Lecture 2 .pdf

Solar Energy
How solar Panel convert light into electricity Lecture 2
Dr. Basman M. Hasan Alhafidh
Department of Computer Engineering
College of Engineering
Mosul University

Agenda
Solar energy basics
 Overview of the major sources of energy
- Primary Energy Resources
- Transformation of Energy
- Solar Energy
 How solar Panel convert light into electricity
 Calculating Energy Efficiency
 Electrical and Mechanical components of a solar panel system
2

How solar Panel convert light into electricity
 Photovoltaic cells and modules
In the previous slides, you learned about the solar resource, the Sun. That's the largest
available energy source on earth, in that we can transform that light energy into electrical
energy using photovoltaics or solar panels.
 In this lesson, we're going to look more closely at solar panels and how they convert
that sunlight into electricity.
 By the end of this lesson, you should be able to
 Describe the major components of a solar panel,
 Distinguish between the different materials that are commonly used in solar panels,
 Describe how a semiconductor functions,
 and recognize new and emerging types of solar panels.
3

The most common type of photovoltaic we see in the world today are made of the element silicon.
 The solar cell is the basic unit of a photovoltaic module or panel.
 A single solar cell produces about a half a volt of electricity and up to about eight amps depending on
the type of cell.
 That's about one-third the voltage of a double A battery.
The solar cell consists of a piece of silicon with contacts or electrodes that are put across the surface and
on the back.
Often, you'll see many smaller contact is connected together by a few, larger contacts on the cell's surface.
Now, a half a volt isn't going to be able to do very much. So, cells are connected in series to create what's
called a series string Thus, increasing the voltage.
This is similar to how batteries are put together in electronics, front to back, front to back, so they add up
to a higher voltage. So, for example, you might put two double A batteries into a flashlight, which increases
the total voltage to three volts.
4

 Photovoltaic module (Solar Panel):
The voltage of the series string is simply the
sum of the half volt cells, which in this
illustrated example of eight cells would be four
volts. The series string is laminated to backing
material, sealed in a weather proof plastic
coating, and then a cover glass is placed on top,
often with an aluminum frame around the
edges. This assembly is called the photovoltaic
module.
- The typical solar panels you see on a home or
a commercial building will usually be a lot
bigger than our simplified example here, and
may contain series strings of 60 or even 72 cells
per module.
5

 Photovoltaic array:
- When designing a photovoltaic system,
photovoltaic modules, also known as panels, we
put together in what's called a photovoltaic array.
- Just like when the series strings of cells are
wired together to make the module, we can also
wire modules together in series to increase the
voltage of the overall system. - In this case, our
four four-volt modules would create 16 volts
when connected together in series.
- An array of modules is what you're looking at
when you see a roof-mounted photovoltaic system
or even a ground-mounted system.
6

 Silicon-based Photovoltaics
Silicon Types:
There's some variety to the type of silicon and how it's processed that impacts the overall
cost of production in the light to electricity conversion efficiency of the module.
1) Amorphous silicon
2) Polycrystalline silicon
3) Monocrystalline silicon
7

8

9

Silicon Types:
There's some variety to the type of silicon and how it's processed that impacts the overall
cost of production in the light to electricity conversion efficiency of the module.
1) Amorphous silicon
 The least efficient but cheapest to produce.
 It has an efficiency of about 5-7% and is not commonly used for commercial photovoltaics.
 However, you've probably seen amorphous silicon on the surface of pocket calculators and
other small electronic devices.
Note: Most commercially available modules are either made of monocrystalline silicon or
polycrystalline silicon. 10

2) Polycrystalline silicon:
 Sometimes also referred to as a multicrystalline silicon,
 Has a flaky appearance.
 It's a little less efficient in converting light to electricity than the monocrystalline silicon in
the range of 15-17%,
 But it's cheaper to manufacture because it's not as pure or energy-intensive to produce.
 The silicon is deposited in a chemical vapor process that forms multiple crystals giving it that
characteristic flaky-like appearance.
 The ingot can then be sliced into wafers to make photovoltaic cells or serve as the stock for
making monocrystalline silicon.
11

3) Monocrystalline silicon or single crystal silicon
 Is more efficient in converting light to electricity in the range of about 15-22%,
 But it's also the most expensive to produce.
 The silicon must be first:
- melted down and then a seed crystal is attached to a rotating thread or rod,
- then grown around the seed and is slowly pulled up into what's called a bowl, which is one
single crystal piece of silicon.
- That round bowl is then cut into thin slices and that round shape often results in cells with
rounded corners or rectangles often seen in those monocrystalline modules.
 The overall appearance of silicon is uniform, flat, black and non flaky.
12

Sunlight conversion into electricity by silicon
silicon => semiconductor => electrons can flow or conducted under the right conditions.
In both monocrystalline and polycrystalline silicon production,
 there's also a doping process where impurities are specially added to silicon to slightly alter
its conductivity and its charge.
 The typical dopants are:
- Boron which creates a positive charge.
- Phosphorous which creates a negative charge.
 The positive charge => p-type material.
The negative charge => n-type material. 13

14

A cross-section of our solar cell.
 As we were down from the surface of the solar cell,
 There's a top anti-reflective coating.
 There's also the top contacts that will carry the electricity generated from the silicon out of
the cell and into the circuit.
 Even though we're showing them as two layers, the next two sections are actually one piece
of silicon.
 The upper part is the n-type region that was doped with phosphorus, and the lower part is
the p-type region which was doped with boron.
 The area where the n-type and p-type regions meet up is referred to as the np junction.
 Lastly, on the bottom, there's another contact that will complete the circuit, => electricity
flows from the top through the system and then back to the bottom of the solar cell.
15

16

When photons of light hit that photovoltaic cell:
 Electrons are ejected from the n-type region, then move into those top contacts
through the circuit creating an electrical current.
 There's also a positive hole left by the n-region by the absence of that electron.
That's when the backfill movement occurs where the electron from the p-region fills
the whole left in the n-region.
 When the electron returns from the circuit through the bottom contact of the
silicon, it fills the positive hole that was left behind in the p-region.
17
https://www.youtube.com/watch?v=L_q6LRgKpTw
https://www.youtube.com/watch?v=UJ8XW9AgUrw

 Other photovoltaic materials
One of the newer types of photovoltaic materials is Copper, Indium, Gallium,
diSelenide, usually referred to by the acronym CIGS.
CIGS Cells:
- CIGS cells are projected to be better in (cloudy conditions),
- and have achieved a maximum of efficiency of 22% in a lab setting.
- There are also gallium arsenide cells which have high efficiency about 29% in lab
settings.
- However, there are concerns over health concerns with those materials.
18

 Over the last 40 years, researchers and manufacturers have made significant
efficiency improvements, and developed several types of photovoltaic cells like
silicon, CIGS, dye sensitized, and multijunction.
 The best performing cells, become the benchmarks for further improvements. So,
how do these different types of cells compare to one another, and how are they
improved over time?
19

20

On graph, we have time on the, from the mid 70's on the X-axis, and the overall cell
efficiency on the Y-axis.
 Silicon efficiency has gone up and remained pretty flat for the last two decades.
 That's because silicon has essentially reached its maximum, and can't get much
better.
 Thin film cells such as CIGS and cadmium telluride have made great improvements
over the years, and it become more and more efficient.
 However, there are concerns with toxicity which limits some of their
commercialization.
 Emerging technologies cells like dye-sensitized solar cells, perovskite, and organic
cells, are making quick gains, but they are many years from being towards
commercialization. 21

 The multijunction cells, show the highest efficiencies, but those cells are mainly in
the lab stage, and at this point are prohibitively expensive for commercial purposes.
 Although there have been some used recently in some highly specialized applications
by NASA for the Dawn space probe in the Mars Rover. You can see a little more
detailed breakdown of the efficiencies of the different types of solar cells over time
in the National Renewable Energy laboratory's graph of solar cell efficiencies.
22

 Efficiency Vs. Cost
 In nearly all cases, efficiency improvements are continuous, but cost inefficiently
tend to be directly related.
 Increased efficiency, typically comes at increased cost.
23

Future for commercialized photovoltaics
 Silicon will likely continue to be the primary material for commercial photovoltaics, for the foreseeable future.
 Because there are large quantities of the raw material available, and it's been in production for over 40 years.
 While the electrical and safety concepts are universal. The industry has evolved around working with traditional flat
panels.
 So, that keeps us as using this traditional silicon photovoltaic, as a current market driver.
 Within the crystal and silicon based photovoltaic market:
 Polycrystalline silicon currently has the largest market share, accounting for more than two-thirds of the crystalline silicon-based solar
cell production.
 Polycrystalline silicon will continue to dominate overall photovoltaics markets.
 However, the ratio of monocrystalline to polycrystalline photovoltaics, may vary with changing manufacturing methods and costs, as well
as changes in electricity pricing.
 The introduction of these novel types of solar panels into the commercial market, will likely be limited since silicon based
technology is very well matured.
Note: it's important to keep in mind that, unlike appliances that get energy guide or energy star rating to the United States, or
the European Union energy labels in the EU, there is no universal standard on size, power output or material for the solar
panel.
 You need to research each brand before designing an installation.
24

So now, you should be able to:
 Recognize and describe the major components of photovoltaics, which include the cell,
the module or panel, and the array.
 Distinguish between the types of materials used commonly in the solar panels;
monocrystalline and polycrystalline silicon.
 Describe the system, how the system convert light to electricity through the semiconductor.
 Recognize some of the other types of photovoltaic cells that are currently being developed.
25

Thank you
26

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