Photovoltaic Cells: Energy Source of the Future. As populations increase and countries industrialize, the world’s demand for energy increases. Our supply of petroleum and gas is limited, but the photovoltaic cell offers a solution to the problem of a future energy shortage. This cell is already an important source of energy. In fact, it seems almost like magic. The photovoltaic cell changes sunlight directly into energy. Solar energy – energy from the sun – is clean, easily available, inexhaustible, and free, if the equipment is available. Did you ever reach to open the door at a stories or hotel and see it open by itself? Does your camera always let in the right amount of light for your picture? These are examples of uses of photovoltaic cells. They are also used in calculators and watches, in remote telecommunication units, and in central power stations to produce electricity. Another important use is in the space exploration program. This program could not exist without the energy produced by photovoltaic cells. The photovoltaic cell is simple. It has transparent metallic film at the top. Below this is a layer of silicon. A metal base is at the bottom. The sunlight falls on the boundary between the two different types of semiconductors in the photovoltaic cell, the silicon and the metal base. A conductor is the something that electricity can pass through. Water and metal conduct electricity, but wood does not. A semiconductor conducts electricity poorly at low temperatures, but when heat or light is added, conductivity is increased. As the light falls on this boundary between the two types of semiconductors, it creates an electric current. The sunlight is converted directly into electricity. One advantage of the photovoltaic cell is that it is solid-state; that is, there are no moving parts. Since there are no moving parts to break down, the cell will last the long time if it is protected from damage. This protection is important. If the top of the cell get dusty, less light enters, and the cell doesn’t work as efficiently as it should. In addition, silicon is one of the most common elements in the world; for example, sand is made up mostly of silicon. At one time, the chemical preparation of silicon for used a photovoltaic cell was very expensive. Now the cost has gone down a great deal. Scientists have also found a way to produce silicon in long sheets, similar to the way plastic for plastic bags is made today. This is helping the cost of a units of solar energy to fall even more. Today, there are large factories using solar- cell systems in a number of countries. About 18% of the sunlight that reaches the photovoltaic cell is converted into electricity. This is a small amount, so many cells must be used to create a reasonable amount of electricity. However, technology can be developed to make the cells more efficient and raise the percentage of sunlight converted to 27%. What does solar energy mean to the world? Photovoltaic cells have several advantages over fossil fuel (gas, oil, and coal). Fossil fuels that we use today were formed from plants and animals that lived millions of years ago. Those plants and animals were able to exist because of the sun. Obviously, we can’t wait million years for more fossil fuels. The photovoltaic cell gives us ability to produce energy directly from the sun. The sun’s energy can be converted for use immediately. At the present time, gas and oil are expensive. Developing countries can not export enough agricultural products and other raw materials to allow them to import the fuel that they need to produce energy. At the same time, petroleum supplies are limited, and in a few decades, they will run out. However, the supply of sunlight is limitless, and most of the poor countries of the world are in the tropics, where there is plenty of sunlight. The photovoltaic cell has another very important advantage. It is a clean source of energy. The fossil fuels that we use today are the main source of the pollution in our atmosphere. Although many individuals and government have been reluctant to reduce their dependence on fossil fuels, there is a growing market for solar energy on satellites and then beaming it to Earth. This process is called Space Solar Power. If we truly want cheaper and better ways to create energy, solar power offers many possibilities. Biosphere in Space. Will it ever for possible for people to live on faraway planets such as Mars? In the past, colonies in space were possible only in science fiction stories. Today, however, we are experimenting with ways to build real space colonies. Many scientists actually consider it possible that people will live far from the Earth in the future. The Environment Research Laboratory at the University of Arizona is one place that designs biosphere (bio mean life, and a sphere is a circle, like a ball) which could use to live on other planets. Biospheres are complete, enclosed environment where people can be born, live their whole live, and die without returning to the Earth. To be successful, a biosphere has to have perfect balance among everything within it- the planets, the animals (including humans), and the chemical elements. Specialist and experts from many different fields are needed to work on these complex projects. Building a greenhouse for growing planets in winter is the first step in creating a biosphere. A greenhouse is a closed environment except for the sun’s heat entering through the glass or plastic. Of course, there is water system from outside, and people bring in nutrients for the planets and take out the waste material. A biosphere in space will have to have its own system to provide water that can be used and reused. It will need bacteria or something else to take care of the wastes. Everything must be perfect balanced, or else the whole system will break down. The Earth itself is the best example of a real biosphere. Nothing important enters except sunlight, and nothing leaves as waste except some heat. Everything in the Earth’s environment needs to be in balance. If we destroy that balance, the system will break down. There are several reasons for building biospheres. One reason is to help out when there is an energy shortage. Dr. Gerard K. O’Neill, a famous physicist from Princeton University, has said that in the future we will have satellites in space to produce solar energy and send it to the Earth. It will be too expensive to continually send people and materials to the satellites, so biosphere will be necessary. He thinks that 10,000 people could live in the space colony sometime in the future. There is another interesting reason to build biosphere. We can use them to do all kinds of research about our own environment and how it works. By studying biosphere, we can understand better what will happen as humans destroy tropical forests, as they create more carbon dioxide by burning fuel, and as they pollute the ocean and the air. So far, only a few experimental biospheres have been built on Earth. One is in Oracle, Arizona, near the University of Arizona. In 1991, four men and four women tried to live inside the biosphere without getting anything from outside. During the experiment, things got out of balance. Oxygen and carbon dioxide levels fell, and the crew had to get help and supplies from outside. In space, people living in a biosphere could not be able to do this. Learning how a biosphere works is one of the most important things we can do. The information we get from biosphere may keep us from destroying our own environment. This information will also help us to travel where once only science fiction could go.