Design optimization of thermoelectric devices for solar power generation

We present an improved theoretical model of a thermoelectric device which has been developed for geometrical optimization of the thermoelectric element legs and prediction of the performance of an optimum device in power generation mode. In contrast to the currently available methods, this model takes into account the effect of all the parameters contributing to the heat transfer process associated with the thermoelectric device.The model is used for a comparative evaluation of four thermoelectric modules. One of these is commercially available and the others are assumed to have an optimum geometry but with different design parameters (thermal and electrical contact layer properties).Results from the model are compared with experimental data of the commercial thermoelectric module in power generation mode with temperature gradient consistent with those achievable from a solar concentrator system. These show that it is important to have devices optimized specifically for generation, and to improve the contact layer of the thermoelements accordingly.     

Heat extraction from salinity-gradient solar ponds using heat pipe heat exchangers

This paper presents the results of experimental and theoretical analysis on the heat extraction process from solar pond by using the heat pipe heat exchanger. In order to conduct research work, a small scale experimental solar pond with an area of 7.0 m² and a depth of 1.5 m was built at Khon Kaen in North-Eastern Thailand (16°27′N102°E). Heat was successfully extracted from the lower convective zone (LCZ) of the solar pond by using a heat pipe heat exchanger made from 60 copper tubes with 21 mm inside diameter and 22 mm outside diameter. The length of the evaporator and condenser section was 800 mm and 200 mm respectively. R134a was used as the heat transfer fluid in the experiment. The theoretical model was formulated for the solar pond heat extraction on the basis of the energy conservation equations and by using the solar radiation data for the above location. Numerical methods were used to solve the modeling equations. In the analysis, the performance of heat exchanger is investigated by varying the velocity of inlet air used to extract heat from the condenser end of the heat pipe heat exchanger (HPHE). Air velocity was found to have a significant influence on the effectiveness of heat pipe heat exchanger. In the present investigation, there was an increase in effectiveness by 43% as the air velocity was decreased from 5 m/s to 1 m/s. The results obtained from the theoretical model showed good agreement with the experimental data.     

Heat pipes thermoelectric solar collectors for energy applications

This study investigates the load characteristics of heat pipe thermoelectric solar collector (HPTSC) in practice. Heat pipe thermoelectric solar collector converts the heat generated by the Sun directly into electrical energy and produces hot water as well. The maximum power in HPTSC is obtained when the internal resistance of the thermoelectric module is equal to the load resistance. It has been observed to be possible to produce both hot water and electricity by improving available solar collectors or producing new generation HPTSC. While it is possible to generate an electrical power of 160 W from a HPTSC of one square meter using the thermoelectric method, the power produced with an average photovoltaic panel with the same area is only 132 W. Accordingly, HPTSC is a superior alternative not only to available solar collectors, but also to available PV panels. HPTSC, involving three different technologies, is environmentally friendly and certainly a product that allows for more efficient use of solar energy.     

Comparative analyses of a novel solar tower assisted multi-generation system with re-compression CO2 power cycle,thermoelectric generator,and hydrogen production unit

In the present paper, a new energy generation system is suggested for multiple outputs, including a hydrogen generation unit. The plant is powered by a solar tower and involves six different subsystems; supercritical carbon dioxide (sCO₂) re-compression Brayton cycle, ammonia-water absorption refrigeration cycle, hydrogen generation, steam generation, drying process, and thermoelectric generator. The thermodynamic assessment of the multi-generation system is carried out for three different cities from Turkey, Iran, and Qatar. The energy and exergy efficiencies are calculated for base conditions to compare the different locations. The operating output parameters for the suggested system and simple re-compression Brayton system are compared. A parametric analysis is also done for investigating the influences of different system variables on plant performance. According to the results, Doha city is found to be more effective due to its geographical conditions. Moreover, based on the comparative study, the proposed cycles produce more power than the basic re-compression cycle with 64.59 kW, 47.33 kW, and 52.25 kW for Doha, Isparta, and Tehran, respectively. Additionally, the analyses revealed that in the term of energy efficiency, the suggested system has 32.29%, 32.28%, and 32.29% better performance than the simple cycle, and in terms of exergy efficiency, it has 4%, 4.8%, and 5% better performance than the simple cycle in Doha, Isparta, and Tehran, respectively.     

Numerical study of thermoelectric power generation for an helicopter conical nozzle

This paper investigates the electric power extractable from an helicopter conical nozzle equipped with thermoelectrical modules. The thermoelectric nozzle is heated by the final exhaust gas from helicopter turbine and cooled by oil. A computer model has been developed to simulate the performance of the thermoelectric system. Results were obtained for various operating conditions showing that the electrical power produced in real operating conditions is significant but currently insufficient if we consider the weight-to-power ratio. The numerical model is also used to optimize the electric power showing a good potential for the future.     

Thermal management of solar photovoltaics modules for enhanced power generation

Industry and government interest in solar energy has increased in recent years in the Middle East. However, despite high levels of solar irradiance in the Arabian Gulf, harsh climatic conditions adversely affect the electrical performance of solar photovoltaics (PV). The objective of this study is to compare the annual performance characteristics of solar PV modules that utilize either sun-tracking or water cooling to increase electrical power generation relative to that of stationary, passively cooled modules in the Middle East climatic conditions. This is achieved using an electro-thermal model developed and validated against experimental data acquired in this study. The model is used to predict the annual electrical power output of a 140 W PV module in Abu Dhabi (24.43°N, 54.45°E) under four operating conditions: (i) stationary geographical south facing orientation with passive air cooling, (ii) sun-tracked orientation with passive air cooling, (iii) stationary geographical south facing orientation with water cooling at ambient air temperature, and (iv) stationary geographical south facing orientation with water refrigerated at either 10 °C or 20 °C below ambient air temperature. For water cooled modules, annual electrical power output increases by 22% for water at ambient air temperature, and by 28% and 31% for water refrigerated at 10 °C and 20 °C below ambient air temperature, respectively. 80% of the annual output enhancement obtained using water cooling occurs between the months of May and October. Finally, whereas the annual yield enhancement obtained with water cooling at ambient air temperature from May to October is of 18% relative to stationary passive cooling conditions, sun-tracking over the complete year produces an enhancement of only 15% relative to stationary passive cooling conditions.     

An experimental investigation into the performance of a domestic thermosyphon solar water heater under varying operating conditions

An experimental investigation has been carried out on a thermosyphon solar water heater. The system consisted of a flat-plate collector of 1.5 m² absorber area with 21 tubes/m width and storage tank of 125 litre capacity. Experiments were carried out for both cloudy and clear weather conditions in winter and summer. The hourly system performance was evaluated for all test conditions. The final mean tank temperature was measured daily which enabled the calculation of the possible contribution of solar energy for domestic hot water supply in Basrah, Iraq (latitude 30.76°N). The system was tested at both no-load and loading conditions. Intermittent and continuous load was imposed, and system performance was evaluated for each condition.     

Numerical model of a solar pond

This paper points out an idealization of considerable significance in a recent numerical model of a solar pond due to Wang and Akbarzadeh [3] and outlines the refinements required in the formulation of the above model. Typical temperature calculations from teh resultant model are also presented. of the above model. Typical temperature calculations from the resultant model are also presented.     

Examining potential benefits of combining a chimney with a salinity gradient solar pond for production of power in salt affected areas

The concept of combining a salinity gradient solar pond with a chimney to produce power in salt affected areas is examined. Firstly the causes of salinity in salt affected areas of northern Victoria, Australia are discussed. Existing salinity mitigation schemes are introduced and the integration of solar ponds with those schemes is discussed. Later it is shown how a solar pond can be combined with a chimney incorporating an air turbine for the production of power. Following the introduction of this concept the preliminary design is presented for a demonstration power plant incorporating a solar pond of area 6 hectares and depth 3 m with a 200 m tall chimney of 10 m diameter. The performance, including output power and efficiency of the proposed plant operating in northern Victoria is analysed and the results are discussed. The paper also discusses the overall advantages of using a solar pond with a chimney for production of power including the use of the large thermal mass of a solar pond as a practical and efficient method of storing collected solar energy.     

Critical evaluation of solar chimney power plant performance

This paper evaluates the influence of a recently developed convective heat transfer equation, more accurate turbine inlet loss coefficient, quality collector roof glass and various types of soil on the performance of a large scale solar chimney power plant. Results indicate that the new heat transfer equation reduces plant power output considerably. The effect of a more accurate turbine inlet loss coefficient is insignificant, while utilizing better quality glass enhances plant power production. Models employing Limestone and Sandstone soil produce virtually similar results to a Granite-based model. The plant collector height is found to differ from previously obtained optimal values.     

Investigation on a mini-CPC hybrid solar thermoelectric generator unit

A hybrid solar hot water and Bi₂Te₃-based thermoelectric generator (TEG) unit using a heat pipe evacuated tube collector with mini-compound parabolic concentrator (mini-CPC) is proposed. In this unit, the heat from the heat pipe evacuated tube solar collector is transferred to the hot side of TEG. Simultaneously, water cooling is used at the cold side to maintain the temperature difference. Electricity is generated by TEG and the remaining heat is transferred to water at the same time. This paper investigates how to convert excess solar heat into electricity more effectively. A mathematical model regarding this unit is developed and validated. It is found that the mini-CPC can significantly improve the electrical efficiency. The optimal thermal conductance of TEG is determined, which could make the best use of excess solar heat. The excess solar heat can be effectively converted into electricity when ZT of Bi₂Te₃ can be improved from 100 °C to 200 °C. Using TEG with ZT = 1.0 and a geometrical concentrating ratio at 0.92, electrical and thermal efficiencies of this system are predicted to be 3.3% and 48.6% when solar radiation and water temperature are 800 Wm⁻² and 20 °C, respectively.     

Electric energy generation from small-scale solar and wind power in Brazil: The influence of location,area and shape

Power production from renewable sources is identified as one of the tools to attain sustainable development in economic and social terms in Brazil. Awareness of how to prioritize renewable energy sources and technologies becomes increasingly important. Solar and wind energy have been highlighted in this context as being clean, safe and also relatively mature technologies. In addition, they are also renowned for having great energy potential and allowing different mounting options for energy harvesting systems. This article seeks to contribute to the knowledge of the effects that the key attributes, location, area and shape, of a site can have on the potential of renewable generation. In order to incorporate these attributes into an integrated analysis, a comparison method is developed and subsequently applied in a case study for two Brazilian cities. Results indicate that the amount of energy obtained by a given power generation system can undergo large variations depending on the characteristics of attributes such as site location, area and shape. This variation may ultra-pass 200%, in some cases, which demonstrates the importance of a better understanding of the role of these attributes in determining energy production.     

Experimental investigation on heat extraction using a two-phase closed thermosyphon for thermoelectric power generation

An experimental investigation on heat extraction using a two-phase closed thermosyphon charged with water (a filling ratio of 40%) for thermoelectric power generation was conducted to study the temperature gradients on the thermosyphon and the thermoelectric conversion characteristics. Results showed that the thermosyphon had a relatively stable working state at 100–300°C, and the maximum output power increased exponentially with temperature difference, being 20 W at a temperature difference of 210°C. The power generation efficiency increased in Hill function with increasing heating power input, the maximum value being approximately 0.01924.     

Experimental and analytical performance study of a thermosyphon water heater

The performance of a thermosyphon solar water heater was studied analytically and experimentally. A finite-difference model was used to predict year-round performance. Tests were conducted on an experimental heater subjected to acutal weather conditions in Benghazi, Libya. Satisfactory qualitative and quantitative agreement was found between experimental and predicted results. A storage volume of 60 liters per unit collector area was found to be optimum for Benghazi conditions. The day-end temperature was found to vary between 23° and 51°C for the test period, which occurred in winter, with an average of 41°C.     

Network benefits of embedded solar systems: A case study from western Sydney

This paper presents a simulation study based on actual load, sunshine and wind data. A distribution feeder simulation model was constructed using this data to determine what potential benefit embedded wind, solar and storage elements could give to the distribution network. The results were compared to earlier studies. It was discovered that over the past 5–10 years, the hot weather peak load has extended from 3 pm to 6 pm and that a more northwesterly orientation of solar panels is of assistance. It was also found that wind is of little assistance in hot weather peaks, in contrast to data for the NSW central tablelands region; however solar contributes at least 50% of its nominal peak capacity. As hot weather peaks are now extending into the early evening, it was found that storage would be of great benefit and would enhance the use of renewable energy sources. As part of the feeder model, the optimal method of Var control from the embedded sources was also studied.     

A hybrid model for the optimum integration of renewable technologies in power generation systems

The main purpose of this work is to assess the unavoidable increase in the cost of electricity of a generation system by the integration of the necessary renewable energy sources for power generation (RES-E) technologies in order for the European Union Member States to achieve their national RES energy target. The optimization model developed uses a genetic algorithm (GA) technique for the calculation of both the additional cost of electricity due to the penetration of RES-E technologies as well as the required RES-E levy in the electricity bills in order to fund this RES-E penetration. Also, the procedure enables the estimation of the optimum feed-in-tariff to be offered to future RES-E systems. Also, the overall cost increase in the electricity sector for the promotion of RES-E technologies, for the period 2010–2020, is analyzed taking into account factors, such as, the fuel avoidance cost, the carbon dioxide emissions avoidance cost, the conventional power system increased operation cost, etc. The overall results indicate that in the case of RES-E investments with internal rate of return (IRR) of 10% the cost of integration is higher, compared to RES-E investments with no profit, (i.e., IRR at 0%) by 0.3–0.5 €c/kWh (in real prices), depending on the RES-E penetration level.     

Carbon pricing and the diffusion of renewable power generation in Eastern Europe: A linear programming approach

The purpose of this paper is to analyze the costs for reducing CO₂ emissions in the power-generating sectors in Croatia, the European part of Russia, Macedonia, Serbia and the Ukraine in 2020 by using a linear programming model. The model takes into account the impact of technology learning and is based on the underlying assumptions of the so-called RAINS model frequently used to assess the potential and the costs for reducing air pollution in Europe. The results based on an exogenously given 15 percent reduction target for CO₂ emissions show that the marginal cost for switching from a carbon-intense fuel to either a low-carbon or to a renewable energy source differs significantly among the countries. The marginal costs range from 4 to 90€ per ton CO₂, and are mainly due to country differences in the availability of renewables, existing technologies and costs. The results also indicate that although it is clear that the Eastern European countries are not homogeneous in terms of CO₂ abatement potential and costs, no general conclusions can be made of the region. This may have important implications for future JI/CDM activities. For instance, risk factors such as policy uncertainty and institutional obstacles may become crucial in determining the future allocation of JI/CDM projects across the region.     

Performance review of a novel combined thermoelectric power generation and water desalination system

A novel combined thermoelectric power generation and water desalination system is described with a system schematic. The proposed system utilises low grade thermal energy to heat thermoelectric generators for power generation and water desalination. A theoretical analysis presents the governing equations to estimate the systems performance characteristics combined with experimental validation. Experimental set-up consists of an electric heat source, thermoelectric modules, heat pipes, a heat sink and an evaporator vessel. Four heat pipes are embedded in a heat spreader block to passively cool the bottom side of the thermoelectric cells. The condenser of these four heat pipes is immersed in a pool of saline water stored in an evaporation vessel which is maintained at sub-atmospheric pressure. The liquid to vapour phase change cooling method achieve low saturation temperature and offers a high heat transfer coefficient for the cooling of the thermoelectric generators. At the same time this method utilises the low temperature heat extracted from the cold side of the thermoelectric generator for water desalination. It was observed that at low saturation temperatures greater heat flux could be supplied to the thermoelectric generators with less heat losses to the atmosphere.     

Design of 3 kW integrated power generation system from solar and biogas

Energy/Power is an important element of social and economic development. Without availability of energy at a reasonable price, there is little prospect of developing the country's economy and people's living conditions. A quarter of Pakistani population have no access to electricity, and currently a shortage of 5.0–7.0 GW power supply causes load shedding/blackout problems. In Pakistan, most of the power is generated from non-renewable sources like natural gas etc. Pakistan receives almost 15.525 × 10¹⁴ kW-hour of solar energy per year and sunshine duration is normally 8.0–10.0 h per day. Animal/farm wastes are readily available in Pakistan. Residues from these sources produce 103.0 billion m³ of biogas per year that is equivalent to 63.20 TWh. The objective of this study is energy production by using easily available indigenous resources. In this study a 3.0 kW integrated solar/biogas power generation system consist of 2.84 kW solar system and 4.0 m³ biogas system is designed and installed. This paper also present simulation model of system. A hybrid inverter is used to convert DC power of photovoltaic modules and the battery bank in to AC power and combines with the output power of biogas generator. Performance of the hybrid system are analysed from May 1, 2018 to June 15, 2018. During the test maximum power produce by the integrated system is 1.10 kW in morning, 2.14 kW in noon and 1.16 kW in afternoon.     

Thermal behavior of a small salinity-gradient solar pond with wall shading effect

The thermal behavior of a small-scale salinity-gradient solar pond has been studied in this paper. The model of heat conduction equation for the non-convective zone has been solved numerically with the boundary conditions of the upper and lower convective zones. The variation of the solar radiation, during a year, and its attenuation in the depth of the pond has been discussed. The wall shading area for a vertical wall square pond has been elaborated and its effect on the reduction of the sunny area has been included in the model. The temperature variation of the storage zone has been calculated theoretically and compared with the experimental results. The sensitivity analysis demonstrates the importance of the side and bottom insulation and the thickness of the non-convective zone, as well as the wall shading effect on the performance of the pond. The application of several loading patterns gives an overall efficiency of 10% for the small pond.