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Solar Energy

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See the wikipedia article for more general information: [1]

Solar energy can be obtained with photovoltaics, various concentration techniques, chemical reactions, and several experimental methods such as solar updraft towers.

In photovoltaic panels, solar energy is obtained via the photoelectric effect in which electrons are forced to flow during light exposure. This effect is very easily obtained through many multiple processes. For example a homemade solar panel can be easily created by simply heating a sheet of copper and scraping off the black cupric oxide that appears and placing it with some unheated copper in an ionic solution such as salt water. The material used in commercial solar panel production is silicon because, among other useful properties, it has only four electrons in its valence shell The downside of solar energy production is that it is inefficient and takes up large amount of space, the upside is that it is renewable and more panels can be added as needed, or as materials are obtained. It is likely that in a new habitat solar panels would resemble home made ones of varying materials and efficiency rather than highly efficient commercial ones. Thus much research is needed to identify what photoelictrically efficient compounds are available in each possible habitation site and how they can be utilized the most efficiently.

Contents

Heating

Most possible sites for human habitation require a large amount of energy to be used for heating, even with the best of insulation systems. Much energy can be saved by using solar power directly for heat without storing it as electricity first. This can be done by heating materials with a high specific heat capacity, such as water. Many heating systems here on Earth have proven that such a heating system can be extremely efficient.

Power Storage

One of the main problems with solar energy is that it is hard to store. One way to minimize this problem is to design habitats to draw little or no energy at night and use most energy as it is generated, though the need for a back-up system is unavoidable.

Battery Storage

Traditional galvanic cells can be used to store solar energy.

Thermal Storage

Solar energy can be stored as heat in some materials.

Basic Chemical Theory

Knowing some of the chemistry behind this process is helpful in the selection of materials used to construct panels. See wikipedia, as always: [2]

The process begins when a photon hits a valence electron which is excited enough to escape the covalent bond it is in between two molecules of the solid and enter the conduction band (sea of mobile electrons). This creates a positive "hole" which is filled by bonded electrons in nearby atoms, which in turn creates a new whole. This process repeats, so the holes can be considered mobile.

Once electrons are freed, the charge carriers either drift (if the process is in a p-n junction) or diffuse (in thin films and dyes). A p-n junction is simply when one type of silicon dopant is introduced into a material made of the second type of silicon.

Photovoltaic Design Basics

At the heart of a basic solar cell is a layer of N type silicon over a layer of P type silicon. An antireflective material is needed to reduce the amount of light reflected by the shiny silicon, and a protective glass layer is needed on top of that.

For a good overview see this site: [3]

Possible Materials

It should be noted that anything on Mars is free, so price is only discussed here for an initial colony, ISRU solar panels would be dependent only on the amount of supplies available.

Silicon is the most common light absorbing material. Many different forms of it can be used, including high efficiency but expensive monocrystalline silicon and less efficient but cheaper polycrystalline silicon.

Cadmium Telluride is often used in thin-films, and is a accumulative toxin.

Compounds made of combinations of certain group I, III, and VI elements can make somewhat more expensive, but more versatile, materials.

Multiple juntion Gallium Arsenide is the most efficient, but also one of the most expensive, materials being used. It is the type used on sattelites and the Mars rovers.

Dyes using ruthenium metalorganics and TiO2 are possibilities.

Organic and Polymer cells have very low efficiency rates.

A table comparing many different materials and their efficiencies or a link to such a chart should be placed here.