The size of a solar inverter refers to the rated output power of the inverter, which determines how much DC power from the solar cells the inverter can convert into AC power. Choosing the right size solar inverter will improve the efficiency and performance of your solar system and avoid inverter overloads or blackouts.
How to size an inverter?
Total and peak power of solar panels
Generally speaking, the rated output power of the inverter should be close to or slightly greater than the peak power of the solar panel to ensure that the inverter can handle the output current of the solar panel at the optimal operating point. If the rated output power of the inverter is too small, it will cause the inverter to cut off the output power of the solar panel, 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 efficiency to decrease, wasting cost and space.
Solar panel connection method and maximum input voltage
Solar panels can be connected in series or in parallel; series connection increases voltage, and parallel connection increases current. The maximum input voltage of the inverter should be greater than the maximum open circuit voltage of the solar panel to prevent overvoltage from damaging 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.
Solar panel orientation and tilt
The orientation and tilt of the solar panel will affect the output power curve of the solar panel, and different orientations and tilts will result in different peak powers at different times. If the orientation and tilt of the solar panel are inconsistent, an inverter with multiple maximum power point tracking (MPPT) can be used to improve the utilization of the solar panel and the efficiency of the inverter.
Grid voltage and frequency
The output voltage and frequency of the inverter should match the grid voltage and frequency to generate electricity. Different regions and countries may have different grid standards, and you need to choose an inverter that is suitable for the local grid. For example, China’s grid voltage is 220V/380V and the frequency is 50Hz, while the US grid voltage is 120V/240V and the frequency is 60Hz.
Load type and power
The load is the device that uses solar energy, such as lights, TVs, refrigerators, etc. 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 needs 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 will also affect the output waveform of the inverter. Generally speaking, inductive and nonlinear loads require a sine wave inverter, while resistive loads can use square wave or step wave inverters.
Solar Inverter Sizing Formula
Inverter size (W) = solar panel peak power (W) × inverter load factor (%)
The load rate of the inverter is the ratio of the actual output power of the inverter to the rated output power. It 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 inverter is loaded at 85%, the inverter should be sized as:
Inverter size (Watts) = 5000 × 85% = 4250 W
This means you need to choose an inverter with a rated output of around 4250 watts.
What happens if you size your solar inverter incorrectly?
Power loss: Selecting an undersized inverter may result in power loss. The rated power of the inverter should match the total power of the solar panels to ensure the performance of the power generation system is maximized. If the inverter power is too low, it may not be able to effectively convert all the DC power from the solar panels, resulting in a certain degree of power loss.
Overload and overheating: Selecting an inverter that is too small can cause overload and overheating problems. The voltage generated by the solar panel under strong light conditions may exceed the rated operating range of the inverter, causing the inverter to overload. Overload can cause the inverter to overheat, damage the equipment, or even cause a fire.
System instability: Improper inverter sizing may lead to system instability, which manifests as frequent downtime, failures, or grid connection problems. This will increase maintenance costs, reduce system reliability, and even affect the profitability of the power generation system.
Impact on grid connection: An inverter that is too small may not meet grid connection requirements. Many regions have strict regulations on solar power systems connected to the grid , including the power range of the inverter. If an inverter with an inappropriate size is selected, it may not meet local grid connection standards, thus delaying the installation and use of the system.
Shorten system life: Inverter overload and overheating may accelerate equipment aging and damage, thus shortening system life. Selecting the right size inverter can reduce the workload of the equipment, extend the service life of the system and reduce maintenance costs.
Impact on power generation efficiency: Improper inverter size may result in reduced system power generation efficiency. For example, if the inverter is too small, it may not effectively utilize all the electricity generated by the solar panels, thereby reducing the total power generation of the system.
How to choose the size of different types of solar inverters
Different types of solar inverters come in different sizes, and we provide examples of how to size the three most common types: string inverters, central inverters, and microinverters.
String Inverter
-String inverter connects multiple solar panels in series and then connects them to the input of the inverter. Its size depends on the peak power and maximum input voltage of the solar panel. Generally speaking, the rated output power of the inverter should be slightly greater than the peak power of the solar panel, and the maximum input voltage should be greater than the maximum open circuit voltage of the solar panel.
Centralized inverter
– On the other hand, a centralized inverter connects multiple solar panels in parallel and then connects them to the input of the inverter. Its size depends on the total power of the solar panels and the maximum input current. Generally speaking, the rated output power of the inverter should be slightly greater than the total power of the solar panels, and the maximum input current should be greater than the maximum short-circuit current of the solar panels.
Micro inverter
-Microinverters, on the other hand, connect each solar panel individually to a small inverter, and then connect the outputs of multiple inverters in parallel to the grid. Its size depends on the peak power and output voltage of the solar panels. Generally speaking, the rated output power of the inverter should be equal to or slightly greater than the peak power of the solar panels, and the output voltage should match the grid.
Frequently asked questions
Can I increase the size of my solar inverter?
Generally speaking, it is not recommended to increase the size of the solar inverter, because this will lead to lower inverter efficiency, waste cost and space, and increase the no-load loss of the inverter, thereby reducing the 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 improve 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.
Are bigger solar inverters better?
The size of a solar inverter is not necessarily the bigger the better. You need to choose a suitable inverter based on the power, voltage, current and other parameters of your solar panel. Generally speaking, the capacity of the inverter should be slightly larger than the peak power of the solar panel to ensure the efficiency and stability of the inverter.
What size inverter do I need to run a house?
– The size of the inverter you need to run your house depends on your load power and the grid voltage. Generally speaking, the total load power you need is about 1.2 or 1.5 times the inverter power size. For example, if your total load power is 5kW, then you can choose a 6kW or 7.5kW inverter. In addition, you also need to consider whether the output voltage of the inverter matches the grid voltage. For example, if the grid is 220V single-phase, then the inverter needs to be a single-phase grid-connected model.
How much solar 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.