How to choose your solar inverter

It is often said that life is short, so you should enjoy it as best you can. But honestly, how are you supposed to enjoy life when you have to waste time sorting out things like solar panels, batteries and inverters?

Allow me to give you some clarity on solar inverters, why you need them and how to choose the right one for your needs.

what is a solar inverter

What is a solar inverter?

Looking at a solar inverter, you will see a rather underwhelming, flattish, rectangular device. This device works with your solar panels to enable you to enjoy energy from the sun and forget about Eskom’s woes.

To give you a clearer picture, let’s look at the whole process of converting rays from the sun into electricity that can power your home or business.

Carbontrack.com gives a quick and easy explanation. It starts with your solar panels collecting energy from the sun by capturing the sun’s rays.

When the sun shines on your panels, electrons inside the panels start moving around, creating direct current (DC) energy. This is collected by circuits, converting it into electrical power.

This power is then sent off to the solar inverter. This happens all day, every day – when the sun is shining of course. The inverter converts DC electricity into AC electricity and sends it to the fusebox.

Now the AC electricity can be delivered to appliances as needed to power them up. Excess power is sent to either batteries or back into the grid, depending on your chosen setup. 

Based on this you can see that the inverter is not optional if you plan to go solar. Without it you won’t be able to use the energy captured by your solar panels.

And if the tech enthusiast in you was wondering: solar inverters consist of the following components:

  • Capacitors. Used to filter ripple contents on DC liines and to keep the DC voltage stable and minimise losses between the solar panel setup and the inverter.
  • Software and monitoring. These run on the inverter’s digital signal processor or microcontroller. It allows the owner of the inverter to know the status of the system and provides alerts in case of faults.
  • Solid state switches. A combination of power semiconductors that convert DC to AC.
  • Magnetic components. They bring AC voltages to the correct levels for grid interconnection.
Where do you keep your inverter?You are simply going to mount it on a wall close to the power board. It needs to be in the shade and away from extreme weather conditions. The garage works well.
There are types of inverters that go on the roof with your panels too. Keep reading.

First things first: how solar will you go?

There are different types of inverters on the market, but as the inverter is the ‘brain’ of your solar system, it’s worthwhile to consider your exact goals with going solar.

These are the types of solar system you can choose from:

  1. Off-grid

Going off-grid means that you will be divorcing Eskom, and waving them goodbye completely. 

You will not be connected to the grid at all, and therefore your solar system needs to be designed in such a manner that you always have power – even when the sun isn’t shining.

The implication of this is that you will need to significantly invest in batteries and inverters, because obviously you want maximum energy conversion and storage.

If you live in an area where there isn’t much sun, a backup generator is recommended to make double sure you are always powered up. In most parts of South Africa this probably won’t be necessary though.

This makes going off-grid the most expensive option, but definitely the one to consider in South Africa if you can afford it, as the grid is becoming increasingly unreliable.

  1. On grid (grid-tied)

In this scenario you are still connected to the grid and therefore don’t require battery storage. Since the batteries store excess power, a grid-tied system needs to be designed in such a manner that the excess is minimal.

The result is a smaller, and therefore more affordable system that will power essentials such as the fridge, freezer and pool pump during the day.

  1. Hybrid system (grid backup)

If frequent loadshedding continues each winter there will be continued demand for grid-backup systems that can operate without the grid for prolonged periods of time.

Adding an inverter and battery to your system lets you combine the energy from the system with the stored battery power to power your essentials.

This type of system, as the name implies, is connected to the grid, but makes use of power stored in batteries as well. 

Therefore, you can store energy generated during the day, and use it at night. When stored energy is depleted, the grid is still there as a backup.

types of inverters 1

Types of inverters

The main types of inverters are string inverters, hybrid inverters and micro-inverters.

String inverters are so named because of the way solar panels are installed. They are placed in rows, each on a string. For example, if you have 25 panels, you might have five rows of five panels.

DC power from the solar panels are carried to the inverter via multiple strings that are connected to one string inverter. String inverters are nothing new and are commonly used and less expensive than other kinds.

As the panels are placed in a series, the overall efficiency will be influenced if even just one panel doesn’t receive sufficient sunlight due to shade. Your system will then function at the efficiency of the least efficient panel.

One drawback of a string inverter is that the noise-sensitive won’t want to be around it. They emit a humming, buzzing or ticking sound that could potentially irritate people.

This problem is solved by simply keeping it in an area of the home or business that people don’t occupy much.

The hybrid solar inverter is a newer option which has a battery installation along with the set-up of the inverters. It supplies DC power to the battery, but also provides power to the grid and your home’s appliances.

Micro-inverters are different in the sense that one is installed behind each solar panel. A string inverter is not needed because power is converted from DC to AC right there at the panel.

This also means that should the efficiency of one solar panel be compromised for some reason, the others can still function optimally. 

This makes systems with micro-inverters generally more efficient, but they can be more pricey. The use of microi-nverters is a good choice in the following instances:

  • If you want to measure the efficiency of each individual solar panel.
  • If some of your solar panels are in the shade.
  • If you want to expand your solar system in the future.
  • If your system is small and you don’t have enough space for a string inverter. 

How to choose a solar inverter

Ask yourself these questions before buying a solar inverter. This helps you to clearly define your solar power goals:

  • Do you want to switch to solar or do you want an inverter for load shedding only?
  • Are you planning to add more solar panels later?
  • Will you need batteries?
  • Are you adding another inverter later?
  • Do you require a UPS function?
  • Do you have Single Phase or 3-Phase supply?

They further advise that, as a general rule of thumb, a hybrid inverter is suggested for all applications. 

This is especially the case if you need a UPS function and if you are planning to add solar panels later on, in which case the hybrid inverter is an investment that will save you money in the long run.

If, however, you are only looking to deal with loadshedding and don’t plan to expand, an off-grid inverter will do the job.

Here’s handy advice on determining the size of the inverter you will need.

Check out their formula:

Step 1: Take your average monthly electricity bill and divide the amount by 2.2 (the average price per kW in June 2021 – you can adjust accordingly).

Example:

R1800 / R2.20 = 818.18.kW

Step 2: 

Take your monthly usage in kW and divide that by 30 (days in a month) to determine your daily usage.

Example: 818.18kW / 30 = 27.27kW

Step 3: Take your daily usage and divide it by 5.5 – this is the number of hours in the day during which you are most productive and consume the most electricity.

Example: 20.27kW / 5.5 = 4.96kW

Conclusion: 

You will need at least a 5kW inverter to cover the 4.96kW.

Upon choosing your inverter you need to keep your needs in mind, but also your budget. Prices vary greatly depending on the size of your system as well as the brand and features of the inverter.

If you need an inverter for running a business, you are looking at over R50 000. For use at home you can look at between R8 000 and 14 000 for off-grid inverters, and between R18 000 and R44 000 for hybrid inverters.

Final word

Avoiding loadshedding is of course not the only reason to invest in a solar system. You might just want to reduce your electricity bill – and you will.

MyBroadband recently reported how Bidorbuy CTO James Ostrowick managed to cut his electricity bill in half by investing in a solar system to the value of R65 000.

The initial investment might be a bit steep, but nothing beats the peace of mind of knowing that you can go on with your life when the lights go off.

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