Solar bottle bulb Dr. S.S. Verma Professor, Department of Physics, S.L.I.E.T., Longowal, Distt.-Sangrur-148 106 (Punjab). E-mail: ssverma@fastmail.fm Many times, a very simple science, put to use in the form of technology can prove to be a life-changing technology affecting human living standards and comfort and such is the case of solar bottle bulb. Solar bottle bulb has proved to provide an ecologically and economically sustainable source of light to underprivileged households that do not have access to electricity or are unable to afford it. The invention is relatively simple. It involves filling up a 1.5L PET bottle with purified water and bleach and installing it onto the roof of a house. The water inside the bottle refracts the sunlight during the daytime and creates the same intensity as a 55 watt light bulb. With the correct installation and materials a solar bottle can last up to 5 years. The idea of using plastic bottles for daylight was first pioneered by Alfredo Moser from Brazil in 2002. Using the technology as a social enterprise was first launched in the Philippines by Illac Diaz under the MyShelter Foundation in April 2011. In order to help the idea to grow sustainably, the foundation implemented a “local entrepreneur� business model, whereby bottle bulbs are put together and installed by locals who can in turn earn a small income for their work. Within months, the organization was able to install 15,000 solar bottle bulbs in 20 cities and provinces around the Philippines and began to inspire local initiatives around the world. In less than a year since inception, over 200,000 bottle bulbs were installed in communities around the world. The foundation has a goal to light up 1 million homes by the end of 2015. Technology Thousands of poor homes in every nation have a lighting problem, not uncommon for cramped and small settlements. These houses are so close together, with metal roofing that all the light is blocked off and no light reaches the homes even during daylight. The solar bottle bulb is helping poor communities in developing countries. The solar bottle bulb is installed in the roof of homes with the purpose of refracting sunlight in order to light up a room. The project’s innovation lies in its utilization of cheap, durable and readily available materials to produce high quality natural lighting enabling the urban poor to have access to an affordable, environmentally friendly longterm alternative to electric light for use during the day. Most of the plastic bottles used are recycled, 1.5 liter bottles that lend the technology its name. After being filled with water and bleach, the bottle is pushed through a steel sheet that serves as a metal lock to prevent it from slipping. It is then embedded into a corrugated iron roof. A small part of the bottle is left outside while the rest of it protrudes into the house. Sealant is put around the hole made in the roof to keep it weather proof. The refractive properties of water ensures that the light from the sun that reaches the inside of the bottle becomes omni-directional mimicking an electric light bulb and emitting the same amount of light as a 40-60 W incandescent bulb depending on the amount of solar insolation available. Adding bleach to the water prevents it from turning green with algae and ensures a high quality light keeping the water clear for a longer time. Simple physics 1
The physics of the concept is straightforward. Without a solar bottle bulb, only a small amount of sunlight would be collected. Because of multiple reflections and different paths caused by Snell’s Law refraction and internal reflection, light spreads out as it passes through the water column. The device work by refracting sunlight in a 360-degree arc around the room, which provides superior light to a window or skylight, only allowing light into a room in a direct beam. When light moving through the air runs into a denser medium such as water, it changes direction because of refraction. The light beam “bends” when it enters the bottle so that it’s travelling more directly down into water. That’s very helpful to get more light to go down through the bottle into a dark room below. Despite this, some of the light will still be on a path to the opposite side of the cylinder. A portion of the light is trapped in the cylinder because of simple reflection, which can happen anytime light passes from one transparent material to another. However, during much of the day, the light will strike the cylinder walls in such a way that lots of light will be reflected down toward the hole, as total internal reflection. Light reflected this way will bounce back and forth as it travels down through the water column, much like signals passing through an optical cable. Advantages and disadvantages The solar bottle bulb is an environmentally-friendly, zero carbon emitting alternative to the daytime use of incandescent light bulbs and kerosene. The plastic bottles and the other materials used in the technology are easily available eliminating the need for energy-intensive processes involved in gathering, manufacturing and transporting new bottles. Coupled with the simple assembly, this means that even people in the most deprived neighborhoods can install and enjoy the benefits that are associated with access to better lighting. The affordability of the technology means that the majority of slum households can install it. The advantages are overwhelming for communities that are deprived of daylight. The bulb does not produce any harmful pollutants and also reduces the dangers from faulty and temporary electrical connections that cause devastating fires. However, this innovation does not have any provision for energy storage as the bulb will not work at night. The bulb is also not suitable for a permanent structure as it can cause permanent damage to the roof as well as invite outdoor elements into the home. There are hundreds of millions of families in rural areas or crowded city slums who have no light in the daytime. People without electric light usually rely on kerosene, a terrible alternative. It gives poor light — really, not enough to study by — produces noxious fumes, and is a major hazard for burns and fires. Indoor air pollution kills millions of people each year and kerosene is a major source for it. This project and its success is a great example of the ‘market-based’ solutions that should be pursued for socio-economic problems worldwide, strategies that are smart, effective & resourceful. Acknowledgement: The use of information retrieved through various references/sources of internet in this article is highly acknowledged. 2