Life-cycle energy analysis of building integrated photovoltaic systems (BiPVs) with heat recovery unit

Building integrated photovoltaic (BiPV) systems generate electricity, but also heat, which is typically wasted and also reduces the efficiency of generation. A heat recovery unit can be combined with a BiPV system to take advantage of this waste heat, thus providing cogeneration. Two different photovoltaic (PV) cell types were combined with a heat recovery unit and analysed in terms of their life-cycle energy consumption to determine the energy payback period. A net energy analysis of these PV systems has previously been performed, but recent improvements in the data used for this study allow for a more comprehensive assessment of the combined energy used throughout the entire life-cycle of these systems to be performed. Energy payback periods between 4 and 16.5 years were found, depending on the BiPV system. The energy embodied in PV systems is significant, emphasised here due to the innovative use of national average input–output (I–O) data to fill gaps in traditional life-cycle inventories, i.e. hybrid analysis. These findings provide an insight into the net energy savings that are possible with a well-designed and managed BiPV system.     

Trade-off between environmental and economic implications of PV systems integrated into the UAE residential sector

PV technology offers clean resource and environmental advantages over fossil-fuel-based electricity generation; however, it remains more expensive than conventional technology in most grid-connected applications. The trade-off between environmental and economic parameters represents a challenge for governments. The objectives of this study are: firstly, to review studies in relation to the use of PV systems in the Gulf region and secondly, to assess the trade-off between environmental and economic parameters that influence the value of building integrated photovoltaic (BiPV) technology applied into the UAE building sector. This work examines residential buildings and concludes that the economic viability of BiPV systems is subject to capital cost, system efficiency and electricity tariff. To be a cost-effective option in the UAE, subsidies for PV investments and reasonable electricity tariff must be implemented. It is suggested that BiPV systems offer cost reductions in both energy and economic terms over centralised PV plants, especially if the costs of saved operating energy and avoided building materials are taken into account. Each square meter of BiPV is capable of making a significant reduction in CO₂ emissions generated by conventional power plants. This will limit the impact of global warming on the UAE and others.     

On the value of decentralised PV systems for the GCC residential sector

Based on the rich natural potential of the Gulf region, solar energy is expected to play a greater role in the future of the Gulf Corporation Council (GCC) countries. This study examines whether the integration of the photovoltaic (PV) into individual residential buildings in the GCC countries is worth the investment. A prototype residential building is developed and a building integrated photovoltaic (BiPV) system is then designed. The system performance is simulated, and through economic analysis, it is shown that the current BiPV technology is not a cost-effective option for the GCC countries based on the present electricity tariff, PV system cost and system efficiency. The only way such a system would be viable with current technology is if the electricity tariff were to increase substantially. However, if the tariff remains constant for the foreseeable future, BiPV solar energy technology will only be feasible if the total system cost drops drastically. This study shows that BiPV systems offer cost reductions in both energy and economic terms over centralised PV plants, especially if the costs of avoided building construction materials are taken into account. To bring about the benefits of BiPV technology for the GCC residential sector, therefore, the first logical and most practical step is the implementation of a continuous promotion strategy that consists of both subsidies for investments and reasonable tariffs.     

Modelling of a photovoltaic heat recovery system and its role in a design decision support tool for building professionals

A numerical model has been created to simulate the performance of a residential-scale building integrated photovoltaic (BiPV) cogeneration system. The investigation examines the combined heat and power system in the context of heat transfer. The PV cogeneration system will be based on existing BiPV roofing technology with the addition of a modular heat recovery unit that can be used in new or renovation construction schemes. The convection of the air behind the panels will serve to cool the PV panels while providing a heat source for the residence. This model was created in the Engineering Equation Solver software package (EES), from a series of highly coupled non-linear partial differential equations that are solved iteratively. The model's ability to utilize climatic data to simulate annual performance of the system will be presented along with a comparison to experimental data. A graphical front-end has been added to the model in order to facilitate its use as a predictive tool for building professionals. It will thus become a decision support tool used in identifying areas for implementation of a PV cogen system.     

Energy and economic evaluation of building-integrated photovoltaics

This paper applies energy analysis and economic analysis in order to assess the application of solar photovoltaics (PVs) in buildings. Comparison is made both to electricity supply from centralised PV plants and to conventional electricity sources. The comparison with conventional sources reveals that there is currently a significant trade-off between the environmental and economic implications of PVs: there are substantial resource benefits to be gained from using PVs to supply electricity, but the economic cost of doing so is significantly higher than conventional sources. This trade-off is reduced when the benefits of building integrated PVs (BiPVs) are considered. By comparison with centralised PV plants, BiPV systems offer the “double dividend” of reduced economic costs and improved environmental performance. This double dividend is increased if the economic and energy costs of avoided cladding materials are taken into account.     

Thermographic analysis of a building integrated photovoltaic system

A residential-scale building integrated photovoltaic (BiPV) cogeneration system has been thermographically investigated. The results are useful in calibrating the numerical models created to predict the system's operational temperatures. The combined heat and power system is based on existing BiPV roofing technology with the addition of a modular heat recovery unit. The convection of the air behind the panels will serve both to cool the photovoltaic panels and provide a heat source for the residence. The analysis allows for the interpretation of the surface emissivities and operating temperatures, as well as qualitative graphic analysis of temperature gradients.     

Thermodynamic evaluation of hydrogen and electricity cogeneration coupled with very high temperature gas-cooled reactors

Hydrogen production using thermal energy, derived from nuclear reactor, can achieve large-scale hydrogen production and solve various energy problems. The concept of hydrogen and electricity cogeneration can realize the cascade and efficient utilization of high-temperature heat derive for very high temperature gas-cooled reactors (VHTRs). High-quality heat is used for the high-temperature processes of hydrogen production, and low-quality heat is used for the low-temperature processes of hydrogen production and power generation. In this study, two hydrogen and electricity cogeneration schemes (S1 and S2), based on the iodine-sulfur process, were proposed for a VHTR with the reactor outlet temperature of 950 °C. The thermodynamic analysis model was established for the hydrogen and electricity cogeneration. The energy and exergy analysis were conducted on two cogeneration systems. The energy analysis can reflect the overall performance of the systems, and the exergy analysis can reveal the weak parts of the systems. The analysis results show that the overall hydrogen and electricity efficiency of S1 is higher than that of S2, which are 43.6% and 39.2% at the hydrogen production rate of 100 mol/s, respectively. The steam generators is the components with the highest exergy loss coefficient, which are the key components for improving the system performance. This study presents a theoretical foundation for the subsequent optimization of hydrogen and electricity cogeneration coupled with VHTRs.     

Advancement in solar photovoltaic/thermal (PV/T) hybrid collector technology

This article presents an overview on the research and development and application aspects for the hybrid photovoltaic/thermal (PV/T) collector systems. A major research and development work on the photovoltaic/thermal (PVT) hybrid technology has been done since last 30 years. Different types of solar thermal collector and new materials for PV cells have been developed for efficient solar energy utilization. The solar energy conversion into electricity and heat with a single device (called hybrid photovoltaic thermal (PV/T) collector) is a good advancement for future energy demand. This review presents the trend of research and development of technological advancement in photovoltaic thermal (PV/T) solar collectors and its useful applications like as solar heating, water desalination, solar greenhouse, solar still, photovoltaic-thermal solar heat pump/air-conditioning system, building integrated photovoltaic/thermal (BIPVT) and solar power co-generation.     

CO_2 Mitigation in Coal Gasification Cogeneration Systems with Integration of the Shift Reaction, CO_2 Absorption and Methanol Production

Cogeneration of electricity and liquid fuel can achieve higher efficiencies than electricity generation alone in Integrated Gasification Combined Cycle (IGCC), and cogeneration systems are also expected to mitigate CO2 emissions. A proposed methanol-electricity cogeneration system was analyzed in this paper using exergy method to evaluate the specified system. A simple cogeneration scheme and a complicated scheme including the shift reaction and CO2 removal were compared. The results show that the complicated scheme consumes more energy, but has a higher methanol synthesis ratio with partial capture of CO2.In those methanol and electricity cogeneration systems, the CO2 mitigation is not merely an additional process that consumes energy and reduces the overall efficiency, but is integrated into the methanol production.     

Performance evaluation of an electricity base load engine cogeneration system

Decentralized electricity production by cogeneration can result in primary energy economy, as these systems operate with a high‐energy utilization factor (EUF), producing electricity and recovering energy rejected by the prime mover to meet site thermal demands. Because energy demands in buildings vary with such factors as the hour of the day, level of activity and climatic conditions, cogeneration case studies should consider different system configurations, energy demand profiles and climatic profiles. This paper analyzes an engine cogeneration system as an integrated thermal system by means of a computational simulation program. The simulation takes into account characteristics of the system, characteristics of the pieces of equipment, design choices and parameters, the variability of operating conditions, site energy demand profiles and climatic data to evaluate the performance of the cogeneration plant. Performance evaluation is based on: (i) the EUF, (ii) the exergy efficiency and (iii) primary energy savings analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimal planning and economic evaluation of cogeneration system

Cogeneration plants, which simultaneously produce electricity and heat energy, have been introduced increasingly for commercial and domestic applications in Korea because of their energy efficiency. The optimal plant configuration of a specific commercial building can be determined by selecting the sizes and the number of cogeneration systems and the auxiliary equipment based on the annual demands of electricity, heating and cooling. In this study, a mixed-integer, linear programming, utilizing the branch and bound algorithm was used to obtain the optimal solution. Both the optimal configuration system equipment and the optimal operational mode were determined based on the annual cost method for the installation of a cogeneration system to a hospital and a group of apartments in Seoul, Korea. In addition, the economic evaluation for the optimal cogeneration system depending on the fuel tariff system was calculated. A short payback period and higher internal rate of return on the initial investment were found to be essential for the adoption of cogeneration plants to hospitals and apartments.     

CO<Subscript>2</Subscript> mitigation in coal gasification cogeneration systems with integration of the shift reaction,CO<Subscript>2</Subscript> absorption and methanol production

Cogeneration of electricity and liquid fuel can achieve higher efficiencies than electricity generation alone in Integrated Gasification Combined Cycle (IGCC), and cogeneration systems are also expected to mitigate CO₂ emissions. A proposed methanol-electricity cogeneration system was analyzed in this paper using exergy method to evaluate the specified system. A simple cogeneration scheme and a complicated scheme including the shift reaction and CO₂ removal were compared. The results show that the complicated scheme consumes more energy, but has a higher methanol synthesis ratio with partial capture of CO₂. In those methanol and electricity cogeneration systems, the CO₂ mitigation is not merely an additional process that consumes energy and reduces the overall efficiency, but is integrated into the methanol production.     

Photovoltaic collectors efficiency according to their integration in buildings

A model for building integrated photovoltaic systems has been developed and implemented in a dynamic simulation tool. This tool takes into account the thermal interactions between the PV collector and the building. The influence of the type of integration upon the PV collector efficiency has been evaluated and hybrid PV/air collectors have been studied. An overall efficiency is defined, including the production of electricity and heat. A case study has been performed on two different typical buildings. In the case of a multi-crystalline silicon PV collector integrated on the roof of a single family house located in Paris, the efficiency of unventilated PV modules fixed on the roof is 14%. If the PV collector is used to preheat the ventilation air, the efficiency reaches 20%. A proper building integration also improves the environmental balance of PV technologies over their life cycle.     

Modeling the life cycle energy and environmental performance of amorphous silicon BIPV roofing in the US

Building integrated photovoltaics (BIPV) perform traditional architectural functions of walls and roofs while also generating electricity. The displacement of utility generated electricity and conventional building materials can conserve fossil fuels and have environmental benefits. A life cycle inventory model is presented that characterizes the energy and environmental performance of BIPV systems relative to the conventional grid and displaced building materials. The model is applied to an amorphous silicon PV roofing shingle in different regions across the US. The electricity production efficiency (electricity output/total primary energy input excluding insolation) for a reference BIPV system (2kW_p PV shingle system with a 6% conversion efficiency and 20 year life) ranged from 3.6 in Portland OR to 5.9 in Phoenix, AZ indicating a significant return on energy investment. The reference system had the greatest air pollution prevention benefits in cities with conventional electricity generation mixes dominated by coal and natural gas, not necessarily in cities where the insolation and displaced conventional electricity were greatest.     

Process integration of a steam turbine

Cogeneration consists of combined production of electricity and heat using fuel which allows remarkable energy savings in comparison with a system producing electricity and heat separately. The possibilities for integrating a cogeneration system with chemical processes has been studied in this paper. Improvement in the systems where high temperature process streams exist can be achieved by direct integration of steam turbine with them. A hot reactor stream was used instead of fuel to produce electricity and steam for further process heat requirements. A thermodynamics oriented approach to identify a cogeneration plant that completely satisfies process heat and power demand is highlighted. Pinch analysis with extended grand composite curve enables rational choice of utilities. The acrylic acid process was used to illustrate the procedure proposed. Economic attractiveness based on payback time and net present worth indicated that the steam turbine based cogeneration system would yield a return period of less than 3 months, showing that the investment in cogeneration could be of interest for this plant.     

Energy and cost analysis of semi-transparent photovoltaic in office buildings

Solar energy conversion systems and daylighting schemes are important building energy strategies to produce clean energy, reduce the peak electrical and cooling demands and save the building electricity expenditures. A semi-transparent photovoltaic (PV) is a building component generating electricity via PV modules and allowing daylight entering into the interior spaces to facilitate daylighting designs. This paper studies the thermal and visual properties, energy performance and financial issue of such solar facades. Data measurements including solar irradiance, daylight illuminance and output power for a semi-transparent PV panel were undertaken. Using the recorded results, essential parameters pertaining to the power generation, thermal and optical characteristics of the PV system were determined. Case studies based on a generic reference office building were conducted to elaborate the energy and cooling requirements, and the cost implications when the PV facades together with the daylight-linked lighting controls were being used. The findings showed that such an integrated system could produce electricity and cut down electric lighting and cooling energy requirements to benefit the environmental, energy and economic aspects.     

A review on the performance of photovoltaic/thermoelectric hybrid generators

Utilization of a broad range of solar spectrum has the potential for high power output from solar cells. However, solar photovoltaics (PVs) can convert only part of the solar electromagnetic spectrum into electricity efficiently. The remaining of the solar radiation is often dissipated in the form of heat, which causes performance reduction and reduces the life expectancy of the solar PV cell. Thermoelectric generators (TEGs) are devices that operate like a heat engine by converting thermal energy into electricity through thermoelectric effect. Integrating a TEG into a PV converter will enhance its efficiency and reduce the amount of heat dissipated. Different studies have been carried out and are still taking place to increase the total efficiency of a coupled photovoltaic thermoelectric generator (PV-TEG) system. This review discusses the concept of PV converters and thermoelectric devices and presents the various models and numerical and experimental investigations on performance enhancement of integrated PV-TEGs. The influence of key parameters on the performance of PV-TEG were also discussed. The review is expected to serve as a reference to recent work on research and development of integrated PV-TEG systems.     

Multi-Objective Particle Swarm Optimization(MOPSO) for a Distributed Energy System Integrated with Energy Storage

Distributed energy systems are considered as a promising technology for sustainable development and have become a popular research topic in the areas of building energy systems. This work presents a case study of optimizing an integrated distributed energy system consisting of combined heat and power(CHP), photovoltaics(PV), and electric and/or thermal energy storage for a hospital and large hotel buildings located in Texas and California. First, simulation models for all subsystems, which are developed individually, are integrated together according to a control strategy designed to satisfy both the electric and thermal energy requirements of a building. Subsequently, a multi-objective particle swarm optimization(MOPSO) is employed to obtain an optimal design of each subsystem. The objectives of the optimization are to minimize the simple payback period(PBP) and maximize the reduction of carbon dioxide emissions(RCDE). Finally, the energy performance for the selected building types and locations are analyzed after the optimization. Results indicate that the proposed optimization method could be applied to determine an optimal design of distributed energy systems, which reaches a trade-off between the economic and environmental performance for different buildings. With the presented distributed energy system, a peak shaving in electricity of about 300 kW and a reduction in boiler fuel consumption of 610 kW could be attained for the hospital building located in California for a winter day. For the summer and transition seasons, electricity peak shaving of 800 kW and 600 kW could be achieved, respectively.     

Energy and economic assessment of desiccant cooling systems coupled with single glazed air and hybrid PV/thermal solar collectors for applications in hot and humid climate

This paper presents a detailed analysis of the energy and economic performance of desiccant cooling systems (DEC) equipped with both single glazed standard air and hybrid photovoltaic/thermal (PV/t) collectors for applications in hot and humid climates. The use of ‘solar cogeneration’ by means of PV/t hybrid collectors enables the simultaneous production of electricity and heat, which can be directly used by desiccant air handling units, thereby making it possible to achieve very energy savings. The present work shows the results of detailed simulations conducted for a set of desiccant cooling systems operating without any heat storage.System performance was investigated through hourly simulations for different systems and load combinations. Three configurations of DEC systems were considered: standard DEC, DEC with an integrated heat pump and DEC with an enthalpy wheel. Two kinds of building occupations were considered: office and lecture room. Moreover, three configurations of solar-assisted air handling units (AHU) equipped with desiccant wheels were considered and compared with standard AHUs, focusing on achievable primary energy savings.The relationship between the solar collector’s area and the specific primary energy consumption for different system configurations and building occupation patterns is described. For both occupation patterns, sensitivity analysis on system performance was performed for different solar collector areas. Also, this work presents an economic assessment of the systems. The cost of conserved energy and the payback time were calculated, with and without public incentives for solar cooling systems. It is worth noting that the use of photovoltaics, and thus the exploitation of related available incentives in many European countries, could positively influence the spread of solar air cooling technologies (SAC). An outcome of this work is that SAC systems equipped with PV/t collectors are shown to have better performance in terms of primary energy saving than conventional systems fed by vapour compression chillers and coupled with PV cells.All SAC systems present good figures for primary energy consumption. The best performances are seen in systems with integrated heat pumps and small solar collector areas. The economics of these SAC systems at current equipment costs and energy prices are acceptable. They become more interesting in the case of public incentives of up to 30% of the investment cost (Simple Payback Time from 5 to 10 years) and doubled energy prices.