Exergoeconomic analysis of glazed hybrid photovoltaic thermal module air collector

In this paper, an exergoeconomic analysis has been carried out and on the basis of this analysis it has been concluded that in terms of energy saving the glazed hybrid photovoltaic thermal (PVT) module air collector offers a greater potential compared to PV module. The experimental validation for glazed hybrid PVT module air collector has also been performed and it has been observed that there is a good agreement between the theoretical and experimental values with correlation coefficient in range of 0.96–0.99 and root mean square percentage deviation in range of 2.38–7.46. The experiments have been carried out on clear days during the month July 2010 to June 2011. For the validation of theoretical results with experimental results, a typical day of winter month (December 08, 2010) and summer month (April 11, 2011) has been considered. An experimental uncertainty for December and April month is 11.6% and 2.1% respectively. The annual overall thermal energy and exergy gain are 1252.0 kWh and 289.5 kW h respectively. The annual net electrical energy savings by glazed hybrid PVT module air collector is 234.7 kW h.     

The effect of hybrid photovoltaic thermal device operating conditions on intrinsic layer thickness optimization of hydrogenated amorphous silicon solar cells

Historically, the design of hybrid solar photovoltaic thermal (PVT) systems has focused on cooling crystalline silicon (c-Si)-based photovoltaic (PV) devices to avoid temperature-related losses. This approach neglects the associated performance losses in the thermal system and leads to a decrease in the overall exergy of the system. Consequently, this paper explores the use of hydrogenated amorphous silicon (a-Si:H) as an absorber material for PVT in an effort to maintain higher and more favorable operating temperatures for the thermal system. Amorphous silicon not only has a smaller temperature coefficient than c-Si, but also can display improved PV performance over extended periods of higher temperatures by annealing out defect states from the Staebler–Wronski effect. In order to determine the potential improvements in a-Si:H PV performance associated with increased thicknesses of the i-layers made possible by higher operating temperatures, a-Si:H PV cells were tested under 1 sun illumination (AM1.5) at temperatures of 25 °C (STC), 50 °C (representative PV operating conditions), and 90 °C (representative PVT operating conditions). PV cells with an i-layer thicknesses of 420, 630 and 840 nm were evaluated at each temperature. Results show that operating a-Si:H-based PV at 90 °C, with thicker i-layers than the cells currently used in commercial production, provided a greater power output compared to the thinner cells operating at either PV or PVT operating temperatures. These results indicate that incorporating a-Si:H as the absorber material in a PVT system can improve the thermal performance, while simultaneously improving the electrical performance of a-Si:H-based PV.     

Energy matrices analyses of hybrid photovoltaic thermal (HPVT) water collector with different PV technology

In this paper, an attempt has been made to evaluate and compare the energy matrices of a hybrid photovoltaic thermal (HPVT) water collector under constant collection temperature mode with five different types of PV modules namely c-Si, p-Si, a-Si (thin film), CdTe and CIGS. The analysis is based on overall thermal energy and exergy outputs from HPVT water collector. The temperature dependent electrical efficiency has also been calculated under composite climate of New Delhi, India.It is observed that c-Si PV module is best alternative for production of electrical power. Maximum annual overall thermal energy and exergy is obtained for c-Si PV module. The maximum and minimum EPBT of 1.01 and 0.66 years on energy basis is obtained for c-Si and CIGS respectively, whereas on exergy basis maximum EPBT of 5.72 years is obtained for a-Si and minimum of 3.44 in obtained for CIGS PV module. EPF and LCCE increase with increasing the life time of the system.     

Energy metrics of photovoltaic/thermal and earth air heat exchanger integrated greenhouse for different climatic conditions of India

In this paper, a study is carried out to evaluate the annual thermal and exergy performance of a photovoltaic/thermal (PV/T) and earth air heat exchanger (EAHE) system, integrated with a greenhouse, located at IIT Delhi, India, for different climatic conditions of Srinagar, Mumbai, Jodhpur, New Delhi and Bangalore. A comparison is made of various energy metrics, such as energy payback time (EPBT), electricity production factor (EPF) and life cycle conversion efficiency (LCCE) of the system by considering four weather conditions (a–d type) for five climatic zones. The embodied energy and annual energy outputs have been used for evaluation of the energy metrics. The annual overall thermal energy, annual electrical energy savings and annual exergy was found to be best for the climatic condition of Jodhpur at 29,156.8 kWh, 1185 kWh and 1366.4 kWh, respectively when compared with other weather stations covered in the study, due to higher solar intensity I and sunshine hours, and is lowest for Srinagar station. The results also showed that energy payback time for Jodhpur station is lowest at 16.7 years and highest for Srinagar station at 21.6 years. Electricity production factor (EPF) is highest for Jodhpur, i.e. 2.04 and Life cycle conversion efficiency (LCCE) is highest for Srinagar station. It is also observed that LCCE increases with increase in life cycle.     

Technical and economic assessment of grid-independent hybrid photovoltaic–diesel–battery power systems for commercial loads in desert environments

Solar photovoltaic (PV) hybrid system technology is a hot topic for R&D since it promises lot of challenges and opportunities for developed and developing countries. The Kingdom of Saudi Arabia (KSA) being endowed with fairly high degree of solar radiation is a potential candidate for deployment of PV systems for power generation. Literature indicates that commercial/residential buildings in KSA consume an estimated 10–45% of the total electric energy generated. In the present study, solar radiation data of Dhahran (East-Coast, KSA) have been analyzed to assess the techno-economic viability of utilizing hybrid PV–diesel–battery power systems to meet the load requirements of a typical commercial building (with annual electrical energy demand of 620,000 kW h). The monthly average daily solar global radiation ranges from 3.61 to 7.96 kW h/m². NREL's HOMER software has been used to carry out the techno-economic viability. The simulation results indicate that for a hybrid system comprising of 80 kWp PV system together with 175 kW diesel system and a battery storage of 3 h of autonomy (equivalent to 3 h of average load), the PV penetration is 26%. The cost of generating energy (COE, US$/kW h) from the above hybrid system has been found to be 0.149 $/kW h (assuming diesel fuel price of 0.1 $/L). The study exhibits that for a given hybrid configuration, the operational hours of diesel generators decrease with increase in PV capacity. The investigation also examines the effect of PV/battery penetration on COE, operational hours of diesel gensets for a given hybrid system. Emphasis has also been placed on unmet load, excess electricity generation, percentage fuel savings and reduction in carbon emissions (for different scenarios such as PV–diesel without storage, PV–diesel with storage, as compared to diesel-only situation), cost of PV–diesel–battery systems, COE of different hybrid systems, etc.     

Thermal modeling of a packed bed thermal energy storage system during charging

The process of charging of an encapsulated ice thermal energy storage device (ITES) is thermally modeled here through heat transfer and thermodynamic analyses. In heat transfer analysis, two different temperature profile cases, with negligible radial and/or stream-wise conduction are investigated for comparison, and the temperature profiles for each case are analyzed in an illustrative example. After obtaining temperature profiles through heat transfer analysis, a comprehensive thermodynamic study of the system is conducted. In this regard, energy, thermal exergy and flow exergy efficiencies, internal and external irreversibilities corresponding to flow exergy, as well as charging times are investigated. The energy efficiencies are found to be more than 99%, whereas the thermal exergy efficiencies are found to vary between 40% and 93% for viable charging times. The flow exergy efficiency varies between 48% and 88% for the flows and inlet temperatures selected. For a flow rate of 0.00164 m³/s, the maximum flow exergy efficiency occurs with an inlet temperature of 269.7 K, corresponding to an efficiency of 84.3%. For the case where the flow rate is 0.0033 m³/s, the maximum flow exergy efficiency becomes 87.9% at an inlet temperature of 270.7 K. The results confirm the fact that energy analyses, and even thermal exergy analyses, may lead to some unrealistic efficiency values. This could prove troublesome for designers wishing to optimize performance. For this reason, the flow exergy model provides the most useful information for those wishing to improve performance and reduce losses in such ITES systems.     

National-scale wave energy resource assessment for Australia

A nationally consistent wave resource assessment is presented for Australian shelf (<300 m) waters. Wave energy and power were derived from significant wave height and period, and wave direction hindcast using the AusWAM model for the period 1 March 1997 to 29 February 2008 inclusive. The spatial distribution of wave energy and power is available on a 0.1° grid covering 110–156° longitude and 7–46° latitude. Total instantaneous wave energy on the entire Australian shelf is on average 3.47 PJ. Wave power is greatest on the 3000 km-long southern Australian shelf (Tasmania/Victoria, southern Western Australia and South Australia), where it widely attains a time-average value of 25–35 kW m^?1 (90th percentile of 60–78 kW m^?1), delivering 800–1100 GJ m^?1 of energy in an average year. New South Wales and southern Queensland shelves, with moderate levels of wave power (time-average: 10–20 kW m^?1; 90th percentile: 20–30 kW m^?1), are also potential sites for electricity generation due to them having a similar reliability in resource delivery to the southern margin. Time-average wave power for most of the northern Australian shelf is <10 kW m^?1. Seasonal variations in wave power are consistent with regional weather patterns, which are characterised by winter SE trade winds/summer monsoon in the north and winter temperate storms/summer sea breezes in the south. The nationally consistent wave resource assessment for Australian shelf waters can be used to inform policy development and site-selection decisions by industry.     

Maximising the energy output of a PVT air system

Simultaneously generating both electricity and low grade heat, photovoltaic thermal (PVT) systems maximise the solar energy extracted per unit of collector area and have the added benefit of increasing the photovoltaic (PV) electrical output by reducing the PV operating temperature. A graphical representation of the temperature rise and rate of heat output as a function of the number of transfer units NTUs illustrates the influence of fundamental parameter values on the thermal performance of the PVT collector. With the aim of maximising the electrical and thermal energy outputs, a whole of system approach was used to design an experimental, unglazed, single pass, open loop PVT air system in Sydney. The PVT collector is oriented towards the north with a tilt angle of 34°, and used six 110 Wp frameless PV modules. A unique result was achieved whereby the additional electrical PV output was in excess of the fan energy requirement for air mass flow rates in the range of 0.03–0.05 kg/s m². This was made possible through energy efficient hydraulic design using large ducts to minimise the pressure loss and selection of a fan that produces high air mass flow rates (0.02–0.1 kg/s m²) at a low input power (4–85 W). The experimental PVT air system demonstrated increasing thermal and electrical PV efficiencies with increasing air mass flow rate, with thermal efficiencies in the range of 28–55% and electrical PV efficiencies between 10.6% and 12.2% at midday.     

Assessing the influence of four bonding methods on the thermal contact resistance of open-cell aluminum foam

A thermal application of open-cell aluminum foam typically requires it to be bonded on a substrate. The resulting thermal contact resistance is investigated for four bonding methods. This is done by minimizing the difference between the calculated heat transfer via a zeroth order model and experimental data. The bonded metal foam, used to obtain the experimental data, are manufactured in-house. This allows varying pore size, porosity, aluminum alloy, foam height, air mass flow rate, air inlet temperature and bonding method. The latter is found to have an overwhelming impact. The resulting four thermal contact resistances are: 0.7 × 10^?3 m²K/W for brazing, 0.88 × 10^?3 m²K/W for co-casting, 1.25 × 10^?3 m²K/W for a single-epoxy bonding and 1.88 × 10^?3 m²K/W for a press-fit bonding. The uncertainty on these values is 11%.     

Comparison of numerical and experimental performance criteria of an ammonia–water bubble absorber using plate heat exchangers

A mathematical model for ammonia–water bubble absorbers was developed and compared with experimental data using a plate heat exchanger. The analysis was performed carrying out a sensitive study of selected operation parameters on the absorber thermal load and mass absorption flux. Regarding the experimental data, the values obtained for the solution heat transfer were in the range 0.51–1.21 kW m^?2 K^?1 and those of the mass absorption flux in the range 2.5–5.0 × 10^?3 kg m^?2 s^?1. The comparison between experimental and simulation results was acceptable being the maximum difference of 11.1% and 28.4% for the absorber thermal load and the mass absorption flux, respectively.     

Analysis of combined thermal and magnetic convection ferrofluid flow in a cavity

A numerical analysis of the magnetic gradient and thermal buoyancy induced cavity ferrofluid flow is conducted by a semi-implicit finite element method. The physical model for a square cavity containing two different temperature side walls and a magnet near bottom wall is described by mass, momentum and energy equations. Conditions for the fixed Prandtl number, Rayleigh number and different ferro-hydrodynamic interaction parameter are studied for 5 × 10⁸ ≤ β ≤ 1.6 × 10¹⁰. Results show the flow strength increases with the strengthening magnetic field. However, the side-wall heat transfer rate presents a decrease trend with the increase in magnetic field strength, for the magnet located near the bottom central area evokes the circulation to move toward the central portion. In summary, a proper choice of magnet strength and location can adjust the flow field and local heat transfer rate to fit the practical application.     

System analysis of a multifunctional PV/T hybrid solar window

The work presented in this article aims to investigate a PV/T hybrid solar window on a system level. A PV/T hybrid is an absorber on which solar cells have been laminated. The solar window is a PV/T hybrid collector with tiltable insulated reflectors integrated into a window. It simultaneously replaces thermal collectors, PV-modules and sunshade. The building integration lowers the total price of the construction since the collector utilizes the frame and the glazing in the window. When it is placed in the window a complex interaction takes place. On the positive side is the reduction of the thermal losses due to the insulated reflectors. On the negative side is the blocking of solar radiation that would otherwise heat the building passively. This limits the performance of the solar window since a photon can only be used once. To investigate the sum of such complex interaction a system analysis has to be performed. In this paper results are presented from such a system analysis showing both benefits and problems with the product. The building system with individual solar energy components, i.e. solar collector and PV modules, of the same size as the solar window, uses 1100 kW h less auxiliary energy than the system with a solar window. However, the solar window system uses 600 kW h less auxiliary energy than a system with no solar collector.     

Geothermal resource assessment in Korea

To estimate available geothermal energy and to construct temperature at depth maps in Korea, various geothermal data have been used. Those include 1560 thermal property data such as thermal conductivity, specific heat and density, 353 heat flow data, 54 surface temperature data, and 180 heat production data. In Korea, subsurface temperature ranges from 23.9 °C to 47.9 °C at a depth of 1 km, from 34.2 °C to 79.7 °C at 2 km, from 44.2 °C to 110.9 °C at 3 km, from 53.8 °C to 141.5 °C at 4 km, and from 63.1 °C to 171.6 °C at 5 km. The total available subsurface geothermal energy in Korea is 4.25 × 10²¹ J from surface to a depth of 1 km, 1.67 × 10²² J to 2 km, 3.72 × 10²² J to 3 km, 6.52 × 10²² J to 4 km, and 1.01 × 10²³ J to 5 km. In particular, the southeastern part of Korea shows high temperatures at depths and so does high geothermal energy. If only 2% of geothermal resource from surface to a depth of 5 km is developed in Korea, energy from geothermal resources would be equivalent to about 200 times annual consumption of primary energy (～2.33 × 10⁸ TOE) in Korea in 2006.     

Hybrid electrochemical capacitors based on polyaniline and activated carbon electrodes

The performance of a newly designed, polyaniline–activated carbon, hybrid electrochemical capacitor is evaluated. The capacitor is prepared by using polyaniline as a positive electrode and activated carbon as a negative electrode. From a constant charge–discharge test, a specific capacitance of 380 F g⁻¹ is obtained. The cycling behaviour of the hybrid electrochemical capacitor is examined in a two-electrode cell by means of cyclic voltammetry. The cycle-life is 4000 cycles. Values for the specific energy and specific power of 18 Wh kg⁻¹ and 1.25 kW kg⁻¹, respectively, are demonstrated for a cell voltage between 1 and 1.6 V.     

New lightweight bipolar plate system for polymer electrolyte membrane fuel cells

The use of metal based bipolar plates in polymer electrolyte membrane (PEM) fuel cells, with an active coating on titanium to reduce voltage losses due to the formation of passive layers has been demonstrated. Lifetime data in excess of 8000 h has been achieved and power densities in excess of 1.8 kW dm⁻³ and 1 kW kg⁻¹ are predicted.     

Energy and exergy analysis of hybrid photovoltaic thermal water collector for constant collection temperature mode

This paper deals with the analysis of hybrid photovoltaic thermal (PVT) water collectors under constant collection temperature mode unlike constant flow rate mode. The analysis has been carried out in terms of thermal energy, electrical energy and exergy gain for two different configurations namely case A (collector partially covered by PV module) and case B (collector fully covered by PV module). The results are compared with the conventional flat plate collector (FPC). The effect of collector area covered by PV module on the performance of hybrid PVT water collector has been studied. The characteristic equations have also been developed for both the cases.It has been observed that case A is more favorable for thermal energy point of view, while case B is suitable for electricity generation. On the basis of the numerical calculations the annual thermal energy gain is found to be 4167.3 and 1023.7 and annual net electrical energy gain is 320.65 and 1377.63 for cases A and B respectively. The annual overall thermal energy gain is decreased by 9.48% and an annual overall exergy gain is increased by 39.16% from case A to case B.     

Energy and exergy of potato drying process via cyclone type dryer

This paper is concerned with the energy and exergy analyses of the single layer drying process of potato slices via a cyclone type dryer. Using the first law of thermodynamics, an energy analysis was performed to estimate the ratios of energy utilization. An exergy analysis was accomplished to determine the location, type and magnitude of the exergy losses during the drying process by applying the second law of thermodynamics. It was concluded that the exergy losses took place mostly in the 1st tray where the available energy was less utilized during the single layer drying process of potato slices. It is emphasized that the potato slices are sufficiently dried in the ranges between 60 and 80 °C and 20–10% relative humidity at 1 and 1.5 ms⁻¹ of drying air velocity during 10–12 h despite the exergy losses of 0–1.796 kJ s⁻¹.     

Quantitative appraisal and potential analysis for primary biomass resources for energy utilization in China

As the largest agricultural country, China has abundant biomass resources, but the distribution is scattered and difficult to collect. It is essential to estimate the biomass resource and its potential for bioenergy utilization in China. In this study, the amount of main biomass resources for possible energy use and their energy utilization potential in China are analyzed based on statistical data. The results showed that the biomass resource for possible energy use amounted to 8.87 × 10⁸ tce in 2007 of which the crops straw is 1.42 × 10⁸ tce, the forest biomass is 2.85 × 10⁸ tce, the poultry and livestock manure is 4.40 × 10⁷ tce, the municipal solid waste is 1.35 × 10⁶ tce, and the organic waste water is 6.46 × 10⁶ tce. Through the information by thematic map, it is indicated that, except arctic-alpine areas and deserts, the biomass resource for possible energy use was presented a relatively average distribution in China, but large gap was existed in different regions in the concentration of biomass resources, with the characteristics of East dense and West sparse. It is indicated that the energy transformation efficiency of biomass compressing and shaping, biomass anaerobic fermentation and biomass gasification for heating have higher conversion efficiency. If all of the biomass resources for possible energy use are utilized by these three forms respectively, 7.66 × 10¹² t of biomass briquettes fuel, 1.98 × 10¹² m³ of low calorific value gas and 3.84 × 10¹¹ m³ of biogas could be produced, 3.65 × 10⁸ t to 4.90 × 10⁸ t of coal consumption could be substituted, and 6.12 × 10⁸ t to 7.53 × 10⁸ t of CO₂ emissions could be reduced. With the enormous energy utilization potential of biomass resources and the prominent benefit of energy saving and emission reduction, it proves an effective way to adjust the energy consumption structure, to alleviate the energy crisis, to ensure the national energy security and to mitigate the global warming trend.     

Experimental investigation of microchannel coolers for the high heat flux thermal management of GaN-on-SiC semiconductor devices

Experiments on removing high heat fluxes from GaN-on-SiC semiconductor dies using microchannel coolers are described. The dies contain an AlGaN/GaN heterostructure operated as a direct current resistor, providing a localized heat source. The active dimensions of the heat source are sized to represent the spatially-averaged heat flux that would appear in microwave power amplifiers. A wide variety of microchannel materials and configurations are investigated, allowing a comparison of performance and the resulting GaN temperatures. Silicon and AlN microchannel coolers exhibit good performance at lower power densities (1000–1200 W/cm² over 3 × 5 mm² to 2 × 5 mm² active areas). Polycrystalline chemical vapor deposited (CVD) SiC microchannel coolers are found to be extremely promising for higher power densities (3000–4000 W/cm² over 1.2 × 5 mm² active areas with 120 °C GaN temperature). A hybrid microchannel cooler consisting of low-cost CVD diamond on polycrystalline CVD SiC exhibits moderately better performance (20–30%) than polycrystalline CVD SiC alone.     

Preparation,electrical, mechanical and thermal properties of composite bipolar plate for a fuel cell

A novel composite bipolar plate for a polymer electrolyte fuel cell has been prepared by a bulk-moulding compound (BMC) process. The electrical resistance of the composite material decreases from 20 000 to 5.8 mΩ as the graphite content is increased from 60 to 80 wt.%. Meanwhile, the electrical resistance of composite increases from 6.5 to 25.2 mΩ as the graphite size is decreased from 1000 to 177 μm to less than 53 μm. The thermal decomposition of 5% weight loss of composite bipolar plate is higher than 250 °C. The oxygen permeability of the composite bipolar plate is 5.82×10⁻⁸ (cm³/cm² s) when the graphite content is 75 wt.%, and increases from 6.76×10⁻⁸ to 3.28×10⁻⁵ (cm³/cm² s) as the graphite size is longer or smaller than 75 wt.%. The flexibility of the plate decreases with increasing graphite content. The flexural strength of the plate decreases with decrease in graphite size from 31.25 MPa (1000–177 μm) to 15.96 MPa (53 μm). The flexural modulus decreases with decrease of graphite size from 6923 MPa (1000–177 μm) to 4585 MPa (53 μm). The corrosion currents for plates containing different graphite contents and graphite sizes are all less than 10⁻⁷ A cm⁻². The composite bipolar plates with different graphite contents and graphite sizes meet UL-94V-0 tests, and the limiting oxygen contents are higher than 50. Testing show that composite bipolar plates with optimum composition are very similar to that of the graphite bipolar plate.