Determining The Optimum Position For Multifunctional Integrated Photovoltaic Window

Determining the optimum position for Multifunctional Integrated Photovoltaic Window

Marin Radut

University Politehnica Bucharest

Faculty of Electronics, Communication and Information Technology

Bucharest, Romania

[anonimizat]

Oproescu Mihai

Department of Electronics, Communications and Computers

University of Pitesti

Pitesti, Romania

[anonimizat]

Abstract – The purpose of this paper is to determine the optimal installation for a photovoltaic window (PVW) that uses PV cells on each element of the window blind. For this an extensive experimental study was carried regarding different orientation of the windows: vertically, horizontally, tilted at different angles. Based on this the optimal orientation of the window for each cardinal point was established.

Keywords-energy harvesting, solar shading, photovoltaic windows, solar traker, MPP.

Introduction

Building-integrated photovoltaics (BIPV) are defined as an application which uses the solar energy. They can be introduced from the beginning in the projects of new buildings or perform additional functions such as the protective coating, shading, overheating protection and to the radiation of direct sunlight setting the characteristics of the architectural. Also can be incorporated in existing buildings. There are currently a multitude of applications based on the technologies of photovoltaic in buildings. They are not limited to the transformation the roof, the facade for the production of energy, but also bring other benefits: weather protection, thermal insulation, noise protection or solar and smart use of natural light. Used as construction materials, photovoltaic systems can save money by replacing the materials of traditional building.

The photovoltaic materials used have the essential role to replace conventional building materials in parts of the envelope, such as the roof, skylights, or facades. [1]. There are different types of PV windows on the market, but each has some disadvantages related to free view and indoor comfort.

The Multifunctional Integrated PV Window (MIPVW) proposed here is to harvest the maximum energy available based on advanced Maximum Power Point Tracking (MPPT) technique. Thus, every PV window will operate efficiently using an appropriate energy harvesting technique based on a

MPPT control technique proposed by CO and P1. Since the operating point of the PV window mainly depends on the load power dynamic, irradiance and temperature [7], it is obviously that a correct adjustment of position will improve the PV window efficiency.

The paper is organized as follows: in section 2 the motion of the Sun is presented in section 3 the new method is implemented and the FFNN is trained; in section 4 the results obtained from the two models are presented and analyzed and in the last part the conclusions are drawn.

Apparent motion of the sun Trajectory

The Earth evolves around the Sun in an elliptical orbit. The time taken for the Earth to complete this orbit defines a year. The relative position of the Sun and Earth is conveniently represented by means of the celestial sphere around the Earth which is very important for PV panel orientation. The Earth motion round the Sun is pictured by the apparent motion of the Sun in the elliptic which is tilted at 23.45˚ with respect to the celestial equator [2]. The angle between the line joining the centers of the Sun and the Earth and its projection on the equatorial plane is called the solar declination angle (δ). This angle is zero at the venal (20/21 march) and autumnal (22/23 September) positions.

The Earth rotates at the rate of one revolution per day around the polar axis. The daily rotation of the Earth is depicted by the rotation of the celestial sphere about the polar axis, and the instantaneous position of the Sun is described by the hour angle φ, the angle between the meridian passing through the Sun and the meridian of the site. The hour angle is zero at solar noon and increases toward the east. For observers on the earth’s surface at a location with geographical latitude φ, a convenient coordinate system is defined by a vertical line at the site which intersects the celestial sphere in two points, the zenith the angle α with the polar axis – Fig. 1. The great circle perpendicular to the vertical axis is the horizon [2].

The latitude (α) of a point or location is the angle made by the radial line joining the location to the center of the Earth with the projection of the line on the equatorial plane. Any location on the surface of the Earth then can be defined by the intersection of a longitude angle and a latitude angle.

The solar altitude angle (α) is defined as the vertical angle between the projection of sunlight on the horizontal plane and direction of sunlight passing through the point, as shown in Fig. 1. As an alternative, the sun’s altitude may be described in terms of the solar zenith angle () which is a vertical angle between the sunlight and a line perpendicular to the horizontal plane through the point ( ). The solar azimuth angle () is the horizontal angle measured from south (in the northern hemisphere) to the horizontal projection of the sunlight [5].

Radiation on an inclined and tracking surfaces

The solar radiation data is usually given in the form of global radiation on a horizontal surface and PV panels are usually positioned at an angle to the horizontal plane. Therefore, the energy input to the PV system must be calculated accordingly. The calculation proceeds in three steps. In the first step, the data for the site is used to determine the diffuse beam and its components of the global irradiation on the horizontal plane. This is carried out by using the extraterrestrial daily irradiation, as a reference and calculating the ratio ,

Figure. 1. Schematic representation of the solar angles [3].

G is the daily global irradiation on a horizontal plane and KT describes the average attenuation of solar radiation by the atmosphere. In the second step, the diffuse irradiation is obtained using the empirical rule: the diffuse fraction of the global radiation is a universal function of the clearness index (D is the monthly mean daily diffuse irradiation on a horizontal plane in W/m2).

Since , this procedure determines both the diffuse and beam irradiation on the horizontal plane (B is daily beam irradiation on a horizontal plane). In the third step, the appropriate angular dependence of each component is used to determine the diffuse and beam irradiation on the inclined surface. [5].

Figure. 2. Angle of incidence u of the solar radiation [7].

In the case of fixed PV’s, the projection of PV’s area on the plane, which is perpendicular to the radiation direction, is given by function cosine of the angle of incidence (Fig. 2).

The presence of a solar tracker is not essential for the operation of a solar panel, but without it, performance is reduced.

Sun Trkers vs MIPW

Sun-tracking methods

Although solar trackers can boost energy gain of PV arrays, in their installation some problems such as cost, reliability, energy consumption, maintenance and performance must be considered.

Most tracking systems have the following characteristics:

• One or two moving motors.

• Autonomous or auxiliary energy supply.

• Light following or moving according to the calendar.

• Continuous or step-wise movement.

• Tracking all year or all year except winter.

• Orientation adjustment with/without the tilt angle adjustment.

Several methods of sun monitoring have been surveyed and evaluated to keep the solar panels, solar concentrators, telescopes or other solar systems perpendicular to the sun beam. An ideal tracker would allow the PV cell to accurately point towards the sun, compensating for both changes in the altitude angle of the sun (throughout the day), latitudinal offset of the sun (during seasonal changes) and changes in azimuth angle. Sun-tracking systems are usually classified into two categories: passive (mechanical) and active (electrical) trackers.

For tracking the sun, there are two main types of trackers: single-axis trackers (by one axis), and dual-axis trackers (by two axes). The single-axis tracker (fig. 1, a) pivot on it axis to track the sun, facing east in the morning and west in the afternoon. The tilt angle of this axis equals the latitude angle because this axis has to be always parallel with the polar axis. In consequence for this type of single axis tracker is necessary a seasonal tilt angle adjustment. The two-axis trackers (fig. 1, b) follow the sun in both azimuth and elevation, keeping the sun's rays normal to the panel surface. Considering their ability to combine two rotational motions described around perpendicular axis they are able to follow very precisely the sun path along the period of one year, and for this reason the dual-axis trackers are more efficient than the single one.

Figure 3: Basic types of tracking systems [3]

Experimental setup

The experimental study was conducted at University of Pitesti, Romania in the period 27.04.2016 – 27.05.2016. The site is located at 44.854261 latitude and 24.862677 longitude and the MIPW was mounted outside so it could be rotated to face all the cardinal points.

In order to record all the needed data we used a solar meter KIMO SL 200 for the level of irradiance, a LM 135Z temperature sensor and a NI-USB 6008 and PicoScope 2204 digital oscilloscope as data loggers.

In the first part of the study the MIPW was placed vertically oriented south and the PV cells were angled at 0°. The MIPW was connected to a LED module composed of 16 parallel units of 24 V and 0.010 A each. Every day from 14:00 to 17:00 the output voltage, the current, the temperature and irradiance were measured and recorded. During this period every hour the PV cells, of the MIPW, were tilted with 45°. The next day the MIPW was placed horizontally and the study was repeated.

The same measurements were repeated for all the remaining cardinal points.

Results and discussions

Due to the fact that the outdoor conditions differ we only kept the data that were very close in order to draw the appropriate conclusions.

For each data set kept we determined the output power of the MIPW and represented it as a function of output voltage.

Considering the south orientation – Fig. 4, we can conclude that the orientation of the panel vertically or horizontally it produces very slim differences in the output power for the angles of 0 and 45 degrees. For the 90 degrees orientation, instead, the horizontally mount generated with almost 1000% more power.

When the MIPW was oriented west – Fig. 5, the same slim difference was observed only for the 0 degrees case. For angles of 45 and 90 degrees the horizontally mount generated with 30% respectively 900% more power.

After the north experiment was started it was observed that regardless the orientation vertically, horizontally, with the PV cells tilted or not the measured output power was very low, about 0.02 W, in all the cases. The same phenomena was observed also for the east orientation too, so this case were not carried further.

Figure 5: West orientation

To integrate the measured data in the context of the entire panel efficiency we developed a model for our panel which is presented in [2] and overlapped the output power of the panel to the output power of the model. Due to the low fluctuation of the irradiation in the model we used the average value of G = 1161 W/m2 as input alongside the cell temperature T = 20 °C. As can be seen the output power of the panel is very similar to one produced by the model.

Conclussion

In this paper an experimentally study for determining the optimal orientation of a MIPW was carried. Several strategies were investigated including vertically, horizontally or tilted orientation. Based on this for a 600 x 600 mm MIPW located at 44.854261 latitude and 24.862677 longitude during the month April and May the optimal orientation is horizontally with the PV cells tilted at 45 degrees.

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