So you have decided to buy solar panels, what is the best inverter for your system?

A typical solar power system comprises of solar panels, wiring and the inverter; then add on batteries and regulator/ charge controller.

The power generated by the solar panels and batteries is in the form of direct current or DC power. Standard home appliances are run using alternating current, or AC power.

In order for the home appliances to run on the solar power, DC power needs to be converted to AC. This is the job for an inverter, which is connected to the house side of the solar panels and batteries.

DC power flows in the circuit in one direction, providing current to power electrical items. It can be used to power up gadgets like iPods, and MP3 players; small appliances and small gadgets which store DC power in their battery. AC power, is supplied back and forth inside the circuit. It is mostly used for running household appliances like your TV, Refrigerator and Microwave.

A solar inverter is the best inverter for a solar system since the idea behind installing a solar system is to use sun’s energy to the maximum. Inverters today come with several enhanced built-in features like advanced utility controls, data monitoring, systems and applications design engineering.

Solar inverters convert the DC power to AC power. Solar inverters may incorporate MPPT. Consider these electrical formulas for the explanation below.

        1 watt (power ‘P’) = 1 ampere (current ‘i’) × 1 volt (v), and

        1 volt = 1 ampere x 1 ohms (Ω) (resistance)

Basically, MPPT is the acronym for ‘maximum power point tracking’ and MPPT is the process of adjusting (Ω) resistance in the circuit to change current voltage for finding the optimised power point.

The MPPT refers to the intended ability of your solar PV inverter to track output power from the solar modules and find the array’s maximum power point voltage (Vmp). MPPT is designed to make automatic resistance adjustments to extract the most power from your PV solar system. This feature is useful when sunlight is changing with variable weather conditions or when light is poor, such as in passing clouds or similar intermittent shadow.

MPPT therefore addresses the problem of power efficiency of the solar cell, which depends on the amount of sunlight that solar panels access. As the quality of sunlight on the panel varies, the MPPT varies the electrical resistance such that it optimises the power transfer. That might be important for a solar inverter on an RV which is moving. The RV solar inverter used for charging batteries will benefit from this optimised power feature.

Before making a choice based on knowing your requirements you probably want to know and understand the various types of inverters available in the market.

A solar PV system can have one or multiple inverters depending on the size of the photovoltaic system. Central inverters are usually used for large commercial plants. 

Central Inverters

These inverters convert DC to AC. They also handle the power management from one device that is centrally located. The larger industrial installations or utility scale solar farms that handle output in the megawatts range use central inverters.  There can be several central inverters in a solar farm but the size of each central inverter will have to be 1 MW and above. 

Central inverters are the preferred choice for solar farms due to their capacity. The drawback to these inverters is the high-level maintenance that they require because of their size. The central inverter is the best inverter when it comes to large-scale solar installations. They aren’t used in residential or small commercial installations.

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​The following are the main types of inverters used in residential or small commercial solar PV power plants:

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String Inverters

String inverters are small in size as compared to a central inverter. The load of a central inverter is divided amongst multiple inverters using a string inverter. Around 40 of these, 25 kW each, can be used in a 1 MW solar power system. Most residential solar PV installations use string inverters, generally one inverter per several panels in an array installation. A string inverter is so called because you connect a string of panels onto one inverter.

Micro Inverters

Micro-inverters as the name suggests are very small solar inverters that are usually housed on the back of an individual solar panel with one inverter connection per solar panel. Since they support single solar panels, their capacity can be as low as 240 W each. That means you can individually optimise each panel to deliver the most energy from an array even when you have shade over a few panels of the array. The Enphase is only micro-inverter in the list above.

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Hybrid Inverters

A hybrid inverter is also called a multi-mode inverter, which allows you to plug batteries into your solar power system. The hybrid inverter uses 'DC coupling' to interface the solar battery and its electronics control the battery charging and discharging.

Battery inverters

If you want to keep your battery system separate from your solar panels, then a separate battery inverter is an option. This inverter converts your DC battery power into AC power and feeds it into your switchboard to replace grid power.

String and micro inverters, on the other hand require little maintenance.  However, string and micro inverters are expensive when compared to a central inverter on their cost per Watt.   For smaller rooftop solar systems, either of the other three types can be used.

Off Grid Inverters

An off-grid solar system, which as the name inplies, is not connected to the national electricity grid.  The inverter gets its DC power from a battery which is charged by solar panels.  In an off-grid solar system, the need for an inverter might not arise if only DC loads are to be powered. Off-grid systems are not required to match the requirements and regulations of the national electricity grid since they are not connected to it. These inverters can be categorised in two variants.

Off-Grid Modified Sine Wave Inverters

The Modified Sine Wave Inverter is the best inverter for simple solar systems and are relatively cheaper. These inverters can be used for old appliances, motors with brushes, and incandescent lights. However, the modified sine wave inverter is not suitable for electronics, induction motors, rechargeable batteries, and gadgets like digital clocks.

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If your power needs include appliances like an HDTV or any other appliance that requires a high energy load, then this inverter is not for you. They might the right choice if you have a DIY solar system such as a simple PV system that is used to power the needs of a small rural cabin.

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Off-Grid Pure Sine Wave Inverters

The pure sine wave inverter is the preferred choice for large solar system setup although it is on a higher price point. These inverters are the ideal selection for powering electronics, dimmers, and fluorescent lights. Pure sine wave inverters work efficiently with almost all type of off-grid solar systems. The pure sine wave inverters are preferred for larger off-grid solar systems, and they can be used for the smaller systems too.

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Grid Tied Inverters

Grid-tied Inverters form part of the solar system connected to the grid and work to the utility grid’s requirements and regulations. These inverters transfer your solar generated power to the electricity grid. A grid-tied inverter must generate AC voltage of a strictly sinusoidal form. They are programmed to automatically shut down in case they detect supply loss from the utility. This protects the technicians repairing the utility network from getting an electric shock. The inverter can be any of the types noted above.

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A Grid-tied PV system is made up of solar panels attached to a grid-tied inverter, and can be configured with or without batteries. The inverter converts the DC voltage coming from the solar panels directly into AC power for matching the grid. If batteries are attached to a grid-tied system, then, the power is transferred to the grid after the batteries are charged. Then the power from the batteries can be used at night.

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Battery Backup Inverters

These inverters draw energy from a battery of the solar system. The battery charge is preserved through a charger. Any excess energy is transferred to the grid. Battery backup inverters can provide AC power during power outages.

Hybrid Inverters

A hybrid inverter operates bidirectionally, converting DC power to AC and then converting AC power for storing in the batteries that power loads at the time of requirement. Hybrid inverters are available in various sizes, features and price levels. These inverters can be grid-tied and use renewable as well as mains energy sources for charging batteries and load-offsetting. Hybrid inverters can be used in urban residential applications as well as remote off-grid home applications.

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Inverter Price

Most grid-connected inverters are offered with the solar power system quote. A good quality small 5kW single-phase solar inverter can cost around $1,000 for a simple, no frills inverter and add another $400 for a 3-phase model. A good 5kW premium model solar inverter from the above range can reach to $2,000.

Solar inverters are rated in both "DC input" and "AC output". The solar inverter needs to be capable of handling the maximum power that your solar power system can generate, so, for 5kW of DC output from your solar panels consider a 5kW inverter. However, the solar inverter’s AC kilowatts output can be rated at 25% less than your panel because there are up to 25% losses during daily operation.

Inverter For PV System To Be Upgraded

Sometimes your quoted price will offer you the option of a larger (say 6kW) inverter (with the 5kW array) assuming later you may wish to add solar panels. You need to confirm how much roof space you have for solar panels and then if that number is enough for your needs. Put the number of solar panels that comfortably fit on your roof, and then purchase the inverter to fit that system’s power. You could possibly consider micro-inverters, or a multi-string array or a MPPT expandable solar inverter if you intend expanding the solar array later.

Inverter Weatherproof

Some grid-connected inverters are weatherproof. You can check your specification sheets for those details but remember your solar inverter has a lot of sensitive electronics. It’s best to put the inverter in the shade out of the weather and keep your solar panels in full sun.

Inverter Warranty

Solar inverters have warranties ranging from 5 to 12 years. Typically, a grid-connected inverter will last between 10 to 20 years. You should expect an inverter warranty of 10 years minimum.

Inverter Display

Most solar inverters have a digital display indicating that the unit is on, off or standby mode. The better ones have displays that indicate some of the following information:

Consider a remote monitoring option if you don’t want to check the meter box to see if your system is performing as it should.

Tips For The Solar System Inverter Buyer

The inverter forms an integral part of a solar PV system. Any electrical component in a competitive market will have its advantages as well as disadvantages. These could also be considered before choosing a solar inverter.

You can watch the video below to see how an inverter works.

Choose A Solar Inverter

Transformerless Inverter

​Previously, grid connected solar inverters that used to be sold were transformer-based and had a lower efficiency than the transformerless inverters typically sold now.

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What does this particular component of your solar power system do? Inverters are devices that convert DC produced by your solar panels into AC that is used by your household appliances.

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All your solar PV’s power will pass through your inverter before going to the house, or if there is excess AC power and your system is grid tied, across to the grid. Grid-interactive inverters are required to produce AC power that exactly matches the voltage, frequency and phase of the utility grid power line. The Grid system’s safety shutdown electronics is an important safety feature built into all grid inverters law. This feature is called ‘Anti Islanding Protection’.

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Anti-Islanding

A grid tie inverter has sophisticated monitoring circuits that can detect the loss of grid power immediately and automatically switch off power transfer through the inverter. It’s vital that you choose an inverter that offers the best performance for your money.

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When the electricity grid is down home solar panels will still be providing energy. That home's solar system has the potential to be sending power back into the otherwise inactive electricity grid’s supply lines.

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For example a house with an array of solar panels on its roof has inverters attached to the panels to convert the erratic DC current from the panels into AC power that matches the grid supply. When the grid is momentarily disconnected, such as when a tree branch makes a connection and disconnects, the voltage on the grid line could drop to zero as an indication of a service interruption.

And, when power resumes there is the potential for a power surge. Grid lines have automatic circuit re-closers that are like a circuit breaker release mechanism. They are designed for overhead electricity distribution networks to detect and interrupt momentary power breaks and cut power, then reconnect as soon as the disruption has passed.

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However, say at the instant of the grid interruption the house's electrical load exactly matched the converted output of the solar panels then there will be no net change (potential of non-detection at the household power site wherein a real grid failure could be filtered out). Then a failure of the grid might not signal a grid interruption at the meter. The customer’s equipment could theoretically be damaged by the power surge if their operating parameters differed seriously from the standard, in which case, the utility would be liable for actual damage.

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If a house system was generating solar power into a section of line it’s potentially islanding. The sudden resumption of power could cause the line conditions to suddenly surge. This is a situation that the grid requires should be avoided. So, methods have been developed to detect the possibility for islanding.

This non-detection is avoided as the grid causes additional signals to be generated during the decrease in line voltage, which signals the fault condition to be seen by the inverter and to shut down. Yet, such power drops can also be caused by normal operation on the grid, like a customer starting of a large electric motor, which cause false signals if not calibrated correctly.

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Compliance Testing

Utility companies insist on inverters having anti-islanding protection to prevent this happening and before inverters are deployed to the field, grid-interactive inverters are required to be tested. Equipment is fed with electrical signals reproducing specific grid conditions and the effectiveness of the inverter’s software detecting the particular islanding conditions and false signals is evaluated.

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Look to see if the solar inverter complies with the relevant International Standard. There are several certifications that apply to solar inverters, including EN 50524, EN 50530, UL 1741, IEC 61683, IEC 62109-1 & IEC 62109-2.

All grid connected solar inverters should be certified for these standards.

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Your Solar Powered Home Is Also Off In A Blackout

One disadvantage of this Anti Islanding Protection is that during a blackout, your house, like all the others in the street, will also lose its power!

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You bought a solar system, and really, why would you want this to happen? You need to buy inverters that will isolate your home from the grid when a grid blackout happens, and let you use solar power of your home until the grid comes back on. This type of inverter is used when you add a battery bank for storage of your excess power.

Here are four inverter brands that you might consider and they have that isolation feature to let you continue using solar power.

Each of these inverter systems in the same output range will be within adjacent price points, albeit they might be at the higher end for inverters.

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Solar Inverter - SMA

SMA solar inverters for domestic and commercial use are produced in Germany and China. The SMA Sunny Island 3.0M / 4.4M inverter is an example of a custom-fit solution for small on-grid and off-grid mixes.

High Quality

The SMA Sunny Island 3.0M / 4.4M inverter represents good quality and is efficient, but it’s also more expensive. This SMA inverter can be used for stand-alone and grid-connected systems with a power output range of 2 kW to 13 kW.

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The SMA Flexible Storage System stores generated solar power and delivers obligatory off-grid reliability. The SMA Sunny Island intelligent load and energy management system ensures safe operation even in adverse situations.

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Adaptable

The Sunny Island Inverter is adaptable and works well with other equipment, so that the system can precisely meet your applicable power requirements; including all well-known brands of lithium-ion battery and all lead-acid batteries; new and existing PV systems as well as for single-phase and three-phase systems.

Tough

The Sunny Island is tough and works reliably under all conditions, like the wide temperature range of working in harsh ambient conditions. It has sufficient overload capacity in the event of high in-rush currents without compromising its efficiency.  It runs in all conditions including the most extreme temperature fluctuations, in fine dust of desert sand, rainforest humidity as well as the salt spray of coastal regions, thanks to IP54.

Solar Inverter -  SolarEdge

SolarEdge is an Israeli inverter company. It was started in 2006. It uses a string inverter matched with a 'DC optimiser' on each solar panel. These optimisers allow Individual panel monitoring and optimisation. That means one panel being shaded will not affect the other panels in the array setup. 

The remote monitoring allows rapid shutdown of panels in the case of an emergency, maintenance or bushfire. The Multi Power Point Tracking is done at the panel level, so needing a smaller inverter.

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The SolarEdge single-phase inverter is for on-grid applications. In addition to its usual function as a DC-optimized PV inverter, the backup power inverter manages the battery and the system energy. Backup Power inverter includes the hardware required for automatic backup power in case of grid interruption.

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The SolarEdge single-phase inverter is designed for solar PV, on-grid storage, and backup power and designed to safely eliminate high voltage and current during installation, maintenance, and fire fighting.

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The inverter comes with built-in monitoring software for remote access of battery status, PV production, remaining backup power, and self-consumption data.

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SolarEdge has a DC coupled storage solution that automatically provides homeowners with backup power in case of grid interruption. The battery storage allows homeowners to maximize self-consumption and enables energy independence.

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The backup power is based on the StorEdge™ solution for on-grid applications and works with their solar products.

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Solar Inverter  - Fronius

The Fronius Galvo, Fronius Primo and Fronius Symo are Hybrid transformerless Wi-Fi enabled inverters that will integrate seamlessly with most solar power battery banks. Depending on your needs and specifications, you will be able to choose from amongst grid-connected inverters, string inverters for residential solar power and central inverters for commercial and industrial solar applications.

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The Fronius Galvo is a super lightweight residential single-phase inverter. The Fronius Primo is a compact single-phase inverter for most residential applications. The Fronius Symo is a fully integrated commercial three-phase inverter with power capability between 3 kW and 24 kW with dual MPPT. The Fronius Symo works well for an irregularly shaped roof of unusual orientations.

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Most models have built in "smart grid" features that allow you to meet all electricity networks’ grid connection rules. Their MPPT efficiency is well documented. They have good connectivity and with standard wireless Internet connection that make Fronius inverters a ready integration with third-party components.

The Fronius Symo is one of the most communicative inverters on the market with a meter interface that enables dynamic power management and graphical visualisation of consumption. These inverters are top quality, with many features and good performance but they are at the expensive end of the price spectrum.

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Solar Inverter - Enphase

Enphase Energy is a US-headquartered manufacturer that develops micro-inverters for the solar PV energy market. Enphase Energy’s international profile includes offices in France, Italy, the United Kingdom, China, New Zealand, and Australia.

Enphase Energy is a global leader in micro-inverter technology. These miniaturised inverters work at a very different level to a single string inverter working with multiple solar panels; one is installed on each single solar panel of solar power system installation.

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Enphase micro-inverters offer several advantages over string inverters, such as more flexible system design, a level of redundancy, ability for monitoring individual panels and thus mitigating the impact on a system of single solar panel shading. However, given their panel level operation, you will pay a bit more for a micro-inverter based system.

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The company's seventh generation micro-inverter, the Enphase IQ 7 series, is 50% lighter and 23% more productive power.  The IQ 7 range is suited to both residential and commercial applications.

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Enphase Energy provides other energy-related services and produces solar batteries and accessories, communication gateways and monitoring systems. The company’s micro inverter products are top quality and Innovative.

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The Future Technology In Inverters

There are both centralized, string and decentralized inverter designs. This refers to using multiple inverters throughout a project to achieve higher efficiency while simultaneously lowering the cost across the same timeframe. This is happening in the micro-inverter set-up in some places. Using three-phase string inverters for a decentralized PV system off grid solution is gaining popularity.

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Inverters are the spine of a solar PV system and smart inverters with MPPT are moving to take a larger share of the inverter market.  Smart web interactive inverters will be matched with utility smart grids and smart home technology.

Inverter Summary

A solar inverter is used for converting DC into AC or topping up your bank of solar batteries. 

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A multi function hybrid solar inverter is the best inverter for many commercial establishments because it converts DC to AC efficiently and is the most adaptive.

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The best string inverter is the Fronius Primo, a compact single-phase inverter suitable for most residential applications.

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The best micro-inverter is the Enphase IQ 7 series, which is lighter and more productive and suited to both residential and commercial applications.

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