Solar Notes

7/27/2019 Solar Notes

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Whew...

Lots of questions.

Lets start with a few basics.

kw per square foot is not a good way to think about it, and therein lies the problem with solar panels.

A typical 6"x6" cell puts about Volt, and about 7 Amps DCPower.

Watts = Volts x Amps

So one gets about 0.5 Volts * 7 Amps = about a maximum of 3.5 Watts from the cell.

If you put 4 of the cells together, you get about 14 watts per square foot, or about 0.014 kw per square

foot (with 1000 watts per kilowatt). This is more or less the maximum power you might expect to get

with noon-time sun during the summer. You will get a lot less with morning or evening sun.

Solar panels are made up of multiple solar cells. If the cells are wired in parallel, one increases the

amps. If the cells are wired in series, one increases the volts.

The Open Circuit Voltage and Short Circuit Amps that the cell puts out are more or less theoretical

maximums. You find that the greater the power draw, the lower the volts that the cell puts out. Thus,

there is a tradeoff between Amps and Volts. Most panels now have a "Peak Power" rating.

A typical 12V Car battery actually is about 12.6V when fully charged. But, it is generally charged at about

14V.

So...

Older solar panels were often rated to put out 12V, but actually had a peak output of about 18-20V.

More modern (consumer grade) panels usually have power ratings of about 30-50V. Usually one uses a

charge controller to isolate the system or batteries, and the charge controller can automatically adjust

to the "Peak Power" output of the panel.

I have some panels that are about 3' wide, 4.5' tall, with an output of about 200W, maximum voltage of

68V, and Maximum Power Point (MPPT) of about 56V.

AC vs DC.

If you are just running lights and such from a solar panel, then it is easy enough to set up a DC system,

and use DC light bulbs. No inverter to turn on and off, and no inverter loss.

However, as most of the appliances in the USA require 110V/220V AC current, one can also attach an

AC/DC inverter to provide the correct voltage. And, of course, people typically choose 60 HZ for USA

and 50 HZ for Europe.


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You can run the system entirely "off grid" meaning that one has to generate 100% of one's own power

needs, and setup one's own batteries for backup power. Or, one can run the system "on grid",

essentially using the power company's system as a super-battery. One sends the surplus power to the

grid, and can take extra power from the grid as needed. No batteries are required, although some

systems use them for backup power.

Traditionally the inverters have been centralized, but some companies such as Enphase have an option

of connecting mini-inverters directly to each panel, in effect converting the DC panels to AC panels.

Here is a good picture of the construction of a solar cell/panel. The top most layers listed are actually

part of the panel, and outside of the cells.

http://www.specmat.com/Overview%20of%20Solar%20Cells.htm

Most cells are silicon cells with a layer of pure silicon covered by a layer of silicon "doped" with Arsenic

or Phosphorous, then with electrodes attached.

There are also variations such as cells sprayed onto ordinary glass, or flexible cells. Boeing & Emcore

make what they term as a "triple junction" cell that absorbs a wider bandwidth of energy, and thus has

higher efficiency ratings than the typical household cells. These high efficiency triple junction cells are

used in space applications where space & weight is a premium, as well as in commercial concentrated

light solar panels.

Heat vs Electricity.

A typical solar panel is only about 10 to 20% efficient at converting sunlight to electricity. An appliance

such as a hot water heater will also have efficiency losses. For hot water, it is much cheaper, and more

efficient to heat the water directly (or with an antifreeze heat exchange medium) than to generate

electricity, then using the electricity to heat the water. Likewise, solar panels can be devised to heat air

directly, again with efficiency gains over electric solar panels and electric heating. However... at least in

Oregon, peak power needs are also during the winter when the sun is most scarce.

What is MPPT?MPPT orMaximum Power Point Trackingis algorithm that included in charge controllersused for extracting maximum available power from PV module under certain conditions. The

voltage at which PV module can produce maximum power is called maximum power point (orpeak power voltage). Maximum power varies with solar radiation, ambient temperature and solarcell temperature.

Typical PV module produces power with maximum power voltage of around 17 V whenmeasured at a cell temperature of 25C, it can drop to around 15 V on a very hot day and it can

also rise to 18 V on a very cold day.
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How MPPT works?The major principle of MPPT is to extract the maximum available power from PV module by

making them operate at the most efficient voltage (maximum power point). That is to say:

MPPT checks output of PV module, compares it to battery voltage then fixes what is the bestpower that PV module can produce to charge the battery and converts it to the best voltage to

get maximum current into battery. It can also supply power to a DC load, which is connected

directly to the battery.

MPPT is most effective under these conditions:

Cold weather, cloudy or hazy days: Normally, PV module works better at cold temperatures and

MPPT is utilized to extract maximum power available from them.

When battery is deeply discharged: MPPT can extract more current and charge the battery if the

state of charge in the battery is lowers.

MPPT solar charge controllerA MPPT solar charge controller is the charge controller

embedded with MPPT algorithm to maximize the amountof current going into the battery from PV module.

MPPT is DC to DC converter which operates by taking DC

input from PV module, changing it to AC and converting it

back to a different DC voltage and current to exactly match

the PV module to the battery.

Examples of DC to DC converter are

Boost converteris power converter which DC input voltage is less than DC output voltage. That

means PV input voltage is less than the battery voltage in system.

Buck converteris power converter which DC input voltage is greater than DC output voltage. That

means PV input voltage is greater than the battery voltage in system.

MPPT algorithm can be applied to both of them depending on system design. Normally, forbattery system voltage is equal or less than 48 V, buck converter is useful. On the other hand,if battery system voltage is greater than 48 V, boost converter should be chosen.

MPPT solar charge controllersare useful for off-grid solar power systems such as stand-alone solar power system, solar home systemand solar water pump system, etc.


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Main features of MPPT solar charge controller

In any applications which PV module is energy source, MPPT solar charge controlleris used to

correct for detecting the variations in the current-voltage characteristics of solar celland shown by

I-V curve.

MPPT solar charge controlleris necessary for any solar power systems need to extract maximum

power from PV module; it forces PV module to operate at voltage close to maximum power point

to draw maximum available power.

MPPT solar charge controllerallows users to use PV module with a higher voltage output than

operating voltage of battery system.

For example,if PV module has to be placed far away from charge controller and battery, its wire

size must be very large to reduce voltage drop. With a MPPT solar charge controller, users can

wire PV module for 24 or 48 V (depending on charge controller and PV modules) and bring power

into 12 or 24 V battery system. This means it reduces the wire size needed while retaining full

output of PV module.

MPPT solar charge controllerreduces complexity of system while output of system is high

efficiency. Additionally, it can be applied to use with more energy sources. Since PV output power

is used to control DC-DC converter directly.

MPPT solar charge controllercan be applied to other renewable energy sources such as small

water turbines, wind-power turbines, etc.

How to choose MPPT solar charge controller for PV module

Table 1 Specifications of PV modules separated by manufacturers

PV Manufactures Model Wp Vpm Ipm Isc Voc

SHARP[View Specifications]

NE-78T1 78 17.1 4.57 5.08 21.4

ND-130T1 130 17.4 7.48 8.09 22

Kaneka[View Specifications]

GPA 64 68 0.94 1.17 92

SANYO[View

Specifications]

HIP-180B2 190 54 3.33 3.15 66.4

Bangkok Solar

[View Specifications]

BS 40 40 44.8 0.9 1.16 62.2

Standard Test Condition: Irradiance = 1000 W/m2, Cell temperature = 25C, Air mass = 1.5
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Maximum Power Point Tracking (MPPT)

Solar charge controller with DC load control

Reverse polarities protection of PV and battery

Battery overcharge and overdischarge protection

Temperature compensation (-3 to -

7mV/Cell/Celsius) Lighting surge protection (TVSS)

3-step charging to provide quick and safe charging

for battery

Automatic cooling fan (outside enclosure)

7 modes timer control (ON/OFF DC load) selectable

Table 2 Specifications of the SOLARCON SPT-series MPPT solar charge controller

click to enlarge

How to choose MPPT solar charge controller for PV module and battery

Steps to consider for choosing MPPT solar charge controller

SPT-XXYY(XXis nominal battery voltage, YYis maximum charge current)

Find out what is nominal battery voltage that charge controller will charge and select XX

Find out what is Wp of PV module and

Select the suitable charge current (CC) = (Wp) / XX

Find out YYby multiply CC by safety factor (NEC requirement) = (CC) x 1.2
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Select SOLARCON SPT-seriesmodel that covers YY

Check that Vpm(system)is in range that SPT-XXYYcan handle (MPPT voltage range)

If PV modules are in series, need to check that Vpm(system)= Vpm(module)x Module in series

If PV modules are in parallel, need to check that Vpm(system)= Vpm(module)

Check that Voc(system)is not more than SPT-XXYYrange (Maximum open circuit voltage)

If PV modules are in series, need to check that Voc(system)= Voc(module)x Module in series

If PV modules are in parallel, need to check that Voc(system)= Voc(module)

xamples of MPPT solar charge controller selection and calculation

How to Design Solar PV System

What is solar PV system?

Solar photovoltaic systemor Solar power systemis one of renewable energy systemwhich

uses PV modules to convert sunlight into electricity. The electricity generated can be either

stored or used directly, fed back into grid line or combined with one or more other electricity

generators or more renewable energy source. Solar PV system is very reliable and cleansource of electricity that can suit a wide range of applications such as residence, industry,

agriculture, livestock, etc.

Major system components

Solar PV system includes different components that should be selected according to your

system type, site location and applications. The major components for solar PV system are

solar charge controller, inverter, battery bank, auxiliary energy sources and loads (appliances). PV moduleconverts sunlight into DC electricity.

Solar charge controllerregulates the voltage and current coming from the PV panels

going tobattery and prevents battery overcharging and prolongs the battery life.

Inverterconverts DC output of PV panels or wind turbine into a clean AC current for

AC

appliances or fed back into grid line. Batterystores energy for supplying to electrical appliances when there is a demand.

Loadis electrical appliances that connected to solar PV system such as lights, radio, TV,

computer,
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refrigerator, etc. Auxiliary energy sources- is diesel generator or other renewable energy sources.

Solar PV system sizing

1. Determine power consumption demands

The first step in designing a solar PV system is to find out the total power and energy consumption

of all loads that need to be supplied by the solar PV system as follows:

1.1 Calculate total Watt-hours per day for each appliance used. Add the Watt-hours needed for all appliances together to get the total Watt-hours per

day which

must be delivered to the appliances.

1.2 Calculate total Watt-hours per day needed from the PV modules.

Multiply the total appliances Watt-hours per day times 1.3 (the energy lost in thesystem) to get

the total Watt-hours per day which must be provided by the panels.

2. Size the PV modules

Different size of PV modules will produce different amount of power. To find out the sizing of PV

module, the total peak watt produced needs. The peak watt (Wp) produced depends on size of the PV

module and climate of site location. We have to consider panel generation factor which is different

in each site location. For Thailand, the panel generation factor is 3.43. To determine the sizing of PV

modules, calculate as follows:

2.1 Calculate the total Watt-peak rating needed for PV modulesDivide the total Watt-hours per day needed from the PV modules (from item 1.2) by

3.43 to getthe total Watt-peak rating needed for the PV panels needed to operate the appliances.

2.2 Calculate the number of PV panels for the systemDivide the answer obtained in item 2.1 by the rated output Watt-peak of the PV

modules available

to you. Increase any fractional part of result to the next highest full number and thatwill be the

number of PV modules required.

Result of the calculation is the minimum number of PV panels. If more PV modules are installed, the

system will perform better and battery life will be improved. If fewer PV modules are used, the

system may not work at all during cloudy periods and battery life will be shortened.

3. Inverter sizing


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An inverter is used in the system where AC power output is needed. The input rating of the inverter

should never be lower than the total watt of appliances. The inverter must have the same nominal

voltage as your battery.

For stand-alone systems, the inverter must be large enough to handle the total amount of Watts

you will be using at one time. The inverter size should be 25-30% bigger than total Watts ofappliances. In case of appliance type is motor or compressor then inverter size should be minimum 3

times the capacity of those appliances and must be added to the inverter capacity to handle surge

current during starting.

For grid tie systems or grid connected systems, the input rating of the inverter should be same as

PV array rating to allow for safe and efficient operation.

4. Battery sizing

The battery type recommended for using in solar PV system is deep cycle battery. Deep cyclebattery is specifically designed for to be discharged to low energy level and rapid recharged or cycle

charged and discharged day after day for years. The battery should be large enough to store sufficient

energy to operate the appliances at night and cloudy days. To find out the size of battery, calculate as

follows:

4.1 Calculate total Watt-hours per day used by appliances.4.2 Divide the total Watt-hours per day used by 0.85 for battery loss.

4.3 Divide the answer obtained in item 4.2 by 0.6 for depth of discharge.4.4 Divide the answer obtained in item 4.3 by the nominal battery voltage.

4.5 Multiply the answer obtained in item 4.4 with days of autonomy (the number of daysthat youneed the system to operate when there is no power produced by PV panels) to get the

required

Ampere-hour capacity of deep-cycle battery.

Battery Capacity (Ah) = Total Watt-hours per day used by appliances x Days of autonomy

(0.85 x 0.6 x nominal battery voltage)

5. Solar charge controller sizing

The solar charge controller is typically rated against Amperage and Voltage capacities. Select the

solar charge controller to match the voltage of PV array and batteries and then identify which type of

solar charge controller is right for your application. Make sure that solar charge controller has enough

capacity to handle the current from PV array.

For theseries charge controllertype, the sizing of controller depends on the total PV input current

which is delivered to the controller and also depends on PV panel configuration (series or parallel
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configuration).

According to standard practice, the sizing of solar charge controller is to take the short circuit

current (Isc) of the PV array, and multiply it by 1.3

Solar charge controller rating = Total short circuit current of PV array x 1.3

Remark: ForMPPT charge controllersizing will be different. (SeeBasics of MPPT ChargeController)

Example: A house has the following electrical appliance usage:

One 18 Watt fluorescent lamp with electronic ballast used 4 hours per day.

One 60 Watt fan used for 2 hours per day.

One 75 Watt refrigerator that runs 24 hours per day with compressor run 12 hours and off 12

hours.

The system will be powered by 12 Vdc, 110 Wp PV module.

1. Determine power consumption demands

Total appliance use = (18 W x 4 hours) + (60 W x 2 hours) + (75 W x 24 x 0.5 hours)

= 1,092 Wh/day

Total PV panels energy needed = 1,092 x 1.3

= 1,419.6 Wh/day.

2. Size the PV panel

2.1 Total Wp of PV panel capacity

needed

= 1,419.6 / 3.4

= 413.9 Wp

2.2 Number of PV panels needed= 413.9 / 110

= 3.76 modules

Actual requirement = 4 modules

So this system should be powered by at least 4 modules of 110 Wp PV module.
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3. Inverter sizingTotal Watt of all appliances = 18 + 60 + 75 = 153 WFor safety, the inverter should be considered 25-30% bigger size.

The inverter size should be about 190 W or greater.

4. Battery sizingTotal appliances use = (18 W x 4 hours) + (60 W x 2 hours) + (75 W x 12 hours)

Nominal battery voltage = 12 VDays of autonomy = 3 days

Battery capacity = [(18 W x 4 hours) + (60 W x 2 hours) + (75 W x 12 hours)] x 3

(0.85 x 0.6 x 12)

Total Ampere-hours required 535.29 Ah

So the battery should be rated 12 V 600 Ah for 3 day autonomy.

5. Solar charge controller sizing

PV module specificationPm = 110 Wp

Vm = 16.7 Vdc

Im = 6.6 A

Voc = 20.7 AIsc = 7.5 A

Solar charge controller rating = (4 strings x 7.5 A) x 1.3 = 39 A

So the solar charge controller should be rated 40 A at 12 V or greater.

Basics of Solar Cell

Solar energy is the ultimate source of energy, which is naturally replenished in a short period

of time, for this reason it is called "renewable energy" or "sustainable energy" source. To takeadvantages of solar energy, the variety of technologies is used to covert solar energy to heat

and electricity. The use of solar energy involves 'energy conservation' because it is the way to

use energy source that comes from the nature and uses it more wisely and efficiently. That

way includes Solar Cell, which is described as follows:

What is Solar Cell?

Solar Cell or Photovoltaic (PV)cell is a device that is made up of

semiconductor materials such as silicon, gallium arsenide and cadmium

telluride, etc. that converts sunlight directly into electricity. When solar cells

absorb sunlight, free electrons and holes are created at positive/negative

unctions. If the positive and negative junctions of solar cellare connected to

DC electrical equipment, current is delivered to operate the electrical

equipment.

Solar cell types


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There are three major cell types that classified by its manufacturing technology and thesemiconductor.

Single Crystalline Silicon

PV Module

Polycrystalline Silicon

PV Module

Amorphous Silicon

PV Module

1.Crystalline Silicon PV Module:Two types of crystalline silicon (c-Si) are used to produce PV

module; single crystalline silicon or known as monocrystalline silicon and multi-crystalline silicon,

also called polycrystalline silicon. The polycrystalline silicon PV module has lower conversion

efficiency than single crystalline silicon PV module but both of them have high conversion

efficiencies that average about 10-12%.

2.Amorphous Silicon PV Module:Amorphous silicon (a-Si) PV module or thin-film silicon PV module

absorbs light more effectively than crystalline silicon PV module, so it can be made thinner. It suits

for any applications that high efficiency is not required and low cost is important. The typical

efficiency of amorphous silicon PV module is around 6%.

3.Hybrid Silicon PV Module:A combination of single crystalline silicon surrounded by thin layers of

amorphous silicon provides excellent sensitivity to lower light levels or indirect light. The Hybrid

silicon PV module has highest level of conversion efficiency about 17%.

Solar cell structure

The most semiconductor material currently use for solar cell production is silicon, which hassome advantages as; it can be easily found in nature, does not pollute, does not harm the

environment and it can be easily melted, handled and formed into monocrystalline silicon

form, etc. The commonly solar cell is configured as a large-area p-n junction made from

silicon.

How solar cell works?


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When sunlight strikes solar cell surface, the cell creates charge carrier as electrons and holes.The internal field produced by junction separates some of positive charges (holes) from

negative charges (electrons). Holes are swept into positive or p-layer and electrons are sweptinto negative or n-layer. When a circuit is made, free electrons have to pass through the load to

recombine with positive holes; current can be produced from the cells under illumination.

The individual solar cells are connected together to make a module (called 'solar module' or

'PV module') to increase current and the modules are connected in an array (called 'solar array'or 'PV array'). Depending on current or voltage requirement, solar arrays are connected in a

variety of ways:

If the solar arrays are connected in parallel, the output current will increase.

If the solar arrays are connected in series, the output voltage will increase.

Solar PV systemSolar cells produce direct current (DC), therefore they are only used for DC equipments. Ifalternating current (AC) is needed for AC equipments or backup energy is needed, solar

photovoltaic systems require other components in addition to solar modules. These

components are specially designed to integrate into solar PV system, that is to say they are

renewable energy products or energy conservation products and one or more of componentsmay be included depending ontype of application.The components of solar photovoltaic

system are
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1.Solar Moduleis the essential component of any solar PV system that converts sunlight directly

into DC electricity.

2.Solar Charge Controllerregulates voltage and current from solar arrays, charges the battery,

prevents battery from overcharging and also performs controlled over discharges.

3.Batterystores current electricity that produces from solar arrays for using when sunlight is not

visible, nighttime or other purposes.

4.Inverteris a critical component of any solar PV system that converts DC power output of solararrays into AC for AC appliances.

5.Lightning protectionprevents electrical equipments from damages caused by lightning or

induction of high voltage surge. It is required for the large size and critical solar PV systems, which

include the efficient grounding.

Solar cell advantagesSolar cell or PV cell produces clean with non-polluting energy source of electricity that is

environmental-friendly. Since it uses no fuel other than sunlight, gives off no waste, no

burning, and no moving part when it operates. It reduces collection of gases such as carbonmonoxide, sulfur dioxide, hydrocarbon and nitrogen, etc., which generated from fuel, coal andfossil fuel burning power plants. All decrease the impacts of energy on the environment like

greenhouse effect, global warming, acid rain and air pollution, etc. It is easy to install and

transportable. With the modular characteristic, it can be constructed any sizes as required.

Moreover, it requires minimal maintenance and has long life span (more than 30 years) andstable efficiency.


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Solar cell applications

Home Indoor and outdoor lighting system, electrical equipment, electric

gate opener, security system, ventilator, water pump, water filter and

emergency light, etc.

Lighting system Bus stop lighting, telephone booth lighting, billboard lighting, parking

lot lighting, indoor and outdoor lighting and street lighting, etc.

Water pumping Consumption, public utility, livestock watering, agriculture, gardening

and farming, mining and irrigation, etc.

Battery charging system Emergency power system, battery charging center for rural village and

power supply for household use and lighting in remote area, etc.

Agriculture Water pumping, agricultural products fumigator, thrashing machines

and water sprayer, etc.

Cattle Water pumping, oxygen filling system for fish-farming and insect

trapped lighting, etc.

Health center Refrigerator and cool box for keeping medicines and vaccines and

medical equipment, etc.

Communication Air navigational aid, air warning light, lighthouse, beacon navigation

aid, illuminated road sign, railway crossing sign, street lighting and

emergency telephone, etc.

Telecommunication Microwave repeater station, telecommunication equipment, portable

communication equipment (e.g. communication radio for service and

military exercise) and weather monitoring station, etc.

Remote area Hill, island, forest and remote area that the utility grids are not

available, etc.

Space Satellite, international space station and spacecraft, etc.


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r

lectricity, the high price of oil and the growing concerns for our environment are some of severalhance the uses of alternative energy sources. Among a variety of renewable energy sources, solar

native option that can be utilized in various ways and can be used for many applications.

collecting sunlight and converting into electricity, heat and lighting. This is done by using solarnto electricity, and using solar thermal collectors to absorb solar energy for heating water.

r

m the sun is free and unlimited.

uting. Solar power usage does not emit any greenhouse gases or harmful waste.nd saving for power generation in remote areas or where the cost of expansion utility grid is high.

It can be used for low-power purpose as well as larger ones - from hand-held calculators, watches,en lights to water heaters, cars, buildings and satellites.uires very little maintenance and last for many years.

gy

tion is daylighting. Daylighting system collects and distributes sunlight to provide effective

ide buildings. Daylighting design implies careful selection of window types, sizes and orientationell. There are also other architectural features such as light shelves and even active sun tracking

with fiber optics or mirrors to provide light to interior of large buildings.


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ogiescan be used for water heating in homes or commercial and space heating or space cooling for

eating systems use different type of collectors to gather and store the solar energyfor heatingl, commercial and industrial applications. For space heating and cooling in warm temperature

s materials is needed to keep building cool by absorbing solar energy during a day and radiate

mosphere at night. However they can be used in cold temperature areas to maintain warmth as well.

Generationectly converted to electricity by photovoltaic cells. Solar photovoltaic (PV) systems provide

usiness for lighting, TV, fan, computer, stereo, refrigerator, water pump or livestock feeders,tility grid. They are also used to power watches, calculators and sign lights.

What is Electricity?

Any appliances that we use in our daily lives

such as household appliances, office

equipments and industrial equipments,

almost all of those things take electricity.

Therefore, we should understand electricity.

The first question that we will find out the

answer is "where does electricity come


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from?"

All matters are made up of atoms. Then ask the next question, "What are atoms?"

Atoms are the smallest part of an element. They are composed of nucleus and electrons, electrons

surround nucleus. Elements are identified by the number of electrons in orbit around nucleus of

atoms and by the number of protons in nucleus.

Nucleus is made up of protons and neutrons, and the number of protons and neutrons are balanced.

Neutrons have no electric charge, protons have positive charges (+) and electrons have negative

charges (-). A positive charge of proton equals a negative charge of electron.

Electrons are bound in their orbit by attraction of protons, but electrons in the outer band can

become free of their orbit by some external forces. These are referred to as free electrons, which

move from one atom to the next, electron flows are produced. These are the basis of electricity.

Materials that allow many electrons to move freely are called conductorsand materials that allow

few free electrons to move are called insulators.

All matters are made up of atoms that have electric charges. Therefore, they have electric charges.

For the matter that has a balanced the number of protons and electrons, positive charge force and

negative charge force are balanced. It is called neutral state of an atom. (The number of protons and

electrons remains equal.)

"Static electricity" represents a situation that all things are made up of electric charges. For example,

the rubbing of material against another can cause the static electricity. Free electrons of one material

move forcefully till they are freed of their orbits around nucleus and move to another. Electrons of

one material decrease, it presents positive charges. At the same time, electrons of another increase,

it has negative charges.


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In general, charge producing of the matter means the matter has electric charges. It has

positive and negative charges, which is expressed in coulomb.

Current, Voltage and Resistance

What is Current?An electrical phenomenon is caused by

flow of free electrons from one atom to

another. The characteristics of current

electricityare opposite to those of static

electricity.

Wires are made up of conductors such as

copper or aluminum. Atoms of metal are

made up of free electrons, which freely

move from one atom to the next. If anelectron is added in wire, a free electron

is attracted to a proton to be neutral.

Forcing electrons out of their orbits cancause a lack of electrons. Electrons,

which continuously move in wire, are

called Electric Current.

For solid conductors, electric current refers to

directional negative-to-positive electrons from one

atom to the next. Liquid conductors and gasconductors, electric current refers to electrons and

protons flow in the opposite direction.

Current is flow of electrons, but current and electron

flow in the opposite direction. Current flows from

positive to negative and electron flows from negative to

positive.


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Current is determined by the number of electrons passing through a cross-section of a conductor in

one second. Current is measured in amperes, which is abbreviated "amps". The symbol for amps is a

letter "A".

A current of one amp means that current pass through a cross-section of two conductors, which are

placed in parallel 1 meter apart with 2x10-7

Newton per meter force occur in each conductor. It canalso mean charges of one coulomb (or 6.24x1018electrons) passing through a cross-section of a

conductor in one second.

What is voltage?Electric current is flow of electrons in a

conductor. The force required to make

current flow through a conductor iscalled voltageand potentialis the other

term of voltage. For example, the first

element has more positive charges, so ithas higher potential. On the other hand,

the second element has charges that are

more negative so it has lower potential.The difference between two points is

called potential difference.

Electromotive forcemeans the force which

makes current continuously flows through a

conductor. This force can be generated from

power generator, battery, flashlight battery

and fuel cell, etc.

Volt, abbreviated "V", is the unit of

measurement used interchangeably for

voltage, potential, and electromotive force.

One volt means a force which makes current

of one amp move through a resistance of

one ohm.

What is resistance?Electrons move through a conductor when electric current flows. All materials impede flow of

electric current to some extent. This characteristic is called resistance. Resistance increaseswith an increase of length or decrease of cross-section of a material.

The unit of measurement for resistance is ohmsand its symbol is the Greek letter omega ().The resistance of one ohm means a conductor allows a current of one amp to flow with a


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voltage of one volt.

All materials are difference in allowing electrons flow. Materials that allow many electrons to

flow freely are called conductorssuch as copper, silver, aluminium, hydrochloric solution,

sulphuric acid and saltwater. In contrast, materials which allow few electrons to flow are

called insulatorssuch as plastic, rubber, glass and dry paper. Another type of materials,semiconductorshave characteristics of both conductors and insulators. They allow electrons

to move while being able to control flow of electrons and examples are carbon, silicon and

germanium, etc.

The resistance of conductor depends on two main factors as the followings:

1. Types of material

2. Temperature of material

How to measure current

The instrument used to measure current is called ampere meteror ammeter.

Steps for current measurement Connect a small light bulb to a dry cell.

Measure current that passes through light bulb by connecting positive

terminal (+) of ammeter to negative terminal (-) of a dry cell (see figure)

Safety instructions for current measurement;

1. Estimate current that required measuring then choose a suitable

ammeter, since each ammeter has different limit of current

measurement.

2. Be sure that the connection to positive terminal (+) and negative

terminal (-) of ammeter are correct.

3. Do not directly connect ammeter terminals to dry cell terminals.

Since it can damage the meter.

How to measure voltageThe instrument used to measure voltage, difference potential or electromotive force is called

voltmeter.

Steps for voltage measurement

Connect a small light bulb to a dry cell. A voltmeter is wired in parallel


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with the light bulb to measure voltage across the light bulb. Connect

positive terminal (+) of voltmeter to positive terminal (+) of a dry cell

and connect negative terminal (-) of voltmeter to negative terminal (-)

of a dry cell (see figure).

Safety instructions for measuring voltage;

1. Estimate voltage that required measuring then choose

a suitable voltmeter, since each voltmeter is designed with

the limit of voltage measurement.

2. Be sure that the connecting of positive terminal (+) and negative

terminal (-) of voltmeter are correct.

How to measure resistance

The instrument used to measure resistance is called test meteror multimeter. The multimeteror test meter is used to make various electrical measurements such as current, voltage andresistance. It combines the functions of ammeter, voltmeter and ohmmeter.

Steps for resistance measurement

Turn the face dial to a position for required measuring,

resistance, then touch both of terminals of multimeter (see

figure 1) and adjust the meter range to 0 . Touch both of

terminals of meter to a resistance and take the reading (see

figure 2).

How Electricity works?

Electric current is the ability to do work. Electric current can be converted to heat, power and

magnetism, to name a few.

Electric current is classified by its functions and three primary types are:

1.Heat and power

2.Electrochemistry

3.Magnetism


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1. Heat and poweris used to make heat and power.

For example, current-carrying nichrom wire that nichrom wire has a high resistance and creates

heat. This is applied to be component of electric ovens, toasters, electric irons and light bulbs, etc.

Experiment is made by measuring heat quantity of water by calorimeter. Increase voltage across

wire by the variac and connect ammeter and voltmeter to measure current and voltage.

Set the variac scale to adjust voltage and current value of nichrom wire and current is passed

through periodically and measure heat quantity from nichrom wire. There are any indications of

voltage and current. If voltage, current and time increase, heat quantity will also increase. They are

expressed by the relation as below.

This is called Joule's law. Heat quantity depends on voltage time current and interval of time.

From Ohm's law, V (Voltage) = I (Current) x R (Resistance) therefore

Heat quantity depends on current squared times resistance and interval of time.

When current is passed through nichrom wire in water, current is converted to heat and

temperature rises. Work is done by heat generated in an electrical circuit, which is calledElectric

power.


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Electric power is measured in Watts-hour (Wh) and heat quantity is measured in calories (Cal).

Work is done by heat generated in an electrical circuit is written in power, which it means that the

rate work is done in a circuit when 1 Amp flows with 1 Volt applied and its unit of measurement is

Watt.

Conclusion

2. Electrochemistry

For example, when current is passed through sodium chloride (NaCl) solution, a chemical reaction

called electrolysis occurs. This is applied to produce electrolysis, galvanizing and battery, etc.

Experiment is made by soaking two platinum

(Pt) plates in molten salt. Connect batteries to

two platinum plates, current is passed through

molten salt and produces chlorine bubblesaround positive plate (+) and hydrogen bubbles

around negative plate (-) since sodium chloride

composes of sodium (Na) and chloride (Cl).

When sodium chloride melts in water, the

elements are separated. Sodium has positive

charges (+), while chlorine has negative charges


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(-) and these charges are called ions. The molten

salt has both positive charges, called anodes,

and negative charges called cathodes. The state

of separated elements is called ionization. If salt

is melted by water, solution is available ions,

called electrolyte solution. And if current is

passed through electrolyte solution, a chemical

reaction known as electrolysis occurs.

3. Magnetism

The example of this electric work is a current-carrying wire, magnetic lines of flux occur. This is

applied to produce electric motors, electric transformers and tape recorders, etc.

Understanding meaning of magnetism:

What is magnetism?

The compound formula of magnet is Fe3O4. All magnets have two

characteristics. First, they attract and hold iron. Secondary, if free to

move like the compass needle, they will assume a north-south position.

Any materials have these characteristics, they are called magnet.

The characteristics of magnet are

Every magnet has two poles, one north pole and one south pole.

Opposite poles attract each other, while like poles repel each other.

Electricity and magnetic field

When magnetic needle is placed near electric wire,

which current is passed through, magnetic needle

turns on the direction of current flow (see figure 1 and

2). Therefore, electric current flow also produces an

associated magnetic force or it is said that electricity is

able to produce magnetic field.


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When magnetic needle is placed in wire coil with one

loop (see figure) and current is passed through wire

coil, magnetic needle turns on the direction as shown

in above figure. And the directions of magnetic lines of

flux are shown by the arrows.

When magnetic needle is placed in wire coil with many

loops as shown in right figure, then current is passed

through coil. The direction of magnetic lines of flux

parallels wire coil. The characteristics of magnetic lines

of flux like the characteristics of magnet, but no

magnetic pole.

When a current-carrying wire coil is placed near iron

bar, the iron bar move slightly (see figure 1). If core is

placed in a wire coil, the iron bar is attracted strongly

(see figure 2). Because core is a soft iron, which

conducts magnetic lines of force, when current is

passed through wire coil around core, the core

becomes magnetized with high power that is called

electromagnets. This function is widely applied for

using in industries.

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Basics of Current

Current is classified into two types:
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Current characteristic ofincandescent lamp,

which power factor = 1

Current characteristic ofa set of PC,

which power factor = 0.52

What are Watt and VA?

Watt is unit of power. Its measures a rate of energy use or production and its symbol is W.

VAor volt-ampere is unit of electrical power consumed by non-linear load. It measuresapparent power.

ExampleA Computeris consumed power as a non-linear load then VA should be the measuring unit

that indicates power consumed by PC.

A UPSis used to supply power to PC once the utility power is failed then a UPS should bedeclared its power in VA as well.

AC power (Watt) measuringTo measure real AC power of electrical appliances, the measuring equipment called "Power

meter" is requested. This equipment will measure voltage and current at the same time andmake calculation to get power in "Watt".The following figures show measuring of a PC with 17" monitor power consumption by

using power meter.

AC apparent power (VA) calculatingWe can measure the power of the same set of a PC with 17" monitor by measuring voltage

(RMS) and current (RMS) after calculation power by multiply working voltage with

consumed current.


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AC apparent power= Voltage (RMS) X Load Current (RMS) = VA

= 229.3 X 1.10 = 252.23 VA

The relation of AC power and AC apparent power

AC power(Watts)

= AC apparent power X Power factor

= (VA) X Power factor

Power factor (pf)of an AC electrical power system is defined as ratio of real power to theapparent power and is a number between 0 and 1.

Power factor of linear load equals one (=1) and power factor of non-linear load is less than one

(


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Maximum Power Point Tracking (MPPT)Enable the solar panel always work at the Maximum Power Point of the V-A curve. Increase

efficiency of solar panel modules by 10% to 30%.

MPPT Principle

The maximum power point is mainly affected by the ambient temperature and the intensity ofsunshine. The intensity of sunshine being constant, the maximum power decreases with the rise

of temperature. The temperature being constant, when the sunshine intensify, the voltage of PV

module keep unchanged but the current increase substantially thus the maximum output powerincrease.

This MPPT solar charge controller can intelligently regulate the working voltage of solar panels,

letting the solar panels always work at Maximum Power Point of V-A curve. Compared with

ordinary solar controller, this MPPT controller can increase the efficiency of PV modules byabout 30%. However, due to many factors, such as the different in solar panel making, the

change of sun illuminance, temperature, etc, the actual available increase rate is 10% - 30%

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