If you’ve spent any time looking into solar energy, you will have heard the word “inverter” more than a few times. Clearly this device is an important part of the chain that turns rays of light into power that can run your appliances. So what is an inverter and what does it do that’s so darn important? Let’s get down to the dirty details.
Before we get to inverters themselves, let’s talk about electricity for a bit. Electricity is, when you get down to it, the movement of electrons from one place to another. This is what we call current. That movement of electrons is what does the actual work as it passes through wires and circuits.
While all electrical systems work by making use of electron flow, the flow itself comes in two types – alternating current and direct current. Direct current has a continuous flow of electrons in one direction. Alternating current does what the name suggests and rapidly alternates the direction of electron flow. This might seem like a silly thing to do, but AC current is perfect for transmitting electricity over long distances. That’s why AC current won out over DC current as grid power – it would mean having many small power-generating stations inside cities and towns. AC current can be sent out from large central power stations far away from where people actually live.
The problem is that many things in the home do not run directly from AC power. Specifically, anything electronic will need DC current to work. The charger you use with your smartphone exists to convert AC power into DC power. The same goes for the power supply in your PC or the adapter that charges your laptop. Your vacuum cleaner might run happily on AC power straight from the outlet, but that kind of supply would fry the delicate components of an electronic device.
Going the Other Way
We’ve become pretty good at converting AC power to DC power. It’s not a perfect conversion, as quite a bit of power is lost as heat in the process, but the circuit design that straightens out that AC current into simple DC is very well understood. At least, it’s well understood by people smarter than me!
But what about taking a DC power source and turning it into AC power? That’s not as easily done. AC power exhibits the flow it has because of the design of the generator that supplies it. If you put mechanical power into the generator it will generate an AC current by virtue of the way it physically works.
If the electricity you want is stored in a battery or coming as DC current from a solar panel, you can’t feed it to your home power grid. Every device is expecting an AC current at a specific voltage and frequency. How can you do this without an AC generator?
Enter the Inverter
That’s exactly what an inverter is meant to do. It takes a DC power source and then converts to AC power so that the various appliances in our homes can run from it. If you run a solar power system that has no battery backup and is grid connected, then the inverter can seamlessly balance where your power comes from. If the solar panels are not producing enough power for your needs, then additional power will come from the grid. If you are making more solar power than you need then it can be fed into the grid. In many countries you will even receive credit for pushing energy into the grid!
Solar power setups with battery backups are, of course, essential for a completely off-grid or standby system; this is why many modern solar inverters also have a full battery management system built into them. In grid-connected setups, inverters with battery management systems can even charge backup batteries from AC grid sources in addition to incoming solar energy.
So as you can see, the solar inverter is in many ways the heart of your setup, making sure all the various components work in harmony and that the power goes where it is meant to go.
Main Types of Solar Inverter
Inverters are used in many different solar power scenarios, but there are only three main types of solar inverter found out in the wild.
Standalone inverters are connected to a battery array and create AC power from the energy stored within. The batteries themselves can be charged from any suitable source – solar, wind, generators, and so on.
Grid-tie inverters are hooked up to the grid and sync perfectly with them using a sine-wave signal that the utility company supplies. These systems are not designed to provide backup power, so if there’s a blackout this kind of system will also shut down. This might sound like a bad thing, but if you are using a hybrid solar-grid setup in a place that almost never has blackouts, it makes perfect sense. The inverter manages the system balance between the different power sources.
But why does it need to shut down? The main reason for this is because of something known as “islanding”, which is where your solar power keeps pumping electricity into a dead grid. This can cause all sorts of safety issues, so utilities require inverters that are connected to the grid to have protection against it.
Battery backup inverters are like standalone inverters in that they pull power from a battery. But they are tied into the grid, which means they also need to prevent islanding. Unlike grid-tied inverters, however, they can still provide backup power during a blackout.
Dealing with PV Inconsistency
When you hook up your smartphone to one of those portable solar panels, you don’t get a consistent stream of electricity. It can become weaker or go away completely, depending on circumstances. The temperature of the cell and whether a cloud is passing overhead are just two things that can influence power delivery.
The solar cells on your roof are no different. They don’t provide a consistent and smooth supply of power. The inverter uses a method known as maximum power point tracking to change the load characteristics in response to changing power delivery conditions in the solar cells.
It’s becoming more and more common for solar panels to use micro inverters, which are small individual inverters attached to each solar panel. The panels therefore directly output AC power. There are a few neat advantages that come with the use of micro inverters. It means that every panel can be optimized individually, which is good since different panels are in different states and varying levels of sunlight. It also means you can tie all of the panels together in parallel, so that if one goes down, it doesn’t affect anything else. You can easily just add more panels in without much fuss, too. Replacing them has the same advantages.
Overall, they are more efficient than setups with a centralized inverter – between 20 and 27 percent more compared to “string connected” traditional PV setups.
One of the most important questions to ask about any component in the solar power chain is how efficient it is. A string of inefficient components means that you are doing a lot of expensive work while throwing away too much of your collected power. Inverters are by far the most efficient component in a solar power system. It’s normal for them to be more than 90% efficient, and modern, good-quality inverters can be as much as 98% efficient!
Inverters are essential to any solar setup where AC devices need to be powered, so unless all you want to do is charge a smartphone, you’re going to need one or more of these puppies to make your power system work. Thankfully, modern inverters are efficient, smart, and reliable. They can tell you how well your system is working and optimize power delivery so you get more bang for your solar panel buck.
Even cooler than that, inverters can now be so small that some power banks have them! That means you can run a hair dryer or something from them. Plugging an inverter in your car’s lighter socket also suddenly opens up more on-the-go possibilities. Whatever you want to use them for, inverters are a neat technology for sure!