1] Introduction

What is scheffler ?

Scheffler is a Parabolic dish solar concentrator which gives a fixed focus with automatic tracking system. Heat from sun’s rays can be harnessed to provide heat to a variety of applications. But in general, sun’s rays are too diffuse to be of direct use in these applications. So solar concentrators are used to collect and concentrate sun’s rays to heat up a working fluid to the required temperature.

It converts solar energy into thermal energy (heat energy).

Some of the common application where Scheffler systems are used are

• Boiler feed water preheating
• Washing in laundries
• Steam genration
• Milk pasteurization
• Steam cooking

2] Problem Definition

The Scheffler in the Vigyan Ashram is not in working state. Following are the challenges I found/worked:

A] Maintenance and rework:

➢ Focal point adjustment .[Caution -i) Take senior person advice ii)Use safety equipment’s.]
➢ Clean all mirrors.
➢ It’s performance analysis and efficiency calculations like,

i) Heat gain from Scheffler ii) Storage of energy iii)Use energy.

B] Automation :

➢ Making it’s automatic single axis rotation possible.

➢ Application/Utilization of Scheffler.

3] Details Of Scheffler: (Present status)

• Dimensions of 1 mirror: 203mm x 183mm x 3mm
• Area of 1 mirror: 373.1 cm2
• Total Scheffler area : 16 m2
• Total Scheffler mirror area: 13.31 m2
• Total no. of mirrors: 359
• Window size is : 90 cm * 90 cm.

• Secondary reflector area = 0.35 m2(approximately).
• Thickness of Aluminum sheet used in secondary reflector = 0.5 mm.

To make Scheffler rotate automatically w.r.to sun motion.

• Study: Studied various methods & possibilities for automatic rotation.
• Delay and time of rotation: Calculated time interval required for the Scheffler to rotate to keep focus point at position. It’s time interval (delay) = 4 minutes, time of rotation (motor) = 15 seconds
• Motor Connections: Worked on different connections for Forward and Reversal of wiper motor (12V). Finally decided to go with 2 relay-center tap connection.
• Battery sizing: Calculated Battery size required to run motor approximately for 2 & 1/2 hours. Battery used – 12V, 4.5AH Lead Battery.
• Arduino Programming: Program for automatic rotation is written mainly using ‘for’ loop and ‘delay’ functions. Through this program Arduino controls 2 module relay which in turn operates motor.
• The code used is:
int relay1 = 8;
int relay2 = 9;
void setup() {
pinMode(relay1, OUTPUT);
pinMode(relay2, OUTPUT);
Serial.begin(9600);
}
void loop() {
for (int i = 1; i < 99; i++) {
Serial.print(“i “);
Serial.println(i);
digitalWrite(relay2, HIGH);//motor is at rest for 4 min.
digitalWrite(relay1, HIGH);
delay(240000);
7
digitalWrite(relay1, HIGH);//forward rotation of motor for 15 sec.
digitalWrite(relay2, LOW);
delay(15000);
}
digitalWrite(relay2, HIGH);
digitalWrite(relay1, HIGH);
delay(180000);
for (int j = 1; j < 25; j++) {
Serial.print(“j “);
Serial.println(j);
digitalWrite(relay1, LOW); reverse rotation of motor for 15 sec.
digitalWrite(relay2, HIGH);
delay(60000);
digitalWrite(relay2, HIGH); motor is at rest for 4 min.
digitalWrite(relay1, HIGH);
delay(240000);
}
digitalWrite(relay1, LOW);
digitalWrite(relay2, HIGH);
delay(30000);
digitalWrite(relay2, HIGH);
digitalWrite(relay1, HIGH);
for (int k = 1; k < 16; k++) {
Serial.print(“k “);
Serial.println(k);
8
delay(3600000);
}
}
• Arduino Supply: A DC step down converter is used to step down voltage from Battery (12v) to Arduino (5V).
• Installation of Solar Panel: To make control circuit and Motor supply circuit independent of grid a Solar Panel (17.2V, 37W) is installed on Scheffler window room. The size of the solar panel is calculated based on load (motor) usage.
• Charge controller: A Charge controller (12V, 5A) is used to control Battery charging from Solar panel and Battery discharging to the load. Field Testing on Scheffler:

4] What is focal point ?

i] The point at which rays meet after reflection or refraction.

ii] The point of a lens / mirror is point in space where parallel light rays meet after passing through lens / bouncing of mirror .

• The area of primary focal point of the scheffler = 0.1427 m2
• The area of secondary reflector focal point =0.06 m2

5] Energy (Heat) Calculation:

Available (Input) Heat at Scheffler = 10.01 KWh

Heat utilization by scheffler = 1.28 KWh

Efficiency of scheffler = 12.78 %