Solar cells
Solar cells today are mostly made of silicon, one of the most common elements on Earth. The crystalline silicon solar cell was one of the first types to be developed and it is still the most common type in use today.
They do not pollute the atmosphere and they leave behind no harmful waste products. Photovoltaic cells work effectively even in cloudy weather and unlike solar heaters, are more efficient at low temperatures. They do their job silently and there are no moving parts to wear out. It is no wonder that one marvels on how such a device would function.
To understand how a solar cell works, it is necessary to go back to some basic atomic concepts. In the simplest model of the atom, electrons orbit a central nucleus, composed of protons and neutrons. each electron carries one negative charge and each proton one positive charge. Neutrons carry no charge. Every atom has the same number of electrons as there are protons, so, on the whole, it is electrically neutral. The electrons have discrete kinetic energy levels, which increase with the orbital radius.
When atoms bond together to form a solid, the electron energy levels merge into bands. In electrical conductors, these bands are continuous but in insulators and semiconductors there is an "energy gap", in which no electron orbits can exist, between the inner valence band and outer conduction band [Book 1]. Valence electrons help to bind together the atoms in a solid by orbiting 2 adjacent nucleii, while conduction electrons, being less closely bound to the nucleii, are free to move in response to an applied voltage or electric field. The fewer conduction electrons there are, the higher the electrical resistivity of the material.
In semiconductors, the materials from which solar sells are made, the energy gap Eg is fairly small. Because of this, electrons in the valence band can easily be made to jump to the conduction band by the injection of energy, either in the form of heat or light [Book 4]. This explains why the high resistivity of semiconductors decreases as the temperature is raised or the material illuminated. The excitation of valence electrons to the conduction band is best accomplished when the semiconductor is in the crystalline state, i.e. when the atoms are arranged in a precise geometrical formation or "lattice".
At room temperature and low illumination, pure or so-called
"intrinsic" semiconductors have a high resistivity. But the resistivity can be greatly reduced by "doping", i.e. introducing a very small amount of impurity, of the order of one in a million atoms. There are 2 kinds of
* No energy is lost e.g. sound and heat which would be a result of
Energy can never be created or destroyed. Energy may be transformed from one form to another, but the total energy of an isolated system is always constant.
type of energy is lost or gained, and whether or not a factor that is
Another positive note is that this powerful energy is relevant, which means it does not have to be created. If this energy was too relevant then we humans would have to try and c...
The Effect of Intensity on the Power of Solar Cells This experiment involves changing the intensity of light falling on different cells and measuring their power outputs. Higher intensity of light means that there are more photons hitting the surface of the cell per unit area per second. The more hit the cell, the more rapidly the electrons move across the p-n junction, so the larger the emf produced. If the rate of movement of electrons is inhibited, then the greater the rate of supply of photons (intensity), the more will not successfully excite an electron, so the lower the efficiency of the cell.
energy was given out or taken in. We can show this on a graph. Alcohol
a. This is due to the properties of all matter and energy was needed for life to arise , so we originated .
The Ultimate Nature of Matter. The theory of quantum mechanics has divided the atom into a number of fundamental sub-atomic particles. Although the physicist has shown that the atom is not a solid indivisible object, he has not been able to find a particle which does possess those qualities. Talk of particles, though, is misleading because the word suggests a material object.
The nuclei are ejected from heavy, unstable nuclei so as to remove excess protons and neutrons. However, the formed nuclei may still be radioactive in which even further decay will occur. Alpha emissions occur in nuclei with atomic numbers greater than 83. E.g 23892U 42He + 23490Th (both mass and No. of protons are conserved during the reaction)
For the past few weeks, my classmates and I have been collecting data on the amount energy in kilowatts produced by solar panels on a given day. We have been guessing how many kilowatts of energy would be generated based on the forecast for each day, and then we were left with our estimates and the actual production of that day. In order to make this activity useful, we then took both numbers and found our percent error both weekly and daily. My best percent error days throughout the whole time were 1.09 and 0.44%. Now, needless to say, there were some bad days too. It was only easy to get a good percent error when the weather did what is was supposed to do, when we had an accurate scale to follow, and when there wasn’t
Energy is an odd concept, it is something that is neither here nor there yet has a profound impact on everything, both organic and inorganic. However, energy surrounds us in more ways than is commonly believed; it is possible that matter is only a form of energy. In fact, according to Albert Einstein, matter and energy are different forms of the same thing (“Do Antimatter and Matter Destroy Each Other?”). Through analyzing the superposition of bosons (particles without mass) and fermions (particles with mass), transformations between energy and matter, the creation of mass, and the mass of energy, the existence of what humans consider to be matter will be questioned.
Green plants convert the radiant energy emitted by the Sun into useful chemical energy, such as the oxygen that we breathe. The energy transferred between any surroundings and any system can be in the form of various types of work, chemical, mechanical, radiant, electrical, or heat. The second law of thermodynamics is expressed as a cycle in which “all processes occur spontaneously in the direction that increases the entropy of the universe (system plus surrounding).” Entropy, the number of ways the components of a system can be rearranged without changing the system, plays a major role in the second law of thermodynamics.
Heat is thermal energy being transferred from one place to another, because of temperature changes. This can take place by three processes. These three processes are known as conduction, convection, and radiation.
have been used throughout the past twenty years that have played a large role in society,
• A second principle, which concretises the beginning of the universe, is the second law of thermodynamics. As I quote the cosmologist Sir Arthur Eddington, said,