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The difference between

The SolarEdge distributed power harvesting system

AndConventional Systems

The typical specifications of a solar panel

Output Current (A)

Output Voltage (V)

Isc

Voc

Vmpp

Impp

Maximum power point

Isc – the output current of the panel when

output terminals are short circuited

Voc – The voltage at the output terminals

without any load connected to the panel

Maximum power point is the point which

gives the maximum value for the V x I

To harvest power from the solar panel

requires to monitor where this point is.

This process is called Maximum Power

Point Tracking or MPPT

The values of V and I at the maximum

power point is referred to as Vmpp and

Impp respectively.

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Solar irradiation level

Pout = 150W

Pout = 128W

Pout = 96W

Pout = 66W

Pout = 35W

The variation of maximum power point of a solar panel according to

solar irradiation

Maximum power point at

corresponding solar

irradiation level

1000Wm-2 is the sun light

level at noon under clear sky

or bright day light

The panel output voltage is

almost constant, but the

output current significantly

varies with solar irradiation

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The variation of maximum power point between similar brand and

power rated solar panels for the same level of solar irradiation

All the three panels are

manufactured by the same

manufacturer, in the same

production line. But the power

output is not similar and

unmatched.

Also the maximum power

point is not same, and exists a

considerable variation among

each other. That is at the same

voltage, the output current is

different

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The panel layout of a typical solar power generation system

+ - + - + - + -

+ - + - + - + -

String of PV panels

Inverter

DC

AC

230 Vac

Typical string may have up to 20 panels

per string and two or three such strings

are connected in parallel to form the DC

supply to the inverter.

The problems and disadvantages of a typical solar power generation

system

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Averaged String current ( )1.The panel mismatch

When several modules are connected in series,

each one has a slightly different MPP current. The

series connection does not allow the optimal MPP

current to be drawn from each module. The

inverter will select the current which gives the

average peak power point of the string or array.

This peak power is always less than the theoretical

sum of the individual peak power points of every

module.

This is referred to as mismatch loss. In standard

residential and commercial PV installations, it can

be as high as 5% !

Ou

tpu

t C

urr

en

t (A

)

Output Voltage (V)

The problems and disadvantages of a typical solar power generation

system

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2. Partial shadingShading on any part of the array will reduce its output,

but this reduction will vary in magnitude depending on

the electrical configuration of the array. Clearly, the

output of any shaded cell or module will be lowered

according to the reduction of light intensity falling on it.

However, since this shaded cell or panel is electrically

connected to other unshaded cells and modules, their

performance may also be lessened since this is

essentially a mismatch situation.

Partial shading of crystalline solar modules will result in

dramatic reduction of solar module output. One

completely shaded cell can reduce a

solar module’s output by 40% to 95%.

In residential systems, partial shading losses are

estimated to contribute between 5% to 25% annual

power losses

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The problems and disadvantages of a typical solar power generation

system

3. Inefficient MPPT algorithmsThe MPPT algorithms must be able to efficiently track the power point variation as the solar irradiation

changes time to time. If it is not, there will be tremendous amount of loss in the harvestable power.

4. System feedback and trouble shootingA solar installation will cost a considerable amount of money. But the problem is, There is no way to find out

individual panel performance except entire systems performance. This becomes tragic since a malfunctioned

panel can be hidden inside the system, while the clouds being the guilty party!

5. Retrofit and long term fault toleranceFor conventional solar installations, it requires all the solar panels to be in same ratings. That is no way to

connect a different panel. The solar panels comes with a 20 years or more warranty period and the

technology behind the panels keeps developing each day like mobile phones. So after 10 years how can

some one can find a panel that is exactly similar to the ones that was installed 10 years ago! The

conventional systems becomes a dead end in this case.

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The problems and disadvantages of a typical solar power generation

system

6. System safetyWhen solar panels are installing it is very difficult to cover from the sun. There for the series connected solar

panel string is always live. Even a series connected three panels (36V) produce enough power to electrocute

a person if accidently touched.

Also in case of a fire, there is no way to shut down the strings. In such a cases these Dc power lines can be

short circuited and become another fire causing factor.

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ConclusionWe described the structure of PV systems and several drawbacks and disadvantages in the

way these systems are designed and built. Though previous works focused on improving

different aspects of photovoltaic systems, no single holistic approach was presented that

could solve many of the current problems present in PV installations.

Solar Edge Technologies distributed power harvesting system is the only power harvesting

system and architecture that offers a full, robust solution that harvests up to 25% more energy

and resolves the issues described in this paper.

The next sections describe how the SolarEdge distributed power harvesting system handle all

these issues.

Back to some basics….Power = Voltage x Current

That is a 100W can be expressed as,

The idea here is Power Conversion. To do this a special device known as DC-

DC converter has to be used. It does the same thing above. That is we can

input it a 100W (20V x 5A) and take a 100W of power at 50V x 2A. This alsocan be done in the opposite way.

Power (W) Voltage (V) Current(I)

100 10 10

100 20 5

100 25 4

100 50 2

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The SolarEdge System

The SolarEdge System…How this works

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The method of connection

1. Each panel must be connected to a power optimizer

2. These power optimizers are then connected in series to form the strings

3. There must be at least 8 such power optimizers per string

The method of functionality

1. As the sun rises the panels start power production and wakes the power optimizers

2. The power optimizers check how much POWER can be take from the panel they connected

3. Then all the power optimizers send these details to the inverter

4. The inverter process these data and commands all of them to start power production. The output

voltage of the power optimizers will be changed so as to maintain a constant current and also to

response shading conditions. This will be explained in detail in coming sections.

The SolarEdge System VS All known MismatchesAs we said earlier, solar panels are not matched even they are power

rating is similar and from same brand

The problems and losses due to the series connected such panels are werealso discussed in greater detail.

Since in SolarEdge system, the actual string is made of series connectedpower optimizers and the panels are connected to the poweroptimizers.

That is the panels are buffered by the power optimizers from the DC bus.The power optimizer harvest energy from the panel and supply it tothe DC bus.

There for not only mismatched panels, but even different panels can beused for the installation.

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The SolarEdge System VS Shadings

The SolarEdge System VS Mixed panels

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1. The solar panels are connected to the power optimizers

2. There for the panels and the string are independent from eachother.

3. So as the input of the power optimizer any panel can be connected.The power optimizer converts what ever the available power fromthe panels to the required level by the inverter as explained earlier.

4. This is the only system that can be used with mixed panel types.

The SolarEdge System VS Monitoring and Safety

1. This is the only system that comes with a WEB based monitoringfacility as a standard feature.

2. It monitors entire system performance to each panels performancein every 30 minutes and updates the web portal provided by themanufacturer.

3. So isolating a fault is just a few minutes job and locating it in theinstallation is even simpler and can be done even from the office.There for only the required panel can be removed without shuttingdown the system.

4. Also until inverter commands the power optimizers does notoutput power and it will output only 1V. This very much helpfulsince the number of panels installed is equal to the output voltage.For example 15 series connected panels means 15V. Any looselyconnected panel or polarity changed panel can be identified easily.

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The SolarEdge System VS Power Point Tracking

1. A conventional system can have maximum of 2 maximum powerpoint tracking's. This too is not the optimum and it is a averagedone as explained earlier.

2. But in solaredge system. The power point tracking is implementedin each power optimizer. There for every panel has a dedicatedmaximum power point tracking implemented for its own.

3. The end result is solaredge system has minimum of 8 maximumpower point tracking and increases with addition of every poweroptimizer to the system.

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