Calculating solar irradiance without shading geometry: a point cloud-based method

Abstract

Accurate simulation of solar irradiance on facades and roofs in a built environment is a critical step for determining photovoltaic yield and solar gains of buildings, which in an urban setting are often affected by the surroundings. In this paper, a new modelling method is introduced that uses Digital Surface Model (DSM) point clouds as shading geometry, combined with a matrix-based approach for simulating solar irradiance. The proposed method uses the DSM as shading geometry directly, eliminating the need for 3D surface geometry generation and conducting ray-tracing, thus simplifying the simulation workflow. The real-world applicability is demonstrated with two case studies, where it is shown that if the site is shaded, ignoring the shading from the surroundings would cause overprediction in the simulated annual PV yield, underprediction of the annual heating and overprediction of the annual cooling demand.

KEYWORDS:

• Solar irradiance
• photovoltaics
• solar heat gains
• shading

Acknowledgements

We would like to acknowledge Kristóf Horváth from the Budapest University of Technology for enlightening discussions about sphere parametrization.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1 A sensor point is defined by its location [x, y, z] and its orientation vector [xi, yi, zi]. The field of view of a sensor point is 2π steradians.

2 Discretized skies are explained in Section 2.1.2.

3 Note: In Tregenza and Waters’ article they defined Equation (1) with photometric units: illuminance [cd*sr/m²] for $\mathrm{\Delta }{I}_{\alpha }$ and luminance [cd/m²] for $L_{\alpha }$. In this paper, radiometric units are used: irradiance [W/m²] for $\mathrm{\Delta }{I}_{\alpha }$ and radiance [W*sr^-1*m^-2] for $L_{\alpha }$.

Additional information

Funding

This work has been supported by the project ‘PV OpMaat’, financed by the cross-border collaboration programme Interreg V Flanders-Netherlands with the financial support of the European Regional Development Fund (CCI 2014TC16RFCB046).