How to chose the best inverter for your home?

A buyer’s guide to solar panels

By Maz Mirzakhani

Mechnical Engineer, SolarNova.

Our Buyer’s Guide to Inverters is for people who are new to solar, so that they can understand the different inverters, their specifications, compare features and pricing.

What is an inverter?

If the panels are the heart of the solar system, the inverter acts like the brain of the solar system. The inverter manages the flow of power from your panels to your home and converts the energy into a usable form.

What does the inverter do?

Converting DC to AC- When panels generate energy from the sun, the energy flow is DC (Direct Current). Home appliances connected to the grid use AC (Alternating Current). The inverter will convert the DC to AC in order for the power to be consumed by the household appliances.

Sending energy where it is needed. The inverter decides whether the energy is to be used by household consumption, to charge the battery or if the energy needs to be sent back to the grid. During the night, the inverter draws from the battery’s stored energy instead of drawing on grid power if there is charge in the battery.

How do I pick the right inverter for me?

The differences between inverters is significant, every product has its own features. Picking the right inverter is not a straight forward process and it is best answered in consultation with a solar system designer and installer. The following factors that you should consider in choosing the right inverter;

  • How big is your system? which is dependent on your power bill and what you are trying to achieve from going solar – being 100 % self-sufficient from the Grid or just saving on your bill by a certain percentage.
  • Your roof space – the orientation and shading
  • The number of phases to your property as not every brand has solution for three phase systems
  • The desired level of self-consumption, time of use and whether you need (want) to add a battery – there is a difference between adding a battery to an existing solar system compared to installing the battery to a new system (AC coupled or DC coupled)
  • How often do you have blackouts (not a reliable Grid) -you might consider an inverter with backup capability combined with abattery

Your solar installation company should have a couple of solutions for each circumstance and the ones that have enough product knowledge and engineering expertise would be able to provide the best value for money. Buying an expensive system doesn’t guarantee the best result, so it is important to engage the right designer and installer at the early stage of your decision-making process.

Here is our walkthrough of the main brands and types of inverters in the market

What is the difference between a Microinverter and a String Inverter?

There are 2 types of inverters; String inverters and Microinverters (optimisers can also be installed on each panel in addition to a string inverter).

String inverters are used when there is simple panel designs and there is ample usable roof space. String inverters are  installed next to metering, typically in your garage or low levels of your home with easy access. String type of inverters can either be  a Grid Tie inverter or a Hybrid inverter. The Hybrid inverter  will work even when the grid is down. The Hybrid inverter is used in places where blackouts  regularly occur, as they are easy to be installed with the battery in storage. In those cases where String inverters are used and there is shading, an optimiser can be added to the panels.

Microinverters are small individual inverters installed on each panel. The DC current from each panel is transformed to AC at the panel level (sometimes referred to module level inverter). Enphase is the most commonly used and known microinverter in the market, at SolarNova we have installed hundreds of Enphase microinverters. Enphase have a reputation for being a premium product with individual panel level monitoring. Enphase is an American company and they have great service and a large footprint in the Australian market.

Finally the choice on inverter will come down to how much energy you need your solar system to generate.

What are the advantages of using Microinverters over String inverters?

  • they are the most suitable product for the roof with limited space where panels are scattered in different directions on the roof such as on East, North, West profiles and split roof profiles
  • can be used if shading occurs on some parts of the roof
  • they are not limited in the number of panels that can be installed with as little as 3-4 panels only
  • excellent after sales service with 12 years warranties for Enphase Microinverters
  • system more efficient compared to a design with DC optimisers with a minimum 3% more efficiency
  • if one microinverter fails, the system doesn’t fail – if a single panel is out, it doesn’t drag down the other panels production
  • individual monitoring by Enlighten platform to control each panel and microinverter function

 

What are the disadvantages of using Microinverters over String inverters?

  • additional cost compared to the string inverter
  • not easy to access for maintenance as they are on the roof and installed on each panel
  • to add a battery into an Enphase design system, it has to be a AC coupled battery, not a DC battery. AC coupled batteries have an additional cost (Tesla and Sonnen). Read about the battery pricing in our Battery section

What are the 3 types of Enphase microinverters?

There are 3 types of Enphase Microinverters available in Australia. The IQ7, IQ7+ and IQ7X Models are listed in the table below for comparison

Enphase InverterIQ7 (Residential and commercial)
IQ7+(Residential and commercial)IQ7 (Residential and commercial)
Input Power 195 - 330W235 - 400W320 W - 460 W
Module Compatibility60 - cell modules60- and 72-cell96 - cell PV modules

When do I need to use an Enphase microinverter?

If there is shading or a split array in the roof design, Enphase Microinverters are a perfect option, but you have the option of  a String Inverter design with DC Optimizers. We recommend the Enphase microinverter under the following conditions;

if you are limited to only a few panels due to shading or,

the roof design requires panels to be scattered on the roof facing different directions, or

if you have a limited space for a string inverter next to the switchboard.

What are DC Optimisers?

DC optimisers are installed on each panel, as with the microinverters, and optimise the panels power output by decreasing or increasing the voltage (different manufacturers have different specifications and functions). DC optimsers allow each panel to function individually with regards to performance. For instance, when there is shading on one panel, we can install an optimiser, to stop that panel from dragging down the other panels power output. The most well know DC optimisers in the market are; SolarEdge, Tigo and Huawei ( a new one to the market). SolarEdge DC optimisers are compatible with the SolarEdge inverters for single and 3 phase systems.

What are SolarEdge inverters with optimisers?

SolarEdge inverters with optimisers, are an excellent solution in those cases where we have shading, multiple split arrays or a combination of these two. SolarEdge optimisers are  limited to a minimum number of 8 panels per string, so, if you have a smaller string size than this on your roof, it is better to go with the Enphase system solution.

A SolarEdge solution is more competitive in pricing compared to an Enphase system of similar size, being around 30 % cheaper.

Solaredge inverter comes in both single or 3 phase to match your home’s powerline. The MPPT (maximum power point tracking) is done by the Solaredge optmisers at the panel level (DC to DC conversion), with the inverter controlling the DC output.

More information on optimisers is available at the end of this guide.

SolarEdge have a broad range of sizes from 2.5kW to 10kW. A Standard 12-year warranty applies (extendable to 20 or 25 years). Quick and easy inverter commissioning is achievable from your smartphone using the SolarEdge SetApp for both single and 3 phase power lines. Commissioning is where the system’s and inverter’s performance is checked on installation. After installation you can monitor your solar system performance with the app from any remote location in mobile range.

The SolarEdge Inverter can be a good solution for the addition of a DC coupled battery by using a battery ready inverter or the SolarEdge StoreEdge Box. StoreEdge is for new installations or to upgrade existing SolarEdge systems. The StoreEdge interface supports the simple installation and connection of the high voltage storage battery (LG chem) and the SolarEdge energy meter to the inverter. It is suitable for indoor or outdoor installations and includes a 10-year standard warranty.

Fronius Inverters

If new clients ask us what is the best inverter in the market, our answer is Fronius. The Austrian made inverter is not only the most reliable, it comes with the best customer service, is simple and straight forward for installers to install and commission. The Fronius inverter is a good match with Tigo optimizers if your system design requires optimisation. The Austrian made inverter has been the market leader in Australia and at SolarNova, we have installed hundreds without a single issue. Customers who pay a premium price for  Fronius inverters do so for the peace of mind quality brings.

There is a hybrid version of the Fronius Inverter which can be used as a string inverter. They are double the price of normal string inverters.

How do I match the right battery to my inverter?

If households use most of the power generated by their solar system (self-consumption) the return on investment on these systems takes typically on average 3 to 4 years, even sooner for bigger system sizes. If self-consumption is low when homeowners are out, the power generated by the solar system is sent to the grid and the feed in tariff is only a fraction of the power cost at the peak times. Meaning you pay more for energy off the grid than is paid to you when you feed it in. (up to 6 times more expensive depending on the grid provider).

In cases where people would rather store energy for later use than feed it to the grid, it may be worth adding a battery to the system which will pay back in as little as 4 – 5 years ( See our Buyer’s Guide to Batteries ,“ Is it time for a Battery?” for a better understanding of the differences of battery types and their cost and the pay-back time frame)

The cost of adding a battery into the existing system depends on the type of system initially installed and your type of inverter. You need to consider whether your inverter and battery are a strong match. Deciding on the right battery to go with your inverter is a decision best made at design stage when you are designing a whole system based on your goals in going solar.

What are the top string inverter brands?

The top end of the string type of inverters are the Fronius (Austrian made) inverter with single phase or 3 phase options followed by SMA (German), SolarEdge (Israel), Sungrow ( Chinese) and Huawei (Chinese) inverters. These are our most frequently recommended brands because they cover the different design and application requirements of our customers, they have a track record of product quality and good level of manufacturer after sale service. In addition to these brands there are many more brands that have gained trust in the market such as Goodwe.

What are Hybrid Inverters?

There is another type of string inverter called the hybrid inverter which allows DC couples batteries to be added to the system. Our pick of hybrid inverters is the Fronius and most the affordable and reliable hybrid inverter for adding a battery is the Sungrow (LG chem Resu models). The system can be designed very cost effectively compared to having a string inverter not compatible with DC coupled batteries. A battery can be added at a later stage although it would need to be an AC coupled design like the Tesla Battery or Sonnen.

What is the Huawei battery ready string inverter?

As the industry evolves and specialty batteries are becoming more viable financially, some companies like Huawei have a battery ready string inverter which are very competitive in pricing. Huawei also have optimisers as well for shading or multiple panels in different orientations on the roof. The Huawei inverter is not a backup inverter, which means they do not have a back-up option when the grid is down. Their main purpose is to increase your self-consumption and reduce your power bills by adding a battery.

The Huawei  battery is best for people who want to increase their self-consumption, who have a single phase power line and need a solar system which generates 5 to 7.5 kW. In this case the Huawei is the most efficient inverter and cost effective design. (Another choice is the new Sun2000 Models, which have both the optimiser and battery connectivity feature for a very competitive price.)

There are some other advantages of the Huawei design, apart from being one of the biggest tech companies in the world (180 thousand employees) the Huawei optimiser design doesn’t have to be installed on each panel. You can have them on the panels only affected by shading (similar to Tigo Optimizers). If you wish to add a battery to the system there is no need for extra hardware for the LG chem Resu 7.5 or 10 HV models.

However, The Huawei SUN 2000 -5KTL inverter (picture below) is limited for the single phase design. For solar only systems it can be oversized to 7.5 kW  but the design is  limited by the  LG Chem RESU HV Battery to 500V, which minimizes the string voltage and the whole PV system gets downsized to 6.5 kW .  The Huawei is working to resolve that limitation and also they are releasing a new inverter for the battery storage capabilities for 3 phase systems.

What are the 3 main optimisers in the market?

The table below compares the 3 main optimisers in the market

OptimisersSolaredge
TigoHuawei
Compatiable inverterSolaredge - HD wave Any type of String inverter (like Fronius)Huawei 2000L-Ktl
Minimum number of panels8Not limited5
extendibilityYesYesYes
All the panels need optimisersYesNONO
Minimum string Voltage300150150
MPPT tracking In Panel level by OptimizerBy InverterBy Inverter
SafetyModule level voltage shut down for installers and fire fighterRapid Shut downSafety box DC Disconnection
MonitoringAvailable on the platformAvailable on Deployed versionStandard

Conclusion;

The above information should give you some ideas of your path to choosing the right inverter and design. We recommend you get in touch with the SolarNova engineers to find the best solution for your solar projects. Our team can give you a free consultation on your journey to choose the right inverter and system for your home’s needs.

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