Comparison of Modelled and Measured Tilted Solar Irradiance for Photovoltaic Applications

Riyad Mubarak,Martin Hofmann,Gunther Seckmeyer,Stefan Riechelmann

doi:10.3390/en10111688

Riyad Mubarak, Martin Hofmann + Show 2 more

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https://doi.org/10.3390/en10111688

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Abstract

This work assesses the performance of five transposition models that estimate the global and diffuse solar irradiance on tilted planes based on the global horizontal irradiance. The modelled tilted irradiance values are compared to measured one-minute values from pyranometers and silicon sensors tilted at different angles at Hannover (Germany) and NREL (Golden, CO, USA). It can be recognized that the deviations of the model of Liu and Jordan, Klucher and Perez from the measurements increases as the tilt angle increases and as the sensors are oriented away from the south direction, where they receive lower direct radiation than south-oriented surfaces. Accordingly, the vertical E, W and N planes show the highest deviation. Best results are found by the models from Hay and Davies and Reindl, when horizontal pyranometer measurements and a constant albedo value of 0.2 are used. The relative root mean squared difference (rRMSD) of the anisotropic models does not exceed 11% for south orientation and low inclination angles (β = 10–60°), but reaches up to 28.9% at vertical planes. For sunny locations such as Golden, the Perez model provides the best estimates of global tilted irradiance for south-facing surfaces. The relative mean absolute difference (rMAD) of the Perez model at NREL ranges from 4.2% for 40° tilt to 8.7% for 90° tilt angle, when horizontal pyranometer measurements and a measured albedo value are used; the use of measured albedo values instead of a constant value of 0.2 leads to a reduction of the deviation to 3.9% and 6.0%, respectively. The use of higher albedo values leads to a significant increase of rMAD. We also investigated the uncertainty resulting from using horizontal pyranometer measurements, in combination with constant albedo values, to estimate the incident irradiance on tilted photovoltaic (PV) modules. We found that these uncertainties are small or negligible.

Highlights

To estimate the expected energy output of a PV system, yield estimation models are used which need specific input parameters such as global solar irradiance
The relative mean absolute difference of the Perez model at NREL ranges from 4.2% for 40◦ tilt to 8.7% for 90◦ tilt angle, when horizontal pyranometer measurements and a measured albedo value are used; the use of measured albedo values instead of a constant value of 0.2 leads to a reduction of the deviation to
We investigated the uncertainty resulting from using horizontal pyranometer measurements, in combination with constant albedo values, to estimate the incident irradiance on tilted photovoltaic (PV) modules

Summary

Introduction

To estimate the expected energy output of a PV system, yield estimation models are used which need specific input parameters such as global solar irradiance. Since small uncertainties in the model parameters can lead to large deviations from the expected returns on investment, uncertainties resulting from model input should be reduced as much as possible. Estimating solar irradiation incident on tilted surfaces of various orientations is essential to estimate the electric power generated by PV, to design solar energy systems and to evaluate their long-term average performance [1]. The available measurement data are suboptimal, since global horizontal or diffuse horizontal irradiance measurements provided by pyranometers are often. Energies 2017, 10, 1688 the only available measurements at most locations. Even if tilted measurements are performed, the tilt angle chosen for the measurement is not necessarily the optimal tilt angle for the location. The tilted solar irradiance must be determined by converting the solar irradiance on a horizontal surface to that incident on the tilted surface of interest [2]

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