One doesn’t need a PhD to understand the different components of a solar PV system. The two most fundamental components of a solar PV system are the solar panels that convert sunlight into electricity and the inverter, which is the brain behind everything.
To most of us laymen, we see the inverter as being this black (or white) box with wires going into it and all we know is that it works. It does its job and that’s it.
What Does an Inverter Actually Do?
In its simplest form, an inverter converts DC current to AC current—and we’re not talking about the infamous AC/DC rock band here!
DC, short for Direct Current, is electric current that flows in one direction only. A battery is a good example of a DC power supply source that works with renewable energy sources such as solar and wind power. Direct current is also used to charge batteries and as a power supply for electronic systems.
Unfortunately, we use AC power in our homes to power many of our electrical equipment. The power that comes from the utility grid along the high voltage power lines also uses AC power. AC power, also known as Alternating Current, periodically reverses current direction.
Different types of inverters exist depending on the application of the inverter and also vary in size depending on the size of the DC power source.
Depending on the type of inverter, they can produce different AC waveforms such as the square wave, modified sine wave and sine wave. Pure sine wave inverters are more suited for sensitive electronic equipment, such as the computers found in most homes and offices.
Lower quality inverters produce square wave and modified sine waves. Although much cheaper, it’s best to avoid these as you could end up with damaged electronic goods in your home!
PV inverters are a special beast though altogether and are specifically designed for solar PV applications.
Do I Need an Inverter for My Solar Panels?
Unfortunately you do if you are using AC current in your home (which you are, by the way)—they are a critical component of any solar PV system. The solar PV inverter’s most basic function is to convert the DC power produced by the solar panels into AC current that your home appliances use. Solar PV inverter technology has also made some major technological advances in recent years to maximise system performance. These include data monitoring, advanced utility controls, applications and system design engineering.
Solar PV inverters are also considered the gateway between the solar panels and the grid, controlling where the power goes and sometimes, depending on the country, controlling how much power is fed into the grid.
However, if you are using a solar PV system for an off-grid application and use DC power for all your electrical requirements, you won’t require a PV inverter but will require a DC controller. The purpose of the DC controller is to charge the solar PV battery system and ensure the battery system isn’t overcharged. It regulates the voltage and current coming from the solar panels and going to the battery.
What is the Difference Between an Inverter and a Converter?
You have to love these fancy technical terms! Whereas an inverter’s basic function is to “invert” DC current into AC current so it can be used for all your electrical appliances, a converter does the exact opposite: it converts AC current into DC current.
Converters are mainly used in the radio communications space, detecting AM radio signals, or where there is a requirement to convert AC current to DC current. They are also used to supply polarised voltage for welding.
How Do You Connect Solar Panels to the Grid?
If your house is connected to the utility grid then you will be using AC power. A PV inverter is required to convert the DC power generated by your solar panels during daylight hours into 240V AC power.
This AC power is used in the household or property. Any excess power produced is fed into the grid by the PV inverter. The utility has a meter installed that will track the amount of excess clean energy that is injected into the grid.
During the evening when there is no sunlight, the property will consume energy from the grid again.
What’s the Difference Between a PV Inverter and a Hybrid Inverter?
That’s a good question actually! A PV inverter purely converts DC power into AC power, but what if you want to include an energy storage system into your solar PV system or have an off-grid house?
When you include a battery system you then need a battery inverter. The purpose of the battery inverter is to charge the batteries with DC power and ensure the batteries aren’t over-charged or fully discharged.
Typically, these would be seperate systems from the PV inverter. With technological advances, you now get the Hybrid inverter. The hybrid inverter combines both the solar PV inverter and the battery charging system.
These hybrid inverters are more economical as they combine both aspects required for converting DC power into AC power and for charging the energy storage system.
Hybrid inverters also allow you to increase your self-reliance through the use of batteries and to store clean energy produced during off-peak times to use during peak periods.
When investing in hybrid inverters, you need to do your homework as many o the hybrid inverters on the market don’t work in off-grid mode and won’t be able to provide a power source during periods of blackouts.
Some of them also have minimal monitoring functionality, so it’s best to investigate and shop around before investing. Your PV installer is an ideal way to get more information on a recommended hybrid inverter.
Another economical option if you are looking to include an energy storage system in your solar PV system is to consider the Tesla Powerwall. The Tesla Powerwall has the advantage of including the solar PV inverter, battery inverter and an energy storage system all in one package!
However, you would be limited to using the Lithium-ion battery that comes with the system.
Using other versions of hybrid inverters would allow you the flexibility to choose other types of batteries in your solar PV system.
How to Choose an Inverter
Now, choosing an inverter is a big decision, but luckily not one of those life-changing decisions such as deciding what career to take or who to marry!
As already outlined, the inverter is a major system component of any solar PV system and is the brains behind everything. Therefore, it’s vital the correct inverter is chosen.
There are hundreds of different inverter suppliers out there.
It’s best to go with a reputable brand that has been around for a while and has a good warranty. Check the inverter’s track records in terms of quality and if others have had any technical issues. Investing in a poor quality inverter can leave you with malfunctioning appliances—or even worse, exploding inverters that can cause an electrical fire!
When it comes to inverters, it’s probably best to stick with reputable brand names and invest a little more, thereby providing peace of mind!
The PV inverter also needs to be sized correctly as they are rated in kWs. The kW rating tells you what size PV system it can take on. If you have a 5kW PV system then you will need an inverter that can handle 5kW of DC power.
The efficiency of the inverter is another key criteria.
You want to be sure that you maximise the amount of power your solar panels are producing. Nothing in life is 100% efficient and unfortunately the same applies to solar power. There will always be losses.
Some of the lower quality inverters only provide efficiency levels of between 70 and 85%. What does that mean? Well, it means you’re only getting 70 to 85% of AC power out of your solar panels—the rest of that power is lost, gone forever!
The higher quality inverters, although a bit more costly, have efficiency levels sitting at 90 - 95%!
Inverters may seem like a black box to most of us, but they are marvels of modern technology and some do much more than just convert DC power to AC power. They are the brains behind our solar PV system and without them, well, solar panels wouldn’t be able to do much of anything at all.
When selecting the right inverter, it’s crucial to do your homework and background checks. The PV inverter must be sized correctly according to the total size of your solar panel kW output and should be a respectable brand name with a good track record.
Invest a little more in a high-efficiency inverter so you get more bang for your buck!
Last but not least, and probably the most important of all, talk to your local PV installer about choosing the right inverter as they have experience with all of the different inverter brands.
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