Basics of Solar Energy The Sun There: Will Therefore average achieve Earth's surface? Here we show the energy balance in the atmosphere. The main components in this diagram are the following: Short wavelength light (optical wavelengths) From the Sun enters the surface of the atmosphere. Clouds reflect 17% back into space. If the earth gets more cloudy, as some climate models predict, more radiation will be reflected back and less will reach the surface 8% is scattered backwards by air molecules: 6% is actually directly reflected off the surface back into space. . So the Earth's total reflectivity is 31 per cent. This i s known as an Albedo technically. Note that the Ear th's Albedo improves during the Ice Ages, as more of its surface is reflecti ve naturally this exacerbates the problem. How much energy from the sun reaches the surface of the Earth on Average? Note that we measure energy in units of Watt-hours. A watt is not a unit of energy; it is a measure of power. ENERGY = POWER x TIME 1 Kilowatt Hour = 1KWH = 1000 watts used in one hour = 10 100 watt light bulbs left on for an hour . Incident Solar Energy on the ground: Total over the whole earth = 164 Watts per square meter over a 24 hour day Thus the whole earth consumes 84 Terawatts of Energy our actual worldwide consumption is around 12 Terawatts and is this a solution? And note, none of the modern system runs on Renewable fuels. Entropy: is calculation of a system's disorder. Often described as the energy of a machine inaccessible for doing work. Systems decrease in energy and the entropy decreases over time. It's not a reversible operation. A stack of blocks falling over, for example, would result in lower energy state and higher entropy of the network. The Second Law: remains apparent in our modern universe, but the law is continuously broken on the subatomic level, however scientifically the law holds true. Perhaps one curious reader will consider interesting ideas of quantum mechanics outside the reach of this paper. A quest of the "hook of time" will produce fascinating Second Law variations. An air conditioner is a device used to cool down a room by extracting heat from the atmosphere and transferring it to a certain location outside. Then, the cold air can be transferred by ventilation in a house. Air conditioners allow some work input to perform, else entropy will necessarily decrease which is prohibited by the Second Thermodynamics Principle. Air conditioners work similarly to a heat pump, but obey a refrigeration process instead. One can see this cooling process in Figure 2. In the following steps a substance known as a refrigerant is treated to cool: • Cold liquid refrigerant removes heat in the evaporator from the colder room, cooling down the air. • The refrigerant then transitions to the gas phase and is forced into a compressor to increase the temperature. • The coolant then flows into the condenser tubes and removes the heat from the coolant to the outside air. • The coolant expands to decrease its density and cool down to below room temperature to repeat the process again. The air conditioner is a key component of the HVAC system, which focuses on regulating home temperature to optimize comfort and livability in a room. If there is an outside machine (the condenser) and an indoor device (the evaporator), air conditioners are labeled "splitsystems" Such two devices work together to perform the function of refrigerating an indoor room while still dehumidifying it. This dehumidification occurs when warm air flows into the cold evaporator from the inside, where the warm air condenses and loses moisture much like the air on a cold glass of lemonade The split-system defines an air-conditioner with different parts inside and outside. There is also another form of air conditioner, known as a "packaged" system, which incorporates all elements into one outdoor system. Often known as the "Claudius argument" this is central to how a cooling system works: "Heat will still flow from hot substances to cooler ones spontaneously." It is known as the Claudius theory, which explains that an ice cube will dissolve when it is put in a hot water tank, but on a hot day ice does not form out of snow. That argument is definitely reinforced by daily reality, but it's a profound physical idea that restricts what's possible with electricity. The second law of thermodynamics: states that heat cannot flow naturally from a cold body to a hot body, but if any sort of research is performed it will travel in that direction. That is how the cooling cycle operates, and you can see an explanation in Figure 1. Refrigerators operate by moving heat inside the system from the cold regions to hot regions outside it, rendering the cold regions much more hotter. That is how fridges work to keep food cold inside them, and why they can be heard blasting hot air out of their winds. Figure 3: The Claudius declaration of the Second Law of Thermodynamics forbids heat from moving from cold to hot unless external work is carried out. In Figures 2 and 3, the right section of the diagram defines the unlikely situations that the second law forbids, and a ideal refrigerator is similar to the heat transfer running at 100 per cent capacity of a device. The refrigerator in Figure 3 takes some heat out of the cold reservoir, QcQc, does some work on it, WW, and rejects some QHQH heat into the hot reservoir. Hence the refrigerator's net result is to cooler the cold reservoir by withdrawing heat from it and transferring the heat to the hot reservoir. Because of this a refrigerator is basically a heat energy running in reverse. When measuring how quickly a refrigerator will cool the cold tank, the coolers bear a output coefficient with them. This statement is nicely captured in the humorous song 'The First and Second Laws of Thermodynamics' by Flanders and Swann. For a more rigorous (but not as funny) write up of the refrigeration statement of the second law please see the hyper physics Second Law: refrigerator page. Disorder Statement: Another statement, perhaps the most crucial in terms of understanding why the Claudius and Kelvin-Planck statements are true is about entropy (which can be thought of as disorder): "The entropy of a closed system can never decrease." It is important to note that this assertion applies to a "closed structure," meaning the structure has no external effects. This is because an open system might have reduced its entropy, because this capacity to decrease entropy is how the refrigerators operate! Having that said, because of the solar radiation on Moon, the Moon is an transparent network that leads to the energy flows of the Sun. Entropy is essentially a "disorder" measure, so the higher the entropy, the greater the disorder the system has. This can be seen when shaking bricks in a can: a loose pile is more likely to form the bricks than to turn into a house. For a more comprehensive overview, see the Entropy hyperphysics article. Associated with entropy is the idea of "energy quality". Heat is low-quality energy, whereas mechanical energy is high-quality energy. Seen in Figure 4, the energy quality decreases as entropy increases. Therefore in general, since entropy naturally increases, energy quality will deteriorate. The association between an increase in entropy and a decrease in energy quality explains why all of the energy in fuels cannot be converted into mechanical energy. It is possible to burn fuel, therefore directly converting all its energy to low-quality heat, but this low-quality heat cannot then be turned fully into highquality mechanical energy or electricity For a more detailed description of the entropy statement of the second law of thermodynamics please see the hyper physics page on the second law: entropy. Figure4 why entropy decreasing as temperature increases, it can be shown that the violation of this entropy statement would violate the Claudius statement of the Second Law. Thermoelectric refrigeration: Thermoelectric cooling uses the Peltier effect to create a hea t flux between the interplay of two material types. This effect is widely used to cool electronic components and small instruments in camping and portable coolers. Peltier coolers are often used where a traditional vaporcompression cycle refrigerator is impractical or takes up too much space. Compact and lightweight, if inefficient, way of achieving very l ow temperatures, using 2 or more stadium peltier coolers arr anged in a cascade refrigeration arrangement, which means th at 2 or more peltier elements are stacked on top of each other, each stadium being larger than the previous one[57] to absorb mor e heat and waste heat generated by the previous stadiums. References 1. ↑ Wikimedia Commons [Online], Available: http://upload.wikimedia.org/wikipedia/commons/8/83/ Kuehlregal_USA.jpg 2. ↑ Jump up to:2.0 2.1 Hyper physics, Second Law of Thermodynamics [Online], Available: http://hyperphysics.phyastr.gsu.edu/hbase/thermo/seclaw.html#c2 3. ↑ Jump up to:3.0 3.1 3.2 Hyper physics, Refrigerator [Online], Available: http://hyperphysics.phyastr.gsu.edu/hbase/thermo/seclaw.html#c3 4. ↑ Jump up to:4.0 4.1 4.2 R. Wolfsan, "Entropy, Heat Engines, and the Second Law of Thermodynamics" in Energy, Environment, and Climate, 2nd ed., New York, NY: W.W. Norton & Company, 2012, ch. 4, sec. 7, pp. 81-84