Understanding Pure Sine Wave, Modified Sine Wave and Off-Grid Inverters

Now that we've covered the main types of inverters in a previous article, it's time to dig a little deeper. In this article the focus will be on pure sine wave and modified sine wave inverters. What does the name mean and what's the difference between the two? And last but not least, we'll take a quick look at off-grid inverters if you are considering to make the full transformation.

Pure Sine Wave Vs. Modified Sine Wave

When we talk about an inverter it's important to understand the part it plays. Just to avoid any confusion, an inverter takes the energy collected by the panels (DC) and transforms it into energy you can use in your house or business (AC). It's a completely separate entity from the batteries or the collectors that are used. Without the inverter you won't be able to use any of the energy, and by using a low quality converter it's just going to make you angry. Here is a basic infographic on how the two inverters differ:


Initial inverter designs were based on a modified sine wave, which is a rather unstable surge of energy. For old tube televisions and radios it works just fine, but modern electronics are more sensitive in this regard. In fact, some appliances won't even work with a modified sine wave, and if they do work then you're cutting their durability short. With the dramatic changes motors are going to run hot or not at all.

On the other side we get pure sine wave inverters, which is the general and safer choice. All appliances can work from the consistent energy supply without strain or complications. So why do people actually consider the modified option? Firstly, they cost cheaper than pure sine wave models. Secondly, they are perfect for basic systems where fluctuation isn't really a problem. Here is a quick list of appliances that shouldn't be used with the cheaper option.

    • Electronic units with a thyristor component (eg. photocopiers and laser printers)
    • Appliances with silicon-controlled rectifiers (typically used in washing machines)
    • Most laptops
    • Certain fluorescent lights with electronic ballasts
    • Appliances that have speed or microprocessors (such as sewing machines)
    • Certain battery chargers

When you start comparing a pure sine wave inverter with a modified one, you're looking at functionality over pricing. If you go with the bargain buy then you need to be sure the right appliances are used. However, it's good to know that as technology catches up, the price of pure sine wave options is getting more affordable.

Quick Notes Regarding Off-Grid Converters

For the most part off-grid converters are one-directional. In other words, you can connect it to the grid or a generator, which can then be used to charge the battery unit. But you can't use the inverter to send energy back to the grid. There are some models that will allow this, although South Africans don't really care about feeding back to the grid at this point. There is an array of choices for this specific type of inverter and you have to calculate which size is going to work best. They can be used with 12v, 24v or 48v battery banks depending on the power you need.

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