Introduction to Solar Power
The Sun The energy from the sun is radiated out in all directions as light. Much of the energy striking the earth is reflected back into space by the atmosphere, but a staggering 90,000 TW of power arrives at the earth’s surface, 6,000 times more power than the entire human race uses.
Using sunlight
1. Passive Solar Gain
Thoughtful design can improve this figure further with very
little, if any, increase in the cost of building the property:
2. Solar Thermal Collectors The flat panel solar collectors are generally cheaper systems per unit area. Their common feature is a flat plate with a black surface which absorbs sunlight. This surface may be of a selective coating which absorbs almost all light, but doesn’t radiate heat so well.
Evacuated tube collectors benefit from the extremely high insulation of a vacuum (like in a vacuum flask), which totally eliminates losses by conduction and convection. The vacuum is maintained inside a sealed glass tube. Sunlight is absorbed by a selective coating on a collector plate inside the tube (right). Heat may be removed by direct circulation of the water or by a “heat pipe” that contains a refrigerant. The refrigerant evaporates in the tube, and condenses at the cold end, transferring heat into water circulating there. Evacuated tube collectors are said to be more efficient due to lower losses, and consequently to perform better on cold or cloudy days. Solar thermal systems typically achieve efficiencies over 80%.
3. Photovoltaic Cells The heart of a PV cell is the interface between two different types of semiconductor. When a light photon hits a silicon atom in this region, it throws out an electron. The electron can travel through the n-type semiconductor to metal contacts on the surface. The hole left by the absence of the electron travels in the opposite direction. Once at the metal contact the electron flows through an electrical circuit back to meet up with a hole at the other contact. As it flows through the external circuit, the electron does useful work, like charging a battery, or operating an electrical appliance. Photovoltaic systems have been reducing in cost, and increasing in efficiency in recent years. The most efficient commercially available systems can convert up to 16% of the light energy that strikes them into electrical energy.
4. Solar Concentrators Solar concentrators only work in direct sunshine, with the collector aimed right at the sun. The mirror is held on a support that can turn to follow the sun as it moves throughout the day, adding to complexity and cost. Because of this, they are only used in areas benefiting from a sunny climate, with more clear days. |
Wireless Semiconductors
Solis State Drives
Solar and Wind Energy
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