Three-Dimensional Reconstruction And Solar Energy Potential Estimation Of Buildings

City,as a huge artificial ecosystem,provides a major venue for human living and production activities.In a long time,Social,economic,and environmental factors can maintain a certain dynamic balance.However,with that the urbanization process is accelerating,the city ’s harmonious and sustainable development is being challenged by the inefficient urban management,serious environmental pollution and available energy shortage.Especially for large cities,more resources and energies are needed to prove the normal life and productive activities because of the great population,in which the city’s electricity consumption accounts for a larger proportion of total energy consumption.Therefore,the traditional fossil energy should be replaced gradually by the renewable energy to solve the problem of urban energy supply,and promote the urban low-carbon and green development.When the urban space structure changes from unorderly spreading like standing pancake to three-dimensional expansion,the research about the low-carbon,green and sustainable development of compact city should be studied from three-dimensional perspective to facilitate more harmony between the natural environment system and the socio-economic system.At present,with the gradual development of multi-platform three-dimensional collection technology,the three-dimensional information describing urban structure is accumulating,providing strong data security to study urban three-dimensional research.Airborne Light Detection and Ranging(LiDAR),as a new active remotely sensed measurement technology,has been widely used to collect urban three-dimensional space information due to the advantages of high automation and detection precision.Therefore,in the context of the construction of low-carbon cities,green cities and eco-cities,the ability of the airborne LiDAR should be explored in urban renewable energy research.Building is a main landscape in urban environment,whose large regular envelopes could receive a huge amount of solar radiation.Using building three-dimensional geometric feature information to calculate the solar potential of building envelopes will be more conducive to keep balance between building their own energy consumption and energy supply.The objective of this paper are summarized as two aspects,first macroscopically grasping the city-level solar energy utilization potential of global building roofs and facades,and then microscopically analyzing the solar irradiance change caused by building renewal construction.The starting point of the research is that detecting three-dimensional change information and reconstructing building models from airborne LiDAR,and main intermediate process is that obtaining the solar potential of building envelopes and calculating the corresponding energy conservation and emission reduction information.Therefore,a relatively complete calculation scheme about building roof and facade solar utilization potential is proposed,whose framework is"urban three-dimensional change detection-building roof three-dimensional reconstruction-building solar irradiance calculation".For measuring the city-level building roof and facade solar irradiance,the precise three-dimensional building models should be first reconstructed from the airborne LiDAR,and based on the analysis of the geometrical structure of buildings,the solar irradiance model is used to estimate the solar energy utilization potential.For the analysis of solar energy change,the newly constructed buildings are first detected from the airborne LiDAR,the corresponding three-dimensional building models are reconstructed and the solar energy utilization change information is finely calculated.Furthermore,the impact of tree shading on the solar radiation of building facades will be analyzed to further understand the tree shading effect.The specific contents are as follows:(1)Three-dimensional change detection of buildings and trees based on octrees and classification algorithm.There are some difficulties in the studies about using airborne LiDAR to detect changes to buildings in the urban environment,because of complex urban scene,discrete point clouds and large space range.In addition,some existed approaches using LiDAR DSM to detect change information are disabled to apply to buildings and trees at the same time.Therefore,a method based on octrees to detect changes to buildings and trees is proposed,which calculates the difference of 3D coordinate information between LiDAR point clouds from two dates.The steps of the proposed method mainly includes:LiDAR data registration,non-ground point extraction,octree construction,changed area detection and etc.Those areas of buildings and trees in the urban environment that have changed can be determined and classified effectively and efficiently by the proposed method.The quality of the LiDAR DSM affecting the precision of the traditional DSM-based approaches are avoided effectively.The experimental results demonstrate that satisfactory performance can be obtained using the proposed method,and the total quality of buildings and trees are 94.8%and 83.8%,respectively,proving that the proposed method can be effectively applied to detect changes in the urban environment for buildings and trees.(2)Three-dimensional reconstruction of building roofs based on a layer connection and smoothness strategy.For the studies of using airborne LiDAR data to reconstruct building roofs,the topological connection relationships between different roof patches are different to determine,and the massive number of irregularly distributed points brings new challenges for the reconstruction work.Therefore,this paper develops a new method by using a layer connection and smoothness strategy to reconstruct building roof models.The proposed method include some main steps as follows:building roof point extraction,rooftop patch segmentation,rooftop patch smoothness,roof layer connection,building roof reconstruction and etc.The reconstructed building roof models have a high completeness and precision,and the difficulties of determining connection relationships between different roof layers and optimizing roof ridge lines can be limited to some extent.The experimental results show that the completeness and correctness of the reconstructed rooftop patches are about 90%and 95%,respectively.For the deviation accuracy,the average deviation distance and standard deviation in the best case are 0.05 m and 0.18 m,respectively;and those in the worst case are 0.12 m and 0.25 m.(3)Building roof and facade solar irradiation calculation based on three-dimensional building models.Using airborne LiDAR point clouds to estimate building solar radiation mainly focus on building roofs.A new method based on three-dimensional building models to calculate roof and facade solar irradiation,which combine the analysis of the building shade and sky diffuse,is proposed.The proposed method mainly includes steps as follows:building model discretization,separation between roof points and facade points,building shade calculation,sky view factor analysis,solar irradiation model construction and etc.The shade analysis for building roofs and facades on the horizontal direction could be carried out together.And the solar diffuse irradiation model is optimized by considering the effect of neighboring building radiation.Compared with the current mainstream commercial building irradiation calculation software,the experimental results show that the proposed method has the same consistency with the commercial software.When the roof area account for only 30%of the total building area,the annual solar radiation of building roofs can reach to 60%of the total building solar radiation,indicating that the roof is still the main area for building receiving solar flux.The Nanjing Olympic New Town(32°1′11″ N,118°44′27″ E)is selected as the study area to calculate the solar energy utilization potential of building envelopes,and to analyze the solar irradiation change caused by newly built construction.The cover area of Nanjing Olympic New Town is about 30 km~2.There are 5,216 buildings in the study area,whose roof and facade areas are 5.52 km~2 and 12.41 km~2,respectively.According to the analysis results of solar energy utilization potential of the global building envelopes,some conclusions are listed as follows:(a)The annual roof solar radiation is 10,197.18 GWh,and the photovoltaic(PV)power is about 1,529.58 GWh when the solar radiation of all building envelopes is completely converted.The standard coal could be saved with the amount of 617.95 kt,corresponding to reduce carbon dioxide emissions by 1,333.79 kt;For the building facades,the annual solar radiation is 7,152.80 GWh and the corresponding PV power is 1,072.92 GWh.When the facade solar radiation is all converted to produce electricity,the standard coal and carbon dioxide emissions could be reduced by 433.46 kt and 935.59 kt,respectively.(b)According to the calculated solar energy potential,the use of roof and facade solar radiation will effectively promote the city’s low-carbon development.Especially for the use of high-rise building facade solar radiation,it will be more to promote the balance between the energy consumption and energy supply of building itself.(c)The building roofs have the best effect of energy conservation and emission reduction in the summer due to the different solar incident angle.However,the energy-saving and emission reduction of building roofs in the different seasons are basically similar.(d)There is a clear correlation between the solar energy utilization potential and the aspect-slope of the building roofs.When the aspect is in the range from 100 to 250 and the slope is in the range from 0 to 60,the energy-saving and emission reduction is the best.(e)When the buildings face the southeast,south and southwest,they have a better solar energy utilization potential compared to the buildings with the other orientations.The solar radiation change caused by the newly built construction and the tree shading effect on the building facade solar radiation are further analyzed.There are 212 newly built-up buildings in the study area,and its roof area and facade area are 0.16 km~2 and 0.43 km~2.Some conclusions are as follows:(a)The annual roof solar radiation and PV power of new buildings increase 282.89 GWh and 42.43 GWh,respectively.In the case of solar energy being fully utilized,the standard coal and carbon dioxide could be reduced by 17.14 kt and 37.00 kt,respectively.(b)The annual facade solar radiation and PV power of new buildins increase 195.12 GWh and 29.27 GWh,respectively.And the standard coal and carbon dioxide could be cut down by 11.83 kt and 25.53 kt,respectively.(c)The annual solar radiation of building facades decrease 45.34 GWh because of tree shading effect.(d)Tree shading effect on the building facade solar radiation is the most evident in February,with the annual decrease of 9.83 kWh/m2.In this paper,through the organic combination of urban three-dimensional change detection,building roof three-dimensional reconstruction and building solar radiation calculation,the solar energy utilization potential of roofs and facades is completely measured and analyzed.The proposed three-dimensional change detection approach based on octrees improve the detection efficiency of the point-based method,realizing the multi-objective change detection analysis.In terms of three-dimensional reconstruction of building roofs,the strategy of layer connection and rooftop patch smoothing achieves the quick connection among different roof layers to ensure the correctness of the three-dimensional reconstruction.In the joint calculation method of bulding roof and facade solar irradiance,the shading effect of building roofs and facades is analyzed and calculated at the same time,and the diffuse radiation of adjacent buildings is considered.However,due to the lack of large area of mobile or terrestrial LiDAR data,this paper could not reconstruct and obtain the precise geometric structure of building facades.So in the process of calculating building facade irradiance,the window cannot be excluded.Therefore,in the future work,the multi-source and multi-platform data should be integrated to extract the installation area of photovoltaic power generation equipment on the building envelopes to optimize the solar energy utilization potential.