Promoting solar energy by spreading awareness, training people and demonstrating technologies

A Solar Lantern

Solar Lantern is a self-powering lighting device, which is constitutes a solar power supply, battery and a light source.

The advantages of the solar lantern are that it makes user independent, provides a long-lasting and reliable service. Mostly the solar lanterns sold in India have the following characteristics:

1.       Light output is good enough for reading in close ranges

2.       It functions for about 4 hours per day to sometimes 8 hours

3.       Some particular variety of lanterns also function well under cloudy conditions

4.       The most important part of the Solar Lantern; the Solar PV Panel, comes between 5 – 8 years warranty

Following are the various varieties of Solar Lanterns:

Fig. 1: A typical Solar Lantern 

Solar Lantern Components

Light Source: A light source is typically a CFL or the more advanced LED (Light Emitting Diodes). Use of incandescent bulbs is avoided as they are very energy inefficient. CFLs and LEDs are among the most energy efficient devices and that’s why they are used. When we say efficient it means for a lesser power rating they produce more light. Typical CFL ratings are 5 W, 7W, 9W, 11 Wp. These light sources have a longer life than an ordinary bulb. A standard CFL has a life of about 6000 hours while the more advanced LEDs have a minimum of 20,000 hours.

Fig. 2: Light output is better than the Kerosene Lamp or the candle

Solar Photovoltaic Panel: The Solar PV Panel is the main power source of the Solar Lantern. It is a very reliable component with warranties ranging from 5 – 10 years. The panel comes in a variety of technologies such as crystalline and amorphous. The crystalline panel takes lesser area than the amorphous panel for the same amount of power produced.  However, crystalline panels do not perform satisfactorily under cloudy or less bright conditions. As compared to this, the amorphous panels perform well under cloudy conditions, but under bright conditions they may not be as efficient as the crystalline ones. The choice of the panel depends on the location of user. For e.g., a user in Rajasthan may prefer to use crystalline panels, while in Assam, they may prefer an amorphous panel.

Typical ratings of the Solar PV Panel between 8 Wp to 10 Wp. The area for crystalline panel of 10 Wp is about 1 sq. ft. Amorphous panels are typically 15% - 20% larger.

Battery: Typical batteries include lead acid maintenance free batteries or sometime Nickel Metal Hydride (Ni-MH) rechargeable batteries. Lead acid batteries are the most common ones. They have an average life of about 5 - 6 years if used as specified. Ni-MH has a slightly longer life than lead acid. But they are 5 times more expensive than the lead acid ones.

Battery size or capacity is determined by the Ampere-Hr (Ah). Greater the Ah of the battery longer will be the use of light source. For e.g. a 7 Ah battery will run a 5 W CFL for 8 hours, while a 4.5 Ah battery will run the same CFL for about 4 hours. Therefore lanterns should be decided after considering the location and the number of hours of functioning required.

Charge Controller: The circuit is the hub of system, through which the PV, battery and the light source are connected. It also indicates the battery charging and discharging status indicating us when to switch off the light and the put it for charging.

Using a Solar Lantern

Actually a solar lantern is very simple to use. But some very basic actions should be followed for best use of the device.

Placing the Solar Panel: Any solar based product depends on the sun for its functioning. When the sun is unavailable then the system may not function properly. The solar panel should be compulsorily placed in a shadow-free region. The panel should face south wards for maximum solar radiation. The panel should be inclined at the angle of the latitude of the location.

Cleaning the Solar Panel: The solar panel should be cleaned once every day in the morning for best performance. But cleaning it once in 2 days is also fine. The panel can be cleaned with a simple cloth, dry or moist or a sweep. Only the panel should be dust-free.

Indicators in the Solar Lantern: The lantern has two indicators LEDs. Generally when the Solar Panel charges the battery, a green LED will glow. It takes between 7 – 8 hours for the battery to be fully charged. When the lantern has been used for specified number of  hours, a red LED glows indicating low battery. The user must then switch of the lantern and then put it for recharging.

If the lantern is used for longer hours with low battery, then the battery deteriorates and may degrade faster than the expected.

Choosing the Solar Lantern

A few things should be kept in mind while choosing a Solar Lantern

Location of the User: A bright, sunny region with shadow-free location like Rajasthan may opt for crystalline solar panels. If the location is somewhere in a cloudy region with lesser number of clear sky days such as North-east, choosing an amorphous may be beneficial.

Number of hours of functioning (backup time): If the user needs light for lesser hours, then a small battery can be used, typically like a 4.5 Ah. For more hours like over 6 hours, a 7 Ah battery can be chosen. Of course the number of hours would depend on the power rating of the light source. If a CFL is used then the lantern would run for lesser hours, if LED clusters are used then the lantern will function for more hours.

Solar Lantern Specifications: Two types of solar lantern systems can be designed and used; based on either 6 Volt or 12 Volt. A 6 Volt solar lantern system would use 6 Volt battery and PV module while a 12 Volts solar lantern system would use 12 Volts battery and PV module.

12 volts Based system:-

 6 volts based system:-

 Where to purchase

In India there are several manufactures of solar lantern. There many be as many as 30 to 40. A list of solar PV module manufactures is given below. This list is taken from Ministry of New and Renewable Energy (MNRE), www.mnre.nic.in . Most of these solar PV module manufactures also manufactures solar lantern and sell them.

List of of solar PV lantern manufactures

Top of the page

Copyright © 2008 NEF. All rights reserved. For suggestions write to info@nenf.org