Domestic hot water and solar energy in Ireland

Two systems are discussed which involve the use of solar energy to supply domestic hot-water requirements and their usefulness in Ireland is examined. the systems are evaluated for thermal performance and cost-effectiveness but the use of a computer simulation model of a system involving a typical commercially available solar panel. It is shown that such systems may be economically justified when compared with electricity, but only if the water supply is directly heated by solar panels and only if the installed cost of such panels is low. Further, it appears that the system performance is relatively insensitive to the panel orientation and consequently that retro-fit installations on existing houses are unlikely to cause difficulties.     

Desalination using solar energy: Towards sustainability

This paper describes the theoretical rationale for a new low temperature phase-change desalination process, and six examples of applications to illustrate how this process can be engineered for sustainable desalination. In this process, brackish water is evaporated at near-ambient temperatures under near-vacuum pressures created by the barometric head without any mechanical energy input. Thermodynamic advantages and benefits of low temperature phase-change desalination are discussed and results from simulation studies and a prototype test system are presented. Three of the examples illustrate how the proposed process can be driven by solar energy: a) utilizing direct solar energy; b) inclusion of an external reflector; c) utilizing photovoltaic energy during non-sunlight hours. The other examples illustrate how the proposed process can be driven by waste heat: i) waste heat rejected by an absorption refrigeration unit driven by grid power; ii) waste heat rejected by an absorption refrigeration unit driven by solar collectors; and iii) waste heat rejected by an absorption refrigeration unit supported by a photovoltaic array. Merits of utilizing solar energy and process waste heat in reducing energy consumption and greenhouse gas emissions are discussed in detail.     

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.     

Domestic application of solar PV systems in Ireland: The reality of their economic viability

Renewable sources of energy are anticipated to play a major role in electricity generation in Ireland in the future. Currently, electricity is mainly generated from imported gas and coal due to a lack of indigenous fossil fuel resources in Ireland. Solar energy is omnipresent, freely available and environmental friendly. The utilisation of solar energy to produce electricity has become increasingly attractive worldwide. However, solar electricity generation has not been very popular in Ireland to-date either on a large scale or on a domestic scale. The unclear economics of domestic solar PV systems, under Irish conditions, is considered the biggest obstacle for expanding domestic solar PV system installation in Ireland. This paper presents a methodology to accurately evaluate the economic viability of a domestic solar PV system on a case-by-case basis. The methodology utilises the software programmes HOMER and Microsoft Excel 2007 for the energy and economic analyses. Utilising this methodology, a realistic economic analysis of eight sample domestic solar PV systems available in Ireland is presented. Based on the predictions, the domestic solar PV system is not economically viable under current conditions in Ireland. Domestic solar PV systems still do not look promising even if better financial support is given.     

Domestic hydrogen production using renewable energy

A brief review shows that domestic production of hydrogen to fuel a car is feasible by using various means. Among these, the solar––photovoltaic electricity––electrolysis process seems to be the most practical if a renewable energy source is to be used. A simplified model has been developed to determine and optimize the thermal and economical performance of domestic photovoltaic-electrolyzer systems, either with fixed or sun tracking panels using annual total solar radiation on a horizontal surface and climatic data. Twelve locations in the United Sates from four climatic zones (tropical-sub tropical, dry, temperate, cool snow-forest) have been selected. Simulations have been carried out to produce data for hydrogen production for these various locations and the resulting data have been correlated to obtain hydrogen production in kg/kW_p/year photovoltaic system as a function of total annual solar radiation on horizontal surface. The economical feasibility has been studied by taking the photovoltaic and electrolyzer systems' price as variable parameters. It is assumed that the necessary capital is 100% borrowed from a financial institution to pay back in monthly installments. It has been found that the hydrogen production with fixed photovoltaic panels varies from 26 to 42 kg/kW_p/year and the cost from 25 to 268 $/GJ.     

Thermal response of a series- and parallel-connected solar energy storage to multi-day charge sequences

The thermal response of a multi-tank thermal storage was studied under variable charge conditions. Tests were conducted on an experimental apparatus that simulated the thermal charging of the storage system by a solar collector over predetermined (prescribed) daylong periods. The storage was assembled from three standard 270 L hot-water storage tanks each charged through coupled, side-arm, natural convection heat exchangers which were connected in either a series- or parallel-flow configuration. Both energy storage rates and tank temperature profiles were experimentally measured during charge periods representative of two consecutive clear days or combinations of a clear and overcast day. During this time, no draw-offs were conducted. Of particular interest was the effect of rising and falling charge-loop temperatures and collector-loop flow rate on storage tank stratification levels. Results of this study show that the series-connected thermal storage reached high levels of temperature stratification in the storage tanks during periods of rising charge temperatures and also limited destratification during periods of falling charge temperature. This feature is a consequence of the series-connected configuration that allowed sequential stratification to occur in the component tanks and energy to be distributed according to temperature level. This effect was not observed in the parallel charge configuration. A further aspect of the study investigated the effect of increasing charge-loop flow rate on the temperature distribution within the series-connected storage and showed that, at high flow rates, the temperature distributions were found to be similar to those obtained during parallel charging. A disadvantage of both the high-flow series-connected and parallel-connected multi-tank storage is that falling charge-loop temperatures, which normally occur in the afternoon, tend to mix and destratify the storage tanks.     

Fiber-optic solar energy transmission and concentration

Fiber-optic solar energy transmission and concentration provide a flexible way of handling concentrated solar energy. The high flux solar energy transmission by a flexible fiber-optic bundle and the research on the associated compound parabolic concentrator will largely expand the existing field of applications of solar energy concentrators. We report on a flexible light guide which consists of 19 optical fibers and is capable of transmitting up to 60 W of optical power, with 60% efficiency. A flexible fiber-optic solar energy transmission and concentration scheme by using one single fiber, 2 and 7 fiber bundles is also reported.     

Technical performance analysis of a micro-combined cooling,heating and power system based on solar energy and high temperature PEMFC

A solar energy and high temperature proton exchange membrane fuel cell (PEMFC)-based micro-combined cooling, heating and power (CCHP) system (named system I) is proposed in this work. This system mainly consists of a PEMFC subsystem, an organic Rankine cycle (ORC) subsystem and a vapor compression cycle (VCC) subsystem. System I would reduce to a high temperature PEMFC-based CCHP system (named system II) if there was no solar energy. With the technical performance analysis models developed, the effects of the current density, operating temperature, solar radiation intensity and ambient temperature on the thermal, economic and environmental performances of the systems are theoretically analyzed. The results show that the current density and solar radiation intensity are the main impact factors that can significantly affect the thermal, economic and environmental performances, while the operating temperature and ambient temperature only have remarkable influences on the thermal performance. The coefficient of performance (COP) of system II is approximately 1.19 in summer and 1.42 in winter, which is always higher than that of system I under the same working conditions. The exergy efficiency of system I and system II are approximately 49.7% and 47.4%, respectively. The primary energy saving rates (PESRs) of system I and system II are 64.9% and 31.8% in summer, and 60.0% and 36.2% in winter, respectively. The payback periods of system I and system II are 9.6 yr and 6.0 yr without government subsidy, respectively. Compared with system II, the pollutant emission reduction rates (ERRs) of system I can be increased by approximately 8.4%–23.5% with the addition of solar energy, which indicates that the development and utilization of clean and renewable energy such as solar energy can significantly reduce pollutant emissions.     

Fossil fuels substitution by the solar energy utilization for the hot water production in the heating plant “Cerak” in Belgrade

The main objective of this paper is to evaluate energy and environmental benefits of the large-scale solar heating system connection with district heating system. The assessment of fossil fuels substitution by the solar energy for the hot water production for domestic use, during the summer period, is done. Hot water for district heating and domestic use is produced in heating plant “Cerak” placed in the suburb of Belgrade. The existing production and distribution system are based on fossil fuel energy, mainly on the natural gas. In the first phase of the project plan was to install about 10,000 m² of solar collectors to substitute nearly 25% of natural gas consumption. During the summer period, the saving of natural gas calculated for presented system is approximately 430,000 m³ and in this way 900 t of the CO₂ emissions would be reduced.     

Performance of indirect through pass natural convective solar crop dryer with phase change thermal energy storage

A state-of-the-art solar crop dryer was developed with thermal energy storage to maintain continuity of drying of herbs for their colour and flavour vulnerability. The dryer consists of flat plate solar collector, packed bed phase change energy storage, drying plenum with crop trays and natural ventilation system. Dryer is designed with a maximum collector area of 1.5 m², six crop trays with an effective area of 0.50 × 0.75 m², can hold 12 kg of fresh leafy herbs. The dryer is attached with a packed bed thermal energy storage having capacity of 50 kg phase change material (PCM). The drying system works in such a manner that phase change material stores the thermal energy during sun shine hours and releases the latent and sensible heat after sunset, thus dryer is effectively operative for next 5–6 h. The temperature in drying chamber was observed 6 °C higher than the ambient temperature after sunshine hours till the mid night during the month of June at Jodhpur. Economic performance of the dryer was analysed with return on capital and simple payback period as 0.65 and 1.57 year respectively on optimum cost of raw material and product sale price.     

Domestic hot water storage: Balancing thermal and sanitary performance

Thermal stratification within hot water tanks maximises the availability of stored energy and facilitates optimal use of both conventional and renewable energy sources. However, stratified tanks are also associated with the proliferation of pathogenic bacteria, such as Legionella, due to the hospitable temperatures that arise during operation. Sanitary measures, aimed at homogenising the temperature distribution throughout the tank, have been proposed; such measures reduce the effective energy storage capability that is otherwise available. Here we quantify the conflict that arises between thermodynamic performance and bacterial sterilisation within 10 real world systems. Whilst perfect stratification enhances the recovery of hot water and reduces heat losses, water samples revealed significant bacterial growth attributable to stratification (P<0.01). Temperature measurements indicated that users were exposed to potentially unsanitary water as a result. De-stratifying a system to sterilise bacteria led to a 19% reduction in effective hot water storage capability. Increasing the tank size to compensate for this loss would lead to an 11% increase in energy consumed through standing heat losses. Policymakers, seeking to utilise hot water tanks as demand response assets, should consider monitoring and control systems that prevent exposures to unsanitary hot water.     

Review on solar water heater collector and thermal energy performance of circulating pipe

The effect of thermal conductivity of the absorber plate of a solar collector on the performance of a thermo-siphon solar water heater is found by using the alternative simulation system. The system is assumed to be supplied of hot water at 50 °C and 80 °C whereas both are used in domestic and industrial purposes, respectively. According to the Rand distribution profile 50, 125 and 250 l of hot water are consumed daily. The condition shows that the annual solar fraction of the planning functions and the collector's configuration factors are strongly dependent on the thermal conductivity for its lower values. The less dependence is observed beyond a thermal conductivity of 50 W/m °C for the solar improper fraction and above 100 W/m °C for the configuration factors. In addition, the number of air ducts and total mass flow rate are taken to show that higher collector efficiency is obtained under the suitable designing and operating parameters. Different heat transfer mechanisms, adding natural convection, vapor boiling, cell nucleus boiling and film wise condensation is observed in the thermo-siphon solar water heater with various solar radiations. From this study, it is found that the solar water heater with a siphon system achieves system characteristic efficiency of 18% higher than that of the conventional system by reducing heat loss for the thermo-siphon solar water heater.     

Development co-operation and solar energy

The applications of energy in Colombia, India and Upper Volta, for which an improvement in the situation is the most urgent, are described. to a more limited extent these applications have also been investigated with respect to Niger, Pakistan and Senegal. the technical economic possibilities of achieving these improvements by means of solar energy in the period up to 1985 are discussed. Concerning those cases which offer a reasonable chance of the use of solar energy, the investigation then turns to the kind of co-operative programmes between industrialized countries and the developing countries being considered which might contribute to putting these opportunities into practice. This study has revealed the following programmes as offering the best possibilities. 1. Small thermal electric generators powered by concentrated sunlight at an operating temperature of about 300°C, the principal application being the driving of pumps for irrigation in India and Pakistan. 2. Small absorber cooling systems for India and Pakistan. 3. Drinking-water purification for Niger, Pakistan, Senegal and Upper Volta. 4. Battery-charging systems for India and Pakistan. 5. Reforestation for firewood production, close to the major towns of the Sahel countries. Furthermore, much importance is found to attach to the improving of the efficiency of cooking.     

New method to store heat energy in horizontal solar desalination still

A new approach is proposed to store excess heat energy in horizontal solar desalination stills during daytime for the continuation of the process at night. This technique divides the horizontal still into evaporating and heat storing zones and combines the advantages of shallow and deep stills. The performance of heat storing zone was studied over one year and exhaustive data were collected, analyzed and presented. To show the effectiveness of the system, its performance was compared with that of the shallow still. The heat storing capacity of the system during the daytime was found to be an average of 35.7% of the total amount of solar energy entering the system. The efficiency of recovering process, in the form of portable water produced at night, was found to be an average of 47.2% of the total amount of energy stored during the day. Furthermore, this technique does not require any kind of external power for storing and recovering processes.     

Review on solar air heating system with and without thermal energy storage system

In order to produce process heat for drying of agricultural, textile, marine products, heating of buildings and re-generating dehumidify agent, solar energy is one of the promising heat sources for meeting energy demand without putting adverse impact of environment. Hence it plays a key role for sustainable development. Solar energy is intermittent in nature and time dependent energy source. Owing to this nature, PCMs based thermal energy storage system can achieve the more popularity for solar energy based heating systems. The recent researches focused on the phase change materials (PCMs), as latent heat storage is more efficient than sensible heat storage. In this paper an attempt has been made to present holistic view of available solar air heater for different applications and their performance.     

Enhancement of solar gains through a roof using a thermal trap

This paper investigates the viability of increasing solar gains through the roof of an air-conditioned room using the thermal trap effect. In solving the heat conduction equations through the thermal trap and the concrete slab, the finite difference method has been employed and the initial conditions are derived from the assumption that, initially, the ceiling of the room and the top of the trap material are in equilibrium with constant room air temperature and the ambient air temperature, respectively. The effect of the thickness of the thermal trap and that of the concrete slab on the thermal flux transferred through the roof have been studied.     

Exergy analysis of solar energy applications

Solar energy is a clean, abundant and easily available renewable energy. Usage of solar energy in different kinds of systems provides scope for several studies on exergy analysis. In the present work, a comprehensive literature review has been carried out on exergy analysis of various solar energy systems. The systems considered under study are solar photovoltaic, solar heating devices, solar water desalination system, solar air conditioning and refrigerators, solar drying process and solar power generation. The summary of exergy analysis and exergetic efficiencies is presented along with the exergy destruction sources.     

Design,development and testing of an improved multipurpose solar energy device

This paper reports the design, development and testing of an improved multipurpose solar energy device. The novel feature of the device is that it can be used as a solar water heater and solar still simultaneously and, when required, as a solar cabinet dryer by incorporating minor changes.     

On increasing solar gains through roof/wall with a thermal trap

This paper investigates the feasibility of increasing solar gains through the roof/wall of a building utilizing the thermal trap effect. It is seen that optimum thickness of the thermal trap is 0.05m. Corresponding to this thickness, there is a net positive heat gain into the room at all times for a 0.20m thickness of concrete wall/roof.