Extracción y determinación del agua de poro, cationes de

Because of the chemical reactions within the cells, the capacity of a battery depends on the discharge conditions such as the magnitude of the current, the duration of the current, the allowable terminal voltage of the battery, temperature and other factors. The available capacity of a battery depends upon the rate at which it is discharged. If a battery is discharged at a relatively high rate, the available capacity will be lower than expected.

A battery capacity rating is always related to expected discharge duration.

Where,

Q is the battery capacity (typically given in mA·h or A·h).

I is the current drawn from battery (mA or A).

t is the amount of time (in hours) that a battery can sustain.

The relationship between current, discharge time and capacity for a lead acid battery is expressed by Peukert's law. Theoretically, a battery should provide the same amount of energy regardless of the discharge rate, but in real batteries, internal energy losses cause the efficiency of a battery to vary at different discharge rates. When discharging at low rate, the battery's energy is delivered more efficiently than at higher discharge rates.

9.3 SOLAR PANELS

Solar panels are the solar photovoltaic modules use solar cells to convert light from the sun into electricity. A photovoltaic module or photovoltaic panel is a packaged interconnected assembly of photovoltaic cells, also known as solar cells. An installation of photovoltaic modules or panels is known as a photovoltaic array. Photovoltaic cells typically require protection from the environment. For cost and practicality reasons a number of cells are connected electrically and packaged in a photovoltaic module, while a collection of these modules that are mechanically fastened together, wired, and designed to be a field-installable unit, sometimes with a glass covering and a frame and backing made of metal, plastic or fiberglass, are known as a photovoltaic panel or

simply solar panel. A photovoltaic installation typically includes an array of photovoltaic modules or panels, an inverter, batteries and interconnection wiring.

Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This means that the energy of the absorbed light is transferred to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. PV cells also all have one or more electric fields that act to force electrons freed by light absorption to flow in a certain direction.

This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off to use externally. For example, the current can power a calculator. This current, together with the cell's voltage defines the power (or wattage) that the solar cell can produce.

Photovoltaic panels, the most common form of solar panels in the professional electrical generation industry, are able to absorb energy from the sun through a variety of smaller solar cells on their surface. Much like how a plant is able to absorb energy from the sun for photosynthetic purposes, solar cells behave in a similar fashion. Solar panels are comprised of several individual solar cells. These solar cells function similarly to large semiconductors and utilize a large-area p-n junction diode. When the solar cells are exposed to sunlight, the p-n junction diodes convert the energy from sunlight into usable electrical energy. As the photons from the sun's rays hit the solar cells on a photovoltaic panel, the energy is transferred to a silicon semiconductor. The energy generated from photons striking the surface of the solar panel allows electrons to be knocked out of their orbits and released, and electric fields in the solar cells pull these free electrons in a directional current, from which metal contacts in the solar cell can generate electricity.

The photon is then transformed into electricity and then passed through connecting wires to finally enter a power generation facility. At this point we have generated electricity, but the process is not complete yet. One should make sure they store this energy for times when either there is little or no sunlight, such as at night. This can be done by storing this energy in batteries. Here in SPMUV, Lead Acid batteries are used for this purpose.

Pure silicon is a poor conductor of electricity because none of its electrons are free to move about. Instead, the electrons are all locked in the crystalline structure. The silicon in a solar cell is modified slightly so that it will work as a solar cell. A solar cell has silicon with impurities i.e. other atoms mixed in with the silicon atoms, changing the way things work a bit. We usually think of impurities as something undesirable, but in our case, our cell wouldn't work without them. When silicon combines with an element that has five electrons to share, such as phosphorus, a negative charge is created. Silicon can only take four of the five electrons. This leaves one free electron looking for a spot. These additional electrons are known as free carriers; they carry an electrical current.

On the other hand, when silicon is combined with an element that has three electrons a positive charge is created. Boron is a material which suits this purpose. When silicon and boron are combined, holes are created. These silicon combinations and their differing charges are used to make solar panels.

EXPLANATION

The process of adding impurities on purpose is called doping, and when doped with phosphorous, the resulting silicon is called N-type ("n" for negative) because of the prevalence of free electrons. N-type doped silicon is a much better conductor than pure silicon is.

The other part is doped with boron, which has only three electrons in its outer shell instead of four, to become P-type silicon. Instead of having free electrons, P-type silicon ("p" for positive) has free holes. Holes really are just the absence of electrons, so they carry the opposite (positive) charge. They move around just like electrons do.

The interesting part starts when you put N-type silicon together with P-type silicon.

Every PV cell has at least one electric field. Without an electric field, the cell wouldn't work, and this field forms when the N-type and P-type silicon are in contact. Suddenly, the free electrons in the N side, which have been looking all over for holes to fall into, see all the free holes on the P side, and there's a mad rush to fill them in.