What is Net Metering and How Does Net Metering Work?

Net metering is a special metering and billing arrangement between you and your utility company. It is a simplified method that measures the difference between the electricity you buy from your local utility company that you have consumed and the excess you produce using you own renewable energy generator, such as a wind generating mill or turbine. With net metering, you use the electricity you generate first, reducing what you would normally buy. If you generate more than you use, the excess goes through your electric meter and into the grid. You will be required to sign a net metering agreement. Check with your power company for their requirements.

How does Net Energy Metering work?

If through the use of your wind or solar energy generating system you at any time of the day produce more electricity than your home or business needs, this is excess and it will automatically go through the electric meter into the utility grid to be supplied to other customers. Net metering then allows this electricity to run "backward" through your electric meter and out into the electric grid. When this happens, the meter runs backwards. Generating excess electricity puts it back into the electric grid.

This then is the reason it is classified as a renewable energy solution: generating electricity using free natural energy sources. In the United States of America, under an existing federal law (PURPA, Section 210), power customers can use the electricity they generate with their wind turbines, offsetting electricity use they would otherwise have to purchase from the utility company at the retail price. When you produce any excess electricity, beyond what is needed to meet your own needs, the utility purchases that excess at the wholesale price, which will be lower than the retail price. Net metering simplifies this arrangement and you then are billed only for the net energy if consumed during the billing period. Your first step: contact your local utility company and get the details about the technical requirements, the approval process, and how to obtain your net-metering agreement. Do your part to go green and save money in the process.

For more information on Net Metering and Renewable Energy using wind power, visit us by clicking here!

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Network Analysis for Electric Circuits

Network Analysis for electric circuits are the different useful techniques related to several currents, emfs, and resistance voltages in such circuit. This is somewhat the collection of techniques of finding the voltages and currents in every component of the network. Some of those techniques are already mentioned in this online tutorial of Electrical Engineering.

• Kirchhoff''s Voltage Law or KVL
• Kirchhoff''s Current Law or KCL

There are six remaining useful techniques that we are going to learn. The practical example of each analysis will be given in my next post. This is for you to comprehend first what each theory is all about. So, let's begin the first useful technique in analyzing network. 

Thevenin's Theorem

Consider the figure below which schematically represents the two-terminal network of constant emf's and resistances; a high-resistance voltmeter, connected to the accessible terminals, will indicate the so called open circuit voltage v_oc. If an extremely low-resistance ammeter is next connected to the same terminals, as in fig.(b), which is so called the short-circuit current i_sc will be measured.


Test circuits for Thevenin's Theorem

Now the two quantities determined above may be used to represent an equivalent simple network consisting of the single resistance R_TH, which is equal to v_oc/i_sc. If the resistor R_L is connected to the two terminals, the load current of the circuit will be

I_L = v_oc / R_TH+R_L---------------> equation no.1

The analysis leading to the equation no.1 above was first proposed by M.L. Thevenin the latter part of the nineteenth century, and has been recognized as an important principle in electric circuit theory. His theory was stated as follows: In any two-terminal network of fixed resistances and constant sources of emf, the current in the load resistor connected to the output terminals is equal to the current that would exist in the same resistor if it were connected in series with (a) a simple emf whose voltage is measured at the open-circuited network terminals and (b) a simple resistance whose magnitude is that of the network looking back from the two terminals into the network with all sources of emf replaced by their internal resistances.

Thevenin's Theorem has been applied to many network solutions which considerably simplify the calculations as well as reduce the number of computations.

Norton's Theorem

From the previous topic above, it was learned that a somewhat modified approach of Thevenin was formulated. This modified approach is to convert the original network into a simple circuit in which a parallel combination of constant-current source and looking-back resistance "feeds" the load resistor. Take a look on the figure below



Norton's equivalent circuit

Take note that Norton's theory also make use of the resistance looking back into the network from the load resistance terminals, with all potential sources replaced by the zero-resistance conductors. It also employs a fictitious source which delivers a constant current, which is equal to the current that would pass into a short circuit connected across the output terminals of the original circuit. 

From the fig (b) above of Norton's equivalent circuit, the load current would be

I_L = I_N R_N / R_N+R_L ---------------> equation no.2

Superposition Theorem

The theorem states like this: In the network of resistors that is energized by two or more sources of emf, (a) the current in any resistor or (b) the voltage across any resistor is equal to: (a) the algebraic sum of the separate currents in the resistor or (b) the voltages across the resistor, assuming that each source of emf, acting independently of the others, is applied separately in turn while the others are replaced by their respective internal values of resistance.

This theorem is illustrated in the given circuit below:

Illustration of Superposition Theorem

The original circuit above ( left part ) have one emf source and a current source. If you like to obtain the current I which is equal to the sum of I' + I"using the superposition theorem, we need to do the following steps:

a. Replace the current source I_o by an open circuit. Therefore, an emf source v_o will act independently having a current I' as the first value obtained when the circuit computed.

b. Replace emf source v_o by a short circuit. This time I_o will act independently and I" now will be obtained when the circuit computed.

c. The two values obtained ( I' and I") with emf and current source acting independently will be added to get I = I' + I"

Maxwell's Loop (Mesh) Analysis

The method involves the set of independent loop currents assigned to as many meshes as exists in the circuit, and these currents are employed in connection with appropriate resistances when Kirchhoff voltage law equations are written. Take a look on the given circuit below.

Given circuit can be analyze using mesh method

The given circuit above have two voltage sources V1 and V2 are connected with a five-resistor network in which there are two loop currents i1 and i2. Observe that they are shown directed clockwise, a convention that is generally adopted for convenience. The following Kirchhoff's voltage-law may now be written as:

  -V1 + i1R1 + R3(i1-i2) + i1R2 = 0     (loop 1)
  -V2 + i2R5 +R3(i2-i1) + i2R4 = 0     (loop 2)

You may simplify the equations by using the simple algebra. This will be well explained on my next post for more practical examples of Network Analysis.

Nodal Analysis

For this analysis, every junction in the network that represents a connection of three or more branches is regarded as a node. Considering one of the nodes as a reference or zero-potential point, current equations are then written for the remaining junctions, thus a solution is possible with n-1 equations, where n is the number of nodes.

There are three basics steps to follow when using nodal analysis

a. Label the node voltages with respect to ground.
b. Apply KCL to each of the nodes in terms of the node voltages.
c. Determine the unknown node voltages by solving simultaneous equations from step b.

Take a look on the snapshot on how nodal analysis is being done. This is illustration by Stephen Mendez.  Don't worry I will give you the technique on my next post on how to solve nodal analysis.

Note: In the snapshot below, he used conductance which is G = 1/R.



The Nodal Analysis Snapshot

Millman's Theorem

Any combination of parallel-connected voltage sources can be represented as a single equivalent source using Thevenin's and Norton theorems appropriately. This can be illustrated as :

This is Millman's Theorem

The formula above can be written as:

V_L = V₁/R₁ + V₂/R₂ + .....Vn / Rn 
       -------------------------------
        1/R₁ + 1/R₂ + ......1/Rn +  1/R_L

where:

V1, V2, V3... Vn  are the voltages of the individual voltage sources.
R1, R2, R3... Rn  are the internal resistances of the individual voltage sources.

Vout or V_L= load voltage
RL    = load resistor

I think this is enough for today. Don't forget to read my next post for more  practical examples regarding Network Analysis/Theorems.

Cheers!

On 00:58 by Admin

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Simple Example of Network Analysis

Last time, I have already imparted to you about the theoretical aspects of Network Analysis here in my simple Electrical Engineering educational site. Today, I will just give you some simple example for you to appreciate the last topic I had posted over a year ago. :)

Take a look at the simple electric circuits below. If you have a voltage divider with an external resistance, you could do this by using Ohm' Law and calculating the parallel resistance of R2 and R(Load) and then the voltage divider itself. The simpler method that you can use is the Thevenin's theorem which enables you to calculate quickly the effect of any load.

Simple Circuit using Thevenin's Theorem

Considering you have R(Load) equivalent to 40 ohms is in open circuit condition. We can now calculate the equivalent Thevenin resistance.

Therefore,
R (Thevenin) = R1R2 / R1+R2 = 20X40/ 20+40 = 13.33 ohms.

Also, you can calculate the voltage across R2 at no load using the voltage division method:
E(Thevenin) = Ein R2 / R1+R2 = 20x40 /20+40 = 13.33 Volts

When the resistance load or R(Load) of 40 ohms  is added as shown above, by using Ohms Law for simple series circuits you can now obtain the ouput voltage:

E(Load) = E(Thevenin) x R (Load) / R(Thevenin) + R(Load) = 13.33 x 40/ 13.33+40 = 10 volts - Ans.

Using other method like Norton's Theorem is also a good method to used in this given problem. Now, instead of open circuit condition, let's make it short circuit condition at the load side R(Load).

Simple Circuit Using Norton's Theorem

In this condition, we can calculate the current when R2 is shorted. Let's called it I (Norton):
I (Norton) = Ein / R1 = 20V / 20 Ohms = 1 Ampere

Therefore, the equivalent circuit will comes out like this:

Norton's Equivalent Circuit

From Thevenin's equivalent circuit above for R1 and R2, the parallel combination was computed as 13.33 ohms. We know that the voltage across R(Norton) and R(Load) are the same when R(Load) is connected but the total current is still 1 Ampere.

Let's make an analysis now:

We can get load voltage E (out) in two ways:
1---> E(out) = I1 x R(Norton) = I1 x 13.33
2---> E(out) = I2 x R(Load) = I2 x 40

Then, we can equate the two equations above:
3--->I1 x 13.33=I2 x 40

Using Kirchoff's current law,
I(total) = I1 + I2 = 1 Ampere

We can now solve I1 by substitution method: (Remember, you should used you math technique sometimes to solve particular problems is Electric Circuits)

We can substitute I2 value: I2 = I(total)-I1 or 1- I1 to equation 3.
I1 x 13.33 = (1-I1) 40
I1 = 0.75 Ampere

Since, I(total) is 1 Ampere, therefore I2 = 1-0.75 = 0.25 Ampere
Finally, we can calculate E(out) in either equation 1 or 2 above:

E(out) = I1 x R(Norton) or I2 x R(Load) = 0.25 x 40 = 10 volts - Ans.

The two methods used either Thevenin's or Norton's still have same results obtained. This is the magic of Network Analysis!

On 22:51 by Admin

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Electric Smart Meters - What They Are & How They Save Customers Like You Money

From smart phones that can store your whole life, to smart cars that can map your ride across country, there has been practically no part of our lives that haven't been affected by technology. So it should come as no surprise that your electric company has a "smart" device of its own - the smart meter.

One state that uses them is Texas. It's a leader in the deregulated electricity market, championing changes like this new technology that offer savings to so many customers.

Here, we'll discuss exactly what smarter meters are they are and how they can help you save on energy costs.

Out with the Old, In with the New... Smart Meter That Is

In the past, every private and commercial residence was required to have an electric meter installed on its premises. This was necessary so that energy companies could calculate monthly electric use and properly bill for it. The way they did it was by sending meter readers to the property.

Many of us have looked out the window and been startled by "a strange man" walking onto our property. On closer inspection, we see that it's the meter man from the electric company, so we go back to minding our own business.

Now, you don't ever have to be startled again because with smart meters, energy companies don't have a need for meter readers. The reason is, these meters calculate your energy usage - much the same way that older meters did - but with a twist. They transport the data back to the energy company electronically.

3 Ways Smart Meters Save Consumers Money

Meter Readers: This the first way customers save money with these meters. There is no need for them anymore, as well as the vehicles they drive and the licensing, insurance, maintenance, etc., that came along with them.

States like Texas with deregulated energy markets pass these savings on to consumers.

Record of Use: Another way smart meters save consumers money has to do with how they record energy use. Using these meters, your energy usage is recorded every 15 minute. This is practically real time. Not only that, the smart meter even analyzes a history of your electricity use.

With raw data like this at your disposal, you can better manage your energy consumption month in and month out.

Comparative Shopping: The final way smart meters save customers money is that it gives them real numbers to deal with. That way, they can do some comparison shopping to find out who really has the best electric rates.

The idiomatic expression, "Knowledge is power" has never been more true than in states where consumers can choose their energy provider, eg, the Texas electricity market. Smart meters give consumers the information they need to make "smart" choices to lower their monthly energy bill.

About the Author: The author is a writer for Electricity Bid and has expertise in energy and electricity service-related topics. He writes about electricity service in Texas, California, Maryland, Connecticut and Pennsylvania. You may visit the main Electricity Bid website at ElectricityBid.com. Learn more about Texas electric smart meters and other ways to save on your monthly energy bill.

Article Source: http://EzineArticles.com/?expert=Samuel_Jenkinson

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Introduction to Alternating Current

Last time, we studied the first part of Learn Electrical Engineering for Beginners and this is all about DC Circuits. Today, we will be dealing with our Part 2 of our module and this is all about Alternating Current Circuits.

So, you may now start to learn what this ac is and how it behaves. Alternating Current does not flow through a conductor in the same direction as what dc does. Instead, it flows back and forth in the conductor at the regular interval, continually reversing its direction of flow and can do so very quickly. It is measured in amperes, just as dc is measured too. Remember, one couloumb of electrons is passing a given point in a conductor in one second. This definition also applies when ac is flowing- only now some of the electrons during that 1 second flow past the given point going in one direction, and the rest flow past it going in the opposite directions.

Difference between DC and AC

The industrial applications of alternating current are widespread. These include the many types of induction motor, ranging in size employed in wind tunnels and reclamation projects, transformer equipment used in connection with welders and many kinds of control devices, communication systems, and many others.

The advantages of ac generation are, however, apparent when it is recognized that it can be accomplished economically in large power plants where fuel and water are abundant. But nowadays, solar power is becoming popular as power plants through solar panels. Moreover, generators and associated equipment may be large, an important matter in so far as cost per kilowatt is concerned; also transmission over networks of high-voltage lines to distant load centers is entirely practicable.

Transmission Lines to distant load centers

In Part 2 of Learn Electrical Engineering for Beginners, you will study the nature, behavior and uses of time-varying or alternating current. You will study the for the first time two components - the inductor and the capacitor which are frequently used to control direct as well as alternating current and voltage. The resistors, in which we all know acted in such a way as to restrict the flow of current directly. In other words, the bigger the resistor you put in, the more you restrict the current flow. The inductor and the capacitor, on the other hand, act to control the current and voltage in different ways, and you will see that they do depends on how often the current is reversed. These three components - the resistor, inductor and the capacitor are basic elements of electric and electronic circuits.

Resistor, Capacitor and Inductor Behavior in AC Circuits

As of now, you will not understand the meaning of the behavior of the given diagram shown above. But as we started the first topic of AC Circuits on my next post, you will appreciate and understand gradually what really mean by AC Circuits.

On 20:17 by Admin

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Generation of Alternating EMF's

A voltage can be developed in a coil of wire in one of the three ways:

1. By changing the flux through the coil.
2. By moving the coil through the magnetic field.
3. By altering the direction of the flux with respect to the coil.

The first one is that voltage is said to be induced emf and in accordance with Faraday's law, its magnitude at any instant of time is given by the formula as shown below:

e = N(dΦ/dt) x 10 ^-8 volts

where N is the number turns in a coil
dΦ/dt = rate at which the flux in maxwells changes through the coil

Please take note that in this method of developing an emf, there is no physical motion of coil or magnet; the current through the exciting coil that is responsible for the magnetism is altered to change the flux through the coil in which the voltage is induced. For the second and third method mentioned above, there is actual physical motion of coil or magnet, and in altered positions of coil or magnet flux through the coil changes. A voltage developed on these ways is called a generated emf and is given by the equation:

e = Blv x 10^-8 volts

where B is the flux density in lines per square inch
l is the length of the wire, in., that is moved relative to the flux
v is the velocity of the wire, in.per sec., with respect to the flux

Two-pole single AC Generator

The figure above illustrates an elementary a-c generator. The single turn coil may be moved through the magnetic field created by two magnet poles N and S. As you can see, the ends of the coil are connected to two collectors upon which two stationary brushes rest on it. For the clockwise rotation as shown, the side of the coil on north pole N is moving vertically upward to cut the maximum flux under north pole N, while the other side of the coil on south pole S is moving vertically downward to cut the maximum flux under south pole S. After the coil is rotated one quarter of a revolution to the position as shown below:

Rotated 90 degree

the coil sides have no flux to be cut and no voltage is generated. As the coil proceeds to rotate, the side of the coil on south pole S will cut the maximum flux on north pole N. Then, the side of the coil previously on north pole N will cut the maximum flux on south pole S. With this change in the polarity that are cut by the conductors, reversal in brush potential will occur. There are two important points that would like to emphasize in connection with the rotation of the coil of wire through a fixed magnetic field:

1. The voltage changes from instant to instant.
2. The electrical polarity (+) and minus (-) changes with alternating positions under north and south poles.

In actual, ac generator rotate a set of poles that is placed concentrically within a cylindrical core containing many coils of wires. However, a moving coil inside a pair of stationary poles applies equally well to the rotating poles construction; in both arrangements there is a relative motion of one element with respect to the other.

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Generation of a Sine Wave of Voltage

There are two facts that the voltage developed in a coil of a generator changes; the first one is it changes in magnitude from instant to instant as varying values of flux are cut per second and the other one is it changes in direction as coil side change positions under north and south poles, implies that alternating emf is generated. This means that the voltage is maximum as mentioned in our last topic here when the position of the coil is just like shown in the figure below:

Initial position of the coil

and will diminish to zero as the coil rotates clockwise toward the position as shown below:

As the coil rotates clockwise

Then, as the coil continues to rotate clockwise, the polarities will change. Assuming uniform flux distribution between north and south poles, the generated voltage in a coil located from the vertical will be:

e = Em sin α

Consider the figure below for us to analyze why this relationship mentioned above happened.

Illustrating the generated voltage is proportional to sin alpha 

It was come up to the relationship between instantaneous voltage e and maximum voltage Em is that a coil side such as a, moving tangentially to a circle as indicated, cut lines of force in proportion to its vertical component of the motion. If the vector length ay in the figure above represents a constant rotating velocity, it should be obvious that vector xy is, its vertical component; the vector length ax is the horizontal component and it emphasize that motion in this direction involves no flux- cutting action. Since the velocity ratio xy/ay=sinα is also a measure of the voltage in coil side a with respect to the maximum voltage (when the coil is located horizontally) it follows that sinα is a varying proportionality factor that equates e to Em.

The equation above may be used to determine a succession of generated voltage values in a coil as it rotates through a complete revolution. This is just by computing with its selected angular displacements.

A more convenient way of representing the instantaneous voltage equation mentioned above is to draw a graph to illustrate a smooth variation of voltage with respect to the angular position of the coil, this graph is called a sine wave. The wave repeats itself and it is called a periodic, then each complete succession of values is called a cycle, while each positive or negative half of the cycle is called alternation.

Sinusoidal Voltage Wave

Now, we can say that an alternating voltage as an emf that varies in magnitude and direction periodically. Then, when the emfs are proportional to the trigonometric sine function, it is referred to a sinusoidal alternating voltage. However, there are also some periodic waves which do not follow this shape and they are called non sinusoidal waves. This topic will be covered when we reached more complicated analysis is AC Circuits.

Lets have a practical example of a problem using the equation above just for you to appreciate the presented  formula above:

Problem : The voltage in an ac circuit varies harmonically with time with a maximum of 170V. What is the instantaneous voltage when it has reached 45 degree in its cycle?

Using, e = Em sin α = 170V x sin (45 degree) = 170V x 0.71 = 120 V.

In the common 60 cycle ac circuit, there are 60 complete cycle each second; i.e. the time interval of 1 cycle is 1/60 sec. It should be noted that this corresponds to a reversal in a direction of the current every 1/120 sec. (since the direction reverses twice during each cycle). 

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