In general terms, an inverter is any device which converts DC power to AC. In the context of a solar system, an inverter is the piece of equipment responsible for converting the DC output of a solar array into an AC waveform which is compatible with the national electricity grid.
This means that the average voltage (referred to as the Root Mean Square Voltage, or RMS) will become 230V, and that this voltage will change direction at a rate of 50 cycles per second (50Hz). Solar inverters also Incorporate Maximum Power Point Trackers (MPPTs), which ensure that the solar array is working as efficiently as possible.
How Do Solar Inverters Work?
The role of a solar inverter can be understood as having two parts:
1. Conversion of the array voltage down to 230V,
2. The 'inversion' of this voltage such that it replicates an AC waveform.
To achieve both of these goals, solar inverters use a regimen of co-ordinated, rapid switching. In simple terms, the process looks like this:
To alter the voltage of a DC waveform, an electronic transistor switch (known as a MOSFET) is rapidly switched on and off. This allows for a circuit device known as an inductor to be rapidly charged and discharged.
When the switch is in the ON position, this allows the inductor to briefly store electrical energy in the form of a magnetic field. When the switch is in the OFF position, the inductor releases the stored energy, which it is able to do at a very high voltage.
By using a capacitor to take the average of the waveform at the output of the inductor, it’s possible to yield a DC output signal at a different voltage to the input.
The AC inversion process is similar to the above; again, MOSFETS are rapidly switched, this time creating a 'square wave'. When the average of this square wave signal is taken, the result is a sine wave which replicates the AC waveforms seen in the grid.
There are many players in the commercial inverter space, with key organisations being SMA, Huawei, Sungrow, FIMER, Fronius and Growatt. Most manufacturers will offer a variety of models ranging from residential to utility-scale applications.
A typical inverter would be expected to last approximately 10 years, with most manufacturers offering a 5-year warranty as standard, and the option of extension to 10-years. Given how rapidly the industry is evolving, it’s likely that if an inverter failed more than 10 years into its life, it would simply be removed and replaced with a newer model.
Many aspects contribute to the perceived 'quality' of an inverter, such as its efficiency, reliability, and its ease of use. Most commercial inverters have approximately equivalent efficiency ratings, which typically range from 98-99%. Smaller inverters such as those used in residential applications will be less efficient. In a rapidly growing industry, reliability is difficult to assess - newer players such as Huawei are producing products with extremely promising track records, but it’s difficult to be certain of long-term performance.
Regardless of the manufacturer selected, the underlying function and technology is more or less equivalent - all commercial inverters widely available for sale in Australia will be listed on the CEC approved list, indicating that they meet the minimum performance and safety standards required in this country.