Progress of semitransparent emerging photovoltaics for building integrated applications

With the rapid development of emerging photovoltaics technology in recent years,the application of building-integrated photovoltaics(BIPVs)has attracted the research interest of photovoltaic communities.To meet the practical application requirements of BIPVs,in addition to the evaluation indicator of power conversion efficiency(PCE),other key performance indicators such as heat-insulating ability,average visible light transmittance(AVT),color properties,and integrability are equally important.The traditional Si-based photovoltaic technology is typically limited by its opaque properties for application scenarios where transparency is required.The emerging PV technologies,such as organic and perovskite photovoltaics are promising candidates for BIPV applications,owing to their advantages such as high PCE,high AVT,and tunable properties.At present,the PCE of semitransparent perovskite solar cells(ST-PSCs)has attained 14%with AVT of 22–25%;for semitransparent organic solar cells(ST-OSCs),the PCE reached 13%with AVT of almost 40%.In this review article,we summarize recent advances in material selection,optical engineering,and device architecture design for high-performance semitransparent emerging PV devices,and discuss the application of optical modeling,as well as the challenges of commercializing these semitransparent solar cells for building-integrated applications.

A New Dynamic and Vertical Photovoltaic Integrated Building Envelope for High-Rise Glaze-Facade Buildings

Substantially glazed facades are extensively used in contemporary high-rise buildings to achieve attractive architectural aesthetics.Inherent conflicts exist among architectural aesthetics,building energy consumption,and solar energy harvesting for glazed facades.In this study,we addressed these conflicts by introducing a new dynamic and vertical photovoltaic integrated building envelope(dvPVBE)that offers extraordinary flexibility with weather-responsive slat angles and blind positions,superior architectural aesthetics,and notable energy-saving potential.Three hierarchical control strategies were proposed for different scenarios of the dvPVBE:power generation priority(PGP),natural daylight priority(NDP),and energy-saving priority(ESP).Moreover,the PGP and ESP strategies were further analyzed in the simulation of a dvPVBE.An office room integrated with a dvPVBE was modeled using EnergyPlus.The influence of the dvPVBE in improving the building energy efficiency and corresponding optimal slat angles was investigated under the PGP and ESP control strategies.The results indicate that the application of dvPVBEs in Beijing can provide up to 131%of the annual energy demand of office rooms and significantly increase the annual net energy output by at least 226%compared with static photovoltaic(PV)blinds.The concept of this novel dvPVBE offers a viable approach by which the thermal load,daylight penetration,and energy generation can be effectively regulated.

Economic Feasibility Assessment of Motorized PV Louver System Considering the Near Shading Parameter, Array Incidence Losses and Other Environmental Factors

Seoul has good weather settings for incorporating renewable energies, hence, given its small land area living mode was mostly set in an apartment condition it is an ideal place for building applied photovoltaic (BAPV) for solar energy harvesting. On the other hand, the BAPV energy self-consumption hasn’t been thoroughly examined considering the overall energy consumption requirement. Therefore, presented in this communication are the viability of PVL to produce electricity from solar energy and insights on modulating and improving energy harvesting efficiency. To accomplish this objective, three major factors were considered: 1) the photovoltaic (PV) positioning;2) the solar tracking scenario;and 3) the mechanistic system energy consumption. The overall louver energy generation was thoroughly scrutinized from the net energy conception of the BAPV up to the mechanistic module energy expenditure. This work intends to provide insights into the economic feasibility of BAPV assessing its technological profitability in the specified location and building size.

BUILDING INTEGRATED AGRICULTURE Utilising Rooftops for Sustainable Food Crop Cultivation in Singapore

Burgeoning population and rapid urbanisation have contributed to two challenges facing cities today:food security and an increasing carbon footprint due to food imports.This paper examines the viability of rooftop farming in urban centres in Asia.A context-specific exploration—sited in Singapore—looks at the challenges of building integrated agriculture.Findings suggest that Singapore’s public housing estates are suitable for rooftop farming.Implemented nationwide,such a scheme could result in a 700%increase in domestic vegetable production,satisfying domestic demand by 35.5%.Reducing food imports would also decrease Singapore’s carbon footprint by 9,052 tonnes of emissions annually.

LINKING CONSTRUCTIVE AND ENERGY INNOVATIONS FOR A NET ZERO-ENERGY BUILDING

This article explains the design,construction and energy strategies of LINQ,a net-zero energy building that was successfully entered into the Solar Decathlon Middle East 2018 held in Dubai.Students of engineering,building physics,architecture and urban planning designed,built and operated LINQ.It is mainly powered by solar energy and made of bio-materials.Some of LINQ’s innovations are the ventilated façade with customizable bio-based tiles,the indirect evaporative water cooling system,and the light building integrated photovoltaic-thermal system.LINQ sent more energy to the grid than it drew throughout the competition.However,energy production could have been improved according to simulations and technical specifications.LINQ is a good example of current and future building expectations-combining multiple criteria,strategies,and solutions-to contribute to environmental,social and economic sustainability.

FROM LOW-ENERGY TO NET ZERO-ENERGY BUILDINGS: STATUS AND PERSPECTIVES

“Net Zero-Energy Building”has become a popular catchphrase to describe the synergy between energy-efficient building and renewable energy utilisation to achieve a balanced energy budget over an annual cycle.Taking into account the energy exchange with a grid overcomes the limitations of energy-autonomous buildings with the need for seasonal energy storage on-site.Although the expression,“Net Zero-Energy Building,”appears in many energy policy documents,a harmonised definition or a standardised balancing method is still lacking.This paper reports on the background and the various effects influencing the energy balance approach.After discussing the national energy code framework in Germany,a harmonised terminology and balancing procedure is proposed.The procedure takes not only the energy balance but also energy efficiency and load matching into account.

Design and performance testing of a novel building integrated photovoltaic thermal roofing panel

A novel building integrated photovoltaic thermal(BIPVT)roofing panel has been designed considering both solar energy harvesting efficiency and thermal performance.The thermal system reduces the operating temperature of the cells by means of a hydronic loop integrated into the backside of the panel,thus resulting in maintaining the efficiency of the solar panels at their feasible peak while also harvesting the generated heat for use in the building.The performance of the proposed system has been evaluated using physical experiments by conducting case studies to investigate the energy harvesting efficiency,thermal performance of the panel,and temperature differences of inlet/outlet working liquid with various liquid flow rates.The physical experiments have been simulated by coupling the finite element method(FEM)and finite volume method(FVM)for heat and mass transfer in the operation.Results show that the thermal system successfully reduced the surface temperature of the solar module from 88℃to as low as 55℃.Accordingly,the output power that has been decreased from 14.89 W to 10.69 W can be restored by 30.2%to achieve 13.92 W.On the other hand,the outlet water from this hydronic system reaches 45.4℃which can be used to partially heat domestic water use.Overall,this system provides a versatile framework for the design and optimization of the BIPVT systems.

Stabilizing semi-transparent perovskite solar cells with a polymer composite hole transport layer

Semi-transparent perovskite solar cells(ST-PSCs)have broad applications in building integrated photovoltaics.However,the stability of ST-PSCs needs to be improved,especially in n-i-p ST-PSCs since the doped 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene(Spiro-OMeTAD)is unstable at elevated temperatures and high humidity.In this work,aπ-conjugated polymer poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophene-2-yl)-benzo[1,2-b:4,5-b']dithiophene))-alt-(5,5-(1',3'-di-2-thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'-c']dithiophene-4,8-dione)](PBDB-T)is selected to form a polymer composite hole transport layer(HTL)with Spiro-OMeTAD.The sulfur atom of the thiophene unit and the carbonyl group of the polymer interact with the undercoordinated Pb2+at the perovskite surface,which stabilizes the perovskite/HTL interface and passivates the interfacial defects.The incorporation of the polymer also increases the glass transition temperature and the moisture resistance of Spiro-OMeTAD.As a result,we obtain ST-PSCs with a champion efficiency of 13.71%and an average visible light transmittance of 36.04%.Therefore,a high light utilization efficiency of 4.94%can be obtained.Moreover,the encapsulated device can maintain 84%of the initial efficiency after 751 h under continuous one-sun illumination(at 30%relative humidity)at the open circuit and the unencapsulated device can maintain 80%of the initial efficiency after maximum power tracking for more than 1250 h under continuous one-sun illumination.

A maximum power point tracking strategy applied to building integrated photovoltaics

To solve the problem of permanent-shadow shading of photovoltaic buildings,a maximum power point tracking(MPPT)strategy to determine the search range by pre-delimiting area is proposed to improve MPPT efficiency.The single correspondence between the solar-cell current-voltage(I-V)curve and the illumination conditions was proved by using the single-diode model of photovoltaic cells,thus proving that a change in the illumination conditions corresponds to a unique maximum power point(MPP)search area.According to the approximate relationship between MPP voltage,current and open-circuit voltage and short-circuit current of a photovoltaic module,the voltage region where the MPP is located is determined and the global maximum power point is determined using the power operating triangle strategy in this region.Simulation carried out in MATLAB proves the correctness and feasibility of the theoretical research.Simulation results show that the MPPT strategy proposed in this paper can improve the average efficiency by 1.125%when applied in series as building integrated photovoltaics.

Potential and performance estimation of free-standing and building integrated photovoltaic technologies for different climatic zones of India

The role of Photovoltaic technologies integrated or attached to the building envelope is crucial in managing the building energy demand.In this paper,the performance of PV technologies with the mounting methods of Build-ing integrated and Free-standing(Building attached)is discussed for six different climate zone of the country.A PVGIS program proposed with three PV cell technologies(Crystalline Silicon,Copper indium diselenide,Cad-mium Telluride)is used to evaluate monthly energy generation potential and losses of the 2 kW p grid-connected PV system at the latitude and 90°.A 2 kW p PV system is chosen for Economic Weaker Section(EWS)housing schemes depending upon the roof area.From the evaluation,the performance parameter has been estimated.A new parameter Energy Deviation(ED),is proposed to choose the best PV technology in terms of performance.The results of ED agree with the parameters Performance Ratio(PR)and Capacity Factor(CF)defined under the IEC Standard 61724.The potential generation of PV technologies at 90°varies from 41%(Warm and Humid)to 64%(Cold and Sunny)when compared with the latitude.In case of Cold and Sunny and Cold and Cloudy at 90°,the generation performance of Copper indium diselenide is found better in Building integrated and Free-standing mounting methods,respectively.For the remaining zones,Cadmium Telluride technology shows better results.The Percentage loss in the system is found to be minimum in the case of Cold and Sunny,varies between 17%and 25%,and maximum is found for Warm and Humid and varies between 23.2%and 33.4%for the proposed PV technologies.The grid feed-in energy from these EWS houses for all the technologies and climatic zones is found above 45%.It is seen that the combined energy generation from the envelopes(Roof,walls,and facades)makes the houses energy plus in nature.The study has important implications for the government to promote the building integrated Photovoltaic policies in the country.

EFFICIENT HEATING AND COOLING SYSTEMS FOR LOW-ENERGY HOUSES

Buildings account for a large amount of land use, energy and water consumption, and atmospheric pollution. For example, in the United States, they use 40% of the total national energy consumption (56% by residential dwellings), produce 38% of the total carbon dioxide emissions, and account for 12.2% of the total quantity of water consumed (2006). In this context, buildings with considerably reduced energy consumption are a key strategy to achieving energy savings and climate protection targets in both the residential and commercial/institutional sectors [1]. This article reviews a number of heating and cooling systems-existing and/or under development- available for residential buildings and briefly outlines some research projects and initiatives, as well as technical achievements in Canada and other developed countries over the last few years.

INTEGRATED DESIGN CONSIDERATIONS FOR SOLAR COMMUNITIES

This paper presents design considerations for an integrated design of solar commu-nities highlighting the interactive nature of various design parameters to improve the energy performance of these neighborhoods.These considerations are illus-trated through practical design examples of different neighborhood scenarios and individual buildings,based on extensive studies and analysis of energy performance of a wide spectrum of buildings and neighborhoods.The examples fall under two general categories-design at the neighborhood level,and design at the individ-ual building level.Neighborhood design is illustrated by examples of homogeneous residential neighborhoods consisting of 2-storied housing units and of a mixed-rise neighborhood.Design of individual buildings focuses primarily on design of the envelope-consisting of roof and façades-for maximizing energy generation poten-tial,as a function of height and relative position to adjacent buildings.In addition to examples of application of the design considerations,the paper outlines the process of design of solar communities and the role of simulations in the design process.

Intelligent windows for electricity generation: A technologies review

Buildings are responsible for over 40% of total primary energy consumption in the US and EU and therefore improving building energy efficiency has significant potential for obtaining net-zero energy buildings reducing energy consumption. The concurrent demands of environmental comfort and the need to improve energy efficiency for both new and existing buildings have motivated research into finding solutions for the regulation of incoming solar radiation, as well as ensuring occupant thermal and visual comfort whilst generating energy onsite. Windows as building components offer the opportunity of addressing these issues in buildings. Building integration of photovoltaics permits building components such as semi-transparent façade, skylights and shading devices to be replaced with PV. Much progress has been made in photovoltaic material science, where smart window development has evolved in areas such as semi-transparent PV, electrochromic and thermochromic materials, luminescent solar concentrator and the integration of each of the latter technologies to buildings, specifically windows. This paper presents a review on intelligent window technologies that integrate renewable energy technologies with energy-saving strategies contributing potential solutions towards sustainable zero-energy buildings. This review is a comprehensive evaluation of intelligent windows focusing on state-of-the-art development in windows that can generate electricity and their electrical, thermal and optical characteristics. This review provides a summary of current work in intelligent window design for energy generation and gives recommendations for further research opportunities.

Architectural quality of the productive facades integrating photovoltaic and vertical farming systems: Survey among experts in Singapore

Buildings could play a critical role in energy and food production while making highdensity cities more resilient.Productive facades(PFs),as flexible and multi-functional systems integrating photovoltaic(PV)and vertical farming(VF)systems,could contribute to transforming buildings and communities from consumers to producers.This study analyses the architectural quality of the developed PF concept drawing on the findings of a web-survey conducted among experts e building professionals in Singapore.The developed design variants are compared with regards to key design aspects such as facade aesthetics,view from the inside,materialisation,ease of operation,functionality and overall architectural quality.The study also compares and discusses the results of the web-survey with the results of a previously conducted door-to-door survey among the potential users-residents of the Housing&Development Board(HDB)blocks.The findings confirm an overall acceptance of the PF concept and reveal a need for synergetic collaboration between architects/designers and other building professionals.Based on the defined PF design framework and the results of the two surveys,a series of recommendations and improved PF prototypes are proposed for further assessment and implementation in order to foster their scalability from buildings into communities and cities.

Smart luminescent solar concentrator as a BICPV window

Building integrated concentrating photovoltaic(BICPV)windows have attracted numerous studies in recent years.However,there is a tradeoff between the light transmittance and power generation efficiency in the design of BICPV window.In this paper,a smart luminescent solar concentrator(LSC)is introduced as the BICPV window.The proposed smart LSC system features on the combination of fluorescent dyes with thermochromic materials to enhance photoelectric conversion efficiency as well as form a dynamic response mechanism to ambient solar radiation and environmental temperature.In this study,a BICPV smart window system consists of the waveguide doped with organic dye Lumogen F Red-305(BASF)and the thermochromic hydrogel membrane has been developed.The research on analytic design parameters is executed through optical simulation by ray tracing technology along with outdoor comparative experiments.From simulations for a smart LSC of 100 mm×100 mm×3 mm with a bottom-mounted solar cell of 100 mm×10 mm,the optical effective concentration is found to be with the range of 1.23 to 1.31 when a highest gain of 1.26 in power over the bare solar cell is obtained from experiments.