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A Beginner’s Guide to Solar Inverter Sizing (How to Size Inverter for a Solar System?)

Are you ready to harness the power of solar energy and reduce your electricity bills? Installing a solar system is a great way to do that, but there’s one crucial step you can’t skip—sizing your inverter. An inverter is what makes the electricity produced by your solar panels usable in your home or business, and getting the size right is key to maximum efficiency and performance.

In this article, we’ll take you step-by-step through the process of ‘how to size an inverter for your solar system?’ So get ready to learn everything you need to know to make sure your solar system is running at its best.

We will start with some important factors that determine the size of a solar inverter.

Key factors that determine the size of a solar inverter

Solar inverters come in various sizes and types. But what is the ideal size for your system depends upon certain factors, such as the size of your solar array, geography, and property dynamics. Other factors (like temperature and the angle and direction in which solar panels are installed), which many homeowners may overlook, also affect the size of your inverter.

The size of your solar panel array

Solar array refers to the total number of solar panels installed on your rooftop. It is the most important factor to consider when determining the size of the inverter. Since inverters convert the direct current (DC) coming from the solar array to alternating current, the inverter must be able to handle the maximum amount of power that the solar panels can produce.

Technically, your inverter’s capacity should match that of the solar array. For example, if you have a 10 kW solar panel array, you will need an inverter that can handle at least 10 kW of power. However, your inverter should be a bit bigger than your system’s total rating—we will discuss this in the coming paragraphs.

Exposure to sunlight

Your geography, especially your roof’s exposure to sunlight, also plays an important role in determining the size of your solar inverter. If you live in an area with high solar radiation, you will need a larger inverter to convert the produced power to usable electricity. In contrast, if the sunlight intensity is low, an undersized inverter might do the job.

For example, a 7 kW system installed in Arizona will produce more power as it is exposed to more than five peak sun hours a day. But the same system installed in Maine, which has 3-3.5 peak sun hours, will produce less power. It is obvious now—we will need a bigger inverter for the same solar system in Arizona than the one in Maine. You can find the number of peak sun hours in your state here.

Temperature

Related to exposure is the temperature in your area. The operating temperature of the inverter should be considered, as high temperatures can affect the efficiency and longevity of the inverter. Basically, inverters are designed to work at a certain temperature. When the temperature exceeds the recommended operating temperature, the performance of your solar inverters directly decreases.

For example, an inverter designed for 25°C will experience a 15% decline in its performance when the temperature goes above 40°C. If the inverter is located in an area with high temperatures, you will need an inverter that can operate efficiently at high temperatures. Or, you could increase the size of your inverter to smoothly supply the needed power.

Angle and direction of solar panels

The angle and direction of the solar panels can also affect the overall energy production of the system and hence your inverter size. If your solar panels are not oriented toward the south, they will not be able to produce as much energy as they would if they were oriented towards the south. Since they are not performing at their best, an undersized inverter may be capable of converting all the DC power that comes its way.

The same goes about installation angles—the ideal angle is between 30° to 45°. If the angle is not appropriate, the array would not be able to produce steady power. In that case, a small inverter may be capable of converting all the incoming DC power.

Future expansion plans

Consider the potential to expand the system in the future, as the inverter size will need to accommodate any additional solar panels or electrical loads. If you plan to add more solar panels in the future, you will need to choose an inverter that can handle the increased power output.

However, this is not a deciding factor if you are going for micro-inverters, as they are installed at the solar panel level and can be paired with additional solar panels when needed.

Sizing your solar inverter

We discussed some key factors affecting the size of your solar inverter. Depending upon these factors, your required solar inverter could match your solar array capacity or be lower or higher than that.

Generally, as already discussed, the array-to-inverter ratio should be 1. That is, the total DC rating of your solar array and your inverter size should be equal. If the system is 5 kW, the same size should be the inverter.

But this is not a hard-and-fast rule. Based on some of the factors mentioned above, you could set the array-to-inverter ratio is 1.2—a 5 kW inverter for a 6 kW solar array. But in which cases can an undersized inverter work? It works in cases when your system is large, but it doesn’t produce power to its full capacity. For example, if a 6 kW system is installed in Vermont, it will not generate 6 kW. Instead, it may generate something between 4 to 5 kW, and for this much DC, a 5 kW inverter is perfect.

Similarly, if your system is large but is installed in a direction or angle that cannot generate enough power, an undersized inverter could be a better option in terms of cost.

Understanding ‘inverter clipping’

While you may install a small inverter with a 1.2 ratio, going beyond 1.55 is not recommended. The reason is a phenomenon called ‘inverter clipping.’ It occurs when the output voltage of an inverter exceeds its maximum rated value—you can read this value in the data sheet of your inverter. This can cause the inverter to shut down or malfunction and damage connected electrical equipment.

If your solar array produces too much power but is not converted to AC at the inverter’s end, there would be energy losses. To avoid any issues, we recommend consulting a professional solar installer to set the ideal array-to-inverter issue for you, considering your site, geography, and array size.

Alternatively, you would need a bigger inverter if you live in an area where temperatures could go beyond 40°C or when your array is producing maximum power.

In summary…

An undersized inverter will limit the amount of power generated by the solar panels. Whereas an oversized inverter will result in wasted investment and inefficiency.

What about micro-inverters?

Micro-inverters are small inverters that work at the panel level. They are installed with each panel separately and work independently of other inverters. The rule of thumb for micro-inverters is the same—they should have the same size as the DC rating of your individual solar panel. The manufacturer’s guidelines also mention how much incoming power they can handle.

This was all about how to size an inverter for a solar system. We have tried to mention everything you need to know about sizing an inverter, but as seen above, it is not a straightforward process. If you are unsure of how to proceed, consult a certified solar installer, and they will take it from there. There are many things peculiar to your household and where you live—they will factor in everything and size an inverter that would work well for your designed system.

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