How to Choose a Solar Inverter

While choosing a proper inverter for your solar generating system, take into account the capacity of your solar arrays and whether you plan to retrofit the existing installation with an energy storage. A reliable inverter should be properly certified and have the size sufficient to handle the power output generated.

See also: Best Solar Inverters | Solar Inverters News | How to choose a solar installer | How to choose the best battery for a solar energy system

Choosing the Best Solar Inverter

Solar inverter is a device converting the DC electricity produced by a solar system into the AC that can be used by your home power circuits. It is the most complicated part of a solar installation and, alas, the one that usually gets out of order first. There are several types of solar inverters, most of them are installed on external walls, while others are roof-mounted. Besides, there are quite a few other factors you should take into consideration when choosing between numerous quotes and proposals. If you read the below information and recommendations carefully, the task of selecting the right inverter won't be as challenging as it might seem to you anymore.

Types of Solar Inverters

Which type of an inverter to choose depends on your solar system's size, your future plans and current requirements. So, the types of inverters are as follows:

• string inverters;
• micro-inverters;
• hybrid inverters;
• battery inverters;
• optimizers;
• central inverters.

Let's consider each of them in detail. 

String inverters

String inverters is the most widespread type used by most households. One such inverter is commonly used for one PV installation, where one or a few strings of solar modules are connected to an inverter in series. This inverter type is rather simple and the cheapest one among all options.

The con of string inverters is that a problem with one panel will cause the underperformance of an entire string. Anyway, it is unlikely to happen unless the installation is shaded or you fail to maintain it well. 

One more drawback of this type of inverters is that solar modules are DC-connected to an inverter, and there's a risk of arc or fire in the event of fault or degradation of the system components. However, if you use qualitative components installed by a reliable installer and don't forget about proper maintenance, you have no reason to worry about that.

String inverters are manufactured by most of well-known inverter brands, including Fronius, SMA, SolarEdge, ABB, and others.

Micro-inverters

Micro-inverters are very small and are connected to each individual photovoltaic panel. As an option, there are micro-inverters integrated with solar panels into a single component – AC module. Micro-inverters are a must-have for the installations exposed to partial shading. 

Though individual efficiency of each inverter can be lower than that of string inverters, the overall efficiency of the whole solar system is usually about 12 percent higher because shade, damage and other issues only impact the performance of one panel (not the entire installation). 

It is more costly to install micro-inverters, they are less protected from weather conditions and the maintenance is more laborious (compared to string inverters mounted to a wall).

However, you are protected against the risk of arc or fire because there is no DC-connection. Besides, micro-inverter is a good option for the rooftops that cannot house large strings of solar panels and for the ones who consider expanding the installation in future. 

The best micro-inverter manufacturer is definitely Enphase.

Hybrid inverters

Hybrid inverters are sometimes referred to as multimode inverters. They are used to connect solar generating systems and storage batteries by means of a DC-coupling. Such an inverter is usually priced higher than a conventional string inverter. However, they are becoming more affordable and price competitive with standard inverters.

The main challenge associated with hybrids is battery compatibility. In case you install a hybrid inverter with an idea to add a battery in the nearest future, there's no problem. But if you don't plan retrofitting your solar system with a battery soon, the required battery type can be out of production by the time you need it. That's why, in this situation it would be wiser to get a standard inverter and to leave the question of battery adding for future.

Hybrid inverters are produced by Fronius, SMA, SolarEdge, Huawei, and other manufacturers.

Battery inverters

Battery inverters are for those who already have a solar power system with an inverter installed and would like to add energy storage but prefer to keep an existing inverter instead of replacing it with a hybrid. A battery inverter turns the power stored in a battery into usable AC and delivers the power generated by PV modules to batteries for storing.

There are battery models (for example Powerwall 2 by Tesla) designed as 'all in one' with an integrated battery inverter. This integrated option can be as good as adding a battery and an inverter separately, in case you've got micro-inverters installed.

The key battery inverter producers are SMA, Enphase, Sonnen and Selectronics.

Power optimizers

Power optimizers are not actually inverters, but are used to optimize the inverter performance. A power optimizer is connected to individual panels in a string to eliminate the impact of a failed panel on the entire array. 

Some optimizers have to be attached to each panel in a solar array necessarily, while others allow optimizing only specific panels. 

Optimizer is one more possible variant of dealing with partial shading. And this option is cheaper compared to installing micro-inverters.

While selecting a power optimizer, you can opt between an integrated inverter-and-optimizer system of the same brand (which would enable you to monitor the performance of the entire system) and a separate optimizer by a different manufacturer. Moreover, an honest installation company should explain that you can optimize only some panels (for example, the most shaded ones).

SolarEdge, Huawei and Tigo are among the major optimizer makers.

Central inverters

Central inverters are huge and are never used for residential applications. They are only installed in large-scale industrial and commercial plants, the capacity of which ranges between hundreds of kW and MW. Such inverters usually resemble big metal cabinets and each can deal with up to 500 kilowatts of power.

How to Choose a Good Solar Inverter

Now, you know what types of solar inverters there are and how to choose an optimal type for your particular needs and conditions. However, there are quite a number of other parameters that should be considered while looking for a good inverter. Below we've listed the most essential of them.

Approvals and certifications

Before buying a solar inverter, check it for compliance with the required standards. In Australia, CEC approval is obligatory, and the applicable standard is AS4777. All the large and reputable manufacturers provide the necessary approvals. But if your inverter maker is not so famous, make sure the product is listed among the approved products. Otherwise, using a non-certified inverter can be first of all dangerous and secondly ineligible for incentive programs. 

Besides proper certification, if you're not installing a well-known brand, try to find out more about the manufacturer's track record and competence.

Capacity and dimensions

The capacity of a solar inverter needed is directly dependent on the generating capacity of your solar system. Inverter capacity is measured in kW and means how much power produced by PV modules an inverter can handle. Because a solar system hardly ever performs at its maximum capacity, an inverter size doesn't necessarily have to be the same as the size of an array. According to the Clean Energy Council's requirements, it should be no less than 75 percent of a solar array's capacity. Apart from this rule, some other restrictions regarding the inverter size can exist. Ask your installation specialist about possible limits. By the way, don't forget that inverter ratings are expressed as AC-output and DC-input. Check both parameters to get assured that your inverter suits your solar system.

Your installer can propose getting an inverter with a higher capacity in order to install more solar modules in future. Don't yield to persuasion in case your rooftop is too small for placing additional panels or if you doubt whether your existing panels will still be on the market by the time you need them (otherwise a new panel model can be incompatible with the inverter installed). Optionally, you can think of a multi-MPPT solar inverter that can be expanded. But generally, the optimal choice is getting the maximum possible number of solar panels and an inverter that can manage the power output of your solar system.

In addition to inverter capacity, you should take into account its physical dimensions. Micro-inverters are usually sized as a normal paper book. String inverter size can range between a big brief case and a little suitcase. As a rule, inverters are mounted as close as possible to electrical meters and should be shaded to perform better. So, consider whether you can place an inverter in the proximity of an energy meter and how it will look when mounted.

Expandability

This parameter is essential in case you plan to add extra panels to the existing system later. Currently, the optimal option is a multistring inverter with many MPPT-trackers. This allows both expanding an installation with more solar arrays and placing arrays oriented differently. With a multi-MPPT inverter, you don't have to bother yourself seeking for the same panel model as the ones already installed.  

Weatherproofness and security

The majority of grid-tie inverters are weatherproof (mostly with IP65 enclosure rating). However, some inverters are not and they need to be additionally protected by a special cage or housing. 

Most types of inverters (except for micro-inverters and power optimizers) are located on external walls. Even if an inverter is weather-proof, it must be placed under some shading. Otherwise, direct sunshine and extreme heat can decrease its performance and lifetime. If there is no such shaded place where an inverter can be mounted, a special canopy or cover should be installed over the inverter. 

Besides the protection from weather conditions, pay attention to security issues while deciding where to locate an inverter. It is better to mount such an expensive device in some secure place beyond the reach of thieves (unless your inverter features a special in-built antitheft locking device).

Warranty

An average lifetime of a solar inverter is between 10 and 20 years. Warranty periods usually span the range of 5-12 years. Some companies offer extended warranties for extra payment. Others provide warranties like '5+5', where during the first five years both components and labor are warranty-covered, and within the next five years the labor costs are covered at your expense. 

In case your retailer is no longer available by the time of a warranty event, you can contact an inverter manufacturer directly and they will resolve the issue. 

As a rule, an inverter pays for itself within 5 years, so this is the minimum lifetime you should expect from the unit you install.

If your inverter breaks down after the warranty period has expired, it's not a reason to get upset (unless the product hasn't paid for itself yet). Usually you can get a more advanced model at the price you purchased your current inverter some years ago, because the technologies continue developing and the prices are getting down.

Price

String inverters are usually priced somewhere in between 1 and 2 thousand USD (depending on capacity and manufacturer). An average price of a micro-inverter is about 200 US dollars. However, the overall price of a solar system with micro-inverters is commonly around 20 percent higher than that with a string inverter. 

Power optimizers usually cost a little less than micro-inverters. And don't forget that you don't necessarily have to attach an optimizer to each panel, but can limit the installation by those panels which require optimization. In this case, optimizing your solar system won't cost you more than several hundred USD. 

As for hybrid inverters, you can find a unit costing 1-2 thousand dollars, though in most cases the price reaches or even exceeds 3 thousand USD. Installing a battery inverter as a rule adds about 2-3 thousand USD to the cost of the entire system.

The general recommendation is not to purchase the cheapest models available. Such units will not last long enough to pay for themselves, so don't be penny wise and pound foolish.

Display and monitoring

Display lights usually indicate if an inverter is on and normally operating, whether there're any faults, etc. If your inverter is provided with a display panel, it can show a lot of data including how much energy is being generated right now, has been generated today and during the lifetime of an inverter, how long the energy has been generated, and so on.

There can be also an option of remote data monitoring from your computer or smartphone app. This is very convenient if you don't want to come to your inverter or meter every time to check how it is doing. However, keep it in mind that most people forget to check the data regularly in a few months. So, if you're unsure you're going to use the remote monitoring system, there's no need to overpay.

Working during outages

The majority of solar power systems turn off during power outages. However, at an extra price, one can install a solar inverter allowing the power to run. 

In case of connection to the electrical grid, there must be protection against islanding. Otherwise, the power lines and workers fixing the issues can be damaged. So, most inverters shut down if they indicate a blackout. 

There are more innovative hybrid inverters protecting the grid against electricity islands and at the same time keeping the power flow from a solar system to domestic appliances. This is an expensive option due to the high price of such inverters. Besides, you will need a large solar system and a battery to keep the power running during several hours of outage. 

In order to cut costs, you can leave only a few of the most essential appliances operating (for example, a refrigerator and a few lamps). But this would require additional electrical work, and consequently, additional expenses, too.

Efficiency

Efficiency of a solar inverter means efficiency of converting DC generated by PV modules into AC suitable for home use or injecting into the power grid. The majority of grid-tie inverters with transformers (which were manufactured earlier) are 93-percent or higher efficient. Modern TL inverters are 95-percent efficient or even higher. 

So, as you can see, inverter efficiency is not an essential issue. Check for efficiency only in case it is the only considerable difference between two inverters that are quite similar apart from this.