The size of a solar inverter refers to the rated output power of the inverter, which determines how much of the DC power generated by the solar cells the inverter can convert to AC power. Choosing the right size solar inverter will improve the efficiency and performance of your solar system and avoid overloading or power loss from the inverter.
How to Size an Inverter
The size of a solar inverter can be greater or smaller than the DC rating of the solar array. The ratio of the inverter to the solar array is calculated by dividing the DC rating of the solar array by the maximum AC output of the inverter. For example, if the solar array is 6 kW and the inverter is 6000 W, then the ratio is 1. If you use the same size array with a 5000 W inverter, the ratio would be 1.2. Most installations have a ratio between 1.15 and 1.25, and it’s generally not recommended to exceed a ratio of 1.55.
Total and Peak Power of Solar Panels
In general, the rated output power of the inverter should be close to or slightly greater than the peak power of the solar panels to ensure that the inverter can handle the output current of the solar panels at their optimal operating point. If the inverter's output power rating is too small, it will cause the inverter to cut the solar panel's output power, a phenomenon known as inverter clipping or power limiting. If the rated output power of the inverter is too large, it will cause the inverter to become less efficient, wasting cost and space.
How Solar Panels are Connected and Maximum Input Voltage
Solar panels can be connected in series or parallel; series connection increases the voltage and parallel connection increases the current. The maximum input voltage of the inverter should be greater than the maximum open circuit voltage of the solar panels to prevent over-voltage damage to the inverter. The minimum input voltage of the inverter should be less than the minimum operating voltage of the solar panel to ensure that the inverter can start and operate.
Type and Power of Load
Loads are devices that use solar power, such as lamps, TVs, refrigerators, and so on. The type and power of the load will affect the output current and power factor of the inverter. The output current of the inverter should be greater than the maximum current of the load to ensure that the inverter can meet the demand of the load. The power factor of the inverter should be close to the power factor of the load to minimize reactive power loss. The type of load also affects the output waveform of the inverter. Generally, inductive and nonlinear loads require a sine wave inverter, while resistive loads can use a square wave or step wave inverter.
Calculation formula for solar inverter sizing
Size of inverter (W) = Peak power of solar panel (W) x Load factor of inverter (%)
The load factor of the inverter is the ratio of the actual output power of the inverter to the rated output power, which is generally recommended to be between 80% and 90% to ensure the safety and efficiency of the inverter.
For example, if the peak power of the solar panel is 5000 watts and the load factor of the inverter is 85%, then the size of the inverter should be:
Inverter size in watts = 5000 × 85% = 4250 watts
This means that you need to choose an inverter with a rated output of around 4250 watts.
How to Determine the Size of a Micro Inverter?
A microinverter should be sized for the power of a single solar panel, because it handles the current of a single solar panel, not the output of the entire system. You should choose a microinverter that can handle the peak output of a single solar panel.
The power rating of a microinverter is usually slightly lower than the power of the solar panel. The typical ratio is about 0.8 to 1.2. For example, for a 300W solar panel, a microinverter rated between 250W and 350W will work fine.
How to Size a String Inverter?
To size a string inverter, start by determining the specifications of your solar panels, including their wattage and voltage ratings, such as peak power (e.g., 300W) and voltage at maximum power (Vmp). Next, calculate the total array capacity by multiplying the wattage of a single panel by the number of panels in your system. For example, if you have ten 300W panels, the total capacity would be 3000W. Additionally, check the inverter's voltage range to ensure it matches the total voltage of your string, which is calculated by multiplying the number of panels by the Vmp of each panel.
After calculating the total capacity, select an inverter that can handle this wattage, typically sizing it at about 80-90% of the total array capacity to account for efficiency losses. Be sure to verify that the inverter's maximum DC input voltage and current ratings are not exceeded by your array's configuration.
What Happens If the Solar Inverter is Sized Incorrectly?
Power Loss
Choosing an inverter that is too small can result in power loss. The inverter's rated power should match the total power of the solar panels to ensure maximum performance of the power generation system.
Overload and Overheating
Choosing an inverter that is too small can result in overload and overheating issues. Under high light conditions, the voltage generated by the solar panels exceeds the rated operating range of the inverter, causing the inverter to overload. Overload can cause the inverter to overheat, damage the equipment, or even create a fire risk.
System Instability
Incorrectly sized inverters cause system instability, which manifests as frequent shutdowns, failures, or grid connection problems.
Impact On Grid Connection
An inverter that is too small cannot meet grid connection requirements. Many regions have strict regulations for solar power systems connected to the grid, including the power range of the inverter. If an inverter that is not sized appropriately is selected, it will not meet local grid connection standards, delaying the installation and use of the system.
Shortened System Life
Inverter overload and overheating can accelerate equipment aging and damage, thereby shortening the life of the system.
FAQ
Can I increase the size of my solar inverter?
Generally speaking, it is not recommended to increase the size of the solar inverter because it will lead to lower efficiency of the inverter, wasting cost and space, as well as increasing the no-load loss of the inverter, which will reduce the cost-effectiveness of the solar system. If you want to increase the power generation of your solar system, you can consider increasing the number of solar panels or improving the orientation and tilt of the solar panels to increase the utilization of the solar panels. You can also choose multiple maximum power point tracking (MPPT) inverters to adapt to the output characteristics of different solar panels and improve the efficiency of the inverter.
Is a bigger solar inverter better?
The size of the solar inverter is not necessarily the bigger the better, you have to choose the right inverter according to the power, voltage, current and other parameters of your solar panels. Generally speaking, the capacity of the inverter should be slightly larger than the peak power of the solar panels to ensure the efficiency and stability of the inverter .
What size inverter do I need to run the house?
- The size of inverter you need to run your house depends on your load power and grid voltage. Generally speaking, the total load power you need is about 1.2 or 1.5 times the power size of the inverter. For example, if your total load power is 5 kW, then you can choose a 6 kW or 7.5 kW inverter. Also, you need to consider whether the output voltage of the inverter matches the grid voltage, for example, if the grid is 220 volts single-phase, then the inverter needs to be a single-phase, grid-tied model.
How much solar power do I need for a 2000 watt inverter?
The output power of a solar panel is equal to the solar irradiance multiplied by the area of the solar panel multiplied by the efficiency of the solar panel. For example, if the solar irradiance in your area is 1000 watts per square meter and the efficiency of the solar panel is 20%, then the area of the solar panel you need is 2000/(1000*0.2)=10 square meters.
Want to Determine the Size of Your Solar Inverter?
At Shielden, we offer high-quality solar inverters backed by long-term warranties. If you're unsure about the right inverter size for your system, our experts are here to help! Our provide free solar solutions tailored to your needs. Let us guide you in making the best choice for your solar journey!
