What size inverter for 10kW solar system - Read about solar inverter sizing

Inverters range from $.3 - $1.00 per watt so in a typical 10kW solar system you can expect to pay about $2000-$5000 for a good solar power inverter. It’s important to get a quality inverter since this is the weakest solar link in your home solar system.

The simple answer is while the nominal capacity of your solar panel array is 10kW, the inverter can be less or more of this size. Usually it is between 8kW and 11kW as a maximum AC power output.

This brings up another question: should I Oversize (>10kw) Or Undersize (<10kw) My Inverter For 10kw Solar panel array?

In this blog post, we will answer this question, and we will explore the factors that determine what size inverter needed for 10kw solar system.

Let’s jump right into it.

Understanding solar inverters

There are two different types of inverters: string inverters and micro-inverters . We’ll be discussing only string inverters here since they are cheapest type of inverters (compared to micro-inverters) with a wide variety of reliable manufactures to choose from.

String inverters are just large boxes that are typically mounted near you circuit box or the electric company’s meter. If you’re using two inverters they can be mounted “in parallel” to each other.

Your solar panels will be grouped into “strings” so that they match up with your inverter’s specs. It’s probably best to let an electrician design and perform this tying in. You must keep your panel in evenly grouped multiples so you don’t overload your inverter.

Another important panel consideration is that you should use identical panels. Do not cheap out and buy mixed panels and expect to tie them all in together. It’ll ruin your system’s efficiency.

Since a string inverters are easily mounted in convenient locations they are easy to maintain. But it’s not all peaches and cream with string inverters. When you group the “strings’ of solar panels they will need to be laid out in the sun but if one or more of the panels gets “shaded” the entire string pays the price. The total inverter energy output will start to degrade. Similarly if one of the panels goes bad or breaks the system output is cut considerably.

Factors you should consider when sizing size inverter for 10kW solar system

Your peak electricity usage

The first thing to consider, especially if your system is off-grid, is the maximum power required to operate a set of devices in your home at the same time. The inverter's capacity should not be smaller than the maximum required power. It's important to note that the inverter determines the maximum AC power that will be sent to the devices, not the maximum DC power that can be received from the solar panel array.

Even though your solar panel capacity is limited to 10 kW, if the inverter is larger than 10 kW and the batteries are charged, the inverter connected to the battery bank can send more than the actual power output of the solar panels to the devices when needed.

The amount of sunlight received by solar panels

The amount of sunlight received by solar panels depends on three factors: geographic location, the angle and direction of the panels, and the amount of shading they receive.

1. Geographic Location: Your location determines the amount of available solar radiation. Solar radiation varies significantly depending on the geographic location.

2. Angle and Orientation: The angle and orientation of the panels determine the amount of available solar radiation for the panels installed on your roof. Properly directing the solar panels towards the sun and adjusting their angle can significantly increase their efficiency.

3. Shading: Shading from obstacles such as trees or buildings will reduce the amount of available solar radiation at your location.

These factors determine the efficiency of solar panels. If these factors are favorable, the panels can operate more efficiently, thereby determining the output of your solar array system.

For example, for a 10 kW solar array, it may have an average power output of 9.2 kW in one location and orientation of the solar panels, while the same system may produce only 7.8 kW under different conditions. Therefore, it is important to consider these factors when sizing the inverter.

Your solar panel configuration

The characteristics of the solar panels in your system play also an important role in determining the size of the inverter. If you already have solar panels, you should choose an inverter that has an input voltage and current range that is compatible with the configuration of the solar panel you are using.

Ensuring that the voltage and current levels of the solar panel configuration match the input voltage and current of the inverter helps protect the inverter and ensures the best performance and efficiency of the system overall.

Look for inverter specifications:

PV Start Voltage: Tells you when the inverter starts to convert the power from your solar arrays. This give the true inverter efficiency since all inverters need a minimum power input before they can start to convert into AC. The stronger the required sun-rays need to start converting the less efficient your inverter will be.

The California Energy Commission (CEC) efficiency: the efficiency range over a wide spectrum of diverse conditions, and judge output load, temperature range, and input power.

Maximum recommended PV input power: This tells you what the inverter’s max input power should be from your solar panel array. You need this spec to help you size your system. If you exceed your invert’s capabilities you’ll get a real inefficient inverter.

Should I oversize or undersize my inverter for 10kW solar system?

Oversized Inverter

The cool thing about Oversize the inverters is that if you get an over sized one you can add more solar panels later for more power.

Another benefit is that when your inverter size is larger to that of your solar panel capacity, it can handle the maximum power output from the solar panels without being subjected to excessive stress. This means the inverter may last longer, however it may not operate at the same high efficiency as it would when perfectly sized to the array's capacity.

Undersized Inverter

Using a smaller inverter size can indeed be a good option for cost savings and increased efficiency. Inverters typically operate at their highest efficiency when working at or near maximum power. Therefore, if the inverter size is proportional to the average output of the array, you can benefit from the inverter's maximum efficiency while saving on the extra costs associated with purchasing a larger inverter than necessary.

However, it's important to note that in this case, when the inverter size is smaller than the capacity of the array, the inverter will cut off  the power (power clipping) coming from the array every time it produces more power than the inverter can handle. This can be considered a loss in the overall productivity of the system.

For 10kW solar panel array a 8 kW inverter capacity is the minimum size you can use because installers typically only recommend that get an Array-To-Inverter ratio of less than 1.25.

Solar power inverter features to look for.

You’re looking to get the most efficient inverter you can afford. Manufacturers love to cite peak efficiency as a selling point for their inverters. Don’t be fooled. This peak is only reached at max load when the sun is strongest. You want to see the efficiency over a variety of conditions such as: input power, temperature and output load. So inverters that only show high efficiency for one number are not giving you the whole story.

Conclusion 

If you're having difficulty choosing the size of the inverter for your solar power system between a smaller or larger inverter than your array's capacity, or if you prefer not to go through all these estimations, you can rely on the basic rule of thumb that the inverter size should roughly match the capacity of your solar panel array.

In this case, you would need a 10 kW inverter for a 10 kW solar array. This choice would allow you to add some panels in the future if you find that your array is producing less than expected. It's worth noting that most inverters allow for installing solar panel capacity larger by 110% to 150% of the inverter's capacity.