Research

19 pages, 9126 KiB

Open AccessArticle

Evaluation of Direct Horizontal Irradiance in China Using a Physically-Based Model and Machine Learning Methods

by Feiyan Chen, Zhigao Zhou, Aiwen Lin, Jiqiang Niu, Wenmin Qin and Zhong Yang

Energies 2019, 12(1), 150; https://doi.org/10.3390/en12010150 - 02 Jan 2019

Cited by 11 | Viewed by 3123

Accurate estimation of direct horizontal irradiance (DHI) is a prerequisite for the design and location of concentrated solar power thermal systems. Previous studies have shown that DHI observation stations are too sparsely distributed to meet requirements, as a result of the high construction [...] Read more.

Accurate estimation of direct horizontal irradiance (DHI) is a prerequisite for the design and location of concentrated solar power thermal systems. Previous studies have shown that DHI observation stations are too sparsely distributed to meet requirements, as a result of the high construction and maintenance costs of observation platforms. Satellite retrieval and reanalysis have been widely used for estimating DHI, but their accuracy needs to be further improved. In addition, numerous modelling techniques have been used for this purpose worldwide. In this study, we apply five machine learning methods: back propagation neural networks (BP), general regression neural networks (GRNN), genetic algorithm (Genetic), M5 model tree (M5Tree), multivariate adaptive regression splines (MARS); and a physically based model, Yang’s hybrid model (YHM). Daily meteorological variables, including air temperature (T), relative humidity (RH), surface pressure (SP), and sunshine duration (SD) were obtained from 839 China Meteorological Administration (CMA) stations in different climatic zones across China and were used as data inputs for the six models. DHI observations at 16 CMA radiation stations were used to validate their accuracy. The results indicate that the capability of M5Tree was superior to BP, GRNN, Genetic, MARS and YHM, with the lowest values of daily root mean square (RMSE) of 1.989 MJ m⁻²day⁻¹, and the highest correlation coefficient (R = 0.956), respectively. Then, monthly and annual mean DHI during 1960–2016 were calculated to reveal the spatiotemporal variation of DHI across China, using daily meteorological data based on the M5tree model. The results indicated a significantly decreasing trend with a rate of −0.019 MJ m⁻²during 1960–2016, and the monthly and annual DHI values of the Tibetan Plateau are the highest, while whereas the lowest values occur in the southeastern part of the Yunnan−Guizhou Plateau, the Sichuan Basin and most of the southern Yangtze River Basin. The possible causes for spatiotemporal variation of DHI across China were investigated by discussing cloud and aerosol loading. Full article

(This article belongs to the Special Issue Solar Thermal Energy Utilization Technologies in Buildings)

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18 pages, 854 KiB

Open AccessArticle

Low-Carbon Energy Planning: A Hybrid MCDM Method Combining DANP and VIKOR Approach

by Ruijun Liu, Hao Sun, Lu Zhang, Qianwei Zhuang, Lele Zhang, Xueyi Zhang and Ye Chen

Energies 2018, 11(12), 3401; https://doi.org/10.3390/en11123401 - 04 Dec 2018

Cited by 16 | Viewed by 2905

Abstract

With the development of urbanization, people’s living standards have improved. Simultaneously, the growing aggravation of resource shortages and environmental pollution have also gradually attracted widespread attention. Low-carbon energy planning can effectively reduce dependence on fossil resources and carbon emissions to the atmosphere, as [...] Read more.

With the development of urbanization, people’s living standards have improved. Simultaneously, the growing aggravation of resource shortages and environmental pollution have also gradually attracted widespread attention. Low-carbon energy planning can effectively reduce dependence on fossil resources and carbon emissions to the atmosphere, as well as improve the utilization of resources. Therefore, the formulation and evaluation of low-carbon energy planning have become the focus of attention for related colleges and institutions. This paper puts forward a hybrid multi-criteria decision making(MCDM) method combining decision making trial and evaluation laboratory(DEMATEL), analytical network process(ANP), and VIKOR to obtain the weight of each criterion and evaluate each alternative about low-carbon energy planning for building. A hierarchy structure of criteria involving cost, safety, reliability, and environment protection is built. Afterwards, a case of four alternatives is applied for testifying this methodology. Lastly, a comparison with prior methodologies serves as proof of the raised ranking. The presentation has proved that this methodology offers a more precise and effective foundation for decisions about low-carbon energy planning evaluation. Full article

(This article belongs to the Special Issue Solar Thermal Energy Utilization Technologies in Buildings)

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9 pages, 2176 KiB

Open AccessArticle

Preparation and Thermoelectric Properties of Graphite/poly(3,4-ethyenedioxythiophene) Nanocomposites

by Yong Du, Haixia Li, Xuechen Jia, Yunchen Dou, Jiayue Xu and Per Eklund

Energies 2018, 11(10), 2849; https://doi.org/10.3390/en11102849 - 22 Oct 2018

Cited by 16 | Viewed by 3794

Abstract

Graphite/poly(3,4-ethyenedioxythiophene) (PEDOT) nanocomposites were prepared by an in-situ oxidative polymerization process. The electrical conductivity and Seebeck coefficient of the graphite/PEDOT nanocomposites with different content of graphite were measured in the temperature range from 300 K to 380 K. The results show that as [...] Read more.

Graphite/poly(3,4-ethyenedioxythiophene) (PEDOT) nanocomposites were prepared by an in-situ oxidative polymerization process. The electrical conductivity and Seebeck coefficient of the graphite/PEDOT nanocomposites with different content of graphite were measured in the temperature range from 300 K to 380 K. The results show that as the content of graphite increased from 0 to 37.2 wt %, the electrical conductivity of the nanocomposites increased sharply from 3.6 S/cm to 80.1 S/cm, while the Seebeck coefficient kept almost the same value (in the range between 12.0 μV/K to 15.1 μV/K) at 300 K, which lead to an increased power factor. The Seebeck coefficient of the nanocomposites increased from 300 K to 380 K, while the electrical conductivity did not substantially depend on the measurement temperature. As a result, a power factor of 3.2 μWm⁻¹ K⁻² at 380 K was obtained for the nanocomposites with 37.2 wt % graphite. Full article

(This article belongs to the Special Issue Solar Thermal Energy Utilization Technologies in Buildings)

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17 pages, 2410 KiB

Open AccessArticle

Thermal Performance Analysis of an Absorption Cooling System Based on Parabolic Trough Solar Collectors

by Jiangjiang Wang, Rujing Yan, Zhuang Wang, Xutao Zhang and Guohua Shi

Energies 2018, 11(10), 2679; https://doi.org/10.3390/en11102679 - 09 Oct 2018

Cited by 19 | Viewed by 3760

Abstract

Solar radiation intensity significantly influences the cooling loads of building, and the two are correlated and accorded to a certain extent. This study proposes a double effect LiBr–H₂O absorption cooling system based on the parabolic trough collector (PTC) of solar heat [...] Read more.

Solar radiation intensity significantly influences the cooling loads of building, and the two are correlated and accorded to a certain extent. This study proposes a double effect LiBr–H₂O absorption cooling system based on the parabolic trough collector (PTC) of solar heat energy. Thermodynamic models including PTC and absorption chiller are constructed, and their accuracy is verified by comparing the simulation results and the experimental data. Subsequently, the impact of variable design parameters on the thermodynamic performance is analyzed and discussed. The analysis of a solar cooling system in a hotel case study is related to its operation in a typical day, the average coefficient of performance of the absorption chiller is approximately 1.195, and the whole solar cooling system achieves 61.98% solar energy utilization efficiency. Furthermore, the performance comparison of a solar cooling system in different types of building indicates that higher matching and a higher correlation coefficient between the transient solar direct normal irradiance and cooling load is helpful in decreasing the heat loss and improving systemic performance. The solar cooling system in the office building exhibits a correlation coefficient of approximately 0.81 and achieves 69.47% systemic thermal efficiency. Full article

(This article belongs to the Special Issue Solar Thermal Energy Utilization Technologies in Buildings)

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18 pages, 5510 KiB

Open AccessArticle

The Thermal Behavior of a Dual-Function Solar Collector Integrated with Building: An Experimental and Numerical Study on the Air Heating Mode

by Jinwei Ma, Qiang Zhao, Yuehong Su, Jie Ji, Wei He, Zhongting Hu, Tingyong Fang and Haitao Wang

Energies 2018, 11(9), 2402; https://doi.org/10.3390/en11092402 - 11 Sep 2018

Cited by 8 | Viewed by 3432

Abstract

This paper presented a novel solar collector that can work in air or water heating mode depending on the seasonal requirement. The dual-function solar collector (DFSC) integrated with a building as well as a reference building without the DFSC were built to test [...] Read more.

This paper presented a novel solar collector that can work in air or water heating mode depending on the seasonal requirement. The dual-function solar collector (DFSC) integrated with a building as well as a reference building without the DFSC were built to test thermal behavior in passive air heating mode during winter. The buildings were equipped with an apparatus to control the room temperature. During the testing procedure, experimental study on the DFSC system was carried out under two conditions, where the indoor temperature was controlled and non-controlled. The results showed that the average temperature of the test room was about 3.43 °C higher than that of the reference room under the non-controlled condition. When the room temperature was controlled at 18 °C, the power consumptions of the test room and reference room were 4.322 kWh and 7.796 kWh, respectively. Consequently, the corresponding daily power consumption saved could reach up to around 3.5 kWh. Moreover, a dynamic numerical model on the DFSC along with the building was developed taking the fin effect of the Cu-tubes into account. The numerical results are found to be well consistent with the measured data. A parametric study on with/without Cu-tubes and depth of the air channel was carried out. It is found that the existing Cu-tubes functioning as water heating can enhance the air heating efficiency when the depth of air channel is of a suitable size. Full article

(This article belongs to the Special Issue Solar Thermal Energy Utilization Technologies in Buildings)

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14 pages, 2657 KiB

Open AccessFeature PaperArticle

The Influence of Local Environmental, Economic and Social Variables on the Spatial Distribution of Photovoltaic Applications across China’s Urban Areas

by Alin Lin, Ming Lu and Pingjun Sun

Energies 2018, 11(8), 1986; https://doi.org/10.3390/en11081986 - 31 Jul 2018

Cited by 16 | Viewed by 2806

Abstract

The capacity of new installed photovoltaic (PV) in China in 2017 was increased to 53.06 GW, reaching a total of 402.5 GW around the world. Photovoltaic applications have a significant role in the reduction of greenhouse gas emissions and alleviating electricity shortages in [...] Read more.

The capacity of new installed photovoltaic (PV) in China in 2017 was increased to 53.06 GW, reaching a total of 402.5 GW around the world. Photovoltaic applications have a significant role in the reduction of greenhouse gas emissions and alleviating electricity shortages in the sustainable development process of cities. Research on the factors that influenced the spatial distribution of photovoltaic applications mostly focus on a certain project or a region. However, it is a complicated process for decision-making of photovoltaic installations in urban areas. This study uses zip code level data from 83 cities to investigate the influence of local environmental, economic and social variables on the spatial distribution of photovoltaic applications across China’s urban areas. By analyzing the current situation, the locations of urban photovoltaic applications are collected and presented. Statistical analysis software is used to evaluate the influence of selected variables. In this paper, correlation analysis, principle component analysis (PCA) and cluster analysis are generated to predict urban photovoltaic installations. The results of this research show that Gross Domestic Product (GDP), electricity consumption, policy incentives, the number of photovoltaic companies, population, age, education and rate of urbanization were important factors that influenced the adoption of urban photovoltaic systems. The results also indicate that Southeast China and Hangzhou Province are currently the most promising areas as they have a higher rate of solar photovoltaic installation. These conclusions have significancefor energy policy and planning strategies by predicting the future development of urban photovoltaic applications. Full article

(This article belongs to the Special Issue Solar Thermal Energy Utilization Technologies in Buildings)

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19 pages, 4770 KiB

Open AccessArticle

A Comprehensive Approach for Modelling Horizontal Diffuse Radiation, Direct Normal Irradiance and Total Tilted Solar Radiation Based on Global Radiation under Danish Climate Conditions

by Zhiyong Tian, Bengt Perers, Simon Furbo, Jianhua Fan, Jie Deng and Janne Dragsted

Energies 2018, 11(5), 1315; https://doi.org/10.3390/en11051315 - 22 May 2018

Cited by 12 | Viewed by 5322

Abstract

A novel combined solar heating plant with flat plate collectors (FPC) and parabolic trough collectors (PTC) was constructed and put into operation in Taars, 30 km north of Aalborg, Denmark in August 2015. To assess the thermal performance of the solar heating plant, [...] Read more.

A novel combined solar heating plant with flat plate collectors (FPC) and parabolic trough collectors (PTC) was constructed and put into operation in Taars, 30 km north of Aalborg, Denmark in August 2015. To assess the thermal performance of the solar heating plant, global radiation, direct normal irradiance (DNI) and total radiation on the tilted collector plane of the flat plate collector field were measured. To determine the accuracy of the measurements, the calculated solar radiations, including horizontal diffuse radiation, DNI and total tilted solar radiation with seven empirical models, were compared each month based on an hourly time step. In addition, the split of measured global radiation into diffuse and beam radiation based on a model developed by DTU (Technical University of Denmark) and the Reduced Reindl correlation model was investigated. A new method of combining empirical models, only based on measured global radiation, was proposed for estimating hourly total radiation on tilted surfaces. The results showed that the DTU model could be used to calculate diffuse radiation on the horizontal surface, and that the anisotropic models (Perez I and Perez II) were the most accurate for calculation of total radiation on tilted collector surfaces based only on global radiation under Danish climate conditions. The proposed method was used to determine reliable horizontal diffuse radiation, DNI and total tilted radiation with only the measurement of global radiation. Only a small difference compared to measured data, was found. The proposed method was cost-effective and needed fewer measurements to obtain reliable DNI and total radiation on the tilted plane. This method may be extended to other Nordic areas that have similar weather. Full article

(This article belongs to the Special Issue Solar Thermal Energy Utilization Technologies in Buildings)

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16 pages, 45274 KiB

Open AccessArticle

Simulation and Experimental Study on the Optical Performance of a Fixed-Focus Fresnel Lens Solar Concentrator Using Polar-Axis Tracking

by Hai Wang, Jin Huang, Mengjie Song, Yanxin Hu, Yunfeng Wang and Zijian Lu

Energies 2018, 11(4), 887; https://doi.org/10.3390/en11040887 - 10 Apr 2018

Cited by 23 | Viewed by 7182

Abstract

Most sun-tracking systems of solar concentrators are expensive, sensitive to operational costs, and complicated in optical design in which the receiver must be free to rotate about the axis. To overcome the aforementioned problems, this study presents a fixed-focus Fresnel lens solar concentrator [...] Read more.

Most sun-tracking systems of solar concentrators are expensive, sensitive to operational costs, and complicated in optical design in which the receiver must be free to rotate about the axis. To overcome the aforementioned problems, this study presents a fixed-focus Fresnel lens solar concentrator (FFFSC) using polar-axis tracking which allows the Fresnel lens to concentrate sunlight to a fixed small heat-receiving area and the receiver remained fixed in location and rotation. Experimental research has been conducted to obtain the optical characteristics of the FFFSC for different solar times, tracking errors, and periodical adjustment errors. It has been found that maximum values of the relative optical efficiency loss (η_re-opt_,loss) and minimum value of the optical efficiency (η_opt) of the FFFSC for different solar times are 1.87% and 71.61%, respectively. The mean value and maximum value of the local concentration ratio of the solar flux on the receiver are more than 86.64 and 1319.43, respectively. When the tracking error and periodical adjustment error are within 1°, the η_opt of the FFFSC can reach 70.38% and 68.94%, respectively. The optical characteristics of FFFSC is also verified numerically. Especially, according to the total year simulation of the FFFSC’s optical characteristics, maximum value of η_re-opt_,loss is 0.116%, which means the proposed the FFFSC can achieve fixed-focus. Full article

(This article belongs to the Special Issue Solar Thermal Energy Utilization Technologies in Buildings)

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