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How an Off-Grid Solar Inverter Works

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If you are starting to research ways to incorporate solar power into your home, one of the first things you will learn is that the electricity created by photovoltaic solar panels is direct current or DC electricity. The power that is stored in batteries in a solar system is also DC. While this type of electricity is used by plenty of appliances and machines, it is not what is used in homes. For those who intend to use the power from a solar panel to either supplement or replace the electricity that would traditionally come in from the grid, an inverter is necessary to change the electricity that is generated by the panel from DC to AC or alternating current.

There are many types of inverters available. They all perform the same basic function of converting the DC power to AC power but they can work in different ways and be used in different applications. For starters, inverters that are used in an on-grid solar system are simply used to convert the DC electricity that comes in from the solar panel into AC, which is then sent to the grid or directly to appliances. Off-grid solar inverters with a charge controller, however, are much more complicated since they are being used in a more complex system.

Off-grid solar systems involve both solar panels and battery storage, so the power can be coming into the home from either of these two sources at any given time depending on the solar situation. Sometimes, multiple inverters like a grid-tied inverter or pure sine wave inverters as well as a charge controller may be necessary. A solar inverter would be used to convert the power coming in from the solar panel, while a battery inverter would handle the power coming to the house from the battery source. Inverters that are used in conjunction with batteries are often also responsible for managing the charging and discharging of the battery.

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Solar inverters can be separated into two different types: string inverters and micro inverters. The difference between the two has to do with how the solar panels are arranged within the solar system. A string inverter is used when the solar panels are connected in a single string. This string can be made up of as little as three panels or it can be as many as your system can handle linked together. The DC power that the string generates comes in a single connection out of the end of the line to the solar inverter. At this point, the solar inverter converts the DC power to AC power and sends it on to be used in the home.

The second form of the solar inverter is the microinverter. These inverters are attached to a single panel, usually on the backside, and are only responsible for inverting the power that is generated by that single panel. Obviously, as the number of panels in a system increases, the number of microinverters needed increases by the same magnitude. The now AC power then flows from the individual panels to the home switchboard for use.

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Though it may seem more convenient and cost-effective to use a single string inverter in a system that uses multiple panels, it can actually be better to use micro-inverters on each panel for several reasons. The performance of the overall system is improved with microinverters because there is no power loss as it travels along the string and the load placed on each inverter does not run the risk of overpowering it, whereas a string configuration is a bit riskier. Using microinverters also comes in handy if there is a malfunction either at the panel or inverter. In a string system this could affect the entire group and make diagnostics difficult, but in a system that strictly uses microinverters it is easier to both diagnose the problem and replace the malfunctioning part without disturbing the overall setup.

You might be wondering exactly what happens in those inverter boxes that makes them so important to the overall solar system. It only takes a quick dive into some basic electrical engineering to understand what is going on here.

As we have established, the power that is generated by solar panels is DC while the power that our homes use is AC. The characteristic difference between these two is that the current of electricity in DC power goes in a single constant direction while the current of electricity in AC power switches from one direction to the other many times per second. Think of DC as a steady stream of electrons coming in while AC is more like a line of electrons running in place. The two pictures are very different and this is why DC power cannot simply be used for devices that are made to work on AC power.

To perform the conversion of power from DC to AC, the inverter takes the incoming DC power and uses a system of inductors and capacitors to force the current to change direction. The current within the inverter begins to rise and fall instead of proceeding in a straight line. It then comes out the other end of the inverter in an AC wave. There are many types of inverters that produce different AC output, from smooth wave to square wave, and the voltage that they can handle varies as well so it is important to do your research and get the proper inverter for your system. Inverters also are not 100% efficient since they require some power to operate, so this loss of power should be factored into the overall equation when you are designing your solar system.

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If you are still unsure as to just what is happening with the solar inverter and why it is necessary, take a look at this explanation on the website Explain That Stuff. It includes some real-world examples that can help put the process in terms that are easier to visualize. At the end of the day, just understand that if you want to start generating solar power and using it in a home application, you will be unable to do it without a solar inverter so make sure you get the right one for your needs.