled with river sand, and fins filled with charcoal. The results of the test reveal that, TBSS with charcoal and TBSS with river sand enhance the distillate by 34.2 and 25.6% higher than conventional TBSS distillates. TBSS with cover cooling reduces the glass temperature to about 8 °C compared to the conventional TBSS. The presence of concentrator increases the lower basin water temperature upto 85 °C. The maximum distillate yield of 16.94 kg/m².day is obtained for TBSS with concentrator, cover cooling and charcoal in fins.     

Improving the performance of solar desalination systems

Two modifications for solar desalination systems are presented. The first modification, using a packed layer that installed in the bottom of the basin to increase the efficiency of the still. A packed layer is formed from glass balls which is considered as simple thermal storage system. The second modification, using rotating shaft installed close to the basin water surface. The target of using the rotating shaft to break the boundary layer of the basin water surface, thus increasing the water vaporization and condensation, the performance of the present solar desalination system may also be increased. The numerical analysis presented the equations of the direct coupling of the selected PV-solar panel, DC-motor and inverter for small PV-system. The characteristics of PV array and the DC-motor are presented for the specific PV–DC power. The performance of the two modified solar stills and the conventional one is compared. Three experiments were carried out using the climate conditions of Cairo site, Egypt. Transient temperatures of the two modified solar stills and the conventional one are measured from sunrise to sunset with the same operating parameters. The energy equations that governed the present solar desalination system are presented. Energy absorbed by glass cover, basin water, packed layer and the required power of the rotating shaft are calculated to obtain the water productivity and efficiency of the present systems. The results show that the two modifications enhanced the performance of the solar desalination system. The efficiency of the modified solar desalination system using packed layer thermal energy storage was increased by 5% at May, 6% at June, and 7.5% at July, while it was increased by 2.5% at May, 5% at June, and 5.5% at July for the modified one using rotating shaft and PV-system.     

Development and assessment of a novel solar heliostat-based multigeneration system

In this paper, a comprehensive study on thermodynamic analysis and assessment, through energy and exergy approaches, is conducted for a multigenerational solar based integrated energy system. The system proposed in this study is based on heliostat solar system integrated with steam turbine. The system is also integrated with seawater reverse osmosis desalination unit and absorption cooling system. The desalination unit operates with energy recovery through the utilization of Pelton turbine. The system produces cooling, heating, fresh water and hydrogen through electrolysis. It is furthermore designed to cover the demand of 4 MW electric power with the production of 1.25 kg/h of hydrogen and 90 kg/s of fresh water. The system advisor model software is applied on a case study for the solar heliostat optimization analysis.     

Experimental evaluation of the wind convection heat transfer on the glass cover of the single-slope solar still

Accurate evaluation of the wind convection heat transfer coefficient (h_w) for solar-based systems is essential, especially for solar desalination systems. Thermal behavior and productivity of solar stills are highly affected by the external heat loss through the glass cover. This paper describes a new experimental approach to estimate the h_w on the glass cover of the conventional single-slope solar distiller (CSS). Indoor experiments have been conducted under steady-state conditions for a wind speed between 0 and 3 m/s. The h_w has been evaluated through an energy balance performed on the distiller's glass cover. The results showed that increasing the wind speed increases the hw (from 5.64 to 31.57 W/m² K) and enhances the distillation rate (from 5.28 to 7.61 mL/min). A new relationship for the h_w was proposed for the CSS and compared with the experimental data available in the literature. The comparison shows that the obtained results are close to the data from solar systems, with a deviation ranging from 27.4% to 37%. However, a significant deviation was obtained with earlier models derived from flat plates (from 29.5% to 59%).