Solar inverters are an essential part of a solar energy system. But what exactly do they do and does every solar system need one?
In this simple guide for beginners, we look at the functions of a solar inverter, the different types and how to choose the right one for your system.
How Does a Solar Inverter Work?
Solar panels produce electricity as direct current (DC). Almost all household appliances such as fridges, wifi routers and TV’s run on alternate current (AC), however. Solar inverters convert the direct current (DC) energy from a solar panel into alternate current (AC) energy appliances use.
It’s also important to note that solar batteries store DC energy. Before you can use the energy in a battery to power an appliance, it has to be converted to AC energy using an inverter.
Types of Solar Inverters
There are three main types of solar inverters namely hybrid, off-grid and grid-tied.
1. Grid-tied Inverter
The distinctive feature of a grid-tied or “grid-direct’ inverter is that they shut down when there is no electricity from the utility. This means the solar system shuts down when there is load shedding or a power outage.
This is a safety feature to prevent a solar system from feeding electricity back into the grid.
2. Off-grid Inverter
An off-grid inverter is used in a stand-alone or off-grid solar system where there is no grid-supplied electricity. These inverters are ideal for game lodges, rural areas or new homes that do not have utility supplied electricity.
Some off-grid inverters work as inverter/chargers as they allow you to charge your battery bank from an AC source such as a generator.
3. Hybrid Inverter
Hybrid inverters are becoming the default choice for solar energy systems. This is because they can work in both a grid-tied and off-grid system.
Unlike grid-tied inverters hybrids do not shut down during load shedding or a blackout. Rather they disconnect from the grid and continue supplying electricity.
Choosing The Right Inverter
Choosing the correct inverter is more than just knowing what type you need. There are 3 main specifications you need to consider which are just as important.
1. Sine wave
A sine wave or waveform is the quality of the current signal an inverter sends to an appliance. Think of it as the “broadcast frequency” of a current. Sine wave is important because some appliances will not function properly with some inverters because of the sine wave.
There are three types of waveforms. These are pure sine wave, modified sine wave and square wave.
Pure sine wave is the recommended waveform for inverters because it closely matches the waveform of electricity from the utility. This is critically important if you want to sell electricity back to the grid through net metering. Most modern inverters are pure sine wave.
A modified sine wave is cheaper but produces a lower quality waveform that might affect how your appliances work (poor picture quality on your TV for example). Because it is a lower quality waveform, you might not be able to export electricity to the grid.
Square wave inverters are the least used in solar power systems. This is because they also produce a lower quality waveform that might not work with your appliances.
2. Minimum/Maximum Input
A solar inverter will have a voltage and power range. The voltage range is the minimum and maximum voltage (V) the inverter will work with. The power range is the minimum and maximum power measured in watts (W) it will accept.
These measures are supplied by the manufacturer and are important in designing a solar energy system. Exceeding the maximum voltage or power rating of the inverter will damage the inverter. If the voltage or power is below the minimum rating, it will not function at all.
3. Maximum Output
This is the maximum power an inverter can supply. Most inverters come with a peak power and continuous power rating.
Peak power rating or surge power is the maximum amount of power an inverter can produce for a short period usually when an appliance like a refrigerator starts up.
Continuous power rating is the total power the inverter can support.
Getting an inverter with a bigger power rating (up to 30%) than what you need is considered good practice. This gives you flexibility should you need to expand your system in the future.
Do All Solar Systems Need An Inverter?
Most residential and commercial solar systems require an inverter to convert DC to AC energy. The only exception to this is for appliances or machines that use DC energy. In this case, a solar inverter is not necessary.
What Size Inverter Do I need For My Solar Panels?
Sizing an inverter is largely a factor of the energy requirements or the size of the solar system. For a solar system that produces between 4.5kW to 6.5kW, a 5kW inverter should be used.
In a system that produces between 2.5kW to 4.5kW, a 3kW inverter should be used.
A rule of thumb for sizing an inverter is that the solar panels should not produce more than 30% of the inverter capacity.
How Long Does An Inverter Last?
Solar inverters last between 5 to 10 years. The most critical factor in the lifespan of an inverter is the installation and maintenance.
Heat causes the most damage to an inverter. Installing it in a cool, dry area will ensure you get the most years out of it.
Do All Inverters Need A Battery?
Solar inverters can be directly connected to solar panels. This is the default design for a solar energy system that does not have batteries.
Can A Solar Inverter Work Without Solar Panels?
Solar inverters can be used with batteries to power an appliance. Hybrid and off-grid inverters can also work as AC chargers in that they can run using utility electricity.
To wrap up a solar inverter converts the direct current solar panels produce into alternate current appliances use. There are three main types of inverters of which hybrid inverters are the recommended choice for most solar installations.
Be sure to checkout our next post where we review the best solar inverter brands in Zimbabwe.