We supply off-grid solar inverters, grid-tied solar inverters, and hybrid solar inverters in India. As far as grid-tied inverters are concerned, we have string inverters as well as central inverters. The lower capacity string inverters single phase string inverters, whereas the ones with higher capacity are three phase string inverters. Please click on the links to get the detailed specifications of our PV modules. If you would like to know the price of our solar inverters, please send an email to info@cenergymaxpower and we will get back to you ASAP. Please do mention the order size and the place of delivery so that we can give you our best rates and exact delivery times.

What is an Inverter?

An inverter is a device which a DC (Direct Current) input and produces an AC (Alternating Current) output.

More often than not, the DC input is taken from a battery. However it can also be from solar PV modules in the case of solar applications.

The AC output is for running household appliances like tubes, fans, air conditioners, refrigerators, TVs, computers, etc. and also for industrial appliances.

Why is an Inverter so called?

The inverter has got its name from a commutator which originally were large rotating electromechanical devices. They combined a synchronous ac motor with a commutator so that the commutator reversed its connections to the ac line exactly twice per cycle resulting in “AC-in DC-out”. However, if one inverted the connections to a converter,one could put DC in and get AC out. Hence an inverter was an “inverted” converter and that is how they got their name.

What are the two types of Inverters?

The two main types of inverters are: pure sine wave inverters and modified sine wave inverters.

Pure sine wave inverters, as their name suggests, produce a pure sine wave output which is identical to the power that we get from the grid. Many household appliances like digital clocks, battery chargers, light dimmers, variable speed motors, and audio/visual equipment require a pure sine wave, and therefore it is advisable to power them with pure sine wave inverters. If you do that, it will ensure that all these “sensitive” loads will work properly and last a long time.

Modified sine wave inverters, as their name suggests, do not produce a pure sine wave output; their output is a “stepped wave” which is obviously not as smooth as a pure sine wave. They achieve voltage regulation by varying the pulse width according to the battery voltage and the load. The stepped wave output is not good for “sensitive” loads and can damage them. It also causes a buzzing sound in stereos and ceiling fans. However, modified sine wave inverters should not be underestimated; they are highly capable and by narrowing the waveform they save energy when running only small loads, as happens during most of the day in a typical home. Modified sine wave inverters were successful at one point, and still are to a large extent. However, more and more companies are not coming out with only pure sine wave inverters as the incremental cost to produce pure sine wave inverters reduces with advances in technology.

What is a solar Inverter?

A solar inverter is a device that converts the (constantly varying) DC output of a solar PV module – the input to the solar inverter –into AC. A solar inverter is necessarily a part of a solar PV installation or a solar PV power plant.

What are the types of solar Inverters?

There are three main types of solar inverters: off-grid solar inverters, grid-tied solar inverters, and hybrid solar inverters.

What are off-grid solar Inverters?

Off-grid, as their name suggests, work “off the grid” which means that they are not connected to the grid. Off-grid solar inverters are also called standalone solar inverters.

Which other components are used along with off-grid solar Inverters?

The other components that are typically used along with off-grid solar inverters are:

What does an off-grid solar PV system look like?

off-grid-solar-PV-system-1

The figure above shows what an off-grid system looks like.

  • Solar PV modules generate DC electricity which is the input to the solar charge controller.
  • The solar charge controller takes the DC electricity generated by the solar PV modules and stores it in the batteries. Typically, the solar charge controllers also do one other job which is Maximum Power Point Tracking, or MPPT in short. More information on maximum power point tracking can be obtained in the solar charge controller FAQssection.
  • The batteries convert the electricity (or electric energy) into chemical energy and store it in them. Normally, batteries used along with inverters are called into action (or come into play) only there is grid failure. However, in case of solar applications, these batteries are called into action every single day. Also, they are discharged quite a bit, by as much as 80%, which is the maximum that you can discharge them without impacting their lifetime adversely. This is done so that the batteries are in a fully discharged condition when the sun rises again so that all the electricity generated by the solar PV modules can be stored in them again.

That is why the batteries used in solar applications are deep discharge batteries, or batteries that can withstand daily deep discharges.

  • The inverter converts the chemical energy stored in the batteries into electricity (or electric energy). The input to the inverter (energy stored in the batteries) is DC whereas its output is AC. This off-grid solar inverter is very much like a normal inverter, but is called a solar inverter because it is used in a solar application.

The loads are household appliances like fluorescent lamp, tube light, fan, refrigerator, TV, computer, pumps, among others.

What are the different types of off-grid solar PV systems?

The different types of off-grid solar PV systems are:

  • Solar power packs: They can vary from small to large size. The small ones have only a DC output and are used to charge mobile phones and run other DC applications. The larger ones have an inverter as well and are used to AC appliances.
  • Solar home lighting systems: These can vary from small to large sizes. The small ones can be used to power 1 lamp while the larger ones can be used to power multiple lamps. Typically, solar home lighting systems have only a DC output. So the lights that they power should necessarily be DC powered.
  • Solar lanterns: These can have the solar PV module and battery integrated into the product, or have the battery integrated into the product but have a separate solar PV module in case of higher capacity lanterns. Typically, solar lanterns allow the users to select the luminosity level; lanterns run for fewer hours on higher luminosity levels and for longer hours on lower luminosity levels. Solar lanterns are always DC powered.
  • Solar street lights: Solar street lights comprise of pole, luminaire, solar PV module, solar charge controller, and battery. The luminaire is always DC powered. It almost always has an IP65 environmental rating since it is exposed to the elements. In many cases, the charge controller is embedded inside it. In some cases, even the battery is embedded inside it. If that is the case, then the batteries are invariably Li-ion batteries since they have to be compact.
  • Solar signage’s (or signboards): Solar signage’s or signboards are very much like solar street lights and have the same components as compared to solar street lights.

Solar pumps: Solar pumps have solar PV modules and a three-phase inverter which drives the pumps. Solar pumps do not have batteries since there is no need to store the energy. Whenever the solar PV modules produce electricity, it is used to pump water from the well to the ground level (actually in storage tanks that are slightly above the ground level). And since solar pumping systems do not have batteries, they don’t have solar charge controllers as well.

Is it a must to have solar inverters in an off-grid solar PV system?

No. An off-grid solar PV system is possible and can be functional without solar inverters. However, in that case the loads have to be DC loads. In other words, the loads should be capable of being powered by a DC source.

Solar charge controllers have a DC output which can be used to power DC loads. A 12V solar charge controller will have a 12V DC output, whereas a 24V solar charge controller will have a 24V DC output. In general, a solar charge controller will have a DC output which is the same as its voltage rating.

Solar power packs, solar home lighting systems, solar lanterns, solar street lights, and solar signages are systems which have DC outputs and therefore do not have/needinverters.

What are the advantages of an off-grid solar PV system?

The main advantages of an off-grid solar PV system are:

  • It can generate power (and that too very reliably) in remote locations where no other source of power is available. There are many locations where the grid can be taken but it becomes prohibitively expensive, and therefore off-grid solar PV systems, despite their high upfront cost, are a better option.
  • Diesel Generators (DGs) are an alternative to off-grid solar PV systems in certain situations, but they have high running costs, and is getting costlier with every passing day. The supply chain – to supply diesel to these remote locations – can be a daunting task. And of course, DGs cause a lot of pollution and are harmful to the environment.
  • All the other advantages of solar power (free, unlimited, non-polluting, last for many years) apply to off-grid solar PV systems as well.

What are the disadvantages of an off-grid solar PV system?

The main disadvantages of an off-grid solar PV system are:

  • Cost: Off-grid solar PV systems are quite costly. Solar PV modules are quite costly and contribute a god percentage of the overall system cost. Additionally, off-grid solar PV systems also require batteries, and that too deep cycle batteries, which are quite costly too. That increases the system cost as well.
  • Maintenance: Since off-grid solar PV systems need batteries, it automatically means that they need to be maintained properly. This mainly involves adding distilled water to the batteries (or “topping up” as it is popularly called) if they are of the flooded lead acid type, which they are in many cases. Although flooded lead acid batteries have advanced quite a bit in the recent years and don’t require frequent topping up, it still needs to be done and can be cumbersome if the place of installation is not easily reachable.

Recurring expenses: Off-grid solar PV systems need batteries, and even if you maintain them well, they will wear out in anywhere from 300 to 1000 cycles. (In most cases, these are typical cycle numbers. Batteries that last longer are prohibitively expensive in which case it is what the first disadvantage talks about.) So off-grid solar PV systems necessarily have recurring expenses associated with them.

What is a grid-tied solar Inverter?

A grid-tied solar inverter, as its name suggests, is a solar inverter that is connected to the grid or “tied” to the grid. A grid-tied solar inverter is also called grid-connected solar inverter.

Which other components are used along with grid-tied solar Inverters?

The main other components used along with grid-tied solar inverters are solar PV modules and metering equipment (to measure the electricity generated by the solar inverters).

What does a grid-tied solar PV system look like?

grid-tied solar PV systemThe figure above shows what a grid-tied solar PV system looks like.

  • Solar PV modules generate DC electricity.
  • The grid-tied solar inverter converts the DC electricity generated by the solar PV modules and into AC and feeds it into the grid.
  • The sell meter (or the export meter) measures the electricity fed by the grid-tied solar inverter into the grid.

The purchase mater (or the import meter) measures the electricity drawn from the grid.

Does a grid-tied solar PV system shown in the figure above need support from the state electricity boards?

Yes, the grid-tied solar PV system shown in the figure above needs support from the state electricity boards in two ways:

  1. The state electricity boards need to give you permission to feed electricity into the grid.
  2. The state electricity boards need to pay you and pay you well for the electricity fed into the grid. Otherwise, it is not economically viable/feasible/attractive.

Are utility-scale solar PV plants also grid-tied solar PV systems?

Yes, utility-scale solar PV plants (> 1 MW in capacity) are also grid-tied solar PV systems. However, the only difference with respect to the figure above is that there are no local loads which consume electricity. And therefore, there is no purchase meter either.

What are the advantages of a grid-tied solar PV system?

The advantages of a grid-tied solar PV system are:

  • Simple: A grid-tied solar system is simple with fewer components.
  • Cost-effective: Since there are no batteries in a grid-tied solar system, it is cost-effective since batteries cost quite a lot. A solar system with batteries can cost anywhere from 50% to 100% higher compared to a solar system without batteries.
  • Easy to maintain: Batteries need regular maintenance to ensure that they work properly and last long. However, since a grid-tied solar system does not have batteries, it is a lot easier to maintain. The solar PV modules need to be cleaned periodically.  And the inverters need to undergo preventive maintenance every once in a while.

Apart from the advantages stated above, grid-tied solar PV systems have all the advantages of solar power (free, unlimited, non-polluting, last for many years).

What are the disadvantages of a grid-tied solar PV system?

The main disadvantage of a grid-tied solar PV system is that it can’t be implemented without support from the state electricity boards.

What is a grid-connected solar Inverter?

A grid-connected solar inverter is the same as a grid-tied solar inverter.

What is a grid-paralleled solar Inverter?

A grid-paralleled solar inverter is the same as a grid-tied solar inverter. It is also “tied”or “connected” to the grid. However, there is a slight difference in semantics of it. Grid-paralleled solar inverters imply a “behind the meter” connection and feed the loads in parallel to the grid.

What are “behind the meter” connections?

Net metering policies are not there in most states in India. However, people still go for grid-tied solar PV systems. The output of the grid-tied solar inverter is connected “behind” the purchase meter (if you are sitting on the grid and looking at where the connection is made). Typically, the inverter takes care of the load partially. So for example, if the connected load is 50kW and the minimum load during the day is 30 kW, then the solar inverter would be say 15 kW; it is usually less than 85% of the minimum load during the day. That ensures that all the electricity produced by the solar PV system will be consumed; the remaining will be drawn from the grid.

What are the typical capacities of grid-tied Inverters?

The capacities of grid-tied inverters vary greatly, from 1 kW all the way up to 1 MW. The smaller capacity inverters are called string inverters, whereas the higher capacity inverters are called central inverters.

What are string Inverters?

Small capacity grid-tied inverters are called string inverters. Their capacities vary from 1 kW all the way up to 50 kW.

They are so called because they take “strings” of solar PV modules as inputs.A string of solar PV modules is nothing but many solar PV modules connected in series.

What is the maximum number of solar PV modules that I can connect in a string?

The number of PV modules in a string is determined by the open circuit voltage (VOC) of the PV module and the maximum voltage that the inverter can safely withstand at its input. For example, if the VOC ofa module is 44.68V and the maximum voltage that the inverter can safely withstand is 1000V, then the maximum number of PV modules that can be connected is 22.38. Since we have to take the maximum integer less than this number, we can connect a maximum of 22 PV modules in series.

What is the maximum number of parallel strings that I can connect to an Inverter?

The maximum number of parallel strings that you can connect to the inverter depends on the power rating of the modules and the inverter. For example, assume that the inverter rating is 15kW. Further, assume that the power rating of the PV module in the above example is 300Wp. So the power output of each string = 22 * 300 = 6,600Wp. If we connect 3 such string in parallel, then their total power output will be 19,800Wp. This is 32% higher than the power rating of the inverter.

In most parts of India, the total peak power of the solar PV modules can be 20% higher than the rating of the inverter. Why? Because the operating conditions during the day while producing solar energy are such that the PV modules never produce peak power; they always produce than the peak power and high ambient temperature is the culprit in most cases.The peak power is calculated under Standard Test Conditions (STC)where the specified cell temperature is 25C. In most parts of India, the ambient temperature ranges from 20C to 45C. And since the cell temperature is higher than the ambient temperature by almost 20C, the cell temperature ranges from 40C to 65C, which is 15C to 40C off compared to the STC thus resulting in lower power compared to the peak power.

So in the above case, we can 18,000Wp worth of PV modules to the inverter. So instead of connecting 22 modules in series, we can connect 20, to get a total power of 6,000Wp. Now if we connect 3 such string in parallel, the total will come to 18,000Wp, which is what we want.

 

Do String Inverters have multiple MPPT inputs? If yes, why?

Yes, string inverters typically have multiple MPPT inputs. This allows the inverter to do maximum power point tracking of different sets of strings differently and independently.

For example, if the string inverter allows 6 strings to be connected to it and if it has 2 MPPT inputs, then it will internally divide the strings in two groups and track them independently. How the string inverter groups the 6 strings depends on the inverter: it could put 3 in one group and 3 in another; it could put 5 in one group and one in the second group (SMA inverter actually does that).

This feature comes in handy where the two sets of strings are expected to have a different maximum power point. Let’s say you have one part of the roof pointing in the south-east direction and the other part pointing in the south-west direction. Then these two sets of strings will have different maximum power points; they have a different azimuth and therefore the angle of incidence of sun’s rays will be different.

What are the advantages of string Inverters?

The advantage of string inverters are:

  • Flexibility: String inverters offer the highest design flexibility which is one of their main advantages.
  • High efficiency: String inverters have very high efficiency. The state-of-the-art string inverters have >98% efficiency. Also, since string inverters optimize only a few strings together, that leads to higher system efficiencies, especially if there is shading on some modules, or some modules are faulty or underperforming compared to the other modules, or if the orientation/slope is different areas.
  • Robust: String inverters are quite robust, which leads to low total cost of ownership.
  • Redundancy: String inverter based designs have a high redundancy by definition. If one inverter goes down, the output of only that inverter is lost; all the inverters are not affected in any way and continue to function.
  • Fewer BoS components: If big solar PV power plants are constructed using string inverters, they require fewer Balance of System (BoS) components compared to when a central inverter is used.
  • Lesser DC wiring:If big solar PV power plants are constructed using string inverters, they require lesser DC wiring compared to when a central inverter is used.
  • Cost effective: String inverters represent a very good value for money, especially for capacities from 10 kW to 30 kW.
  • 3-phase variations: String inverters come in 3-phase variations which is desirable and required in many cases.

Well-supported: String inverters, if bought from reputed companies, are backed up with very good after-sales support, which is essential for resolving issues, if and when they crop up.

What are the disadvantages of string Inverters?

The disadvantage of string inverters are:

  • No module level MPPT: Since MPPT is done for the entire string, module level MPPT is not possible with string inverters. This can be a major concern in some situations.
  • No module level monitoring: Since the input to a string inverter in one (or more) strings of modules, module level monitoring is not possible  with string inverters.
  • High voltage levels: Since the input to a string inverter in one (or more) strings of modules, the DC voltage levels are high, as much as 1000V in many cases. This presents a hazard to the people who work with string inverters and proper care must be taken at all times to avoid accidents; DC shocks are far more dangerous than AC shocks. Also, DC arcing is a distinct possibility ifDC-side disconnection is not done properly or if the DC disconnect switch is faulty.
  • Not cost effective for small systems: String inverters are not very cost efficient for small capacities, say up to 3 kW. They start becoming  cost effective upwards of 5 kW. In general, if you compare the price of string inverters from a particular manufacturer, you will find that the prices drop as the capacity increases.

Not cost effective for big systems:Although string inverters require fewer BoS components and lesser DC wiring compared to when a central inverter is used, and although there are significant advantages in terms of design flexibility, system efficiency, and system reliability, they are not cost effective when it comes to big utility-scale solar PV power plants. That is why mostly central inverters are used in big utility-scale power plants, at least in India.

What is the cost of string inverters in India?

The cost of string inverters varies from company and company. The cost of string inverters also varies depending on the capacity of the string inverters.

The low capacity string inverters, say 1 kW to 5 kW, can cost anywhere from Rs.30 to Rs.60 per watt. As the string inverters get bigger and bigger, the cost per watt comes down. The high capacity string inverters, say 15 kW to 35 kW, can cost anywhere from Rs.10 to Rs.20 per watt.

And obviously, the price of string inverters depends on the order size. If the order size is large, then the price per watt decreases. If the order size is small, then the price per watt increases.

What are central Inverters?

Central inverters are essentially string inverters except they have very high capacities. The smaller central inverters have a capacity of 100 kW and the bigger ones might have a capacity as high as 1 MW or even more.

What are the advantages of central Inverters?

The main advantages of central inverters are:

  • Optimal when generation is uniform: If central inverters are used in places where the solar power generation is fairly uniform, then central inverters are quite optimal when it comes to energy production.
  • Highly reliable: Although central inverters, by design, do not have any redundancy built into the system – if they fail, the entire system goes down – they are quite reliable, especially in recent times and if they are bought from Tier I and Tier II companies.

Cost effective:Central inverters are more cost effective in big utility-scale solar PV power plants as compared to when string inverters are used. And this is despite the fact that using string inverters requires fewer BoS components and lesser DC wiring which is expensive.

What are the disadvantages of central Inverters?

The main disadvantage of central inverters are:

  • No redundancy: Although central inverters have gotten quite reliable over the years and especially in recent times and if bought from Tier I and Tier II companies, the fact remains that if they go down, the entire plant goes down.
  • Not optimal when generation is not uniform: If the power generation across the entire solar PV power plant is not uniform, then using central inverters is not optimal. And the chances of this happening are significant. If the central inverter is of a very large capacity, say 1 MW, then it requires around 5 acres of area. That is quite large! And the odds that generation might not be uniform are high.

Requires more BoS components: Central inverters require more BoS components; they require combiner boxes and also require more DC wiring which is quite expensive.

What is the price of central inverters in India?

The price of central inverters in India varies from company and company. The price of central inverters also varies depending on the capacity of the inverters, and it goes without saying that the bigger the central inverter, the lesser is the price per watt.

As a rough estimate, central inverters can cost anywhere from Rs.6 to Rs.12 per watt (as of 1st May 2014).

The prices are also dependent on quantity or order size. If the order size is large, then the price per watt decreases. If the order size is small, then the price per watt increases. Central inverters are big as it is (> 500 kW). But if you bought central inverters for a 50 MW solar PV power plant, you would get a much better price compared to that for a 5 MW solar PV power plant.