The camper and traveller of today expects that the creature comforts of home can be experienced in the great outdoors and as part of that travelling adventure. The evolution of DC to AC converters has seen an increase use of lap tops, GPS systems, DVD and television and refrigerators in most camping or travelling situations.
These additional appliances and gadgets require the ability to be run from electricity and this then requires the batteries to be recharged when required. One of the most cost effective and environmentally friendly ways to recharge batteries is by using the power of the sun through solar cell technology.
How a Solar Cell Works
Light striking certain substances causes the surface of the material to emit electrons. It is as if light somehow kicks electrons right out of atoms. Light striking other substances causes the material to accept electrons. It is the combination of these two substances that can be made use of to cause electrons to flow through a conductor. This is the so called photo-electric effect. Photovoltaic means sunlight converted into a flow of electrons (electricity).
Photovoltaic devices, or solar cells, are like generators that work in sunlight. They make electricity without waste, noise or pollution. They produce electricity without combustion. A solar cell is a solid state device in which there are no moving parts. There are different types, styles and configuration of solar panels available, choosing the one most suited to the application is a very important decision.
There are traditionally three (3) types of solar cells that make up a solar panel.
Single-crystalline silicon is considered the most efficient because the molecular structure is arranged very uniformly, allowing for the most ideal transfer of electrons through the material without interruptions. These modules are also the most expensive to produce since very pure silicon is required.
To manufacture single-crystal cells, the silicon is first melted, and then the crystal is "grown" by placing a seed crystal into the molten material. The seed sets the pattern for the material as it solidifies to create a single crystal (called a boule) that must be sawn into thin wafers before processing it into PV cells. About 20% of the high-grade silicon is wasted while slicing the wafers. These modules characteristically have a number of rounder-shaped cells placed in a rectangular frame, cost slightly more, but have a high degree of reliability and efficiency.
Multi-crystalline silicon modules are considered slightly less efficient, but also are less expensive to produce.
To manufacture multi-crystalline cells, a lesser grade of silicon is melted and cast into moulds where the material hardens into "ingots." Because the ingots are rectangular, the square wafer slices waste less space in PV modules than the rounded slices from single-crystal boules. Multi-crystalline modules have varying grades based on the size of the crystals and the number of impurities.
Amorphous solar-electric modules have less demanding manufacturing processes, and use very thin layers of material, which can be deposited on cheaper substrates like plastic, glass, or metal, so their overall cost can be very competitive.
Amorphous silicon modules have no crystalline structure or molecular order. The major disadvantage is that they produce less power per square foot of collector space. A 60 W amorphous module may take as much as twice the area as a mono-crystalline module. Also, they are initially less stable in power output compared to mono- and poly-crystalline modules.
If a 2 way Freezer/Refrigerator has an average current consumption of 1.5 Amps when operating at +3° C internal temperature in conditions of 32° C external ambient temperature the following calculation can be applied.
Under normal operating conditions and ambient temperatures an 80 W solar panel kit might provide on average 3 Amps current (see individual specifications). This means that for every 1 sunny hour that the solar panel kit is providing power to the battery, 1.5 Amp hours will be used by the refrigerator (1.5 A x 1 hour), whilst a further 1.5 Amp hours will be stored in the battery (3 A - 1.5 A x 1 hour).
*The voltage and current output of the solar panel will vary depending on the weather conditions, wind, direct sunlight or shade and as a result the final output can not be guaranteed.