Siwei Lou

Analysis of vertical sky components under various CIE standard general skies

Vertical sky diffuse illuminance data are important for architecture and daylighting designs. In 2003, the International Commission on Illumination (CIE) adopted a range of 15 standard skies representing the actual sky conditions in the world. This paper studies an approach to computing the vertical sky component (VSC) under the 15 CIE Standard Skies. Regression equations for calculating the VSC under various CIE skies based on the scattering angles (χ) were developed to estimate the vertical daylight illuminance on building façades. The performance of the proposed numerical approach and the regression equation are assessed against the results obtained by computer simulations. Our findings show that the VSC data determined by the numerical method and the regression equation are in good agreement with the simulated results. Our research has provided a simple tool for estimating the vertical daylight illuminance under various sky conditions.

Life-cycle analysis of photovoltaic systems in Hong Kong

This paper studied the payback period of grid-connected photovoltaic (PV) panels by the net present value method. The PV performance data were acquired by on-site measurements of two rooftop projects in subtropical Hong Kong. The sensitivity of various variables to the payback period was evaluated by the Extended Fourier Amplitude Sensitivity Test. The monetary payback periods were evaluated at different values of the most relevant variables and compared with the embodied energy and greenhouse gas payback periods. The PV panels of the two projects produced 122–143 kWh/m2 electricity per year in Hong Kong, which saved 139–163 HKD electricity tariff per square meter per year. The sensitivity analysis showed that the monetary payback period was sensitive to the initial cost and tariff increase rate uncertainties. The PV monetary payback period varied from 13.4 to 16.8 years at different tariff increase rates and investment costs, based on the current carbon trading benefit. The monetary payback period was much greater than the embodied energy and greenhouse gas payback periods, which were 10.8–12.7 years and 5.3–6.2 years, respectively. Implications of the payback period differences were discussed.This paper studied the payback period of grid-connected photovoltaic (PV) panels by the net present value method. The PV performance data were acquired by on-site measurements of two rooftop projects in subtropical Hong Kong. The sensitivity of various variables to the payback period was evaluated by the Extended Fourier Amplitude Sensitivity Test. The monetary payback periods were evaluated at different values of the most relevant variables and compared with the embodied energy and greenhouse gas payback periods. The PV panels of the two projects produced 122–143 kWh/m2 electricity per year in Hong Kong, which saved 139–163 HKD electricity tariff per square meter per year. The sensitivity analysis showed that the monetary payback period was sensitive to the initial cost and tariff increase rate uncertainties. The PV monetary payback period varied from 13.4 to 16.8 years at different tariff increase rates and investment costs, based on the current carbon trading benefit. The monetary payback period was mu...

Hong Kong CIE sky classification and prediction by accessible weather data and trees-based methods

Solar irradiance and daylight illuminance are important for solar energy and daylighting designs. Recently, the International Commission of Illuminance (CIE) adopted a range of sky conditions to represent the possible sky distributions which are crucial to the estimation of solar irradiance and daylight illuminance on vertical building facades. The important issue would be whether the sky conditions are correctly identified by the accessible variables. Previously, a number of climatic parameters including sky luminance distributions, vertical solar irradiance and sky illuminance were proposed for the CIE sky classification. However, such data are not always available. This paper proposes an approach based on the readily accessible data that systematically recorded by the local meteorological station for many years. The performance was evaluated using measured vertical solar irradiance and illuminance. The results show that the proposed approach is reliable for sky classification.