What is Solar Energy?
Solar energy is any energy derived from the sun.
It may be heat or light that is captured and transformed in some way (e.g. converted to electricity); or focused into some particular application (eg. heating water for a swimming pool; or stones to create a heat bank that can be utilized later on).
- Solar is not only used to heat water, but can be used to supply electricity for any use (can be generated from photovoltaic cells).
- Good housing design can provide 60-100% of your heating and cooling requirements.
- Solar energy can be stored in thermal mass (eg. building materials, rocks, water, oils) or thermo chemical reactions so that it is available at any time, including at night, and on overcast days.
- Electricity produced in photovoltaic cells can be stored in batteries.
- Some solar equipment costs less than conventional alternatives to buy, install and run.
- 'Solar' clothesline save considerable energy when compared with electric driers.
Solar energy makes use of a small portion of the electromagnetic radiation (EMR) that comes from the sun. Electromagnetic radiation is energy that travels in waves, the higher the wavelength the higher the energy. We can see only a small proportion of EMR as visible light. A microwave makes use of a higher wavelength than we can see, and many animals can see ultraviolet radiation. This is important to understand as cheaper or lesser quality solar panels may only capture a smaller range of EMR than those of better quality.
The basic component that actually captures the energy is the photovoltaic cell. They rely on the fact that photons (small parcels of light) act as both matter and radiation. These cells convert EMR in the visible light, infra red and ultraviolet spectrums directly into electrical energy. Photovoltaic cells are generally made from treated silicon (S) and are known as silicon PV cells. These cells are actually highly specialised superconductors which are formed from purified silicon with a crystalline structure. This structure has specific electrical properties. Essentially when light hits the panel the photons travel through to the crystalline silicon, the photon dislodges an electron and this is what causes the electrons to flow. The crystalline structure can be either monocrystalline or polycrystalline.
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Monocrystalline
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Polycrystalline.
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Cost is high
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Cost is lower
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Efficiency is high
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Efficiency is also lower
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Can use less space
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Takes up more space
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During manufacturing the purified silicon has special impurities added to it to change the availability of electrons. These are known as P Type and N Type impurities.
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P Type
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N Type
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Manufactured to produce a shortage of electrons
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Manufactured to produce an abundance of electrons
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When the cells are assembled the two types of silicon are layered with a sheet of silicon dioxide between them. This is known as the P-N Junction. The silicon dioxide prevents the electricity flowing until light is present, when a potential difference is developed between the two layers. This is very similar to what we have discussed with batteries. In a solar panel a positive electrode is formed by metal ribbing connected to the P type silicon. The ribs are connected with wires. The negative electrode is formed by a base under the N type silicon known as the substrate.
