Uploaded by MR Mada


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.
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
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
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
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:
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
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.
1. ↑ Wikimedia Commons [Online],
Available: http://upload.wikimedia.org/wikipedia/commons/8/83/
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