Solar Inverters

The increasing awareness of how prone conventional energy resources are to exhaustion has made people turn to other, more cleaner, freely available and renewable energy resources.

Solar energy is one such resource that people have turned to.

Solar energy is derived from the energy of the Sun. Now, it is common knowledge, that to produce solar energy, one needs solar panels. But that is just the tip of the iceberg. Solar panels are definitely the biggest investment one has to make on while looking to use solar energy, but the “brains” behind your solar energy producing system is the solar inverter that you use along with your solar panels. ( Refer Solar Lights Here )

Solar panels produce DC power, but to power your house and household appliances, one needs AC power. This is where the solar inverter steps in. A solar inverter basically converts the DC power produced by the solar panels into usable, AC power that can be used for household electronics and appliances.

As time has gone by, the solar inverter has grown into performing more functions than just converting DC power into AC power, including Maximum Power Point Tracking (MPPT)solar charge controllingstorage of energy in batteries and management of battery charging, while also minimizing utilization of utility power grid.

All this could seem a bit technical, but read on and by the end of this article, we are sure you will have a better understanding of how solar inverters work and will be able to differentiate the bad ones from the good ones.

In this article, you will get to know the types, buyers guide, FAQ and top 7 Solar inverters.

Types of Solar Inverters

There are several types of solar inverters that are available in the market. But there are two major classifications of solar inverters.

1. Based on the working – a) String inverters  b) Central inverters  c) Micro-inverters

2. Based on interaction with the grid power – a) Stand Alone inverters  b) Grid Tie inverters  c) Backup battery inverters

String Inverters

String Inverter

These inverters are connected to several “strings” of solar panels.

A string of solar panels is basically, a row of solar panels that are connected together.

For example, if you have installed 25 solar panels on your rooftop, you could have installed 5 rows of 5 solar panels each. Each row here is called a string. This type of inverter gets its name from the fact that the photovoltaic modules are connected in a series circuit, or a string, before connection to the inverter. A large system might require multiple such string inverters to accommodate a number of such strings. Some of these inverters come with Maximum Power Point Tracking (MPPT) to maximize the energy produced by your solar modules.

This technology has been traditionally used for both residential applications as well as commercial applications and is very reliable while being the cheapest type of inverter that is currently available. Their installation and maintenance are very simple as there is only one point of conversion of DC to AC.

Despite, being a trusted technology, the string inverter comes with its own drawbacks.

One major disadvantage being that, due to the solar panels being connected in series, even if one solar panel performs poorly the performance of the whole string of panels is lowered.

This issue is magnified when even one of the solar panels is affected by shading due to some objects in its vicinity, like trees, or even due to fallen leaves, dust or dirt covering the solar panel. So, when even just one or two solar modules experience shading, the entire string of solar panels will produce lesser power, despite having enough sunshine on most of them. Moreover, the series connection makes troubleshooting difficult i.e., identifying the faulty solar panel(s) is a huge task since the string inverter basically treats the various strings of solar panels as one, really big, solar panel.

Central InvertersCentral Inverter

Central inverters are basically a bigger sized string inverter.

Their working is similar to that of string inverters, but are capable of handling a larger number of strings. Instead of the strings running directly into the inverter as is done in the string type inverter,  a combiner box is used before the inverter where the various strings are connected and then the DC power is sent to the inverter, where it is converted to AC power.

This type of inverter is more suitable for larger systems, of the order of 5 MW. They work best when used with a large system which has a consistent production of power across the various arrays of solar panels.

Just like the string inverter, the central inverter is also very reliable and has been widely used all over the world. The central inverter is comparatively cheaper than the string inverter due to the fewer components that it needs. The central inverter is similar to the string inverter in more ways than one, but as it is a bigger version of the string inverter, both the pros and cons of the string inverter are amplified in the central inverter as is seen in the case of shading. For a central inverter, even 10% of shading could result in 50% reduction of power produced.

Micro-Inverters

Micro Inverters

 

Micro-inverters, as the name suggests, are small inverters that are fixed right behind each solar module. These micro-inverters, convert the DC power that they receive from each of the modules into AC power directly, which is then combined and supplied to the power grid.

Since each solar panel has its own inverter, this allows for the parallel connection of the solar panels which yields better output from the solar panels as compared to string and central type inverters.

Micro-inverters are capable of producing up to 25% more power than string or central inverters.

Moreover, since micro-inverters are fixed to each solar module, they are even capable of maximum power point tracking. Without going into the technicalities, maximum power point tracking (MPPT) is a technique used to maximize power output, despite the varying irradiance conditions.

Micro-inverters also make troubleshooting easier, as any fault in the system can be easily tracked and identified.

Microinverter

 

Micro-inverters, despite being clearly better than the string and central type of inverters, is the most expensive of the three seen so far, which has been a limiting factor in their usage.

Micro-inverters are better suited for residential purposes where shading plays quite a significant role. Moreover, due to the smaller number of solar panels used, and the smaller size of the system, the extra money spent on the micro-inverters is quite less. But it is not suitable where battery storage is being considered since it converts the DC power immediately into AC power.Hence, it does not work well with a battery bank, as batteries require DC power.

Stand Alone Solar Inverters

Stand Alone Inverters are inverters that draw DC power from rechargeable batteries and convert them into usable, AC power. The batteries are connected to the solar modules and are charged by the DC power generated by them.

These inverters are used in places where there is no electrical connection, like in the rural areas, or when one wants to be completely independent of the electric utility grid. Such a system will be unaffected by power outages and any other such issues faced by the electric utility grid.

They have no interaction with the utility grid, which has its own pros and cons.

The major advantage being that, power outages and other technical issues that the utility grid faces will no longer be effective, as you have your own independent power system.

But, on the flip side, it also means that if your power system crashes, then you will be left without any power till the issue is settled.

Grid Tie Solar Inverters

Grid Tie Inverters are inverters that are connected to the local utility grid and sends all the power generated by the solar array back to the local power grid.

In a grid-tie system, the DC power generated by the solar array is sent to the grid tie inverter, which converts it to AC power and sends the AC power to the local power grid. The local power grid then supplies power to your home, just like any other regular home.

In such a system, it is necessary to ensure that the solar energy system is wired to the local power grid through your electricity meter so that the local electricity board can give you credit for the energy that you produce.

Such a system, though, is not immune to power outages due to the lack of a backup battery to provide backup in case of a power outage.

All grid tie inverters are supposed to have anti-islanding protection, which forces them to shut down during a power outage. Without anti-islanding protection, your solar power system will continue to send power to the local power grid even during an outage. This energy will remain in the local grid and is called as an island. These islands can be dangerous to maintenance workers who could be working on the grid, trying to repair the grid during a power outage. Hence, anti-islanding protection is absolutely vital for such an inverter.

Such inverters are particularly useful in urban areas, and such systems are cheaper than the stand-alone power systems.

Backup Battery Solar Inverters

The backup battery solar inverters are known by several names, such as the Dual Inverter, Dual-Function Inverter, Grid-Interactive Inverter and much more. This type of inverter sends the DC power generated by the solar panels to a battery, where it gets stored.

Power from the battery is sent to the inverter, where it converts the DC power into AC power for usage. When the battery is fully charged, and excess energy is produced by the solar modules, the excess energy is sent to the local power grid through the inverter. So, the backup battery solar inverter, basically, takes the pros of both stand-alone inverters and grid tied inverters and puts it in one package.

Such an inverter protects you from power outages through the batteries and uses the local grid power when your solar power system encounters an issue. Like the grid tie inverters, these inverters also need to have anti-islanding protection, to ensure that power is sent to the local power grid during a power outage.

This type of inverter is more expensive than the other two types of inverters but given the functions that it is capable of doing, the extra money will be worth it.

Solar Inverter Buyer’s Guide

IP Rating

IP rating stands for Ingress Protection Rating. The IP rating is a measure of how well your inverter is protected from dust, water etc.

Inverters are subjected to harsh conditions such as high temperatures, water, dust and fluctuating voltages. The IP rating of an inverter will tell you how well your inverter is protected from such harsh conditions.

The IP rating is a double digit number, and each digit stands for a certain protection that the inverter offers. The infographic below will help you understand this better.

 

Inverter IP Rating

Efficiency

The efficiency of the solar inverter is another important parameter to consider while buying a solar inverter.

The efficiency of the inverter determines how much of the energy produced by the solar panel is converted into usable AC power.

Part of the DC power that comes to the inverter is lost due to the production of heat and a few other losses. Hence, greater the efficiency of the inverter, lower will be the losses.

But the efficiency of an inverter increases with increase in the power used by you. This means that when very little power is being utilized the efficiency of the inverter may be somewhere around 50% and can go over 90% when the output approaches the inverter’s rated output.

Hence, most manufacturers give a peak efficiency value, which is the highest efficiency that the inverter can attain. Higher the peak efficiency, more the output.

Output Waveform

Inverters are capable of producing outputs having various waveforms such as sine wave, square wave, modified sine wave etc depending on the circuit design of the inverter. An inverter that produces a true sine wave is what you should be looking for.

A true sine wave is more efficient, especially when powering inductive loads. Other waveforms could use up to 20% more power when powering such loads. This excess power used can also reduce the life of the appliances you use, due to overheating. Hence, a true sine wave output producing inverter is what one should be looking for.

Power Consumption of Solar Inverters

The charging segment should efficiently use energy. Solar energy is required to charge the batteries of Solar Inverter. In case the charging unit is not energy efficient then it may lead to wastage of electricity even when the battery is completely charged.

Duration of the Battery Backup

One of the vital point to check is the duration for which the inverter can provide the facility after starting it for the use. You can calculate the duration that it can last for by using a simple formula.

The formula is given below:

Time =           Battery Voltage x Battery Capacity x Inverter Efficiency / Load

(Battery Voltage in Volts, Battery capacity in AH, Load  in VA)

For example: If the battery voltage is 15 Volts and Battery capacity is 160 AH, and you have to keep running a table light of 50 watts, small bed light of 30 watts and a fan of 80 watts. The inverter’s efficiency is only 80%. You can calculate the duration of the battery for which it will last by using the above formula.

15x160x0.8/160(total load) = 12 hours

1. Luminous Solar NXG hybrid Inverter 1800/24V UPS

Luminous Solar NXG hybrid Inverter 1800/24V UPS
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Luminous solar 1800 with 40 amp inbuilt charge controller is a hybrid inverter. This inverter gives priority to solar power use as it is India’s most intelligent solar system.  The battery is charged either from the grid or the solar panel as per the availability of the sunlight. The battery saving and supplying the load is simultaneously done when there is sufficient solar generation but it generally gives priority to solar battery charging if the solar generation is inadequate.

Main Features
  • Sine wave output offers improved performance and protection to the connected load.
  • Recharge time is about 10-12 hours
  • Low cut off electricity saves up to of three to five units per day.
  • The UPS delivers both AC and DC output.
  • Solar panel compatibility can be reach up to 1000 watt PV.
  • Intelligent logic system gives thorough  consumption of solar energy.
PROS (What we liked)
  • Negligible amount of  heat generation as compare to other Inverters
  • Battery supports all the brands of appliances.
  • Affordable and worth the money.
  • Inbuilt PWM charge controller can run load of up to five lights, five ceiling fan, one television, and one water cooler.
CONS (What we didn’t like)
  • May change the output terminal at times.
  • There is a buzzing sound when it operates on the battery.
  • Noisy when swapping to battery from the mains.
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2. Microtek MSUN 935 12V Digital Display Solar Inverter UPS (Grey)

Microtek MSUN 935 12V Digital Display Solar Inverter UPS (Grey)
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Microtek MSUN 935 VA an off grid solar inverter designed to give power using solar panel. It is a starting model, Microtek M-SUN solar UPS is designed with modern advanced technology. This technology has improved performance and gained great reliability.

It is incorporated with intrinsic 30amp smart solar charge controller. The solar sine wave technology used, improves the battery life and hence minimum effort has to be made for maintaining the battery.

Main Features
  • Micro-controller DSPIC based intelligent control design.
  • Microtek solar inverters with 30 amps chargers which supports a panel connectivity of 600 Wp.
  • Dual charging, mains mode and solar mode (solar panel up to 600w-12v model), dual charging, mains mode and solar mode (solar panel up to 600w-12v model)
  • Smart P.M. regulated multistage atm (automatic trickle mode) for charging.
PROS (What we liked)
  • The inverter has a running power of up to ten lights, three ceiling fan, one television, and one refrigerator.
  • LED and Graphical Display of status and fault
  • Smarter and faster overload intelligence and short circuit guard.
CONS (What we didn’t like)
  • Heats up soon
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3. FlinSlim Lite Solar Hybrid Inverter

FlinSlim Lite Solar Hybrid Inverter
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The FlinSlim Lite Solar Hybrid Inverter is, again, from Flin Energy and this particular inverter is a next generation, hybrid inverter, capable of storing the energy you produce as well as keeping you tied with the local power grid.

Just like its big brother, the Dual MPPT inverter, the Lite Solar Hybrid inverter has also been artistically designed but unlike the Dual MPPT inverter, comes without the MPPT solar charge controller.

Instead, it comes with a PWM charge controller which ensures maximum utilization of solar energy.

Main Features
  • Pure sine wave inverter with peak efficiency up to 93%.
  • Has an in-built charge controller.
PROS (What we liked)
  • Automatically switches between battery power and grid power.
  • The intelligent system gives top priority to solar power.
  • Light weight and wall mountable.
  • Double surge power capacity.
CONS (What we didn’t like)
  • In-built PWM charge controller means lesser power produced compared to the FlinSim Dual MPPT.
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4. Exide Solar Inverter

Exide Solar Inverter
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Exide Solar Inverters have used advanced microprocessor technology to produce high-efficiency inverters which are more than capable of converting DC power coming from the solar modules into usable AC power.

They have used high-quality MOSFETs along with MPPT technology to produce an inverter which is capable of reaching a peak efficiency of 80%.

It has a “Solar Prioritisation” feature which ensures that grid power is only used when absolutely necessary.

Main Features
  • Pure sine wave inverter with a peak efficiency of 80%.
  • Has an IP rating of 20.
PROS (What we liked)
  • In-built MPPT ensures maximum production of power.
  • Thermostatically controlled fan ensures optimum temperature conditions.
CONS (What we didn’t like)
  • The efficiency of 80% is quite poor.
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5. Su-Kam Brainy Eco

Su-Kam Brainy Eco
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Su-Kam’s Brainy Eco is quickly becoming one of the best dual inverters in India. Nicknamed as “India’s Most Intelligent Solar Inverter”, the Brainy Eco comes with an intelligent charging sharing system which ensures that your batteries are always charged while using as little grid power as possible.

It also designed to give solar power the first priority to power your house, while it uses grid power only when there isn’t enough energy coming from the solar modules or from the batteries as well.

Main Features
  • Comes with an in-built PWM charge controller.
  • Protection from overloading in the grid power and short circuit.
  • Comes with a 2 years warranty.
PROS (What we liked)
  • 6 stage battery charging process, helps charge battery efficiently and increases the life of the battery.
  • The intelligent system minimizes grid power usage.
  • Automatic Temperature Compensation (ATC) helps increase battery life.
CONS (What we didn’t like)
  • Uses PWM charge controller.
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6. Microtek Hybrid Solar UPS/ Inverter

Microtek Hybrid Solar UPS/ Inverter
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Microtek’s Hybrid Solar Inverter is designed to make the most of the solar energy. Just like any other hybrid inverter, this inverter is also capable of storing the energy that is produced by the solar modules, while also sending any excess energy produced to the local power grid.

This a pure sine wave inverter, which means that all high-end electronics can also be powered by this, without any fears of damage to the electronics.

Main Features
  • Pure sine wave inverter with a peak efficiency of 80%.
  • Has in-built PWM solar charge controller.
PROS (What we liked)
  • Dual charging mode allows for charging of battery even through grid power, which can be very useful in places with long power cuts.
CONS (What we didn’t like)
  • The peak efficiency of 80% is a deal breaker.
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7. FlinSlim Dual MPPT

FlinSlim Dual MPPT
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The FlinSlim Dual MPPT hybrid inverter is an inverter from Flin Energy, which is a part of Flin Technologies Pvt. Ltd. and is a leading renewable energy company.

The FlinSlim Dual MPPT hybrid inverter is a pure sine wave inverter with an inbuilt MPPT(Maximum Power Point Tracking) solar charge controller. It has a sleek, artistic design and can be easily mounted.

This thing of beauty delivers on the performance side as well, coming with a peak efficiency of 93%.

Main Features
  • Pure sine wave inverter with 93% efficiency.
  • Overload and short circuit protection.
PROS (What we liked)
  • In-built MPPT solar charge controller enables generation of 25-30% more power than other inverters.
  • Double surge power capacity enables it to power inductive loads with ease.
  • Beautifully designed and easy to mount.
  • The intelligent system gives priority to solar power over grid power.
CONS (What we didn’t like)
  • Costs significantly higher than the others on this list.
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Frequently Asked Questions

1. What do Solar Inverters do?

In a solar electric power system, a solar inverter converts the variable direct current of photovoltaic solar panel into alternating current. The AC current can be supplied to the domestic appliances.  .

2. How long does a Solar Inverter last?

Normally, a solar inverter can have a shelf life of up to 20 year depending on the quality of the inverter.

3. What is the ideal capacity of inverter?

The capacity of the inverter is decided based on the duration to back.  The more the time you require the back-up for higher should be the battery’s capacity.

4. Do all the inverters turn off after sunset?

Some of the inverters turn off at night; this is completely normal as there is no power being produced. These inverters then test themselves. So, when the solar radiation is at the utmost level, the inverter will start functioning on a routine basis every morning then it will start feeding the grid with energy.

5. Are solar inverters noisy?

Depending on the quality of the inverter they can create a humming noise while converting DC current to the AC current. However, as solar inverters produce power only during the day when the, they are silent at night.

Conclusion

Solar inverters are the brains behind your solar power system. Therefore, give it a good thought before making your final decision.

The solar inverter should be capable of drawing the best out of your solar modules while being highly efficient.

A good inverter should have high efficiency, produce a pure sine wave output and have a good IP rating. Maximum Power Point Tracking (MPPT) would be a huge added bonus as well.

Having said that, you should also keep in mind your requirements and choose accordingly. However, if I had to go with any of the above-mentioned products, I would go with FlinSlim Dual MPPT. The cost is slightly on the higher side but it is a one-time investment and is totally worth it.

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