Solar Energy

SOLAR ENERGY EDUCATION

Solar power is clean green electricity that is either created from sunlight or from heat from the sun. Having solar electricity in your home usually means setting up a solar photovoltaic system on your roof.

Definition of photovoltaic: Photo = “light” and photons = energy particles coming from sunlight; voltaic = producing a voltage or volts.  Abbreviation = PV

Solar energy is a renewable free source of energy that is sustainable and totally inexhaustible, unlike fossil fuels which are finite. It is also a non-polluting source of energy and it does not emit any greenhouse gases when producing electricity. The solar electricity that is produced can supply your entire or partial energy consumption.

New! Solar education for kids and teens

We’ve put together a page geared more towards older primary school and secondary school age children covering the basics of solar power; plus a basic calculator so kids can see how many solar panels would be needed to power their home.

Solar Workshop video series

This series of videos explains various aspects of solar power and related equipment.

 How a solar panel is made

A solar panel, while rugged and durable in its finished form, requires a complex and very technical process in its production.

In traditional solar modules (polycrystalline and monocrystalline), silicon wafers are impregnated with impurities to create a semiconductor that converts sunlight into electric current. Electrical contacts are then created to join one solar cell to another. As silicon reflects, an anti-reflective coating is placed on top of the silicon wafers, usually titanium dioxide or silicon oxide.

The solar cells are laid between a superstrate layer on the top and a backsheet layer on the bottom. The superstrate is usually glass, and the backsheet is plastic. This is then placed inside an aluminium frame to create a finished solar panel

In thin film solar panels, it’s a different process. It begins with a thin layer of flexible substrate such as coated glass, stainless steel or plastic and metal contact, and the solar cell is then built up in a series of layers. An oxide layer is then applied at the end to form the electrical contact of the cell. The cell is then laminated with a weather resistant superstrate material.

The following is a brief video on how a solar panel is made:

Using solar power means reducing your energy bills and saving money. Also, installing solar PV panels adds value to your home. They are low maintenance and unobtrusive. Read our 10 tips for getting a solar power system, or tips for choosing solar panels.

How does a solar panel work?

As touched on earlier, solar panels use what’s known as the photovoltaic effect to generate power. This is the process by which light is converted to energy at the atomic level.

Put simply; when light hits a solar cell, electrons are knocked loose from a solar cell’s semiconductor material atoms. Positive and negative electrical conductors associated with each solar cell form a circuit that capture this energy in the form of an electrical current.

Solar electricity

The electricity grid

Electricity travels from a power plant to your house via a power grid. This main grid is the national electricity grid found in QLD, NSW, VIC, SA, TAS, NT and WA. If you are not connected to the grid it means that the power lines do not reach your house, usually because you live in a remote area. The power that is supplied to the grid is most often produced by coal-fired power plants, which pollute the environment by releasing tonnes of greenhouse gases.

Grid connected solar power systems

PV systems generate energy from sunlight during the day. This energy goes into a grid connect inverter which converts the DC current into AC current, similar to that of the grid. This solar electricity current can then power all the appliances in your home, such as cooking appliances, phones, computers, lights, radios, etc… Power can be drawn directly from the solar inverter and any leftover electricity can then be fed back into the grid.

 If you need to use more electricity than what is produced by your grid connected solar system, that power will simply be taken from the main distribution grid. On the other hand, if you produce more energy than what you use, then you are credited for the surplus on your electricity bill. Some electricity retailers offer net billing, meaning your supplier buys the excess power you produce for the same retail price they charge you.

Grid connect systems differ from stand alone solar power systems as they eliminate the need for a battery back-up. At night or during cloudy weather you can draw electricity directly from the grid. To install a grid connect solar PV system, you need sufficient space on your north-facing roof.

… more information about grid connected solar power systems.

Stand alone/ off grid solar energy systems

A stand alone solar system means that you are not connected to the public grid. When you are “off grid” it means that you must create your own electricity to run your home.  In this case, solar panels or wind turbines are used to charge batteries which store energy.

 Often batteries are connected to an inverter which supplies 240V AC power to run most appliances in a standard house. An inverter is not required for stand alone systems that run DC appliances.

… more information about off grid solar power systems.

Solar water pumping

Solar PV pumping systems are used for irrigation and drinking water in places where there is no mains power available. Solar PV water pumps make an ideal replacement for diesel and petrol powered pumps as they deliver the most water when it is needed, i.e. when the sun is shining. They also emit no greenhouse gas and last a very long time. Essentially, any DC pump could be converted to a solar pump with the correct controller.

… more information about solar pumping.

Solar thermal / solar hot water

Solar thermal applications are the most widely used category of solar energy technology. These technologies use heat from the sun for water and space heating, ventilation, and many other applications.

Heating water represents the biggest single source of greenhouse gas emissions in an average Australian household (if you don’t count the car). The Australian government is encouraging households to switch to sustainable hot water technologies by introducing financial rebates. The rebates aim to reward homes for replacing traditional hot-water heaters with clean energy hot-water like solar and solar thermal hot water storage systems. Home owners can save up to 75% on their water heating bills with a solar hot water system.

Solar hot water technology is entirely different to the technology that you see when you think of the basic solar PV panels on the roof of a house. Solar hot water systems are usually composed of a solar collector and a tank.

There are two types of collectors:

• evacuated tubes, and
• flat plate collectors

As heat rises, the hot water delivered to the tank from the solar collectors is drawn from the top for use in the house

Boolean Algebra Theorems and Laws of Boolean Algebra

Boolean algebra is a different kind of algebra or rather can be said a new kind of algebra which was invented by world famous mathematician George Boole in the year of 1854. He published it in his book “An Investigation of the Laws of Thought”. Later using this technique Claude Shannon introduced a new type of algebra which is termed as Switching Algebra. In digital electronics there are several methods of simplifying the design of logic circuits. This algebra is one of these methods. According to George Boole symbols can be used to represent the structure of logical thoughts. This type of algebra deals with the rules or laws, which are known as laws of Boolean algebra by which the logical operations are carried out.

There are also few theorems of Boolean algebra, that are needed to be noticed carefully because these make calculation fastest and easier. Boolean logic deals with only two variables, 1 and 0 by which all the mathematical operations are to be performed.
Boolean algebra or switching algebra is a system of mathematical logic to perform different mathematical operations in binary system. There only three basis binary operations, AND, OR and NOT by which all simple as well as complex binary mathematical operations are to be done. There are many rules in Boolean algebra by which those mathematical operations are done. In Boolean algebra, the variables are represented by English Capital Letter like A, B, C etc and the value of each variable can be either 1 or 0, nothing else. In Boolean algebra an expression given can also be converted into a logic diagram using different logic gates like AND gate, OR gate and NOT gate, NOR gates, NAND gates, XOR gates, XNOR gates etc.

Some basic logical Boolean operations, AND OperationOR OperationNot OperationSome basic laws for Boolean AlgebraA . 0 = 0 where A can be either 0 or 1.
A . 1 = A where A can be either 0 or 1.
A . A = A where A can be either 0 or 1.
A . Ā = 0 where A can be either 0 or 1.
A + 0 = A where A can be either 0 or 1.
A + 1 = 1 where A can be either 0 or 1.
A + Ā = 1
A + A = A
A + B = B + A where A and B can be either 0 or 1.
A . B = B . A where A and B can be either 0 or 1.
The laws of Boolean algebra are also true for more than two variables like,

Cumulative Law for Boolean Algebra

According to Cumulative Law, the order of OR operations and AND operations conducted on the variables makes no differences.

Associative Laws for Boolean Algebra

This law is for several variables, where the OR operation of the variables result is same though the grouping of the variables. This law is quite same in case of AND operators.

Distributive Laws for Boolean Algebra

This law is composed of two operators, AND and OR.Let us show one use of this law to prove the expressionProof:

Redundant Literal Rule

From truth table,

Inputs			Output
A	B	ĀB	A + ĀB
0	0	0	0
0	1	1	1
1	0	0	1
1	1	0	1

Inputs		Output
A	B	A+B
0	0	0
0	1	1
1	0	1
1	1	1

From truth table it is proved that,

Absorption Laws for Boolean Algebra

Proof from truth table,

Inputs			Output
A	B	AB	A+A.B
0	0	0	0
0	1	0	0
1	0	0	1
1	1	1	1

Both A and A+A.B column is same.Proof from truth table,

A	B	A+B	A.X(A+B)
0	0	0	0
0	1	1	0
1	0	1	1
1	1	1	1

Both A and A.X or A(A+B) column are same.De Morgan’s Therem,Proof from truth table,

Examples of Boolean Algebra

These are another method of simplifying complex Boolean expression. In this method we only use three simple steps.

1. Complement entire Boolean expression.
2. Change all ORs to ANDs and all ANDs to ORs.
3. Now, complement each of the variable and get final expression.

By this method, will be first complemented, i.e..Now, change all (+) to (.) and (.) to (+) i.e.Now, complement each of the variable,This is the final simplified form of Boolean expression,And it is exactly equal to the results which have been come by applying De Morgan Theorem.
Another example,By Second Method,Representation of Boolean function in truth table.
Let us consider a Boolean function,Now let us represent the function in truth table.Thus we have shown some basic laws of Boolean algebra. In the other page we have described De Morgan’s theorems and related laws on it.

Digital Electronics

We know there are two types of signals, one is analog or continuous signal and the second one is Digital or discrete signal. So the science or field of research in the area of engineering is termed as Analog and Digital Electronics respectively. Now coming to the area of Digital Electronics, it is essential to understand wide range of applications from industrial electronics to the fields of communication, from micro embedded systems to military equipment. The main and perhaps the most revolutionary advantage of digital electronics is the decrease in size and the improvement in technology.
We have chosen to discuss various topics of Digital Electronics from the very fundamentals of this subject such as Number systems, logic circuits going deep into those topics, like discussing various types of number systems, which we should use and how, inter relation among those number systems to the somewhat tougher concepts of Digital Electronics like TTL, PMOS-NMOS logic, Flip Flops etc. to get an idea about the whole subject.
All the topics of the related articles have been amply presented by diagrams, designs, tables and examples to make every topic understandable as much as possible. The topics are written in such a manner that if one go through them he will grasp the very basic idea at first attempt and further reading will enhance the technical knowledge.
Now let us inform you what we have included in the topics of Digital Electronics, as we have already discussed we have started from the very basic topics of Digital Electronics like Number system. Then we have discussed the extension of number system like various types of number system, interrelation among different types of number systems making oneself absolutely comfortable with the fundamentals of Number system. Then we have enlightened the very important field of Digital Electronics i.e. Binary Arithmetic and Boolean algebra. And we have discussed about them in elaborated manner. From binary addition, binary subtraction, binary multiplication and binary division to the basics of Boolean algebra.
After that we have written topics about various types of codes such as ASCII code, Gray Code, Hamming code which have made the input output format very easy. Then various types of logic gates (AND gate, OR gate, NOT gate, NAND gate, NOR gate, EX-OR gate) have been discussed in an elaborated manner with diagrams, explanations and truth tables to make each one of them very easy to understand.
These may be classified as the fundamentals of Digital Electronics without which the subject cannot be understood at all. So after discussing about them we have gone deep into the subject. Topics like TTL, Logic Families, various MOS gates, Flip Flops (J-K, D, T etc.) have been discussed.
The sole purpose of introducing this subject in our Electrical Engineering website is because now days all the engineering streams are interrelated and the knowledge of Digital Electronics is very much essential for an electrical Engineer and we have tried our best to make oneself familiar with the subject technically as much as possible.

Air Core Transformer

If an alternating current is supplied to a coil, an alternating magnetic field is produced surrounding it. If another coil is brought inside this magnetic field, an alternating emf is induced across the second coil also as per Faraday's law of electromagnetic induction. This induced emf in the second coil can be utilized to feed a load. As in this example the flux is linked with both coils through air, so this arrangement can be referred as air core transformer. Here, first coil serves as primary winding and second coil serves as secondary winding of the said transformer. Whenever there is a need of changing voltage level from one level to another in power network we use an electrical transformer.Whenever there is a need of electrical isolation from one circuit to other, we use transformer.For transforming current and voltage to low measurable level we use current transformer and potential transformer respectively. These are not only the applications of transformers.

Electrical transformers are also used for many different purposes. In different electronics applications smaller sized transformers are used. Examples of these transformers are air core transformer, audio frequency transformer etc. These are referred as special purpose transformers and simply called special transformer. Construction wise they are different from general power transformer but basic working principle is same as all other transformers. That means in this case, the working principle of transformer is also based on mutual inductionbetween two magnetically linked windings. Here we will discuss about air core transformers.In an transformer primary winding and secondary windings are coupled with a low reluctance ferromagnetic core. The core is used in an electrical transforme for confining magnetic fluxand facilitating maximum flux linkage between primary and secondary winding. Laminated steel sheets are used to construct the core of transformer. But, ferromagnetic materials like steel as core of transformer, suffers from hysteresis loss, eddy current losses. Also it faces problem of getting saturated after certain level of magnetization. But these can be avoided in air core transformer as ferromagnetic core is absent in this transformer.

In very high frequency applications, distortion in electromagnetic field should be avoided otherwise there may be a significant affect in output signal. So for maintaining quality of signal it is desired to avoid any noise or distortion in the signal. As ferromagnetic material causes noise or distortion in the signal, it should be avoided in high frequency application like signal transmission. Thus air core transformer is introduced, in the application of high frequency radio transmission. Here iron core of transformer is absent and the flux is linked with the windings through air. In addition to the noise-free operation, an air core transformer is quite light weight due to absence of heavy weight iron core. That is why this type of transformer is most suitable for portable, light weight electronic devices and high frequency devices. Air core transformers are are generally used in radio transmitter and communication devices etc.

Construction of Air Core Transformer

The coils of insulated copper wire, are wound on a plastic tube or cardboard etc. There are mainly two forms of air core transformer. One is cylindrical form and other is toroidal form. In cylindrical form of air transformer, insulated copper wires are wound on a non metallic cylindrical structure. This non metallic hollow structure gives the winding necessary mechanical support. The copper winding wounded around the non metallic cylinder is tapped at different points as necessary. The secondary supply is taken across these taps. Sometimes capacitor is connected to the winding to maintain the constant resonance of the tuning circuit. The flux flows through the air surrounding the winding and air inside hollow cylinder. For proper impedance matching, sometime a guard winding is wound surrounding the main copper winding. This guard winding is further connected with antenna receivers or grounded properly.

On the other hand in toroidal form of air core transformer, insulated copper wires are wound around a ring of hard plastic or other non metallic substance. Actually, the wire is wound in circular way around the periphery of the ring. This type of transformers are only used in very high frequency applications. In this case the winding is not tapped, here two separate windings are used for primary and secondary purpose. Therefore, the effect of stray coupling is minimized in toroidal air core transformer. The primary is to secondary ratio of windings varies and it depends upon the frequency range and the type of operation.

Dry Type Transformer

What is Dry Type Transformer?

Dry type transformer never uses any insulating liquid where its winding with core be immerged. Rather windings with core are kept within a sealed tank that is pressurized with air.

Type of Dry Type Transformer

The dry type transformer is of two types. They are

1. Cast Resin Dry Type Transformer ( CRT)
2. Vacuum pressure Impregnated Transformer ( VPI)

Cast Resin Dry Type Transformer ( CRT)

Cast resin dry type transformer (CRT) is used in the high moisture prone areas. It is because of its primary and secondary windings are encapsulated with epoxy resin. This encapsulation helps to prevent moisture to penetrate to affect the winding material. Complete protection is achieved by this cast resin encapsulation so that the transformer can work without disruption in highly moisture prone area. Thus this transformer is non hygroscopic.

This type of transformer is available in ratings of 25 KVA to 12,500 KVA. with insulation class of F (90^oC Temp. Rise).
This type of transformer has some featured advantages. They are-

1. Better over load capacity.
2. Low partial discharge along with low loss. Hence efficiency is very good.
3. As it is with non inflammable winding insulation, it offers zero risk to fire hazard. So it is suitable for indoor installation.
4. Can be fitted outdoor in IP 45 enclosure.
5. And off course non hygroscopic.

Vacuum Pressure Impregnated Transformer (VPI)

This type of transformer is made with minimum flammable material as insulation of windings. The windings of this transformer are made in foil or strip in a continuous layer. But for higher voltages, the winding is made of disks that are connected in series or parallel as per power rating with respect to voltage level.
The insulation of the winding is void free impregnation that is made with class H polyester resin. The primary and secondary winding with core are laced safely within a vacuum protective box. Moisture Ingress Protection is high and it never gets affected by moisture.
This type of transformer is available from 5KVA to 30MVA with insulation grade F(155^oC) and H(180^oC). It’s with Protection up to IP56.
This type of transformer has several advantages. They are-

1. High mechanical strength.
2. Void free insulation.
3. No temperature fluctuation.
4. Easy maintenance.
5. Less prone to fire hazard.

Advantages of Dry Type Transformer

The main advantages of dry type transformer are given below.

• Safety for people and property.
• Maintenance and pollution-free solution.
• Easy installation.
• Side clearance is less.
• Environmentally friendly.
• Excellent capacity to support overloads.
• Reduced cost on civil installation works and fire protection systems.
• Excellent performance in case of seismic events.
• No fire hazard.
• Excellent resistance to short circuit currents.
• Long lasting due to low thermal and dielectric heating.
• Suited for damp and contaminated areas.

Disadvantages of Dry Type Transformer

But there are some disadvantages of dry type transformer. They are-

• Dry type transformer is long lasting and with less chance of winding failure. But once it fails whole set up is to changed, i.e. complete change of high voltage and low voltage winding with limb.
• For same power and voltage rating, dry type transformer is costlier than oil cooled transformer.

Application of Dry Type Transformer

Dry type transformer are widely used in-

• Chemical, oil and gas industry
• Environmentally sensitive areas (e.g. water protection areas)
• Fire-risk areas (e.g. forests)
• Inner-city substations
• Indoor and underground substations
• Renewable generation (e.g. off-shore wind turbines)

Important Factors to Design a Dry Type Transformer

The important design parameters for a dry type transformer are given below.
Choice of Insulation Type
Generally F and H class of insulation of insulation is used to insulate the primary and secondary winding. It is because these classes have high temperature withstand property, i.e. 155^oC for F and 180^oC for H class of insulation. Generally varnish and polyester resin are used as insulation of the winding. Apart from the temperature withstand capability, mechanical strength; dielectric strength and resistance to thermal shock are the basic capabilities that have to be fulfilled by the insulation selected for the windings.
Selection of Winding Material
Generally copper and aluminum are used to make the winding or coil. Though copper is better conductor, aluminum conductor wound transformer possesses low cost and weight. For the same current rating, copper conductor with less cross section is used as the winding material in the transformer. Copper coil provides more mechanical strength than aluminum coil.
Selection of Core Material with Low Hysteresis Loss
Core material selection is very important in transformer design. Core material must possess high permeability and less hysteresis loss. But both cannot be achieved in any core material. Generally silicon steel, CRGO etc are used to allow minimum hysteresis loss with higher permeability.
Regulation
When transformer secondary voltage drops abruptly due to increase in load, this regulation is called poor regulation. Poor regulation is due to transformer higher internal leakage reactance. So, leakage reactance is kept within 2% during design.
Life Expectancy
Life of the transformer depends on the breakdown of winding insulation due to temperature rising effect in winding due to overloading. Normally class B, F and H insulation is preferred for dry type transformer to withstand higher temperature gradient including ambient temperature. So design of the transformer must be done with respect to the rise of the temperature of operating full load condition.
Losses
No load losses mean core loss and eddy current that is independent of loading condition. But in loading condition copper loss occurs that includes the iron loss to increase the value of voltage regulation, i.e. poor voltage regulation. Leakage reactance and winding resistance must be within moderate value to minimize this loss and better voltage regulation, thus higher efficiency.
Overloading
Over loading condition is harmful for transformer for long time span. Overloading is the cause of overheating when transformer has to fulfill its connected load demand. Hence huge amount of current makes copper loss in the winding, and that causes transformer damage. To cool the winding, fan-cooling system is provided in dry type transformer.
K-factor
It is the ability of withstanding of heat generated by non sinusoidal current in the transformer winding. Pure sine wave is not obtained in voltage and current wave form. It is due to today’s various electronic devices uses. Several harmonics are present in the voltage and current wave form. Robust design of a transformer off course bothers k-factor to provide transformer long lasting life.
Insulation Level
In transformer design, insulation level adjustment is an important factor. Generally insulation level is chosen as per basic impulse level and system over voltage. Strong insulation level increases the life of a transformer.