Photovoltaic Generation - Solar Cell

Another lesser widely used method of generating electrical energy today is Photovoltaic cell. This cell is commonly called a Solar Cell, and converts photons, from the sunlight, or any light, directly into electricity.

One common style of solar cell is build using a fused silicon wafer stack. This arrangement is called a P-N Junction sandwich. The bottom plate of the stack is a conductive plate. The next layers in order are the p-type crystal material layer, the n-type material layer, a conductive screen contact area, and a protective covering that allows the light through. This p-n junction is the foundation of the semiconductor process and will be described in more detail in the general semiconductor section later in the book.

When the sunlight hits the stack (sandwich) it converts the sunlight's photon energy directly into electrical energy through the production of electron-hole sets. Recall that electrons carry a negative charge, and the holes are electron receivers with a positive charge. The electrons are "boiled" off the p-type material build up on th n-type plate and the holes are created on the p-type plate of the cell. Once a circuit is attached to the cell the electrons can flow out the negitive terminal through the circuit and back into the positive terminal.

A small array of solar cells are being used to power many low cost calculators, and charge batteries for outdoor landscape lighting. Larger arrays can be connected to a power convertor are used in places where an alternated electrical source is desirable or necessary. One example are the cell arrays supplying power to the self-contained weather monitoring stations in the mountains of Colorado, USA. The stations are places in remote areas across the Rocky Mountains where their only power source is from the solar array. These stations transmit their weather updates to the data center using satellites.

Some caution should be used when speaking of photovoltaic cells and calling them Solar Cells. Other renewable energy fields use the same term Solar Cell to define equipment that heats air or a liquid for use in space heating. These are solar cells but they are not photovoltaic.

Untapped technology to ponder: Think of how much fuel each train could save if the roof of every box car held a large photovoltaic panel. The drive wheels on locomotives are propelled by electric motors which are powered by a diesel engine-generator set under the hood. Box cars do spend a lot of daylight sitting in the sun, and this energy could help reduce the cost of operations.

Thermoelectric, Piezoelectric, and Bata-voltaic Generations
The Thermoelectric Generations

The thermoelectric effect was discovered by Thomas J Seebeck in 1821. He discovered that when heated different metals, as the temperature get hotter a small voltage will increase. By bonding the metals like iron with constantan, for example, and then heating the bonded junction area, a small voltage is generated.

This bonded junction called a thermocouple is widely used as a control device in applications and equipment where heat in used. For example, natural gas devices including furnaces, hot water heaters, gas fireplace inserts and outdoor propane barbeque grills use this thermocouple process to verify the pilot flame is burning prior to allowing the main gas valve to open.

The newer discoveries and developments with the p-n junction are leading to new technologies in P-N thermoelectric usage.

Piezoelectric Generation

The Piezoelectric effect is probably one of the lease talked about in electronics, however uses. It produces a very small level of electricity. It is a bi-directional effect. When a pressure, stress or a vibration is applied to a crystal it generates electricity. Likewise when electricity is applied to the crystal it will flex and vibrate.

Computers, electronic wrist watches, cell phones, radios and televisions, traffic signal lights, microwave ovens, cars, and aircraft navigation equipment, are just a sampling of the devices that use the piezoelectric effect in their electronics. The piezoelectric crystal is made by cutting a thin slice of a crystal, attach a contact point to the two parallel sides, and mount it in a hermetically sealed can.

By placing a small electric charge across the crystal, a vibration takes place within the crystal. If this charge is in the form of a radio output then we will hear the radio on its piezo speaker. This is how most of us experience this effect. However, in a different type of circuit this small charge causes the crystal to vibrate which in turn causes a small voltage pulsing. We can capture that small continuous stream of pulses and use them as a time standard in many of the electronic gadgets we use every day, from our cell phones and microwaves to our automobiles and computers.

Beta-voltaic Generation

This is one of the newest electrical generator discoveries powered from Nuclear power. The radioactive isotopesplaces adjacent to the P-N Junction emits beta particles which cause electrons to flow. This is basically a beta energy to electrical energy pump.

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