Solar, battery and hybrid inverters explained
With the wide variety of solar battery systems on the market, there is a lot of confusion about the different types of inverters and what’s best for a typical household. In this article, we explain the differences and hopefully help clear up some of the confusing and conflicting terminologies such as multi-mode inverter, inverter-charger, battery-ready inverter, and AC batteries.
What does an inverter do?
First, let’s clarify what an inverter is. Solar panels produce DC power, and batteries store DC energy, but households and most appliances run on AC power, which is also supplied by the electricity grid. Inverter converts DC power to AC power, but not all inverters are the same; solar inverters and battery inverters have very different purposes, which we explain in more detail below.
Over the last few years, the increasing demand for home battery systems led to many manufacturers combining solar and battery inverters into one common unit - these are referred to as hybrid inverters. A battery-ready inverter is simply another name for a hybrid inverter.
The 4 main types of Inverters
Solar Inverter – Grid-tie solar inverters are used for feeding energy into your home or the grid. As explained below, these can be string solar inverters or microinverters.
Battery Inverter – Basic inverters used with batteries. These are often used in RVs and caravans.
Hybrid Inverter – Combined solar & battery inverter. These are sometimes referred to as battery-ready inverters.
Off-grid Inverter – Powerful off-grid battery inverters with integrated charger. Many of these inverters can also operate as on-grid hybrid systems.
Solar Charge Controller - (Not an inverter) Solar charge chargers are used to charge a battery directly from solar without using an inverter. See the detailed explanation below.
1. Solar Inverter
Solar inverters convert solar DC power to AC power. These simple grid-connected (grid-tie) inverters use one or more strings of solar panels and are the most common type of inverter used around the world. String solar inverters are available in many sizes for residential and commercial solar installations, from small 1.5kW single-phase inverters, up to large 3-phase 100kW inverters.
MicroInverters
Microinverters, also known as micros, are very small solar inverters attached directly to individual solar panels. Micros are a great option for complex roof layouts or locations with shading issues, as each microinverter and panel operate independently. The main downside is the slightly higher cost. However, micros offer many advantages over string inverters, as explained in the detailed microinverter review article.
2. Battery Inverter
These are the most basic type of inverter used with batteries. Battery inverters convert DC low voltage battery power to AC power. These are available in a huge range of sizes, from simple 150W plug-in style inverters used in vehicles, to powerful 10,000W+ inverters used for off-grid power systems.
Simple ‘plug-in’ style battery inverters are often used in caravans, RV’s, boats and small off-grid homes. These inverters are typically coupled with MPPT solar charge controllers connected to one or more solar panels.
3. Hybrid Inverter - battery ready
Hybrid inverters, sometimes called battery-ready inverters, combine a solar and battery inverter in one simple unit. These inverters are becoming more competitive against solar inverters as hybrid technology advances, and batteries become cheaper. See the detailed hybrid/off-grid inverter review for more details. Hybrid inverters are the most cost-effective way to add batteries, but they generally have limited backup power capability and usually have a slight delay (5 sec to 30 sec) when switching to backup mode during a blackout.
The term ‘battery ready’ is more of a marketing term used to up-sell a solar system. If you want energy storage in the near future, it is worth investing in a hybrid inverter, provided the system is sized correctly to charge a battery system throughout the year, especially during the shorter winter days. Also, not all battery-ready or hybrid inverters have backup capability, so be sure the system will meet your needs. You do not need to install a hybrid inverter if you are considering adding batteries in the future. Any solar system can install batteries anytime using one of many AC-coupled battery options, such as the Tesla Powerwall or Sonnen ECO.
Multi-mode Hybrid Inverters
Multi-mode hybrid inverters are more advanced hybrid inverters designed to operate in on-grid and off-grid modes for a prolonged time. Compared to basic hybrid inverters, which generally have limited backup power, known as emergency power supplies or EPS, multi-mode hybrid inverters are more powerful and can typically back up not only lighting and basic power circuits but even small air-conditioning units up to 3kW.
Multi-mode hybrid inverters and dedicated off-grid inverter-chargers (see below) are often confused as they can operate in both on-grid and off-grid modes. The primary difference is that multi-mode hybrid inverters also contain an integrated solar inverter (MPPT), while off-grid inverter-chargers do not. The reason is off-grid inverter-chargers are modular and designed to be either AC-coupled with solar inverters or DC-coupled with solar charge controllers.
4. Off-grid Inverter-Chargers
Off-grid or stand-alone power systems require powerful battery inverters with inbuilt chargers that can be set up as either AC or DC-coupled systems. Most modern inverter-chargers can also be used to create advanced hybrid grid-tie systems which have the ability to backup an entire home (including most appliances) and can operate off-grid for weeks or months, depending on the solar and battery size.
Off-grid inverters are available in a range of sizes from relatively small 3kW units to powerful 10kW inverter-chargers designed to run energy-intensive appliances like air-conditioners, pumps, electric ovens and hot water systems. High-consumption appliances require high continuous power or high startup ‘surge’ current, which is why inverter-chargers use heavy-duty transformers, making them more expensive than hybrid inverters, which are transformerless. Depending on the output power rating, inverter can cost anywhere from $1500 for a 2.5kW model to $8000 for a 10kW model. See our best off-grid solar system review for more information.
Solar Charge Controllers
Solar charge controllers, also known as solar regulators, are not inverters but solar battery chargers connected between the solar panel/s and battery. These are used to regulate the battery charging process and ensure the battery is charged correctly or, more importantly, not over-charged. Simple DC-coupled solar charge controllers have been around for decades and are used in almost all small-scale off-grid solar power systems. However, more advanced MPPT solar charge controllers are now the most popular choice for off-grid systems.
What is an MPPT Solar Charge controller?
An MPPT solar charge controller is an efficient DC to DC converter used to maximise the power output of a solar panel. In order to generate the most power, the maximum power point tracker sweeps through the solar string voltage to find the best combination of voltage and current to produce the maximum power. The MPPT is designed to continually track and adjust the voltage to generate the most power under all conditions. Using this clever technology, the solar panel efficiency increases and the amount of energy generated can be increased by up to 30% when compared to cheaper (PWM) controllers. Learn more about MPPT solar charge controllers.
