Development of advanced solar assisted drying systems

The Solar Energy Research Group in the Universiti Kebangsaan Malaysia has been set-up more than two decades ago. One of the activities is in the field of solar thermal process, particularly in development of solar assisted drying systems. Solar drying systems technical development can proceed in two directions. Firstly simple, low power, short life, and comparatively low efficiency-drying system. Secondly, the development of high efficiency, high power, long life expensive solar drying system. The group has developed four solar assisted drying systems namely (a) the V-groove solar collector, (b) the double-pass solar collector with integrated storage system, (c) the solar assisted dehumidification system for medicinal herbs and (d) the photovoltaic thermal (PVT) collector system. The common problems associated with the intermittent nature of solar radiation and the low intensities of solar radiation in solar thermal systems can be remedied using these types of solar drying systems. These drying systems have the advantages of heat storage, auxiliary energy source, integrated structure control system and can be use for a wide range of agricultural produce.     

Modelling an off-grid integrated renewable energy system for rural electrification in India using photovoltaics and anaerobic digestion

This work describes the design optimisation and techno-economic analysis of an off-grid Integrated Renewable Energy System (IRES) designed to meet the electrical demand of a rural village location in West Bengal – India with an overall electrical requirement equivalent to 22 MWh year⁻¹. The investigation involved the modelling of seven scenarios, each containing a different combination of electricity generation (anaerobic digestion with biogas combined heat and power (CHP) and photovoltaics) and storage elements (Vanadium redox batteries, water electrolyser and hydrogen storage with fuel cell). Micro-grid modelling software HOMER, was combined with additional modelling of anaerobic digestion, to scale each component in each scenario considering the systems' ability to give a good quality electricity supply to a rural community. The integrated system which contained all of the possible elements – except hydrogen production and storage presented the lowest capital ($US 71 k) and energy cost ($US 0.289 kWh⁻¹) compared to the scenarios with a single energy source. The biogas CHP was able to meet the electrical load peaks and variations and produced 61% of the total electricity in the optimised system, while the photovoltaics met the daytime load and allowed the charging of the battery which was subsequently used to meet base load at night.     

Photovoltaic-thermal solar energy collectors based on optical tubes

In this work, we examine the use of oil filled tubular optical concentrators coupled with a model organic bulk heterojunction photovoltaic: poly-3-hexathiophene-[6,6]-phenyl-C61-butyric-acid methyl-ester (P3HT:PCBM) to create a photovoltaic-photothermal hybrid solar collector. The organic photovoltaic cells were fabricated onto one half of a tubular light pipe and then silicone oil was flowed inside the pipe. This allows solar energy in the visible wavelengths to be effectively converted into electricity by photocell while simultaneously; the silicone oil captures the infrared radiation (IR) part of the spectrum as heat energy. The VIS-IR power conversion efficiency for this model organic system, under normally incident AM1.5G illumination was found to be: PCE ∼ 28%, which is combined by the photovoltaic efficiency (PCE ∼ 2%) and the photothermal efficiency (PCE ∼ 26%). We further show that the oil filled tube, acts as a passive optical element that concentrates the light onto the photovoltaic and thereby increases its overall efficiency but also the range of incident angles in which the light is efficiently captured.     

Efficiency enhancement of stationary solar energy based power conversion systems in Canada

This paper presents the optimum energy conversion conditions of stationary photovoltaic panels used for electrical power generation. The results are arrived at after performing calculations for 180 days in a given year at the latitude of St. John’s, Newfoundland. The latitude of this city is close to other Canadian major population centers. Various angular orientations of sun’s rays on the earth are considered. On a given day, the incident energy flux of sun is resolved into three components, and the conversion efficiency is based on the flux normal to the panels. The efficiency of conversion of the incident energy is measured with respect to a solar tracking process. The numbers of days in a given year are divided into two groups – one between the winter solstice and the spring equinox, and another between the spring equinox and the summer solstice.     

Validation of CFD simulation for flat plate solar energy collector

The problem of flat plate solar energy collector with water flow is simulated and analyzed using computational fluid dynamics (CFD) software. The considered case includes the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between tube surface, glass cover, side walls, and insulating base of the collector as well as the mixed convective heat transfer in the circulating water inside the tube and conduction between the base and tube material. The collector performance, after obtaining 3-D temperature distribution over the volume of the body of the collector, was studied with and without circulating water flow. An experimental model was built and experiments were performed to validate the CFD model. The outlet temperature of water is compared with experimental results and there is a good agreement.     

Optical properties of liquids for direct absorption solar thermal energy systems

A method for experimentally determining the extinction index of four liquids (water, ethylene glycol, propylene glycol, and Therminol VP-1) commonly used in solar thermal energy applications was developed. In addition to the extinction index, we report the refractive indices available within the literature for these four fluids. The final value reported is the solar-weighted absorption coefficient for the fluids demonstrating each fluid’s baseline capacity for absorbing solar energy. Water is shown to be the best absorber of solar energy of the four fluids, but it is still a weak absorber, only absorbing 13% of the energy. These values represent the baseline potential for a fluid to be utilized in a direct absorption solar thermal collector.     

A review of solar thermal technologies

The use of solar energy in recent years has reached a remarkable edge. The continuous research for an alternative power source due to the perceived scarcity of fuel fossils is its driving force. It has become even more popular as the cost of fossil fuel continues to rise. The earth receives in just 1 h, more energy from the sun than what we consume in the whole world for 1 year. Its application was proven to be most economical, as most systems in individual uses requires but a few kilowatt of power. This paper reviews the present day solar thermal technologies. Performance analyses of existing designs (study), mathematical simulation (design) and fabrication of innovative designs with suggested improvements (development) have been discussed in this paper.     

A comparison of PV/electrolyser and photoelectrolytic technologies for use in solar to hydrogen energy storage systems

The approach of using hydrogen for an energy store to offset seasonal variations in solar energy is one very much at the periphery of current renewable energy system design. Nonetheless, its inherent advantages for long term storage in stand alone power systems warrant further detailed investigation. This paper provides a comparative overview of the very disparate technologies within two generic approaches to achieving this goal. These are: photovoltaic (PV) powered electrolysis of water and direct photoelectrolytic (PE) generation of hydrogen from water. Comparison of these is difficult, however, the paper compares devices of similar material system and structure within each generic scheme. PV/electrolysis is the more mature technology but there is still a wide range of potential ‘solar to hydrogen’ efficiencies. A figure of about 9% is estimated for comparison, with justification given. The comparative figure for PE is more difficult to judge because of even more disparate approaches to specific problems of sufficient photovoltage and stability, but an approximate comparative figure of 5% is estimated. Thus making PV/electrolysis more appropriate at present. Nonetheless, inherent advantages of simplicity of system design and potential robustness mean that PE may become more appropriate as the technology develops.     

Performance of a solar dryer using hot air from roof-integrated solar collectors for drying herbs and spices

A solar dryer for drying herbs and spices using hot air from roof-integrated solar collectors was developed. The dryer is a bin type with a rectangular perforated floor. The bin has a dimension of 1.0 m×2.0 m×0.7 m. Hot air is supplied to the dryer from fiberglass-covered solar collectors, which also function as the roof of a farmhouse. The total area of the solar collectors is 72 m². To investigate its performance, the dryer was used to dry four batches of rosella flowers and three batches of lemon-grasses during the year 2002–2003. The dryer can be used to dry 200 kg of rosella flowers and lemon-grasses within 4 and 3 days, respectively. The products being dried in the dryer were completely protected from rains and insects and the dried products are of high quality. The solar air heater has an average daily efficiency of 35% and it performs well both as a solar collector and a roof of a farmhouse.     

Thermal modeling of a combined system of photovoltaic thermal (PV/T) solar water heater

In this paper, an integrated combined system of a photovoltaic (glass–glass) thermal (PV/T) solar water heater of capacity 200 l has been designed and tested in outdoor condition for composite climate of New Delhi. An analytical expression for characteristic equation for photovoltaic thermal (PV/T) flat plate collector has been derived for different condition as a function of design and climatic parameters. The testing of collector and system were carried out during February–April, 2007. It is observed that the photovoltaic thermal (PV/T) flat plate collector partially covered with PV module gives better thermal and average cell efficiency which is in accordance with the results reported by earlier researchers.     

Optimum size and structure for solar energy collection systems

Procedures for sizing and optimizing the structure of solar collection systems are proposed. Four economical indices, including net present value and internal return rate, are given as examples of objective functions. Three solar energy applications were considered. A rather involved but still simple flat-plate solar collector model is used in calculations. The implementation was made for a specific geographical location with a detailed meteorological database available. In the case of solar collectors with uniformly distributed parameters, the procedure allows one to select the best devices from a given set of solar collectors. For every selected device the optimum range of the operation temperature is also determined. The best solution corresponds to systems with optimal non-uniformly distributed parameters. The general theorem proposed here shows how the modified optical efficiency and heat loss coefficient should be distributed for cost minimization. One finds that unglazed, single- and double-glazed collectors should be used on the same collection area in order to obtain the best performance. Also, the bottom insulation thickness should be changed accordingly.     

Comparative study of different solar cooling systems for buildings in subtropical city

In recent years, more and more attention has been paid on the application potential of solar cooling for buildings. Due to the fact that the efficiency of solar collectors is generally low at the time being, the effectiveness of solar cooling would be closely related to the availability of solar irradiation, climatic conditions and geographical location of a place. In this paper, five types of solar cooling systems were involved in a comparative study for subtropical city, which is commonly featured with long hot and humid summer. The solar cooling systems included the solar electric compression refrigeration, solar mechanical compression refrigeration, solar absorption refrigeration, solar adsorption refrigeration and solar solid desiccant cooling. Component-based simulation models of these systems were developed, and their performances were evaluated throughout a year. The key performance indicators are solar fraction, coefficient of performance, solar thermal gain, and primary energy consumption. In addition, different installation strategies and types of solar collectors were compared for each kind of solar cooling system. Through this comparative study, it was found that solar electric compression refrigeration and solar absorption refrigeration had the highest energy saving potential in the subtropical Hong Kong. The former is to make use of the solar electric gain, while the latter is to adopt the solar thermal gain. These two solar cooling systems would have even better performances through the continual advancement of the solar collectors. It will provide a promising application potential of solar cooling for buildings in the subtropical region.     

Parametric study of a thermal trap solar energy collector

A parametric study of a thermal trap solar energy collector with the help of a modified Hottel-Whillier-Bliss equation, is presented. The developed analysis is used to optimize the typical parameters, namely the trap's thickness and the number of flowing channels. The variation of the rating parameters of a collector with typical quantities, such as the fin distance, mass flow rate and thickness of the absorber plate, is discussed in detail.     

Year round performance of a cylindrical solar water heater

A cylindrical collector-cum-storage type solar water heater has been designed, developed and tested. Its year round performance has been carried out and reported in this paper. The heater can provide 50 litres of hot water at 50–60°C in the afternoon and a temperature of 35°C can be retained till the next day for early morning use. The heater receives approximately 30% more radiation as compared to a flat surface. The economics of the heater has been worked out and it has been found that the cost can be recovered within one year.     

Study of hybrid energy system coupling fuel cell,solar thermal system and photovoltaic cell

The present work examines the combination of solar energy systems with Fuel cell. Indeed, fuel cells are green storage systems without any pollution effects. They are supplied by oxygen and hydrogen to produce electricity. That is why it is inescapable to find a source of hydrogen in order to use fuel cell. Several techniques can be adopted to produce hydrogen depending on the availability and the cost of the sources. One of the most utilized techniques is electrolysers. They allow to obtain hydrogen from water by several technologies among them proton exchange membrane (PEM) which is considered in this work. On the other hand, electrolysers need electrical power to operate. A green-green energy system can be constructed by using a renewable energy source to supply fuel cell trough electrolysers. A comparison between two solar systems (Photovoltaic and Parabolic Trough) coupled to fuel cell is performed. A case study on the Lebanese city of Tripoli is carried out. The study shows the performance of each of both combined systems for different parameters and proposes recommendations depending on the considered configuration.     

Techno-economic analysis for clean hydrogen production using solar energy under varied climate conditions

The paper discusses the feasibility of the use solar energy into hydrogen production using a photovoltaic energy system in the four main cities of Iraq. An off-grid photovoltaic system with a capacity of 22.0 kWp, an 8.0 kW alkaline electrolyser, a hydrogen compressor, and a hydrogen tank were simulated for one year in order to generate hydrogen. A mathematical model of the proposed system behavior is presented using MATLAB/Simulink, considering nine years from the 2021 to 2030 project span using hourly experimental weather data. The outcomes demonstrated that the annual hydrogen production ranged from 1713.92 kg up to 1891.12 kg, oxygen production ranged from 1199.74 to 1323.78 kg, and water consumption ranged from 7139.91 L to 7877.29 L. The hydrogen evaluated costs equal to $3.79/kg. The results show that the optimum site for solar hydrogen production systems can be established in the midwest of Iraq and in other cities with similar climates, especially those that get a lot of sunlight.     

A solar test collector for evaluation of both selective and non-selective absorbers

A solar test collector has been designed for the testing of thermally absorbing coatings under controlled conditions. The design consists of a collector fed by a controlled temperature fluid within the range of 25–90°C (77–194°F). This temperature is maintained by a custom electronic controller. A small variable flow pump circulates water through three collector pipes at selected flow rates. Strip heaters coupled with a differential temperature controller compensate for edge losses associated with small collectors. Detailed design and operation data are presented and three black chrome and one non-selective absorber are analysed in detail by test collector measurements. Results show that efficiencies as high as 77 and 75 per cent (ΔT = 0) are obtained for 1.0 μm black chrome on copper and nickel plated steel, respectively. The lowest loss coefficients are about 3.8 W/m^2°C for all black chrome/metal surfaces, with the highest being 8.4 W/m^2°C for the black paint/metal sample. Also, a collector model is presented for comparison.     

Increasing the solar photovoltaic energy capture on sunny and cloudy days

This report analyzes an extensive set of measurements of the solar irradiance made using four identical solar arrays and associated solar sensors (collectively referred to as solar collectors) with different tilt angles relative to the earth’s surface, and thus the position of the sun, in order to determine an optimal tracking algorithm for capturing solar radiation. The study included a variety of ambient conditions including different seasons and both cloudy and cloud-free conditions. One set of solar collectors was always approximately pointed directly toward the sun (DTS) for a period around solar noon. These solar collectors thus captured the direct beam component of the solar radiation that predominates on sunny days. We found that on sunny days, solar collectors with a DTS configuration captured more solar energy in accordance with the well-known cosine dependence for the response of a flat-surfaced solar collector to the angle of incidence with direct beam radiation. In particular, a DTS orientation was found to capture up to twice as much solar energy as a horizontal (H) orientation in which the array is tilted toward the zenith. Another set of solar collectors always had an H orientation, and this best captured the diffuse component of the solar radiation that predominates on cloudy days. The dependence of the H/DTS ratio on the solar-collector tilt angle was in approximate agreement with the Isotropic Diffuse Model derived for heavily overcast conditions. During cloudy periods, we found that an H configuration increased the solar energy capture by nearly 40% compared to a DTS configuration during the same period, and we estimate the solar energy increase of an H configuration over a system that tracks the obscured solar disk could reach 50% over a whole heavily-overcast day. On an annual basis the increase is predicted to be much less, typically only about 1%, because the contribution of cloudy days to the total annual solar energy captured by a photovoltaic system is small. These results are consistent with the solar tracking algorithm optimized for cloudy conditions that we proposed in an earlier report and that was based on a much smaller data set. Improving the harvesting of solar energy on cloudy days deserves wider attention due to increasing efforts to utilize renewable solar energy. In particular, increasing the output of distributed solar power systems on cloudy days is important to developing solar-powered home fueling and charging systems for hydrogen-powered fuel-cell electric and battery-powered vehicles, respectively, because it reduces the system size and cost for solar power systems that are designed to have sufficient energy output on the worst (cloudy) days.     

Potential application of a centralized solar water-heating system for a high-rise residential building in Hong Kong

There is a growing, government-led trend of applying renewable energy in Hong Kong. One area of interest lies in the wider use of solar-energy systems. The worldwide fast development of building-integrated solar technology has prompted the design alternative of fixing the solar panels on the external façades of buildings. In Hong Kong, high-rise buildings are found everywhere in the urban districts. How to make full use of the vertical facades of these buildings to capture the most solar radiation can be an important area in the technology promotion. In this numerical study, the potential application of a centralized solar water-heating system in high-rise residence was evaluated. Arrays of solar thermal collectors, that occupied the top two-third of the south and west façades of a hypothetical high-rise residence, were proposed for supporting the domestic hot-water system. Based on typical meteorological data, it was found that the annual efficiency of the vertical solar collectors could reach 38.4% on average, giving a solar fraction of 53.4% and a payback period of 9.2 years. Since the solar collectors were able to reduce the heat transmission through the building envelope, the payback was in fact even shorter if the energy saving in air-conditioner operation was considered.