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.     

Economic analysis of solar systems

This paper presents a review of various economic strategies to evaluate solar energy systems. A techno-economic criterion for solar collectors has also been presented. The analysis has been illustrated with specific examples of solar drying and solar hot water systems.     

Theoretical analysis of the optimum energy band gap of semiconductors for fabrication of solar cells for applications in higher latitudes locations

In this work some results of theoretical analysis on the selection of optimum band gap semiconductor absorbers for application in either single or multijunction (up to five junctions) solar cells are presented. For calculations days have been taken characterized by various insolation and ambient temperature conditions defined in the draft of the IEC 61836 standard (Performance testing and energy rating of terrestrial photovoltaic modules) as a proposal of representative set of typical outdoor conditions that may influence performance of photovoltaic devices. Besides various irradiance and ambient temperature ranges, these days additionally differ significantly regarding spectral distribution of solar radiation incident onto horizontal surface. Taking these spectra into account optimum energy band gaps and maximum achievable efficiencies of single and multijunction solar cells made have been estimated. More detailed results of analysis performed for double junction cell are presented to show the effect of deviations in band gap values on the cell efficiency.     

An assessment of the feasibility of solar absorption and vapor compression cooling systems

For absorption cooling systems to operate and produce their cooling effects they need both thermal and electrical energy, while vapor compression systems need electrical energy only. When operating on solar energy the absorption system may receive all its thermal energy needs from solar sources while its electrical needs (parasitic power) are to be supplied from conventional sources. In order to conduct a fair comparison between the two cooling systems, it is proposed to supply both systems with equal amounts of conventional power and to supplement the rest of their needs from solar sources. A solar coefficient of performance, defined as the ratio of the refrigeration effect to the solar radiation input, is introduced and used for comparing some parameters of engineering ane economic importance in both systems. Economic analysis of solar cooling systems indicates that their initial cost is a function of both their design capacities and the number of hours of full load operation required to fulfill the total daily cooling demand. It indicates, also, that the initial cost of both solar cooling systems would break even before the cost of their respective solar conversion devices do.     

Thermal analysis of three zone solar pond

This paper presents a periodic analysis of a three zone solar pond as a solar energy collector and long term storage system. We explicitly take into account the convective heat and mass flux through the pond surface and evaluate the temperature and heat fluxes at various levels in the pond during its year round operation by solving the time dependent Fourier heat conduction equation with internal heat generation resulting from the absorption of solar radiation in the pond water. Eventually, an expression, for the transient rate at which heat can be retrieved from the solar pond to keep the temperature of the zone of heat extraction as constant, is derived. Heat retrieval efficiencies of 40.0 per cent, 32.1 per cent, 28.3 per cent and 25.5 per cent are predicted at collection temperatures of 40, 60, 80 and 100°C, respectively. the retrieved heat flux exhibits a phase difference of about 30 to 45 days with the incident solar flux; the load levelling in the retrieved heat flux improves as the thickness of the non-convective zone increases. the efficiency of the solar pond system for conversion of solar energy into mechanical work is also studied. This efficiency is found to increase with collection temperature and it tends to level around 5 per cent at collection temperatures about 90°C.     

Analysis and optimization of solar hot water systems

Use of a simplified method has been made to calculate the time-dependent thermal performance of various solar domestic hot water systems. to establish the value of solar hot water systems under given economic considerations a thermal analysis was carried out on three basic energy system designs, operating at several locations in the Federal Republic of Germany (F.R.G.) with various solar collectors. It is found that systems design can result in variations up to a factor of two in the per cent solar output. the location and year of operation in the F.R.G. result in variations up to 15 per cent in the solar output. A sensitivity study was also done with respect to all solar collector, systems and user parameters. From this it was found that the dominant effects on the systems performance were due to the collector-dependent parameters.     

Solar energy outlook in Malaysia

Predicted to be the clean energy of tomorrow, solar energy has been in the forefront of energy development in many developed countries and a potential source of energy to developing countries like Malaysia. This paper presents Malaysia's solar energy or solar photovoltaic developmental outlook. The study is done by first looking into the country's energy policies related to solar energy. Key players in the solar energy development such as government institutions are introduced. Early solar energy programmes and a key project called Malaysia Building Integrated Photovoltaic (MBIPV) as well as its successful initiatives will be presented. Measures which have taken by the government of Malaysia including attractive incentives to encourage solar photovoltaic development, the country's potential in solar energy, foreign investments and future directions as well a feed-in tariff scheme will be presented in length to provide a broad spectrum of solar energy development in Malaysia. The outlook has been positive and the country is active in promoting solar as an alternative energy and is aware of benefits it will bring toward its economic development in the future.     

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.     

Can solar energy replace fossil-fissile energy sources?

There is scepticism in many quarters as to the ability of solar energy capture devices to replace current fossil-fissile energy sources on a significant scale, even if they are economic on current costings. It has been argued that solar energy devices can deliver neither the quantity nor quality of energy needed to replicate themselves, far less drive the economy. This proposition is normally examined using energy pay-back calculations, using the concept of opportunity energy requirement. It is shown that this calculation, while of short term significance, does not reveal the true viability of a solar energy capture device. That viability is best expressed by calculating the replacement energy requirement, taking into account energy quality.     

Exergy analysis of a hybrid solar hydrogen system with activated carbon storage

A proposed hybrid solar hydrogen system with activated carbon storage for residential power generation is assessed using exergy analysis. Energy and exergy balances are applied to determine exergy flows and efficiencies for individual devices and the overall system. A ‘base case’ analysis considers the proposed system without modification, while a ‘modified case’ extends the base case by considering the possibility of multiple product outputs. It is determined that solar photovoltaic-based sub-systems have the lowest exergy efficiencies (14-18%) and offer the most potential for improvement. A comparison of these two scenarios shows that the additional outputs raise the exergy efficiency of the modified case (11%) relative to the base case (4.0%). An investigation of the energy and exergy efficiencies of separate devices illustrates how energy analyses can be misleading. The hybrid system is expected to have several environmental benefits, which may offset to some degree economic barriers to implementation.     

Optimum concentration ratio for an actively cooled solar concentrator-photovoltaic system with a fin-type absorber

Optimum values of the concentration ratio for an actively cooled solar concentrator-photovoltaic system with a fin-type absorber have been determined, taking into account both series resistance as well temperature effects on the solar cells. Results of some typical numerical calculations, made to study the dependence of the optimum value on various design and operational variables, have been plotted graphically and discussed.     

Technoeconomic optimization of solar natural convection hybrid hot water systems

In this paper a techno-economic model for a hybrid domestic hot water system operating under natural convection mode is presented. Three modes of auxiliary energy supply viz.

• A electric heater fitted in the solar hot water tank.
• B electric heater fitted in a small water tank in series with the solar hot water tank, and
• C an instant electric heater fitted in the tap

have been considered. Taking into account the life and the capital and maintenance costs of the solar and electrical equipments, the cost of useful energy (Rs/kWh) has been calculated for different values of the collector area and the tank capacity, and thereby the optimum collector area and tank capacity (for a given demand), corresponding to minimum cost of useful energy, has been determined. From numerical calculations made for the climate of Delhi, India (a representative composite climate) corresponding to the two cases of monthly hot water demand viz. (i) constant monthly demand, and (ii) variable monthly demand, it is seen that case (C) is the most economic design of the hybrid hot water system; numerical calculations have also been made for this case corresponding to the climates of Srinagar and Madras (representing cold and hot climates). The effect of government subsidy on the optimized values of collector area, tank capacity and cost of useful energy has also been investigated for the climate of Delhi.     

Solar absorption cooling in Spain: Perspectives and outcomes from the simulation of recent installations

In spite of the fact that Spain is one of the EU countries with the highest solar resource on annual basis, the huge seasonal variation in solar radiation availability and the relatively short period with heating demand, make it difficult to reach significant contributions of solar energy to the buildings heating energy demand. This compromises the economic viability of big solar collector areas per capita, and introduces technical difficulties for the dissipation of the excess solar energy available in the summer months. On the other hand, in a large part of the Spanish territory, in other to reach adequate comfort conditions in our buildings, the energy demand for cooling is more important or of the same order than the heating demand. Cooling energy demand is now experiencing a fast growing rate as this comfort requirement becomes internalized. Domestic air conditioning equipments based on vapour compression cycles are being used to reach comfort conditions in some of the rooms of buildings that were designed without taking into account cooling requirements. In spite of their so far small contribution to the total building sector energy demand, these equipments are already imposing important constraints on the environment and the electricity distribution system. Solar absorption cooling arises as an interesting alternative, which at the same time allows reaching a higher solar contribution to the heating demand. However, solar cooling installations present several peculiarities with respect to the more known DHW or even heating installations, which require to incorporate a more detailed approach and additional considerations in the design and performance evaluation processes. Besides, some limitations still persist in solar absorption systems, which could make them loose their market potential for the benefit of other solar cooling options. In this paper, we present some conclusions arising from the experience gained in detailed TRNSYS dynamical simulation of some of the first commercial solar heating and cooling installations recently implemented in Spain, and analyse their perspectives in comparison with other solar cooling options.     

Solar thermal systems: Advantages in domestic integration

Pollution represents a major issue, and so does the ability to utilize, when available, renewable energy sources instead of traditional ones. If, on the one hand, it is possible to utilize renewable energy sources in many contexts, on the other hand they are not exploited because of the high cost of the initial investment needed for the installation of these systems, above all when domestic usage is taken into account.This paper proposes a quantitative approach able to forecast the profitability of the introduction of domestic solar thermal systems operating in parallel with the most common systems for heating domestic sanitary water. The approach is developed firstly by analyzing the most common system for heating sanitary water from both the engineering and economic point of view. At the same time the technical–economic solutions related to the most commercialized solar heating systems, and their compatibility with the most common traditional heating systems are studied. This is carried out by using a differential economic analysis of different possible scenarios in which different matches between traditional and solar heating systems are shown, and their profitability is assessed as a function of the power installed.     

Assessment of solar emissions in the climate of Iraq for efficient multifunctional disposal

The concept of solar-hydrogen energy today provides optimal solutions in light of the climate agenda for all geographic areas of the globe.Iraq's geographical location and climate conditions predetermine ample opportunities for renewable sources, namely solar energy. High air temperatures, the prevailing number of sunny days recorded annually in the region, create a favorable technical platform for the implementation of thermal processes based on the utilization of incoming research. Therefore, for the design of solar plants and in the future, a reliable estimate of solar energy resources is required to determine the generated power depending on seasonal changes. Theoretical methods of calculating the incoming radiation flow for a particular area do not have the required accuracy for a number of reasons, the main of which is the permanent state of cloud cover. Only taking into account the actual climatic conditions for the construction areas under consideration on the basis of long-term actinometric observations gives a fairly accurate distribution of solar energy. The absence of such information in full implies forecasting of resource availability, including for areas not covered by observation systems. Given these limitations, an analysis of the average monthly daily solar radiation revenues for densely populated areas of Iraq is provided. On the basis of actinometric information of many years of observations, dependencies were obtained to determine the solar energy coming at statistical clouds per day per 1 m² of horizontal surface of the area, taking into account its latitude and serial number of the month of the year. The equations allow to fulfill the forecast of the area irradiation for the design of solar plants, to justify the subsequent efficiency of the alternative system, as well as the level of possible replacement of traditional resources and the degree of reduction of their consumption. On the basis of the calculated data, it is possible to justify the most expedient scheme of solar energy utilization depending on the available resources and to select the structures of radiation sensing devices required for climatic conditions for the solved tasks. In view of the analysis of solar energy distributions and average monthly outdoor air temperatures in Iraq, two types of thermal solar plants have been recommended for use, which may have additional circuits for generating electricity and cold. In addition, the fixed irradiation potential of the territories makes it possible to carry out an effective passive transmission to maintain the thermophilic mode of anaerobic fermentation of organic waste. In this case, environmentally friendly utilization of carbon-containing substrates is accompanied by an increase in the rate of formation of biogas, and therefore hydrogen, without the use of traditional heat supply to reactors.     

向太阳索取--中国太阳光-热与光-电应用现状与展望

我国有丰富的太阳能资源,已有25年光-热研究历史。10年来,太阳热水系统的生产发展迅速。2002年各种太阳热水系统销售约1000万m^2,主要是获得生活热水,一些其他的应用正在研究与开发。光-电研究与开发已有30多年了,应用在卫星、灯塔和通信等领域。2002年一个巨大的国家项目“送电到乡”的实施,完成了17MWp,这加速了我国的光-电产业。     

Optimization of a solar cooling system with interior energy storage

This paper focuses on the optimization of the performance of a solar absorption cooling system composed by four units with interior energy storage. A full dynamic simulation model that includes the solar collector field, the absorption heat pump system and the building load calculation has been developed. It has been applied to optimize the coupling of a system based on this new technology of solar powered absorption heat pump, to a bioclimatic building recently constructed in the Plataforma Solar de Almeria (PSA) in Spain. The absorption heat pump system considered is composed by four heat pumps that store energy in the form of crystallized salts so that no external storage capacity is required. Each heat pump is composed of two separate barrels that can charge (store energy from the solar field) and discharge (deliver heat or cold to the building) independently. Different configurations of the four units have been analysed taking into account the storage possibilities of the system and its capacity to respond to the building loads. It has been shown how strong the influence of the control strategies in the overall performance is, and the importance of using hourly simulations models when looking for highly efficient buildings.     

Optimization of a hybrid solar forced-convection water heating system

In this paper, a techno-economic model has been developed for a hybrid solar forced-convection water heating system. Two options of auxiliary energy use, viz. (A) an instant electric heater and (B) use of diesel as the auxiliary energy fuel, have been considered. Numerical calculations have been made for the climate of Delhi, India, corresponding to the two representative demand patterns, viz. (i) hot-water demand of big residential buildings and (ii) industrial hot-water demand. Taking into account the life, capital cost and the maintenance cost of the solar and auxiliary systems, the cost of useful energy has been calculated for different values of collector area and tank capacity. This exercise, thereby, yields the optimum values of collector area and tank capacity corresponding to the minimum cost of useful energy. The effect of government subsidy on the optimized values of collector area, tank capacity and cost of useful energy has also been investigated.     

Employment impacts of solar energy in Turkey

Solar energy is considered a key source for the future, not only for Turkey, also for all of the world. Therefore the development and usage of solar energy technologies are increasingly becoming vital for sustainable economic development. The main objective of this study is investigating the employment effects of solar energy industry in Turkey. Some independent reports and studies, which analyze the economic and employment impacts of solar energy industry in the world have been reviewed. A wide range of methods have been used in those studies in order to calculate and to predict the employment effects. Using the capacity targets of the photovoltaic (PV) and concentrated solar power (CSP) plants in the solar Roadmap of Turkey, the prediction of the direct and indirect employment impacts to Turkey's economy is possible. As a result, solar energy in Turkey would be the primary source of energy demand and would have a big employment effects on the economics. That can only be achieved with the support of governmental feed-in tariff policies of solar energy and by increasing research-development funds.