Abstract:
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The use of PV system as an alternative for electricity generation purposes has increased
during the past years, as well as its inclusion into the architectural design based on BIPV
concepts. Therefore, forecasting power produced by those kind of PV plants is fundamental
for the reliability, safety and stability of the grid, and for the optimization of the design and
of the control strategy of such systems. For these reasons, in this project it has been
developed a model which represents the dynamic performance of an innovative external
shading device, that allows PV integration.
First, a suitable model to determinate the incident irradiance over a tilted surface for any
day of the year was set, starting from the general solar radiation theory, considering the
second order effects provoked by the angular losses and the spectral shift. Consequently,
from such irradiance, it has been designed a suitable PV model characterized by a fiveparameter
model, which is able to forecast the power generated with a good accuracy level.
Such PV model was extended in order to consider shading effects, i.e. non-uniform
irradiance over different cells, since the aim was to develop a model able to represent the
behavior of a PV array integrated on an external shading device. Furthermore, a suitable
optical model was developed to predict the performance of the shading device, with a curved
geometry and the possibility to use any combination of surface material. Subsequently, as the
idea of the project is to forecast output power for any geometry, it has been designed a case
study following a special geometry, which is based on an innovative external shading device
designed by the architect Pietro Franchi and the engineer Stefano Rui.
An experimental apparatus was set up in order to study the impact of shades on the cells
under different configurations of the shading device and validate the PV model. Therefore, a
prototype of a generic lamella system, which might emulate some geometric configuration
and features of the innovative external shading device, was mounted on the roof of the
Energy Department of the Politecnico di Milano. The prototype corresponds of two lamellas,
in two separate levels, over each lamella is placed a flexible monocrystalline PV panel. Thus,
by evaluating the PV production under different conditions, such as the position and
inclination of the lamellas, the PV model was validated against measurements.
Finally, a control strategy has been proposed to regulate the external shading device to
maintain a sufficient daylight level in the room containing overheating risk and exploiting PV generation. Such analysis allowed to quantify the performances of the innovative BIPV
system in terms of hours of daylight exploitation, PV production and effective shading
capability to ensure solar control. |