Low cost developments with Raspberry Pi
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Raspberry Pi Solar Tracker prototyping project

Challenge
InSolem is a start-up company that develops innovative solar tracking solutions, for different applications. As young company, InSolem has to carefully watch its expenses, and wanted to develop modular prototypes at a minimal cost, in order to test its developments. Two different regulation models had to be tested:

- A heliostat regulation, for concentrated solar applications. The regulation consists in always reflecting the sunlight into a target. To do so, the normal to the mirror must always be the the bissector of the angle formed by the target and the sun

-A PV tracker regulation that consists in always having the sunray normal to the PV module in order to minimize the losses due to the reflexion
Functioning principle - Heliostat regulation
For the heliostat regulation InSolem developed a program that calculates the theoretical position of the tracker at any time, based on the day, time and location, and that compares it to its actual position that is calculated thanks to an accelerometer. The hardware set up by Iziproto includes:

One Raspberry Pi for each tracker



One Adafruit GPS sensor

for the three trackers. The GPS communicates the day and time to the Raspberry Pi, so that InSolem can calculate the theoretical position of the tracker

One accelerometer on each tracker

. For test purposes, InSolem installed three accelerometers on each in order to test and compare them: the Adafruit I2C ADXL 345, MMA8452 and LM3030 accelerometers. The accelerometers communicate the positioning of the mirrors on three axis to the Raspberry Pi, so that InSolem can determine their actual positioning.

Two motors have been installed on the tracker that are controlled by the Raspberry Pi through a serial HAT RB-RS485

:
- a Trinamic stepper PD28-1-1021 for the Azimuth position
- a Trinamic stepper PD28-3-1021 for the elevation position

Based on the theoretical and actual positions of the mirros, the Raspberry Pi activates to motor to reach the targeted position and reflect the sunray onto the target
Functioning principle - PV Tracker regulation
The PV tracker regulation is simpler: InSolem uses a sensor with four photoresistances: when the sunray is perpendicular to the PV module, all photoresistances should receive the same light intensity. When it is not the case, the tracker position has to be adapted. The hardware set up by Iziproto includes:

One Raspberry Pi for each tracker



A homemade sensor with four photoresistances that are connected to an Arduino. The Arduino is used as a voltmeter and communicates the voltage of each photoresistance to the Raspberry Pi so that the program can detect when the tracker is not perpendicular anymore. One sensor is installed on each tracker.

The same motors are used as for the heliostat, controlled by the Raspberry Pi through a serial HAT RB-RS485

:
- a Trinamic stepper PD28-1-1021 for the Azimuth position
- a Trinamic stepper PD28-3-1021 for the elevation position

When the Arduino detects different intensities form the photoresistances, the Raspberry Pi activates the motors in order to reposition the tracker perpendicular to the sunray.
Hardware Cost
The hardware cost for each tracker comprises (cost estimations):

- 1 Raspberry Pi: 39
- 1 Arduino: 19
- 1 GPS for the field: 1/3*40 = 13,3
- 1 Accelerometer: 17 (+2 additional optional accelerometers for test purposes)
- 1 Serial HAT RB-RS485 for Raspberry Pi to communicate with the steppers: 14
- 1 Trinamic stepper PD28-1-1021: 170
- 1 Trinamic stepper PD28-3-1021: 180

TOTAL COST: 450
For more information on the solar trackers, contact InSolem!
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