INVERTER

Inverter:

Inverter is an electrical device which converts/inverts DC (Direct current) power to AC (Alternating) power at a desired frequency. It is the arrangement, control of power semiconductor devices making the DC power to flip back and forth, creating AC power. The rate of flipping can be controlled using electronics. The inverter does not produce any power; the power is provided by the DC source. This plays a predominant role in distributed power generation due to renewable sources in particular, as most of the renewable sources like Wind, Solar etc., used for power generation outputs DC power and to utilize the generated power it has to be converted to AC because most of the loads work on AC power. Also in generation side the reason to have AC power is that it can be stepped to very high voltage levels and can be transmitted comfortably over long distances compared to DC transmission which is very complex process & with higher voltages the power losses are very less.

A simple 1-phase inverter circuit

Applications:

• Inverter can be used to run the loads during the outages of utility grid provided a battery is connected to the input of the inverter, here the battery can be stored by any means of power i.e., with the regular supply or from renewable sources (solar, wind etc)

• In Grid tied solar applications “inverter” acts as interface between two energy sources, one is PV generation and other side utility grid.

• Inverters can also be used for wave generators (stepped, square), Voltage controller and frequency controller.

Types of inverters: The following classification is based on the output power (1-pahse/3-phase)

Single phase inverter: It is used to convert the input DC power to single phase AC power which is used to power single phase loads (voltage level of 1-phase is 230V AC).

Three phase inverter: Same as single phase inverter but the output voltage level is like 440V AC. It is used to power 3-Phase loads.

Inverters in Solar Applications:

As solar generation is proven effective over other renewable technologies, it is widely     practicing and energy generation is increasing from MW’s range to GW’s range. In this context the demand for power conversion technologies/devices got increased like anything, however the challenges, complexities are also high in the design of Inverters.

Central inverter: Central inverters are usually of very high capacity, remains as a single unit in power conversion process. Complexity arises to employ single inverter as the generation capacity increases

If the power generations are too high then the process of power conversion (DC to AC) with a single Inverter becomes too complex. Thereby, the concept of string inverters is evolved.

String Inverters: Breaking the generation capacity into convenient levels & employing several small inverters and connected them accordingly to reduce the complexity of inverter design. The entire PV system is divided into several sections (PV strings), each string contains a fixed no. of PV modules. For each string an inverter is connected which in turn called as String inverter.

Advantages of string inverters:

1. Reduces the inverter design complexity.

2.Improvements in overall efficiencies, fault detection is made easy.

Types of different inverters and their connections with PV modules

     Micro inverters:  These are similar to grid tie inverters working wise, but these inverters are of small capacity (Module capacity) inbuilt with an MPP tracker used for each PV module. The output from several micro inverters is combined and often connected to the Utility grid. 

     Micro inverters have several advantages over conventional inverters. The main advantage is that small amounts of shading, debris or snow lines on any one solar module, or even a complete module failure, do not disproportionately reduce the output of the entire array. Each micro inverter harvests optimum power by performing maximum power point tracking for its connected module. Simplicity in system design, added safety are some other factors introduced with the micro inverter solution.

Disadvantages include Installation complexities, higher cost per Watt-peak compared to string/central inverters.

figure showing the connection differences between string and micro inverter.

Inverters mainly used in these categories:

Off grid inverter

 On grid (grid tied) inverter: Two types of on grid inverters

1.      With transformer grid tie inverter

2.      Transformer less (TL) grid tie inverter

Off grid inverter (Stand alone inverter): These inverters are used to drive the loads which are not in touch with the grid (Isolated systems).The loads draws the required AC power from the inverter which extracts DC power from the batteries which are charged by the PV system.

On grid (Grid tied) inverter: The generated DC power from the PV arrays are converted and connected directly to the respective utility grid. These systems do require a UPS just to power the Switchgear in case of any grid outages and not for energy storing. Inverters in this category contain grid synchronizing mechanism which synchronizes input parameters (voltage, frequency) with output parameters. Voltage and frequency are termed as grid stability parameters.

1. With transformer grid tie inverter: Conventional inverters are built with an internal transformer that synchronizes the DC voltage with the AC output. The use of transformer in Grid tie inverters is to normalize the harmonic content at inverter output, also to provide galvanic isolation feature. Used for large power conversions and mostly used for grid tied configuration.

2.Transformer less (TL) inverters:  It uses a computerized multi-step process and electronic components to convert DC to high frequency AC, back to DC, and ultimately to standard-frequency AC. TL inverters are directly connected to grid and no grounding should be done at PV side. Mostly used for small power conversions.

Peak efficiency of 98.8% can be achieved with TL inverters which is 2% more than Conventional inverters. For lower power applications TL inverters are more effective in terms of performance and cost as transformer is avoided.

Characteristics of Inverters:

Generally most of the data sheets by manufacturers will contain the following data irrespective of type inverter. However some additional information needs to be added for respective type of inverter.

Output parameters:

Rated output power (KVA): This is the output power (AC) of an inverter, based on which the inverter is rated.

Maximum Output Voltage (V): It is the maximum output voltage (AC) of an inverter.

Nominal output Voltage (V): It is the average output voltage (AC) of an inverter. (230V for 1-Phase, 440V for 3-Phase).

Maximum output current (A): It is the maximum current (AC) that an inverter can supply.

Peak efficiency (%): The maximum efficiency of the inverter generally ranges from 90% to 95%.

Loss of power (in the form of heat) is due to the power conversion process (DC to AC).

Weighed efficiency (%): It is the average efficiency of the inverter, always less than peak efficiency.

Frequency range (HZ): Output power will have the following frequency (variations).

Harmonics (%): The amount of harmonics that an inverter output contains. It should be less than 3% (lower harmonic inverter is always superior).

Input parameters:

Rated Input power (W): It is the maximum power (DC) that an inverter can take. It depends on the PV system output, also defines the rating of the inverter.

Maximum input current (A): The maximum input current (DC) that the inverter can take (the peak current of MOSFETS/IGBTS used in the inverter).

MPP (maximum power point) Tracking voltage (V): This is the DC voltage range for which the maximum power can be extracted from the Photo voltaic module/string/array.

Start voltage (V): Minimum input voltage (DC) required to start the inverter & its operation.

Protection: As this category is very important to have a safe/optimum operation of the inverter system. The following protections need to be addressed to have a good & safe inverter.

• DC disconnection (Islanding  protection)
• Ground fault protection
• Galvanic Isolation feature( for GTI- with transformer)
• Arc fault circuit interrupter
• DC reverse polarity/Residual current protection.
• AC short circuit protection

Data sheet of an inverter:

The following link gives the typical datasheet of an inverter (SMA manufacturer).

http://files.sma.de/dl/18726/SB5000TL-US-DUS143847.PDF

Manufacturers:

The following is the leading manufacturers of inverters (International).

NAME OF THE COMPANY	MANUFACTURING CAPACITY (MW)
ABB	NA
SMA	1730
SCHNEIDER	693
SUNGROW	638
SANTERNO	462
POWER ONE	433
BONFIGLIOLI	401
EMERSON	317
SIEMENS	239
SATCON	197
INGETEAM	166
ASEA BROWN BOVERI	149
AE ADVANCED ENGERGY	148
GUANYA	148
TBEA SUN OASIS	131
TMEIC	52
XANTREX	51

 The following is the leading Indian Inverter manufacturers.

NAME OF THE COMPANY	ADDRESS
GENUS POWER INFRASTRUCTURES LTD.	Genus Power Infrastructures Ltd. SPL-3, RIICO Industrial Area, Sitapura, Tonk Road, Jaipur -302 022, India Phone: +91 141 7102400 / 500 Fax: +91 141 7102503 / 2770319
DELTA POWER SOLUTIONS INDIA LTD.	Hyderabad Plot No:68, Nagarjuna Hills, Road No:1, Banjara Hills, Hyderabad - 500082, India +91 40 – 67274510
SUKAM POWER SYSTEMS	plot no: 54, udyog vihar, Phase VI, sector 37, Gurgoan, haryana
MICROTEK INTERNATIONAL	B-10, Hemkunt Tower, 98, Nehru Place, Nehru Place, New Delhi, Delhi 110019
HITACHI HIGH REAL POWER ELECTRONICS	B-14/1 & 171, B-117 & 118, GIDC Electronics Zone, Sector 25, Gandhinagar, Gujarat 382044
AMARA RAJA ELECTRONICS LTD.	Astra Tower, 5, Floor, Cii Building, Kondapur, Kondapur, Hyderabad, Telangana 500082 Phone:040 2339 4597
APLAB LTD.	Address: 54 sri lakshmi towers 1st floor malani colony chinna thokota new, Bowenpally, Telangana Phone:040 2775 5101
UNILINE ENGERGY SYSTEMS LTD.	198/23,Ramesh Market, East of Kailash, New Delhi, Delhi 110065 Phone:011 2646 9108
CONSUL CONSOLIDATED PVT LTD.	Block No 508, 5th Floor, Eros Apartment, Nehru Place, New Delhi - 110019
TRUE POWER INTERNATIONAL	29-A, Teacher Colony, Samaypur, Delhi - 110042 E-mail: info@truepower.in Trade Enquiry: 1800 11 2020
CONSUL NEO WATT	119,120,120A, Electrical and Electronics Industrial Estate, Perungudi, Chennai - 600 096, Tamil Nadu (India).
ELENT ELECTRONICS PVT LTD.	39, D.S.I.D.C. Sheds, Okhla Industrial Area Phase - I, New Delhi, Delhi 110020 Phone:011 4070 4444
EPOCH ELECTRONICA	66, Salkia School Road, Howrah-711106, Kolkata Howrah Kolkata, 711106 Phone:033 2665 9123
UPS INVERTER (UTL)	53A/6 , Rama Road Industrial Area, Near Satguru Ram Singh Marg Metro, Station,, Near NDPL Grid Office, Delhi-110015, New Delhi, Delhi 110015 Phone:099532 29883
LUMINOUS	Across India
POWER ONE MICRO SYSTEM PVT LTD	Bangalore
STUDER INNOTEC INDIA PVT LTD.	376, 43rd Cross Rd, 5th Block, Jayanagar, Bengaluru, Karnataka 560070 Phone:080 2665 5771
NOVERGY ENGERGY SOLUTIONS PVT. LTD	208, Second Floor, Daulat Chambers,, Near Lal Bagh Restaurant, Udaipur, Rajasthan 313001 Phone:0294 241 5487
OPTIMAL POWER SYNERGY INDIA LTD.	Phase 3, Peenya, Bengaluru, Karnataka 560058 Phone:080 4214 6833
AEI POWER INDIA PVT. LTD.	Gat.No.433, Near Weikfield Village Lonikand, Taluka Haveli, Pune - 412216 Maharashtra, India
TECHSER POWER SOULTIONS PVT. LTD	1st Floor, Laxminagar, Wellington Road, Picket, Secunderabad, Telangana 500026 Phone:040 2780 4431

* Note: The above information may subject to vary without any notice and we will be not responsible for such happenings.

Here, the source for the manufacturers list is Wikipedia, Electronicb2b.com

SOLAR PV MODULE

Photo Voltaic:

A photovoltaic (PV) module is a packaged, connected assembly of solar cells. Each module is rated by its DC output power under standard test conditions (STC), and typically ranges from 100 to 365 watts. A single solar module can produce only a limited amount of power; most installations contain multiple modules. A photovoltaic system typically includes a panel or an array of solar modules, a solar inverter, and sometimes a battery and/or solar tracker and interconnection wiring.

Most solar modules are mostly produced from crystalline silicon (c-Si). Solar cells made of Poly crystalline and Mono crystalline silicon. However, emerging solar technologies use advanced Thin-film cells. They produce a relatively high-efficiency conversion for the low cost compared to other solar technologies.

Mono crystalline PV module:

Solar PV cells used in this type are made of Single crystalline material (mono - Si). These are made into wafers from the cylindrical silicon ingots and typical appears in a dark black color before making into a cell.

Mono crystalline silicon Solar PV module

Advantages:

• Mono crystalline solar panels have the highest efficiency rates since they are made out of the highest-grade silicon. The efficiency rates of mono crystalline solar panels are typically 15-20%. But the recent advancements in the manufacturing industries can have higher efficiencies.

• A mono crystalline is more efficient in converting solar energy into electricity per sq meter area than a multi-crystalline PV. Thus the space required for the same amount of wattage is less in mono crystalline PV panel. Thus it is costlier than a multi-crystalline PV.

• During low light conditions they perform better than the multi crystalline modules.

Disadvantages:

• Mono crystalline solar panels are the most expensive. In a financial view, a solar panel that is made of polycrystalline silicon (and in some cases thin-film) can be a better choice for some residential applications.
• Mono crystalline solar panels tend to be more efficient in warm weather. Performance suffers as temperature rises, but less than polycrystalline solar panels.

Poly Crystalline PV Modules: 

These modules consisting cells which are based on polycrystalline silicon, known as poly silicon (p-Si) and multi-crystalline silicon (mc-Si). The manufacturing involves raw silicon is melted and poured into a square mold, which is cooled and cut into perfectly square wafers. It is identifiable by its signature light or dark blue color, but not uniformly so, some patches are lighter than others. The differences appear as a result of the manufacturing process.

Poly crystalline silicon Solar PV module

Advantages:

• The manufacturing process is simple and cost effective. The amount of waste silicon is less compared to mono crystalline.
• Polycrystalline solar panels tend to have slightly lower heat tolerance than mono crystalline solar panels. Which means they perform slightly worse than mono crystalline solar panels in high temperatures. Heat can affect the performance of solar panels and shorten their lifespans. However, this effect is minor and will not be a problem for residential users. A good way to separate mono & polycrystalline solar panels is that polycrystalline solar cells look perfectly rectangular with no rounded edges.

Disadvantages:

• The efficiency of polycrystalline-based solar panels is typically 13-16%. Because of lower silicon purity, polycrystalline solar panels are not quite as efficient as mono crystalline solar panels.
• Lower space-efficiency. User generally need to cover a larger surface to get the same electrical power as he would with a solar panel made of mono crystalline silicon. However, this does not mean every mono crystalline solar panel performs better than those based on polycrystalline silicon.

Thin – film PV module:

A thin-film solar cell is made by depositing one or more thin layers or thin film (TF) of photovoltaic material on a substrate, such as glass, plastic or metal. Thin-film solar cells are commercially used in several technologies like,

• Cadmium telluride (Cd- Te)

• Copper indium gallium Diselenide (CIGS)

• Amorphous thin-film silicon (A-Si, TF-Si).

Cadmium telluride (Cd-Te): Cadmium telluride (Cd-Te) is the predominant thin film technology consists about 5 percent of worldwide PV production, it accounts for more than half of the thin film market. The cell's lab efficiency has also increased significantly in recent years and is on a par with CIGS thin film and close to the efficiency of multi-crystalline silicon as of 2013. Cd-Te has the lowest Energy payback time of all mass-produced PV technologies, and can be as short as eight months in favorable locations.

• A prominent manufacturer is the US-company First Solar based in Tempe, Arizona, that produces Cd-Te panels with an efficiency of about 14 percent at a reported cost of $0.59(Rs. 36) per watt.

Copper indium gallium diselenide (CIGS): CIGS cells are made up of copper, indium, gallium, selenide (CIGS), while gallium-free variants of the semiconductor material are abbreviated CIS. With a lab-efficiency above 20 percent, shares 2% in the overall PV market in 2013.

 Amorphous thin- film silicon:  Amorphous silicon (a-Si) is a non-crystalline, allotropic form of silicon and the most well-developed thin film technology to-date. Thin-film silicon is an alternative to conventional wafer (or bulk) crystalline silicon. Silicon-based devices exhibit fewer problems than Cd-Te and CIS such as toxicity and humidity issues with Cd-Te cells and low manufacturing yields of CIS due to material complexity.

Thin film Solar PV modules

Advantages:

• Thin-film technology has always been cheaper than conventional c-Si technology    (almost 10 times less).

•  Homogeneous appearance is made possible, lower manufacturing cost.

Disadvantages:

• Present disadvantages, such as low-conversion efficiencies and requiring larger areas of PV arrays and more material (cables, support structures) to produce the same amount of electricity.

•  Lab tests reports that somewhat faster degradation compared to conventional PV, while a lifetime of 20 years or more is generally expected.

 Solar PV module important characteristics:

• Rated power (Wp) at STC: This is the maximum output power of the module during standard test conditions, this rating is provided at the back of the module. Standard Test conditions: STC conditions are given by NEC (National Electro technical commission) refers to the irradiance, Temperature, Air mass values. Typical values are 1000W/m², 25⁰C, AM (Air mass) = 1.5.

• Type of cell: The type of the cell used in the module, for the price stand point this is very important as price varies with the different existing models like mono – Si, Poly – Si, thin film.

• Cell efficiency (%): It is the energy conversion rate of the Solar cell, usually it is always greater than Module efficiency (in a general case cell efficiency would be 25%).

• Module efficiency (%): It is defined as the ratio of electrical equivalent of the irradiance input to the output of the module, in short it gives the energy conversion rate of a module which is very important in selecting module, the higher the efficiency results higher output.

Eg: If the module (1mX1m) is able to generate 200W as it is getting 1000 W/sq.m irradiation from the sun, then the module efficiency is taken as 20%.

• Rated Tolerance (+ or - %): It is range based on which the PV module perform. The range can varies up to +10% to -10% which means a 200 Wp module can actually produce 180 Wp (Under perform) to 220 Wp (over perform).

Most of the panels have tolerance in the range of +/- 3%.To ensure the panel to be good, always make sure the panel should have less negative tolerance (up to -3%). Some manufacturers provide like 0% to -3% which are very reliable & practical.

• NOCT data: The data of the module (performance) at normal operating cell temperatures.

• Capacity factor (%):  It is the average power delivered over a year compared to the rated power. It is a measure of the actual output compared to the output it could deliver. It will be less than 100% always because

1. Variations in irradiance levels.

2. Performance lag due to maintenance (dust).

• Max Power temp coefficient (% per ⁰C): It is the decrement of output power of the module due to the temperature rise.

Electrical Equivalent of a solar Module:

Generally solar module has two output terminals produces V and I.

• Iph is the output current from the cell. It depends on the area (A), intensity of incoming light & response factor.

• Id is the leakage current (due to recombination of charges inside the cell).

• Rp & Rs are the resistances due to the parallel and series connections of the cell.

·               As Module consists of no of cells connected series and parallel,

V= output voltage of the cell is given by (Np x Voltage of each cell), where Np is the no.   of cells connected in series.

I = Output current of the cell is given by (Ns x Current produced by each cell), where Ns is the no. of cells connected in parallel.

PV module I-V characteristics:

In the following graph, Y- Axis determines the current and X- Axis determines voltage of a solar module. The maximum points on Y and X axes give the Short circuit current and open circuit voltage of the module.

• ISC is the short circuit current at full load (shorting the end terminals and measuring the current through it).

• VOC is the open circuit voltage at no load (measuring the voltage across the open terminals of the module).

• As the current (I) always depends on the irradiance parameter, also it depends on the temperature of the cell.

• Module Voltage (V) also depends on the temperature (as the module have Rp & Rs resistances which are the negative temperature coefficient elements and as temperature goes up Rp and Rs decreases).

• As Rp decreases (non-linearly) Current through it increases, Voltage of the module falls accordingly. Similarly as Rs decreases (non-linearly) current through it increases results in increased output current.

I-V, Power-Voltage characteristics of solar module STC

MPPT (Maximum power point tracking): 

It is the mechanism employed in solar PV system which makes the panel to output the maximum power at every instant; however the maximum power does depends on the conditions (irradiation, temperature) at that moment.

• Vmpp is the voltage of the module, Impp is the current of the module at which maximum power generation is possible, however these parameters always depends on the respective conditions (irradiation, temperature).
• For any characteristic curve, the voltage (Vmpp), current (Impp) are always less than Voc, Isc.

MPP analysis from V-I characteristics

Solar PV Datasheet: 

The following link directs to the Technical datasheet of a module.(company-Tata solar power)

http://www.tatapowersolar.com/images/module/downloads/Datasheet%20-%20TP250%20[June%202015].pdf

Solar panels pricing:

From the solar PV industry, cost of a PV module (just the panel) costs anywhere between Rs 30 to Rs 60 per watt of power generated (depending on the quantity you are buying). A good imported module will cost around Rs 40-45 per watt (for bulk transactions, not for retail). Good ones manufactured in India would come as low as Rs 30-32 per watt (for bulk transactions, not for retail).

Here is the Price list example of a particular company which gives an idea of the price per Watt of solar module.

Products	Inputs / Watt	Price / INR
Special SPV Mono	180W / 190W	Rs. 34/W
Special SPV Multi	230W,240W, 245W, 280W,290W	Rs. 32/W
SPV Mono	10W	Rs. 53/W
SPV Mono	20W – 30W	Rs. 43/W
SPV Mono	30W – 300W	Rs. 41/W
SPV Multi	10W	Rs. 50/W
SPV Multi	20W – 30W	Rs. 40/W
SPV Multi	30W – 300W	Rs. 38/W
Thin Film Multi SPV	100W	Rs. 32/W

Solar PV manufacturers:

Following are the reputed international PV manufacturers (information based on 2015 yr data.)

Name of the Comapany	Country
Bosch	Germany
Bp solar	Spain/Australia
Green shine new energy	USA
Canadian solar	Canada
China solar	China
Conergy	Germany
Delsolar	Taiwan
E-Ton solar	Taiwan
Evergreen solar	USA/Germany/China
First Solar	USA/Germany/Malaysia
Gintech	Taiwan
Grape Solar	USA
Isofoton	Spain
JA solar holdings	China
Just Solar Co. Ltd	China
Kyocera	Japan
Mitsubishi Electric	Japan
Mitsubishi Heavy	Japan
Motech	Taiwan/China
MX Group	Italy
Neo solar Power	Taiwan
Ningbo Solar Electric	China
Photowatt	France
Photovoltech NV	Belgium
Q-Cells	Germany/Malyasia
Renewable Energy Corporation	Norway
Panasonic	Japan
Schott Solar	Germany/USA
Sharp	Japan
Solarday	Italy
Solarpark Korea	South korea
Solar World	Germany/USA
Solland	Netherlands
SunPower	USA/Malaysia
Suntech	China
Sunways	Germany
Trina Solar	China
United solar ovonic	USA
Vikram Solar	India
Yingli	China

Here is the list of reputed Indian PV manufacturers list:

S. No	Name of the Company	Manufacturing Capacity (MW)	Technology
1	TATA SOLAR POWER	200	Polycrystalline
2	LANCO SOLAR	75	Polycrystalline/silicon ingots/wafers
3	VIKRAM SOLAR	500	Polycrystalline
4	WAREE	250	Mono/Poly crystalline
5	MOSER BAER	185/200/50	Crystalline cells &modules /Thinfilm modules
6	INDO SOLAR	450	Mono/Poly crystalline
7	WEBSOL ENERGY SYSTEM	120	Monocrystalline
8	XL ENERGY LTD.	25	Polycrystalline
9	EMVEE	135	Mono/Poly crystalline
10	SOLAR SEMICONDUCTOR PV LTD.	195	Mono/poly crystalline
11	PHOTON ENGERGY	50	Mono/Poly crystalline
12	SWELECT ENGERGY SYSTEMS	40+	Mono/Poly crystalline
13	SURAN VENTURES LTD	130	Mono/Poly crystalline
14	PREMIER SOLAR	50	Mono/Poly crystalline and thinfilm
15	JUPITER SOLAR	130	Poly crystalline
16	TITAN ENERGY	110	Mono/Poly crystalline
17	HHV SOLAR	100	Mono/poly crystalline
18	CENTRAL ELECTRONICS INDIA	40	Crystalline Silicon
19	ACCESS SOLAR	80	Mono/poly crystalline

* Note: The above information may subject to vary without any notice and we will be not responsible for such happenings.

Here, the source for the manufacturers list is Wikipedia.