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
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.
Orientation and tilt of solar panels
The orientation and tilt of the solar panel will affect the output power curve of the solar panel, different orientation and tilt will result in different peak power appearing at different times. If the orientation and tilt of the solar panels are not consistent, an inverter with multiple maximum power point tracking (MPPT) can be used to improve the utilization of the solar panels and the efficiency of the inverter.
Grid voltage and frequency
The output voltage and frequency of the inverter should match the voltage and frequency of the grid for grid-connected power generation. 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, the grid voltage in China is 220V/380V with a frequency of 50Hz, while the grid voltage in the US is 120V/240V with a frequency of 60Hz.
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.
What happens if the solar inverter size is chosen wrongly
Power loss: Selecting an undersized inverter may result in power loss. The power rating of the inverter should match the total power of the solar panels to ensure that the performance of the power generation system is maximized. If the inverter power is too low, it may not be able to efficiently convert all of the DC power from the solar panels, resulting in some degree of power loss.
Overloading and overheating: Selecting an inverter that is sized too small can lead to overloading and overheating problems. The voltage generated by the solar panels under high light conditions may exceed the rated operating range of the inverter, leading to overloading of the inverter. Overloading may cause the inverter to overheat, damaging the equipment or even creating a risk of fire.
System instability: Improperly sized inverters can lead to system instability in the form of frequent shutdowns, malfunctions or grid connection problems. This can increase maintenance costs, reduce system reliability and even affect the profitability of the power generation system.
Impact on grid connectivity: Inverters that are undersized may not meet grid connectivity requirements. Many regions have strict regulations for solar power systems connected to the grid, including the power range of the inverter. If an inverter is selected that is not properly sized, it may not comply with local grid connection standards, delaying the installation and use of the system.
Reduced system life: Overloading and overheating of the inverter may accelerate aging and damage to the equipment, thus shortening the life of the system. Choosing the right size inverter can reduce the workload on the equipment, extend the life of the system and reduce maintenance costs.
Impact on Power Generation Efficiency: An improperly sized inverter may result in a decrease in the system's power generation efficiency. For example, if the inverter is too small, it may not be able to efficiently utilize all the power generated by the solar panels, thus reducing the total power generation of the system
Different types of solar inverters What to choose for size
Different types of solar inverters are sized differently, and we have given examples of how to size the three most commonly used types: string inverters, centralized inverters, and microinverters.
String Inverter
- String inverters connect a number of solar panels in series, which are then connected to the input of the inverter. Its size depends on the peak power and maximum input voltage of the solar panels. Generally speaking, the rated output power of the inverter should be slightly larger than the peak power of the solar panels, and the maximum input voltage should be larger than the maximum open-circuit voltage of the solar panels.
Centralized Inverter
- A centralized inverter, on the other hand, connects several 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 larger than the total power of the solar panels, and the maximum input current should be larger than the maximum short-circuit current of the solar panels.
Microinverters
- 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. In general, the rated output power of the inverter should be equal to or slightly greater than the peak power of the solar panel, and the output voltage should match that of the grid.
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.