Research on Key Technologies of Solar Photovoltaic Building Integration

On December 21,2020,The State Council Information Office issued a white paper titled"China's Energy Development in the New Era,"in which the installed capacity of hydropower,wind power,photovoltaic power and biomass power generation in China ranked first in the world[1].Solar photovoltaic power generation is the most important development direction of clean energy in the world.It is an important energy strategy to combine it with the field of construction in China.This paper mainly introduces the characteristics and problems of the key technologies of solar photovoltaic building integration,and explores its future development direction and ways,in order to constantly promote the industrialization of new energy technology in China.

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.

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.

Multi-Time Scale Optimal Scheduling of a Photovoltaic Energy Storage Building System Based on Model Predictive Control

Building emission reduction is an important way to achieve China’s carbon peaking and carbon neutrality goals.Aiming at the problem of low carbon economic operation of a photovoltaic energy storage building system,a multi-time scale optimal scheduling strategy based on model predictive control(MPC)is proposed under the consideration of load optimization.First,load optimization is achieved by controlling the charging time of electric vehicles as well as adjusting the air conditioning operation temperature,and the photovoltaic energy storage building system model is constructed to propose a day-ahead scheduling strategy with the lowest daily operation cost.Second,considering inter-day to intra-day source-load prediction error,an intraday rolling optimal scheduling strategy based on MPC is proposed that dynamically corrects the day-ahead dispatch results to stabilize system power fluctuations and promote photovoltaic consumption.Finally,taking an office building on a summer work day as an example,the effectiveness of the proposed scheduling strategy is verified.The results of the example show that the strategy reduces the total operating cost of the photovoltaic energy storage building system by 17.11%,improves the carbon emission reduction by 7.99%,and the photovoltaic consumption rate reaches 98.57%,improving the system’s low-carbon and economic performance.

URBAN PHOTOVOLTAIC POTENTIAL OF INCLINED ROOFING FOR BUILDINGS IN HERITAGE CENTERS IN EQUATORIAL AREAS

In situ renewable energy production is a favourable alternative for reducing pollu-tion and combating climate change.The research area,Cuenca,Ecuador,is located in the Andes near the equator with optimal conditions for energy self-supply due to its low energy demands and low levels of irradiation variability.In this study,tem-porary fluctuations in consumption based on 2016 electricity consumption data are characterized.Using GIS,available roofing polygons are obtained,and the amount of usable solar radiation is estimated based on these values.With available surface,orientation,and inclination information,electricity generation based on photovoltaic performance is estimated and compared for monocrystalline silica panels and pho-tovoltaic solar roof tiles,which are architectural alternatives.A potential net supply of 148%is found for monocrystalline silica photovoltaic panels in a typical format,whereas that of photovoltaic tiles is only 61%.In addition,production-demand imbalances are predicted in extreme months and average months and on extreme days due to variations in irradiation and demands.

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.

Visualization Analysis of Literature on Building Photovoltaic Technology Based on CiteSpace

With the proposal of the double carbon target,the task of energy saving and emission reduction of buildings has become more arduous.The application of building photovoltaic technology is identified as a significant breakthrough to address this challenge.In this paper,the visual analysis and interpretation of literature on building photovoltaic(PV)technology were conducted by using the Cite Space analysis tool based on a review of Chinese and international literature databases.Meanwhile,global research on BIPV technology was summarized and compared.This paper provides ideas for the future application of building photovoltaic technology by constructing a knowledge map for the application of building photovoltaic technology to help the construction of a low-carbon society.

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.

Self-Power Consumption Research with the Thermal Effects and Optical Properties of the HCRI-BIPV Window System

The building integrated photovoltaics （BIPV） application is one of the main study topics in the sustainable building field. In this paper, the high color rendering index （HCRI）-BIPV window system is developed to be used in the indoor environmental control, whose module material has appeared to be effective in improving the visible transmittance and reducing the absorption. This paper describes the performance of grid-connected HCRI-BIPV window system with 0.75 kWp capacity installed in an office building for a natural ventilation solution. The experimental results indicate that accumulative power generation of the HCRI-BIPV window system is 157.60 WKh during the 7-month experiment period. For consideration of each evaluated factors, the HCRI-BIPV window system not only offers the passive energy situation for its power loading but also improves the indoor thermal environment by natural ventilation.

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.

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.

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.

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.

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.

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.