After solar panels, the inverter is the most critical component of a solar system. But how big should your inverter be?
In this guide, we share 3 easy steps on how to size a solar inverter correctly. We explain the key concepts that determine solar inverter sizing including your power needs, the type and number of solar panels you need, and the length of your wires.
What Does A Solar Inverter Do?
Solar inverters convert the direct current (DC) electricity produced by solar panels to alternating current (AC) electricity, which is used to power home appliances and electronic devices.
While there are several types of inverters including hybrid, grid-tie, and off-grid inverters they all perform the DC to AC conversion.
What Size Solar Inverter Do I Need?
Inverters come in different sizes starting from as little as 125 watts. The typical inverter sizes used for residential and commercial applications are between 1 and 10kW with 3 and 5kW sizes being the most common.
With such an array of options, how do you find the right size for you? An inverter works best when close to its capacity. Oversizing or having an inverter that is too big for your solar panels will not produce enough electricity. Undersizing or having an inverter that’s too small will convert a limited amount of energy.
You can avoid both of these scenarios by following these three basic steps to solar inverter sizing.
- Determine your power needs
- Determine the number of solar panels you need
- Find the optimal inverter size
Step 1: Determining Your Power Needs
To figure out your power needs, measure the total energy consumption of the appliances you plan to run on solar power. The simplest way to do this would be to look at your daily energy consumption.
Most homes have an average daily consumption of between 9 to 20 kW. Depending on where they fall in that band and the size of their solar array, they will likely use a 3, 5, or 10kW inverter.
Considering Surge Watts and Voltage Drop
You also need to consider surge watts and voltage drop. Surge watts are the extra power required to start appliances that have motors, such as refrigerators and air conditioners.
Voltage drop refers to the decrease in voltage that occurs as electricity travels along the wires from your solar panels to your inverter.
To account for surge watts, check the surge watt rating of your appliances and multiply it by two. Choose an inverter that has a surge watt rating equal to or greater than this value.
As for voltage drop, check the wire length between your solar panels and the batteries. If the wire length is long, you may need to choose a lower voltage system (12V, 24V, or 48V) to minimize voltage drop. As a rule, you typically want to have the distance between your solar panels and inverter be as short as possible.
Once you have worked out your power needs, the next step is selecting the right number of solar panels.
Step 2: Determining the Number of Solar Panels You Need
The number of solar panels you need is a factor of how much energy you require. Other factors that will influence the size of your solar array are the amount of sunshine you receive and the watt rating of the solar panels you decide to go with.
Lower consumption will require fewer panels. If you live in an area that receives a lot of sunshine or you choose solar panels with a high watt rating then you will need fewer solar panels.
For example, if you require 15kW, then your solar array needs to be large enough to produce that much energy. A 4.5 kW array (or ten 450-watt solar panels) would just about cover your consumption.
Choosing the Right Type of Solar Panels
The type of solar panels you choose can also impact the size of the inverter you need. Different types of solar panels have different wattage ratings and efficiency levels. The three main types of solar panels are monocrystalline, polycrystalline, and thin film.
Monocrystalline panels are the most efficient but also the most expensive. Polycrystalline panels are less efficient but more affordable, while thin-film panels are the least efficient. Almost all commercial or residential solar installations use either mono or polycrystalline.
Step 3: Finding the Optimal Solar Inverter Size
The next step is to determine the optimal size for your solar inverter. This is based on the amount of sunlight, or irradiance, your area receives on average per day. Multiply the number of peak sun hours by the wattage rating of your solar panels to get the DC output of your solar array.
For example, if your area receives an average of 5 peak sun hours per day and you have ten 450-watt solar panels, your DC output would be 22,500 watts (5 hours x 10 panels x 450 watts = 22,500 watts). Check how much sunshine your home receives here.
It’s important to point out that solar systems are not 100 percent efficient. To account for power losses assume an 80 percent efficiency.
Your solar inverter should have a similar or slightly higher wattage rating than the DC output of your solar panels (which in this case is 4.5 kW). You can size it between 1.15 and 1.5 times larger. The rule of thumb is to size your inverter 1.25 bigger than your solar array.
Using Multiple Inverters for Increased Power and Voltage
In some cases, you may need to use multiple inverters to meet your power needs or increase your system’s voltage. This practice, known as inverter stacking, involves connecting multiple inverters in parallel or series.
Using multiple inverters can provide several benefits, including increased power output, higher voltage, and redundancy if one inverter fails. However, it also requires more complex wiring and will increase the overall cost of your solar system.
Most inverter brands like Must, Growatt, or Victron can be stacked to increase the power output of a solar energy system.
Basic Inverter Specifications
Reading the data sheet or specifications of an inverter for the first time can be confusing. The most important specifications to consider are
- Power output is the maximum continuous power the inverter can supply to all the loads on the system. Exceeding the power rating by having a larger load (too many appliances) than the inverter can handle will cause it to shut down. The power output of a 3 kW inverter for example is 3000 watts (3 kW).
- Peak output or surge power is the maximum power output an inverter can deliver for a short time. This is important because some appliances like refrigerators, motors, or compressors require a lot of power on start-up then will decrease until it reaches their average power use. The peak output of an inverter is typically over double its rated output power.
- Input voltage range is the minimum and maximum input voltage at which an inverter will function. If the voltage from your solar array is below the minimum (also called the startup voltage) the inverter will not switch on. Going over the maximum input voltage will cause the inverter to fail.
Choosing the right size solar inverter is crucial for the performance and efficiency of your solar system. By considering your power needs, the type of solar panels you have, the number of panels, the length of your wires, and your battery voltage, you can determine the optimal size for your solar inverter.
Remember, the goal is not merely to choose the largest or most powerful inverter but to choose the one that best matches the output of your solar array and your energy needs.