Solar Cells, What's so Complicated About Converting Energy
Solar cells, what’s so complicated about converting energy? Learn about the inner workings of a solar cell.
by Willie Hayes, author of Hayes v. Marriott
A solar cell (also called photovoltaic cell) is a device that converts the energy of sunlight directly into electricity by the so called photovoltaic effect. Assemblies of cells make solar modules, also known as solar panels. The energy generated from these solar modules, is called solar energy. When you look at a solar panel it does not appear to be complicated. However, to look at the molecular activities another story emerges very quickly. I will give a quick overview of the process and then in subsequent articles I will explain in more detail the molecular processes involved in producing solar energy from panels. This is just kind of interesting.
The actual production of electricity in solar panels is done at the atomic level. The atom is a basic unit of matter that consists of a dense nucleus surrounded by negatively charged electrons. The atomic nucleus is a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutrons). The electrons of an atom are held to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other, this is what we call a molecule. An atom containing an equal number of protons and electrons is electrically neutral; otherwise it has a positive charge (electron deficiency) or negative charge (electron excess) and is an ion. This is the same effect we get with the positive and negative poles of magnets. Ordering is the regularity in which atoms appear in a predictable lattice, as measured from one point. In a highly ordered, perfectly crystalline material, or single crystal, the location of every atom in the structure can be described exactly measuring out from a single origin. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.
The name atom comes from the Greek “ἄτομος”—átomos (from α-, “un-” + τέμνω – temno, “to cut”, which means uncuttable, or indivisible, something that cannot be divided further. The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods. D Conversely, in a disordered structure such as a liquid or amorphous solid, the location of the first and perhaps second nearest neighbors can be described from an origin (with some degree of uncertainty) and the ability to predict locations decreases rapidly from there out. The distance at which atom locations can be predicted is referred to as the correlation length ξ. A paracrystalline material exhibits correlation somewhere between the fully amorphous and fully crystalline. During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the ‘atom’ was divisible. Now these guys were serious subatomic. The principles of quantum mechanics were used to successfully model the atom.
Atoms are small objects with tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.9% of an atom’s mass is in the nucleus, with protons and neutrons having roughly equal mass. Each element has at least one isotope with unstable nuclei that can undergo radioactive decay. This can result in a process that changes the number of protons or neutrons in a nucleus. Electrons that are bound to atoms possess a set of stable energy levels, or orbital’s, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and influence an atom’s magnetic properties.
Photovoltaics are related to the practical application of photovoltaic cells to produce electricity from light, though it is often used to refer to the production of electricity from sunlight. Already we see the term Photovoltaics. A solar cell can be made from a single or monocrystalline silicon wafer. What is a monocrystalline solar cell? Now most of us know mono means one usually right? A single crystal or monocrystalline solid is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.
Cells are described as photovoltaic cells when the light source is not necessarily sunlight. In this case the cell is activated by the light energy not necessarily the sun. These are used for detecting light or other electromagnetic radiation near the visible range, for example infrared detectors, or measurement of light intensity.
The absence of the defects associated with grain boundaries can give monocrystals unique properties, particularly mechanical, optical and electrical, which can also be anisotropic, depending on the type of crystallographic structure. These properties, in addition to making them precious in some gems, are industrially exploited in technological applications, especially in optics and electronics.
Because entropic effects favor the presence of some imperfections in the microstructure of solids, such as impurities, inhomogeneous strain and crystallographic defects such as dislocations, perfect single crystals of meaningful size are exceedingly rare in nature, and are also difficult to produce in the laboratory, this is kind of like a rainbow, though they can be made under controlled conditions. Now who would have thought we would be discussing the properties of crystals? On the other hand, imperfect single crystals can reach enormous sizes in nature: several mineral species such as beryl, gypsum and feldspars are known to have produced crystals several meters across. (smile)
The opposite of a single crystal is an amorphous structure where the atomic position is limited to short range order only. So as you can begin to see there is a little more involved in this process than at first might meet the eye? In between the two extremes exist polycrystalline , which is made up of a number of smaller crystals known as crystallites, and paracrystalline phases.
Paracrystalline materials usually have short and medium range ordering in their lattice (similar to the liquid crystal phases) but lacking long-range ordering at least in one direction.
The primary, most accessible source of crystallinity information is X-ray diffraction, although other techniques may be needed to observe the complex structure of paracrystalline materials, such as fluctuation electron microscopy in combination with Density of states modeling of electronic and vibrational states.
So as you can see the process that takes place in solar panels might take a little more study. So the actual exchange of protons and neutrons appears to be what produces the electricity. We will delve into this further, I could be wrong. I have just done a quick study of this process.
Willie Hayes, The Author of Hayes v. Marriott