Research objectives

The principal purpose of this study is to develop and evaluate optimal control methods for PVIS.

Because PVIS is a hybrid PV system and shading device, it combines the benefits of these two systems. Maximizing these benefits is the aim of optimal control. This research investigates methods of achieving the maximum benefits of PVIS.

The objectives of this research and their corresponding research questions are as follows:

As a PV system,

1) does PVIS generate more electricity than wall-mounted BIPVs?

As a shading device,

2) can PVIS provide a comfortable lighting environment for occupants?

As a hybrid of both,

3a) does PVIS offer energy-saving benefits, and if so, what are they?

3b) what control method should PVIS employ to gain maximum benefits?

To answer these questions, optimal control methods to maximize PVIS benefits were devised and evaluated. The specific research objectives were as follows:

1) Develop a prototype motorized PV-integrated exterior louver with adjustable slat angles.

2) Develop ANN-based optimal control methods for a PV-integrated shading system.

3) Develop a wireless system for controlling motorized shading devices that can be operated from either a computer or a wireless node.

4) After building a scale model of a typical office space, experimentally measure the performance of a louver-type PV-integrated shading device using the criteria of

electricity production and visual comfort. The wall PV output is compared to the louver PV output (Question 1). The work plane illuminance and DGI levels are evaluated in terms of the duration of acceptable level (Question 2). Energy benefits comprising electricity production and electric lighting energy savings are also evaluated (Question 3a). Optimal control methods are compared in terms of PV output, visual comfort, and their combined benefits (Question 3b).

3.4 Scope

In determining the optimal operation of the PVIS device, this research considers various energy and visual comfort factors:

1) PV electricity output 2) Work plane illuminance 3) Daylight glare

These three factors are dependent on other factors such as the louver slat tilt angle; therefore, they are the dependent variables in this study. Visual comfort is evaluated according to two

criteria: work plane illuminance and daylight glare. Daylight glare is estimated using the daylight glare index (DGI).

3.4.1 Factors affecting PV output, illuminance, and glare

Louver PV electricity output

The electricity output of the louver PV modules on a louver slat depends on solar availability, louver slat tilt angle, and the physical configuration of the louver. The factors affecting the solar radiation on a louver slat include sun position, sky condition, and reflectance of surrounding objects. The factors involving PV modules include PV efficiency, orientation, and PV coating fraction with regard to slat area. The PV module orientation depends on the slat tilt angle, which is the controlled variable in this study. The sky condition and the sun position are variables, but they are uncontrollable. The other factors are constants.

Visual comfort

Visual comfort can be defined as a state of mind caused by the luminous environment perceived by human eyes. The evaluation of visual comfort is quite subjective; therefore, precise

estimation of an individual’s visual comfort is almost impossible. However, several quantifiable and controllable factors can be used as general guidelines for the general population. These factors include the work plane illuminance and the daylight glare index (DGI), which are used to estimate visual comfort in this research.

The work plane illuminance depends on many factors. When a shading device is present, it has a major effect on the daylight admission into the interior space. A louver, which comprises

multiple horizontal slats, controls the daylight admission by the slat tilt angle. Therefore, the work plane illuminance depends on solar availability and the slat tilt angle of the louver. The solar availability depends on the sky condition and the sun position. Other factors affecting the work plane illuminance include the reflectance of interior surfaces, the room geometry, the transmittance of windows, the number and size of windows, and electric lighting. These factors remain constant in this research.

The daylight glare index also depends on solar availability and louver slat tilt angle. The DGI equation considers four factors: window luminance, background luminance, window size subtended by an observer, and the viewing direction of the observer. The window luminance and the background luminance depend on the solar availability and slat tilt angle. The window size and the viewing direction are constants.

To summarize, the dependent variables are the PV electricity output, the work plane illuminance, and DGI. The independent variables affecting these dependent variables are the slat tilt angle, solar availability as estimated by exterior vertical illuminance, and sun position. The slat tilt angle is the only controlled variable. The other two variables are uncontrollable and thus measured or calculated. The other factors affecting the dependent variables are constants (See Table 3.1).

This study excludes the thermal factors associated with the use of a shading device (e.g., solar heat gain and heating/cooling load control). The PV module temperature, which significantly affects PV efficiency, is also excluded.

Independent variables

Occupant position and viewing direction

…

Table 3.1 Variables and constants in this research