Where and Why to Use Hybrid Inverters in Solar Applications

A hybrid inverter can be an all-in-one solution. Learn where and why to design with this type of inverter.

This is a common question in the renewable energy industry because there are many products available in the ‘inverter’ category.  The differences between products can relate to basic output wave technology, features and functionality.  That means the differences create distinct manufacturing requirements and therefore varying pricing in the market.  From standard solar PV inverters to hybrid solar inverters to battery inverters, the renewable energy market caters to all customer requirements. 

As a consumer or solar system designer, it is important to understand what type of inverter your application needs to be clear you are choosing the right product, maximizing your equipment investment and ensuring system installation success for years to come.  During the research phase, we suggest it is best to think not only of today’s requirements, but also changes planned for the future.  Paying a bit extra today for the right inverter, may well prove to be a money saving decision down the road. 

Before we decide where to use hybrid inverters, we need to define what a hybrid inverter is.

• A hybrid inverter (sometimes referred to as a multi-mode inverter) is an all-in-one solution that contains three totally different functions.  It has an integrated solar charge controller that connects to the solar panel(s) and serves to regulate the voltage from the output of the solar panel to the loads and/or batteries.  Note:   Utility power and generator power can often also be inputs for incoming energy.  A hybrid inverter offers multiple system design options, creating flexibility to implement the right solution for each customer’s conditions.

• This product “inverts” the current from direct current (DC) coming from the solar panels, to alternating current (AC) so typical home and business appliances and equipment can operate.  If approved in the local area, the utility grid can also use the energy created by the solar panels.  This alternating current can normally be 50 or 60 cycles per second or Hertz (Hz), and as each cycle has a rise and fall, the AC current would pass by zero 100 or 120 times per second.

• The hybrid inverter also serves as a battery charger, taking power from PV and/or an AC source to charge the batteries. The energy stored in the batteries can then be used later.

Inverters come with several AC output curves.  Here is a quick review of each type

• Square Wave Inverters – The easiest to design and manufacture, and the cheapest, where the 100 or 120 voltage changes per second would occur only vertically, producing square waves.   These inverters do not allow the AC loads to work under the “normal” conditions they were designed for. This means for some loads such as motors and compressors, these will tend to operate at higher temperatures and lower efficiencies caused by the deviation from a perfect sine wave, for which they were designed. Power supplies as they are used for computers, phones and audio equipment will see more electrical noise and may suffer from decreased life expectancy. These inverters can be less reliable and potentially unsafe for certain equipment (some European countries have banned these products).  To avoid load damage, often only resistive loads (such as heating elements) are used with this type of inverter.  See fig 1

• (Pure) Sine Wave Inverters – This output is ideal for all loads including sensitive equipment. The wave of the output current is one that equals the mathematical sinewave.   See fig 1
  
  This is the waveform that allows equipment to operate under optimal conditions, likely providing a much longer equipment life. Because the AC loads used with such an inverter are operating under the same conditions as a clean power grid, for which they were designed, efficiency is also optimized and electrical noise is minimized. This is often a requirement for audio equipment to function as intended. See Phocos Hybrid Sine Wave Inverter options here. All Phocos inverters are of the pure sine wave type.

• Modified Square Wave or Modified Sine Wave Inverters – Between square wave inverters and sine wave inverters, there is also a “modified square wave” inverter type that some manufacturers have called “modified sine wave” as this sounds more appealing. This is incorrect however, as these types of inverters start as square wave inverters, and the square wave is modified slightly to produce a wave somewhat closer to a sine wave.  See fig 1
  
  The advantage is that the drawbacks of square wave inverters regarding AC load temperature, efficiency, life expectancy and electrical noise may be slightly less pronounced. The bad news is there is usually still a strong deviation from a perfect sine wave and that users may never know the difference. For a typical customer there is no way to really know how much of the output is a square wave or not, unless of course an oscilloscope is used to analyze the signal.  It is worth noting, there is some equipment that does not work with square waves, like clocks for example.  This equipment cannot function accurately using modified square wave or square wave inverter outputs.

When a hybrid inverter should not be used

Hybrid inverters (or any inverters for that matter) are not required in power systems designed with solar panels, battery storage (optional) and DC loads only. In these situations, we suggest using a solar charge controller. Learn more about Phocos, PWM or MPPT charge controllers.

When to use a hybrid inverter

If the power system is going to use AC loads, 120 (110-130) or 230 (208-240) Vac, then a hybrid inverter is important. Since it can work completely off the grid, can sometimes work with or without batteries, and even with or without solar panels a hybrid inverter is a very flexible solution. This product can also function connected to the utility grid with possible injection to the grid (depending on local permissions and the manufacturer requirements) if desired. So, for example a power system can be installed with only a utility grid connection, PV and AC loads, while a battery can be added a few years later when more capital is available. In any case it is more efficient to use a hybrid inverter versus two separate pieces of equipment (solar charge controller and inverter) since not only does it make installation easier, but the hybrid inverter brings many parameters to be modified according to the needs of the project into one single device and thus allows. Inverters and charge controllers sold separately have fewer parameters to be modified and must be wired and programmed to work together. Hybrid inverters also avoid duplication of components when compared to discrete solar charge controllers and inverters, reducing their cost considerably. The ability of hybrid inverters to automatically synchronize their own inverter to an AC source before switching AC loads between these two sources also avoids damage to AC loads due to sudden voltage swings.

In addition, Phocos Any-Grid Hybrid Inverter Chargers can have an internet connection via Wi-Fi using the Any-Bridge AB-PLC, which allows customers to review and modify parameters remotely via the PhocosLink Cloud. Remote monitoring is a feature widely used both for installers to simplify troubleshooting and maintenance issues, but also for consumers who want to know the status of their system performance. At Phocos we are always thinking about installers and end users, to optimize their investment and experience.

Solar installers and DIY customers have been designing and installing inverters into solar systems for decades. While some things have not changed much, other things have evolved, such as hybrid inverters. The consensus is hybrid inverters offer a safe, reliable, comparatively easy and flexible way to fit the needs of a wide array of customers who have different challenges. At Phocos, we are proud to offer our quality Any-Grid PSW-H Hybrid Inverter Series as a global solution for off-grid, on-grid and for unreliable utility grid conditions. Providing value to our customers is a primary goal for our team, and this product checks all the boxes to optimize success for our customers.