Evacuated Tube Research Articles

Impact of spatial and annual solar variability on the economic viability of non-tracking solar heating systems

Solar energy is stochastic, varying with time and space, which is a risk factor hindering the deployment of solar heating systems (SHS) in industries. Little is known about the level of risk associated with SHS due to spatial and annual variation. This research thus seeks to quantify the level of risk due to spatial and annual weather variation. The novelty of the study is that it assesses the variability in energy production of different non-tracking SHS at different operating temperatures (60 and 100 °C), different locations, and different time series. The level of risk is quantified using the coefficient of variation (CV) and the z-score. The yearly energy gains are simulated for each collector using the solar collector energy output calculator. The weather data for each location is produced using Meteonorm for a typical meteorological year (TMY). To analyze the annual variability 3 TMYs were produced from the time range 1981–2020 and the spatial variation was analyzed for 9 different locations. In terms of the annual variation, the results show that the CV of the energy gain for all the SHS was between 13 and 26 %. The highest z-score for spatial energy variation was 1.6 and -1.9. Both results indicate a considerably low risk factor. Economic predictions considering 1 TMY showed an underestimation of 4 and 7 % on the levelized cost of heat (LCOH) when operating at 60 and 100 °C respectively. Furthermore, operating at high temperatures has a high variability risk compared to lower temperatures. In terms of the variability of each SHS the compound parabolic concentrator (CV-10) and evacuated tube collector (CV-11) are more stable compared to the solar air heater (CV-14) and flat plate collector (CV-18). Knowing the extent of variability and risk involved for each collector will help investors plan their entire portfolio.

Comprehensive analyses of solar thermal module with booster mirror integration for adaptation to various application scenarios

Integration of a booster mirror reflector enhances the performance of evacuated tube collector within a prescribed range of solar incidence angles and reject solar rays within others. Seasonal performance adjustment makes it possible to adapt to various scenarios with different seasonal application purposes, for example, only domestic hot water, only space heating, or both. In this study, a mathematical model describing the photo-thermal conversion of this solar module was developed and validated using experimental data. The dynamic contributions of the collector and mirror planes were decomposed, and the optimal combination configurations for adaptation to three different application scenarios in four representative Chinese cities were investigated through the rotation of both planes. The three scenarios were: Scenario 1, annual performance augmentation; Scenario 2, coldest month performance augmentation; and Scenario 3, winter performance augmentation and prevention of summer overheating. It was found that optimal performance was always achieved when the collector plane was perpendicular to the mirror plane in the three scenarios. Depending on the optimal configurations, in Scenario 1 the mirror reflector contributed 30–32% heat energy, in Scenario 2 the mirror reflector contributed 41–49% heat energy during the coldest months, and in Scenario 3 the mirror reflector contributed 40–47% heat energy during the entire heating season. The objective of this study was to develop a comprehensive tool to evaluate the photo-thermal performance of this solar module and determine optimal configurations for various application scenarios.

Experimental investigation of atmospheric air to water generation based on both end open evacuated tube collector solar air heater

Regional economic, social, and ecological security are all entwined and influenced by the availability of water. Since the available water resources are depleting at a very faster rate and people are restricted to access the clean water, it is urgent to discover new & alternative sources of fresh water to meet everyone's requirements. An inexpensive and effective solution to the rising problem of the water shortage can be atmospheric air to water generation (AWG) technology. This study involves the development and experimental investigation of a novel AWG system based on adsorption under ambient conditions. Both end open evacuated tube collector solar air heater (ETC-SAH) with 5.07 m2 solar collector area and an air-to-air condenser is used. The system’s performance is evaluated based on several key parameters, including adsorption & regeneration rate, energy & exergy efficiency, and economic analysis. The fresh water yield reported from the system is 3.08 L/day at 0.12 $/L cost. The energy & exergy efficiency reported by the system is 9.65% & 3.69%, respectively. Additionally, the water produced is subjected to testing at a regionally certified laboratory to confirm its safety for consumption.

Assessment of the Trilateral Flash Cycle potential for efficient solar energy conversion in Europe

The potential of the Trilateral Flash Cycle (TFC) for the efficient conversion of solar energy to power in Europe is assessed in this work. A numerical analysis of a Solar-TFC thermal power unit is performed, by applying an in-house numerical model. Flat Plate Collectors (FPC) and Evacuated Tube Collectors (ETC) are modeled as solar heat sources. Particular focus is on the technological bottleneck of the TFC, i.e. two-phase expansion, by applying a novel two-phase expansion numerical model. Annual simulations are performed with the total efficiency of the Solar-TFC maximized at each time step. The annual total efficiency of the Solar-TFC, exergy efficiency, and thermal efficiency of the TFC can be as high as 5%, 5.3%, and 11%, respectively. ETCs increase the economic viability of the Solar-TFC, particularly as the annual electricity output increases. The Levelized Cost of Electricity (LCOE) of the modeled unit is estimated in the range of 0.25 and 0.75 €/kWh, which can be further reduced by increasing the collectors’ area. The Solar-TFC unit can reduce, on an annual basis, the CO2 emissions by 2.5–47 kg per m2 of solar collectors, with the carbon footprint reduction depending on the collectors’ efficiency and the installation location.

Thermal and thermo-mechanical analysis of a novel pass-through all-glass evacuated collector tube by combining experiment with numerical simulation

The collector tube could be a significant component of a solar water heater (SWH), that directly determines its performance and application eventualities. Here, a completely unique pass-through all-glass evacuated collector tube (ETC) is projected, which includes an easy structure composed inner and outer layers with each ends amalgamate along and no free ends. In addition, the flow pattern of the working medium in the tube also changes from laminar to turbulent flow, and natural convection changes to forced convection, greatly improving the convective heat transfer efficiency. Such a solar collector tube reaches 50% thermal efficiency at 54 °C in operation temperature and DNI = 1000W/m2, and might reach about 82 °C stagnation temperature at identical condition. Compared to standard Dewar tube, the pass-through ECT includes a higher thermal efficiency thanks to a lower inner layer temperature and better exit temperature. Completely different thermal expansions cause thermal stress within the glass structure, however the utmost stress between the inner and outer tubes was unbroken at intervals 40–120 MPa guaranteeing safe and stable operation at intervals the attainable temperature regime.

Evacuated tube collector based solar drying of pre-treated okra (Abelmoschus esculentus): Analysis of thermal performance, bioactive compounds, antioxidant activity, and functional properties

Okra (Abelmoschus esculentus) is a good source of micronutrients and a highly perishable vegetable crop. The okra pods were dried in an evacuated tube collector-based novel solar drying system, i.e. an evacuated tube solar dryer with heat pipe (ETSD_HP), and evacuated tube solar dryer without heat pipe (ETSD_WHP) and sun drying. The okra was pre-treated at different temperatures prior to drying, and the thermal profiling, moisture diffusivity, and retention of quality attributes were investigated and compared. The highest moisture diffusivity was found in the sample pre-treated at 80 °C and dried in ETSD_HP. The results show that Total Phenolic Content (TPC), 2,2-diphenylpicrylhydrazyl (DPPH), and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) content increased across all drying techniques, while the Total Flavonoid Content (TFC) and Ferric Reducing Antioxidant Power (FRAP) content were decreased. The bioactive compounds, namely TPC and TFC retention, were maximum for okra dried in ETSD_HP. The maximum retention of chlorophyll content (76.70 to 93.20%), vitamin C (73.84 to 93.73%), and minimum color changes (7.70 to 13.48) were observed for the all the sample dried in ETSD_WHP. The pre-treatment temperature of 80 °C was found to be appropriate for the maximum retention of quality attributes of okra. FTIR analysis identified functional groups of active compounds in dried okra for all the drying methods. Therefore, both the ETSD_HP and ETSD_WHP techniques areappropriate to retain the bioactive compounds and functional properties of okra as compared to Sun drying. ETSD_HP is recommended for increased moisture diffusion with maximum retention of bioactive compounds.

The regeneration of various solid desiccants using novel heated surface plate based on heat pipe vacuum tube collector: an experimental investigation

ABSTRACT In this article, various desiccants such as silica gel, molecular sieve 13X, and activated alumina have been regenerated using a novel heated surface plate. No experiment for the regeneration of desiccant has been done with the use of a hot surface plate heated by the heat pipe vacuum tube collector. A novel apparatus SHPPCP (solar heat pipe powered copper plate) based on heat pipe vacuum or evacuated tube collector (ETC) has been made. SHPPCP contains a surface plate, which is an open box of copper and this open box is attached to heat pipes. The Heat pipe is made of copper and used to extract heat from ETC. Desiccants regenerate by taking heat from the surface plate. The average temperature range for regeneration was 65–105°C during the experiment. The different parameters like humidity ratio, surface plate temperature, regeneration rate, solar intensity, and so on, have been discussed to get the performance of a desiccant. Silica gel among other desiccants has shown better adsorption rate and regeneration rate. The maximum regeneration rates of silica gel, activated alumina, and molecular sieve are 0.0936 kg/h, 0.072638 kg/hr, and 0.051348 kg/hr, respectively, and the minimum regeneration rates of silica gel, activated alumina, and molecular sieve are 0.0936 kg/h, 0.072638 kg/hr, and 0.051348 kg/hr, respectively.

Experimental study of simultaneous effect of evacuated tube collectors coupled with parabolic reflectors on traditional single slope solar still efficiency

Enhancing the performance characteristics of solar still is considered one of the most significant factors to increase the still efficiency. This research aims to modify the single slope still to enhance efficiency and maximize freshwater productivity. For this purpose, three evacuated tube collectors have been coupled with traditional still to heat up the basin saline water. Also, a parabolic trough reflector has been combined with each evacuated tube collector to increase the amount of solar radiation received. In this work, the performance characteristics and energy analysis of the modified stills were experimentally investigated by considering the effect of traditional still unit only, traditional still unit coupled with an evacuated tube collector, and traditional still unit coupled with both evacuated tube collector and parabolic trough reflectors in combination. The results show that using both modifications simultaneously is more efficient than using each of them separately. According to the results, an increase in productivity of 82.26% when the still coupled with the evacuated tube collectors is used, and 112.57% increase when both modifications are used simultaneously. According to the cost evaluation, using simultaneous mechanisms not only enhances the solar still performance and increase efficiency but also decrease freshwater production cost.

Experimental investigation of a solar evacuated tube collector embedded with a heat pipe using different nanofluids and controlled mechanical exciting pulsations

Numerous studies have been conducted to enhance the thermal performance of evacuated tube solar thermal collectors using various techniques, such as different working fluids, concentrators, and modifications to the absorber design. This work presents a parametric study to improve the thermal performance of a solar-evacuated tube collector embedded with a heat pipe (SETCHP) by utilizing different types of nanofluids and controlled mechanical excitation. The experiment involved six identical SETCHPs operating under the same conditions, with one setup filled with pure acetone as a reference. The second and third setups were filled with (0.5% vol Al2O3)/based acetone and (0.5% vol CuO)/based acetone, respectively. The remaining three setups were modified by imposing controlled mechanical excitation with different frequencies (27–82 Hz) to investigate the effect of vibration on thermal performance. The results demonstrated that the optimal enhancement was achieved with mechanical vibration pulses at 82 Hz, improving efficiency by 91% and 86% with Al2O3/based acetone and CuO/based acetone, respectively. The enhancement percentage of effective heat transfer coefficient (EHTC) and convective heat transfer coefficient (CHTC) varied with solar intensity and vibration, with improvements ranging from 5 to 82% and 3–53%, 26–160% and 5–60%, and 6.5–140% and 6.5–54% for pure acetone, Al2O3, and CuO (0.5% vol) acetone-based nanofluids, respectively.

Development of sensible heat storage based solar hybrid dryer with evacuated tube collector and biomass gasifier for shrimp drying

The work was aimed at developing an energy-efficient solar hybrid dryer with a biomass-based gasifier heat backup suitable for drying shrimps even during off-sunshine hours. In this dryer, water was utilized as a sensible heat storage (SHS) material as well as heat transfer fluid and biomass gasifier as an indirect backup heat source. The performance of the solar-gasifier hybrid dryer was assessed by drying shrimp (Metapenaeus dobsoni) samples and compared it with solar, and gasifier modes. Shrimp obtained the desired moisture content of 15.09 %, 13.46%, and 14.77% (w.b.) in 9 h, 6 h, and 6 h of drying in solar mode, gasifier mode, and solar-gasifier hybrid drying mode, respectively. The average drying rate of the solar, gasifier and hybrid modes of drying were 0.33 g/g dm.h, 0.46 g/g dm.h, and 0.47 g/g dm.h, respectively. Results revealed that the evacuated tube solar water collector harnessed 193104 kJ and 160185 kJ of heat energy during sunshine hours under the solar and hybrid mode of operation. The maximum drying efficiency of 34.97%, 35.62%, and 41.66% was obtained for gasifier mode, solar mode, and hybrid mode of shrimp drying. The economic evaluation revealed that the hybrid mode of operation is highly economical with the annual savings of $10983.06 and the lowest payback period of 0.62 years.

Atmospheric water harvesting by using evacuated tube collector: An experimental investigation

The current global water crisis arises from the combination of limited freshwater resources and a growing world population, which highlights the need for self-sustainable water production system. Atmospheric water harvesting (AWH), leveraging the vast renewable water reservoir of atmospheric air, holds promise as a viable solution to address human water needs. The AWH systems reported in the literature possess low regeneration temperature, vapor leakage and reduced condensation. In the present work, a novel AWH system is developed and experimentally investigated under the ambient conditions. It comprises of 8.46 m2 evacuated tube solar air heater to provide higher regeneration temperature, packed desiccant bed of silica gel to reduce vapor leakage and an air-to-air heat exchanger for improved condensation. Four different cases with 20 and 30 kg desiccant bed are examined at two different mass flow rates of 56.01 kg/h and 102.69 kg/h. The adsorption process is performed during the night-time while the desiccant material regeneration is carried in the day time. The system performance is measured in terms of adsorption rate, regeneration rate, thermal efficiency, overall efficiency and productivity. The developed system demonstrates optimum results for case 1 with 20 kg desiccant bed at 56.01 kg/h mass flow rate. The average adsorption and regeneration rate observed were 0.592 kg/h and 0.461 kg/h, respectively. The maximum fresh water produced is 2.13 L/day with thermal and overall efficiencies of 24.32% and 3.58%, respectively. The cost of produced fresh water is 0.21 $/liter with the system’s payback time of 2 years & 9 months. The quality of the generated water is also tested, which ensures that it is safe to drink.

Nano-enhanced thermal energy storage coupled to a hybrid renewable system for a high-rise zero emission building

Renewable energy sources suffer from intermittent availability. Adding a latent heat thermal energy storage (TES) is often proposed as an efficient solution to address their stability. In this study, a hybrid renewable energy system consisting of solar photovoltaic panels, evacuated tube collectors, and a ground source heat pump (GSHP) is investigated. The system was coupled with an underground nano-enhanced TES system for improved performance to meet the energy demand of a high-rise residential building in Toronto, Canada. The applied energy storage system in this study consists of nano-enhanced phase change material pipes buried vertically underground to address the temperature stability of the ground. To investigate the effectiveness of this hybrid renewable energy system, a novel co-simulation methodology is adopted. The efficiency of this system is analysed on the component-scale using CFD simulations. The results show that adding nanoparticles increases the thermal storage capacity of the GSHP by 26.4 %. Then the impact of the hybrid renewable energy system with improved storage capacity on the building scale was assessed using TRNSYS. The economic, environmental, and energy consumption impacts of the proposed system was evaluated. Without TES, 296 borehole heat exchangers with a depth of 243 m would be needed to meet the heat and cooling demand; however, considering the modified ground source heat pump, the number of boreholes were reduced to 197 with a depth of 163 m. The results showed a significant impact on the drilling cost reduction, and the life span increase of the geo-exchange system. The coefficient of performance of the final system increases by 27.1 %, while the building energy consumption decreases by 36.7 %.

Numerical simulation of wind-induced load on evacuated tube solar water heaters

Solar Water Heater (SWH) has been used as a traditional device in many countries and regions for collecting solar energy. Unfortunately, there are many wind-induced accidents of SWHs, owing to insufficient consideration of wind-resistant design and installation. To better promote the safe use of SWHs, characteristics of wind load acting on them should be clarified thoroughly as far as possible. In this article, a systematic study is carried out by numerical simulation based on computational fluid dynamics (CFD) to analyze the effects of the tilt angle and density of evacuated tube collectors (ETC) as well as wind direction on the aerodynamic characteristics of SWH. Results show that the wind-resistance performance of SWH decreases significantly for wind flows blowing from 0° and 180° due to the influence of aerodynamic characteristics of its main components. When the ETC is located upstream of the water tank, the arrangement form of the tubes will have an impact on the aerodynamic characteristics of the SHW. A lower porosity of ETC can increase wind load on the weak region of water tank and the windward face of vertical supports, it can also increase the bending moment of inclined supports significantly. By contrast, lower tilt angles of ETC are more beneficial to the wind resistance of SHW, although they can result in an increase of the local wind suction on water tank.

Impact of the New Energy Context on the Feasibility of Solar Water Heating Systems in the Agri-Food Industry

The new energy context since 2021 has led to dramatic increases in the energy bills of agribusinesses, affecting the price of foodstuffs. A considerable part of energy consumption is due to the heating of water at high temperatures. The present study analyzed the feasibility of using a Solar Water Heating System (SWHS) with an evacuated tube collector. In particular, the required sizing changes, potential savings and cost-effectiveness were analyzed. The results show that the new energy context makes the SWHS investment highly attractive: a payback of less than 4 years in most of the scenarios analyzed; energy savings of more than 60% in the scenarios with higher irradiation; a reduction in total energy expenditure of more than 50% in the favorable scenarios close to the current reality. The new context especially favors cold and temperate climates, with very sharp drops in payback compared to the previous situation. To achieve these values, it is necessary to design an optimized sizing of the SWHS, reducing the risk of future variations in the price of energy. The results of the study should serve as a reference for decision making in the agroindustrial sector to reduce the energy bill and strategic dependence on fossil fuels from third countries.

Experimental and simulation on night heat dissipation characteristics and freezing process of evacuated tube solar water heaters

The winter operation of all-glass evacuated tube solar water heaters (ETSWH) often encounters the problem of ice damage. Studying their nighttime heat dissipation and freezing characteristics can further reduce the risk of frost damage during winter use. A numerical model for the nighttime heat dissipation of all-glass evacuated tube collectors is proposed in this study. An enthalpy equation is also introduced to analyze the heat dissipation process and freezing conditions of water inside the ETSWH under lower temperature conditions. Based on this, a nighttime heat loss model for solar vacuum tube collectors, including the effects of radiation and phase change factors, is established and validated through nighttime temperature drop experiments, which can effectively predict the temperature distribution and antifreeze performance of ETSWH during the nighttime heat dissipation process. In addition, the independent effects of the initial temperature of the water inside ETSWH, the thickness of the water tank insulation layer, and the absorptive coating emissivity on the heat dissipation process of ETSWH are studied, and the heat dissipation of ETSWH during winter nights in five different climatic zones in China is simulated. Experimental and simulation results show that under cold and clear winter weather conditions in Luoyang, ice forms in ETSWH during nighttime. The icing first occurs at the bottom of the vacuum tube, and the icing length on the wall and the icing thickness at the bottom can reach 1145 mm and 15 mm, respectively. In severely cold areas and cold regions such as Harbin and Beijing, there is a high risk of frost damage to ETSWH during winter. Keeping the initial working fluid temperature in the heater above 50 °C, ensuring a minimum insulation thickness of 50 mm, and reducing the emissivity of the absorptive coating in the heater to below 0.07 can effectively solve the freezing problem and have significant implications for the promotion and application of all-glass evacuated tube collectors.

Unsteady-state thermal performance analysis of cascaded packed-bed latent thermal storage in solar heating system

Thermal storage system is crucial to economically and stably utilize solar energy to address its volatility and fluctuation. A cascaded packed-bed latent heat storage system combined with solar evacuated tube collector is constructed in this paper, and the dynamic thermal performances are numerically investigated. The solar evacuated tube collector model is established to simulate the heat transfer fluid (HTF) charging process, which is experimentally verified by comparing the inlet/outlet temperatures. A latent heat storage system in three-stage packed-bed using phase-change materials with different melting temperatures ranging from 311 K to 335 K is modeled by enthalpy-porosity method, which is validated by comparing with the experimental data of literature. Then, the solar thermal storage system is integrated, and the impacts of the mass flow rate of HTF, solar collector area and initial temperature of packed-bed on its dynamic energetic and exergetic performances are analyzed. The results and discussions are analyzed to obtain optimal operation conditions. The increase of mass flow rate by 0.04 kg/s declines the maximum temperature by 9.53%. The initial temperature of packed-bed ranging from 293 K to 300 K achieves higher HTF temperature, heat storage efficiency and charging capacity. The solar collector area is necessarily matched to the phase-change materials to obtain high efficiency and also avoid HTF vaporization.

Thermal Performance Characterization of Evacuated Tube Collector Solar Water Heater with Constant Inlet Water Temperature

Abstract: With large evolution in the solar technology, research is turned out to be more sophisticated. Evacuated tube collectors (ET Collectors) are the most eco-friendly and efficient solar water heaters used worldwide. A series of experiments have been performed on ETC Characterization System. The research presents the evaluation of the performance of an ET Collector and characterize the solar water heater at different wind velocity of (2, 3, 4 m/s) and solar radiation between 250 to 750 W/m2 by keeping temperature of inlet water as constant. Examining the system performance at different temperature of inlet water of (29 °C, 40 °C, 50 °C). Net heat loss through evacuated tubes (ETs), heat loss coefficient through ETs, & the efficiency of an ET Collector has been recorded.

Thermo-economic performance enhancement of the hemispherical solar still integrated with various numbers of evacuated tubes

Experimental investigations of the hemispherical solar still (HSS) augmentation with various numbers of evacuated tubes (EVT) were performed and evaluated. The modified hemispherical solar still (HSS-EVT) performance was illustrated with two categories of EVT distributions and compared with the traditional HSS (THSS) design. In the first category, the EVT was distributed on the water basin perimeter in all directions (Dis-ɸ), and in the second category, the EVT was distributed in the south direction (Dis-So). The impact of various water heights (Hw) from 1 to 4 cm was also studied. Results revealed that the integration of EVT had a significant influence on distillate performance. The highest daily production rate at 1 cm water height of HSS-EVT was 5860 mL with an increment of 551, 316, 156, and 91% compared to THSS at NEVT = (16, 8, 4, and 2 tubes), respectively. The productivity increment by 7.2%, when compared EVT distribution (Dis-ɸ) with (Dis-So) effect. The reduction of water level to 1 cm increases the yield by about 5.96, 11.61, and 18.74% with HW (2, 3, and 4 cm), respectively. The proposed system's peak energy and exergy efficiency value was 42.29 and 5.57%, with an increment of 47.30 and 124%, respectively, related to the traditional one. The maximum daily production related to the exposed surface area was 6.69 L/m2 at NEVT = 8 tubes. The estimated cost varied between 0.00237, and 0.0101 USD/L.

Thermodynamic and economic analysis of an off–grid photovoltaic hydrogen production system hybrid with organic Rankine cycle

Water electrolysis technology is a potential approach for green hydrogen production and photovoltaic power consumption. However, due to the volatility and uncertainty of the solar energy, supplying photovoltaic power directly to the water electrolysis auxiliary system is instable. An innovative off–grid photovoltaic proton exchange membrane electrolytic cells hydrogen production system is proposed to address that issue. The system integrates an organic Rankine cycle system with evacuated tube collector modules to supply power for the auxiliary system. The electrical power generated by the photovoltaic module is directly supplied to the proton exchange membrane electrolytic cells. The matching of the organic Rankine cycle system output power and auxiliary system power demand has been conducted by comparing the temperature control methods and parameters. The thermodynamic and economic performances of the photovoltaic hydrogen production system have been investigated with the meteorological data of Nanjing. The results demonstrate the organic Rankine cycle system can completely satisfy the power demand of the auxiliary system operation. The annual hydrogen production of the system can reach 26.07 tons (316203.0 Nm3) and the hydrogen average electricity consumption is 4.75 kWh/Nm3. The system has a maximum energy and exergy efficiency of 8.8 % and 9.1 %, respectively. This system is suitable for retrofitting photovoltaic plants, the payback period of the retrofit project is 12 years, which shows higher profitability than that of grid-supplied hydrogen production.

Recent progress in membrane distillation configurations powered by renewable energy sources and waste heat

Membrane distillation (MD) is a promising process for high-quality water reclamation mainly due to its high capacity to retain non-volatile components and operate without the need for hydraulic pressure. However, its low energy efficiency limits its widespread use. With that in mind, this paper critically summarizes the different engineered configurations of membrane distillation coupled with renewable energy sources and waste heat, namely: solar, geothermal, and waste heat, to overcome the limitations associated with low energy efficiency commonly reported. From all sources, solar-driven processes are preferred due to the greater technological maturity related to flat plate collectors (FPCs), evacuated tube collectors (ETCs), compound parabolic concentrators (CPCs), salt-gradient solar ponds (SGSPs), and solar stills. The integration with renewable energy sources represents one of the leading solutions for energy consumption, proving to be a decisive choice for the system's economic viability. The summarized studies suggest membrane distillation's potential to be economically competitive with the classical membrane separation process (ultrafiltration, nanofiltration, and reverse osmosis) when waste heat is considered for wastewater treatment. Even under these conditions, alternative energy sources have a few shortcomings to be investigated in future studies, such as short periods of solar radiation and the intermittence of waste heat sources. These factors still represent obstacles to an uninterrupted and large-scale operation of membrane distillation and must be overcome in a near future. Even so, successful case studies on full-scale systems that integrate membrane distillation and solar energy sources suggest the process's potential for widespread use in the near term.