For those new to solar read this first - How Solar Works
When you first consider getting solar or battery storage on your home or business, one of the first things you will discover is that you will require an inverter and that there are many different types of inverters available. This article is designed to provide an introduction to the different kinds of inverters available and help you to understand which one will suit your installation.
What is an inverter and what does it do?
So what does an inverter do? Simply put an Inverter converts DC power to AC power. Solar panels produce DC power and batteries store DC, however most of our appliances run on AC power, as does the electricity grid. This is why all solar systems and battery storage systems need an inverter however there are several different types of inverters depending on whether or not energy storage batteries are required.
The 3 main types of Inverters
Solar Inverters - Grid connected solar
Hybrid Inverters - Grid connected solar and battery systems
Off-grid Inverters - Powerful battery Inverter/chargers
Now we need to distinguish between the two main types of solar installations, solar on-grid (without battery storage) and solar with battery storage (off-grid or hybrid); inverters play a different role in each type of installation.
On-grid solar installations are the most common and most affordable type of system available at present. These systems use a simple solar inverter, which convert the DC power from your solar panels into AC power which can be fed directly into the grid, or used in your home appliances.
Off-grid and hybrid systems are much more complex because they involve both solar panels as well as battery storage. Multiple inverters are often required in these installations such as a solar inverter and sophisticated battery inverter/charger to manage both grid connection and the charging and discharging of the batteries. These advanced inverter/chargers are known as interactive or multi-mode inverters. However, in recent years a new type of inverter has become available which integrates solar and battery inverter technology into what is known as an all-in-one hybrid inverter.
There are actually two types of solar inverters; string inverters and micro inverters but string solar inverters are the most common type used around the world due to the low cost and simple installation.
String solar inverters are used when the solar panels are linked together to form a string. A typical string can be made up of as little as 3 solar panels or up to 20 or more panels. DC power is brought down from the string into the inverter where it is converted to AC power.
A micro-inverter is a very small inverter that is attached to the back of a solar panel. A micro-inverter only converts the power of one or two solar panels to AC so generally many microinverters are required in a single system. Micro-inverters have several advantages over string inverters including performance, safety and monitoring, however the upfront cost can be significantly greater. For more details about micro-inverters, check out our micro-inverters article.
String solar inverters come in single phase and three phase versions although most residential homes in the US and Australia use single phase power, while many homes in Europe use 3-phase power, also all businesses and factories will have three phase power. As a general rule most String solar inverters between 1-6kW are single phase and greater than 6kW are usually three phase.
Hybrid & Battery Inverters
As home energy storage systems have surged in popularity a new kind of advanced Inverter has emerged known as an hybrid inverter. Hybrid inverters combines a solar inverter and battery inverter/charger into one simple unit. These inverters are a very economical way to enable what is known as ‘self-use’ or 'load shifting' of energy. Allowing you to store solar or off-peak energy in a battery to be used during peak times. Although it is important to know that some all-in-one inverters cannot function during a power outage such as when there is a blackout. They can also have limited functionality and monitoring capabilities.
Backup power - If you require a hybrid inverter which is capable of powering your entire home when the grid is down (Uninterruptible Power Supply or UPS) then you may require an interactive inverter as decribed below.
You can read more about the various hybrid inverters here
Off-grid Multi-mode Inverters
The traditional off-grid solar system uses a simple battery inverter that converters DC power from a battery bank to AC power to supply your home or appliances, these systems need separate battery chargers and regulators. There are more advanced versions of these battery inverters with built in chargers known as inverter/chargers. In recent years very advanced inverters have become available which are inverter/chargers with in-built generator control systems, advanced monitoring capabilities and other features, these are known as interactive or multi-mode inverters. They are typically used in conjunction with a solar inverter to create what is known as an AC coupled system. You can learn more about these and other hybrid inverter types here.
The most powerful inverters are used for off-grid systems. These Multi-mode inverters are also used as grid-interactive inverters as they can function in both hybrid and off-grid modes. These inverters are very powerful and can work with multiple energy sources such as wind, solar and back-up generators, but of course this comes at an extra cost. An multi-mode inverter would normally be required if you wished to add batteries to your existing on-grid solar system. For more in depth information and reviews about different hybrid and solar systems see our hybrid and off-grid inverters article and review.
Truths and Myths about solar
There are many misconceptions in the solar industry. Below are some common truths and myths about solar inverters and their capability.
A marketing ploy used by some solar companies is to say that a system is sold with an ‘up-gradable’ inverter, because the inverter capacity is significantly larger than the panel capacity. This sounds great in theory but in reality the inverter size should be matched to, or be a little less than, the solar array size for the system to operate at its maximum efficiency. Also if you decided you wanted to upgrade in the future then you would need to source the same size and type solar panels, and this can be difficult a few years down the track as they may no longer be available.
What happens during a blackout
Another common misconception is that a typical on-grid or grid-tie solar system can still operate when the grid goes down or there is a blackout. This is wrong. Many people who have invested in a solar setup are surprised when they have no power due to a blackout in the middle of the day. This is because all on-grid inverters are required by law to automatically shut down when there is a grid outage or when the grid voltage is unstable, a feature known as anti-islanding. This is very important to protect line workers who may be repairing a fault in the grid. It would be very dangerous if your system was still producing electricity and feeding it into a faulty grid network. To have backup power during a blackout you will need a hybrid solar system or an AC battery system with grid isolation such as the Tesla Powerwall.
Solar only works when it’s sunny
This is incorrect, solar panels will generate energy when it is cloudy and foggy but the amount of energy is proportional to the thickness and type of clouds. If there is a high, thin cloud layer solar panels can still produce over 50% of there rated output but if there are dark rain clouds then the energy can be 10% or lower. Also the time of year will have a big impact on the solar generation especially if the panels are mounted very flat or at a low angle. To increase winter generation the panels should be tilted towards the midday sun up to 45 degrees if possible.