Ravi Tejwani1, Debanjan Sannigrahi1, B. K. Chakravarthy2, N.C. Narayanan3, Chetan S. Solanki1

1Department of Energy Science and Engineering, IIT Bombay2Industrial Design Centre (IDC), IIT Bombay

3Centre for Technology Alternatives for Rural Areas (CTARA), IIT Bombay

SOLAR LAMP FOR STUDY PURPOSES: DESIGN PERSPECTIVES

CONTENT

• Introduction

• Design

• Product design

• Light right design

• Electrical design

• Solar panel design

• Conclusion

INTRODUCTION

India is a Young country

• July 2011-Population = 1189 million of which

– 0-14 years: 29.7%

– 15-64 years: 64.9%

– 65 years and over: 5.5% 

• Dependency ratio of 0.6; 2030-0.4

• 2020 Average Age: India-29; China-37; Japan-48:

India will have youngest working age population in world

With this young population India ‘can’ grow fast, provided the young population is well-educated and well-trained

CONTINUED…..

• “Right to Education” successfully implemented by Government of India through “Sarva Sikhsha Abhiyan”

• Need to implement “Right to Clean Light”

• LED based Solar Urja Lamp (SOUL) is a Solution to “Right to Clean Light”

• The power consumption for SOUL whole year is even less than a 1 unit

DESIGN PROSPECTIVE:

• Product Design

• Light Right Design

• Electrical Design

• Solar Panel Design

PRODUCT DESIGN

LED Housing

LED

Gooseneck

Base of Lamp

1 feet height

SOUL product model

LIGHT DESIGN

The standard lux level for general purpose lighting is 150 lux and that for studying is 250 lux according to the international standards for lighting.

The LED is a 150 lumen per watt

Mode Power(W)

Lumen ExposedArea under lamp

(m2)

Lux(Lumen/m2)

Standard Light level (Lux)

1 0.192 28.8 0.185 155 150 (general)2 0.352 52.8 0.185 285 250 (study)

Table for Lux level calculations:

Mode 1: low intensityMode 2 : high intensity

ELECTRICAL DESIGN

Battery Electronics Controller

Solar Panel

LED Housing

LED

Goo

sene

ckSun

SOUL basic electrical model

ELECTRICAL DESIGN (CONT..)

Operating Voltage Power Consumption (Pmax) Luminance

3.2 V 0.5 Watts 75 lumen

1. LED Technical Specifications:

2. Design Table for calculation of battery capacity

Mode Volt(V)

Current(A)

Power(W)

Energy(Whr)

Efficiency(%)

Energy(Whr)

Battery voltage

(V)

Charge(mAh)

DoD(%)

Capacity(mAh)

1 3.2 0.06 0.192 1.54 85 1.81 2.4 (NiMH)

753 80 941

2 3.2 0.11 0.352 1.76 85 2.07 2.4 (NiMH)

863 80 1078

1 3.2 0.06 0.192 1.54 85 1.81 3.7 (Li Ion)

490 80 611

2 3.2 0.11 0.352 1.76 85 2.07 3.7 (Li Ion)

560 80 700

ELECTRICAL DESIGN (CONT..)

3. Design Table for calculation of Solar Panel capacity

• Nearest available capacity of battery is 1200 mAh NiMH

• Peak Power rating of solar module can be 1 approximated to 1 Wp

Mode Energy(Wh)

BatteryEfficiency

(%)

Energy(Wh)

SunshineHours

(H)

Power(W)

Fill Factor

(%)

Peak Power(Wp)

1 1.81 90 2.01 4.5 0.447 70 0.642 2.07 90 2.30 4.5 0.511 70 0.73

Design Table for calculation of Solar Panel capacity

SOLAR PANEL DESIGN

Vmp (STC) V

Temp coefficient mV/ C

Temp differenceC

Voltage drop per cellV

Net Voltageper cell

V0.47 2.3 40 0.092 0.378

Solar cell parameters:Power O/P of Solar Panel : 1 WVoltage : 0.47 VCurrent density : 30 mA/m2

Temp : 25 C. Voltage Coefficient : 2.3 mV/ C

• Battery voltage : 2.4 V• Charging voltage : 2.4 + 1.4 = 3.8 V• No. of Cells = 3.8 V ÷ 0.378 V = 10 numbers (approx.).

SOLAR PANEL DESIGN (CONT…)

No. of Cells = 3.8 V ÷ 0.378 V = 10 numbers (approx).

Power Rating /Cell = 1 W ÷ 10 = 0.1 W.

Current Rating /Cell = 0.1 W ÷ 0.47 V = 0.212 A = 212 mA.

Area of each Cell = 212 mA ÷ 30 mA/sq. cm. = 7 sq. cm.

Total area of 10 Cells = 10 x 7 sq. cm. = 70 sq. cm.

Packaging density = 50 %

Area of panel Panel = 70 sq. cm. ÷ 0.5 = 140 sq. cm

CONCLUSION:• A powerful component of design for need which looks at the user needs, service

needs , distribution issues and most important the empowerment of children .

• The design using the best technology for various components and deploying it in system

• The proposed solar study lamps will have

• 1 Wp solar panel

• 0.5 Watt LED

• 1200 mAh of battery storage

• Provides light intensity of about 280 Lux (good enough for study)

• 6 to 7 hours of daily service.

THANKS FOR YOUR ATTENTION !