Sunlight Director

Sunlight Director is a device which allows you to direct reflected Sun to a predefined location. As the Sun moves, Sunlight Director adjusts the angle of the mirror to make sure that the reflected rays continue to hit the same spot.

Objective

Sunlight Director was created to better utilize the sun's energy. By directing the sun's light to where it is needed, it is possible to:

1. Generate productive warmth such as heating buildings during the Winter, or complement other energy sources to produce hot water
2. Generate electricity, by vaporizing water into steam, which then turns the turbines
3. Sending sunlight into special light-conducting ducts can complement indoor lighting

Theory

Often, the sun's energy is not where our needs require it. Hence, we have developed heating and air-conditioning technologies, to compensate for too little, or too much Sun. With one or more Sunlight Directors, users can send the sun's energy to where it is needed.

Design

The solution uses a pan/tilt platform, set of sensors, and a microcontroller to change the direction of the mirror. The mirror's position makes sure that the sun's reflected light always hits the predefined location.

The mirror is attached to the arms at a point which is equal in distance from the pivot point. If the Sun-tracking arm always points to the Sun, while the Target arm always points to the target, then the mirror will form an Isosceles Triangle. This way, incoming rays are parallel to the Sun-tracking arm, hit the mirror, and are reflected exactly along the Target arm.

A. The light path setup:

- Sun-tracking arm (moving)

- Target direction arm (fixed)

- Mirror (attached to both arms equidistant from the pivot point)

The Sun-tracking arm is fixed to the pan/tilt base. As the base pans and tilts, so will the Sun-tracking arm. Target arm points to the object we want to illuminate. This arm is fixed in place, so that it always points to our target object.

The mirror is attached to both arms. It has to be able to slide onto one of the arms, to maintain the equal distance from the pivot (see photo showing a slit in the mirror platform). The goal is to make sure that the mirror is equidistant from the pivot, regardless what the angle between the arms is - this way, the light comes in along the sun-tracking arm, and is reflected along the target arm. The mirror also has to be perpendicular to the plane of the two arms.

B. Electronic Setup

This specific implementation uses the following components:

1) Intel Edison microcontroller

2) Grove light sensors x 4

3) Grove sensor shield

4) Electrical Relays x 4

5) Pan/Tilt Camera base (can be obtained online http://www.mcmelectronics.com/product/82-12440?sc...

For this project Intel Edison provides:

• WiFi connectivity
• Analog inputs and digital GPIO
• Sufficient computing power to develop complex applications

The four sensors are arranged in 2x2 matrix, with a barrier separating them. The four quadrants allow us to know how to better position the sun-tracking arm. For left/right decision, we sum up light values from sensors 1 and 3 and compare the result with the sum of 2 and 4. For up/down decision, we sum up values from sensors 1 and 2 and compare result with 3 and 4. If the percentage difference is greater than the threshold value (5%), we send a move command.

The sensors supply microcontroller with information. Microcontroller decides if the arm needs to be re-positioned. Motion is performed using a security camera pan/tilt base. This particular base uses high voltage inputs, so we need to control AC current using relays. This part of the implementation is specific to the base you are using. In our case, we needed two relays per dimension. For each dimension, first relay controls power, second relay controls direction.

The code

The attached C++ code was developed in Eclipse, with Intel IoT plugin. Using Intel's IoT toolkit it is possible to build and deploy the application to Edison, right from within Eclipse.

The source code has comments describing the purpose of each major section.

This video shows how the sun-tracking arm moves toward the sun. At about 40 seconds, the arm reached the brightest area and started to move back and forth (this vacillation can be avoided by increasing the threshold value).