Solar Inverter

A fundamental part of every Solar Power set up is the Inverter, it is a piece of equipment that is very important to understand.

After you read this definitive guide you will understand:

What is an Inverter?

Pure sine inverter
A Pure Sine Inverter

In simple terms this component  converts DC power  (Direct Current) into  AC power  (Alternating Current). DC flows in just one direction , this is ideal for Solar Panels because you need it to simply absorb the sunlight and push it through the system in one direction. This might be an oversimplified explanation but for now, that’s all you need to know for the purpose of this article.

 AC flows in both directions , all of your appliances are powered in this way.

Now we have that out the way let’s move on to the next part.

How do they Work?

The energy from your Panels or your Batteries are fed to the inverter, then, in turn, handles that energy by transforming the DC power to AC.
Solar Inverter diagram
You get three main types of Inverters you can use, each one functions a bit differently to the other:

Grid-Tied & Hybrid Types

The Panels are connected directly into the inverter which then, in turn, plugs into your building electrical box (DB Board).

Hybrids are used for Grid-Tied / Off-Grid / Storage and generator inputs. All different Solar Power applications are possible with Hybrid variations, which is the most versatile option.  Hybrid inverters accept DC and AC power .

Here are the general functions that Grid-Tied and Hybrids typically perform:

  • Synchronise to the grid
  • Disconnect if the grid goes down
  • Use an alternative power source (solar, battery or wind)
  • Detect if any power sources are depleted and switch to another
  • Monitor power usage

Here are the different types available:

String Inverters

String Solar Inverter

Features

  •  Lowest solar inverter price 
  • Multiple MPPT inputs
  • Provides backup power

The modern string inverter has improved over the years making it the  most cost effective , the panels are wired in a series, simply put all the panels are  connected together and is then connected into the component .

It’s a standalone box that is installed close to your fuse box and meter, the newer versions don’t tend to make much or any noise compared to older ones.

If you have an unshaded roof that gets 100% of the sun spread evenly and you have no shade from a chimney or tree the string variation is perfect, but if there are obstructions it can cause it to be  less efficient .

Another factor is scaling, if your energy needs exceed your inverters output you will need to  purchase a bigger version  so scaling up can increase your overall solar inverter price. We suggest purchasing one with a higher capacity just in case you need it.

Pros

  • Efficient
  • Affordable
  • Long lasting (around 15 years)

Cons

  • Not efficient if panel/s are shaded
  • Expanding is difficult

Micro-Inverters

Micro Inverter

Features

  • Easy to install
  • Expandable
  • Maximises output of each panel

These small variations are connected to the panel itself, they are easy and safe to install.  They can produce up to 25% more energy maximising the panel output .

 Ideal for expanding  the Micro-Inverter monitors (module-level monitoring) each panel independently making them  operate independently , they are the better option when dealing with rooftops that have different pitches and partly shaded.

 Because each panel is independent it maximises each panel  which means if there is a shaded or low-efficient panel it won’t hinder the rest of the group of panels (solar array) as the string variation does.

The downsides to these variations are the price, although they have come down they are the more expensive route.

Pros

  • Easy to install
  • Long-lasting (25-year warranties)
  • Expandable and modular

Cons

  • More expensive
  • Maintenance requires rooftop access
  • Exposure to the elements can cause issues (extreme cases)

Solar Optimisers

SolarEdge Solar Optimiser Cell

The Solar Optimiser works with a String Inverter and  performs much like the Micro-inverter  by maximising the output of the Solar Panel (More about Solar Panels here).

Features

  •  Works with String Inverters 
  • Performs in the same way as a Micro-inverter
  • Affordable

These components are perfect if you already have the String variation or if you know which Panels are shaded or pitched differently.  They are connected to the panel itself much like the Micro-inverter .

Pros

  • Easy to install
  •  Long lasting (25-year warranties) 
  • Expandable and modular

Cons

  • Maintenance requires rooftop access
  • Exposure to the elements can cause issues (extreme cases)

Off-Grid Solar Inverters

Unlike the Grid-Tied options, an Off-Grid variation requires batteries, the power from the Panels charge the batteries directly then the battery power is then inverted to AC from DC batteries.

Off-Grid systems are more complicated, this is due to the extra components you will need such as the Charge Controller, Battery Monitors Circuit Breakers, Surge Suppressors and so on.

Here are the different types of Off-Grid variations available:

Pure Sine wave

Pure sine inverter

Features

  •  Delivers quality power output 
  • Quieter than Modified Sine wave
  • Ideal for modern appliances

Safer, the Pure Sine option is the main choice for Off-Grid, affordable and deliver higher quality output. Almost all appliances will work with these making them highly compatible with most systems.

Modified Sine wave

Modified Sine Wave Inverter

Features

  • Lowest price

These output lower quality power and are only compatible with certain appliances. They can be problematic for electronic equipment,  we recommend the Sine wave option .

What Size Do I Need?

Solar Inverter options

This section might get a little tricky because there is a difference between the capacity of the inverter and the output. The capacity speaks to the max DC energy can be fed into the device, while the output speaks to the max AC current you’ll be using to power your home. For example,  if you buy a 3kW converter, but your panels are only capable of delivering 1kW, there’s an imbalance .

If you plan on adding more panels, then you’ve made a pretty good investment. However, getting 3kW from your panels while your inverter can only handle a 1kW output seems like somewhat of a waste.  You’re not using your system to its full benefits .

Work out what appliances you will be running

Typical households that run the standard number of appliances such as these:

Appliance Watts (per hour)
Standard Fridge 150
Fridge Freezer 150
Washing Machine 1000
Tumble Dryer 2800
Personal Computer 200
46″ LCD Flat screen TV 250
Modem 12
Alarm System 15
12 LED Lights 240 (20 Watts Each)
DSTV Decoder 30
Total: 4847 watts

In the example above you can work out that the size you will need to cover these appliances, this equates to 5kw (rounded up).

 We also add an extra 1kw to ensure we cater for any additional appliances that might be added in the future which takes us to 6kw .

You might be thinking that this is already a large system, but…

If you one with the dual MPPT output feature you can split that load in 2.

  • 2800 watts (2.8kw) for the Tumble Dryer and Washing Machine – Non-essential.
  • 2047 watts (2.1kw rounded up) for the rest – Essential.

The ability to have to Essential and Non-essential load outputs allows you to prioritise your energy, bundling them all together is not only going to push up the price of your inverter (because you need a larger one),  it also gives you the option to only use your batteries exclusively on the essential load , driving down the cost of storage needed.

What does this mean? 

It means that your device size comes down, so instead of a 6kw option to handle it the complete load, you can get a 4kw or a 5kw option instead.

Here’s an example of a 4.6kw kit that handles the above with some room to spare:

Goodwe – Lithium Storage 3.92kwh – Solar Power Kit

System Specs:

  •  NRS approved  (National regulation standards) and on the approved list of inverters for most SA municipalities
  • Array size: 2970W (peak hours)
  • Est daily production: 16.35kwh
  • Storage: 3.96 kwh for daily usage
  • Peak load: 4.6kw
  • Annual yield: 5886kwh
  • Grid-tie / off-grid / grid support
Kit includes 2 x PylonTech US2000 Batteries

In conclusion…

After working out what size you think you need simply double check with our team at SolarAdvice to make sure, don’t forget that advice is always free.

Solar Inverter Prices, How Much Do They Cost?

Grid-Tied

Here are our Grid-Tied options and their prices, they all vary depending on size and manufacturer.

Single Phase Grid-Tied Options

3 Phase Grid-Tied Options

Hybrid

Micro / Power Optimisers

Best Solar Inverters in South Africa

To name the best pound for pound brand is tricky, each brand does have its strengths and weaknesses depending on its application.

Here are the best brands that we would recommend:

  1. Goodwe – this brand is of great quality and a great price
  2. SolarEdge – a wide range of options available and great quality
  3. SMA – aesthetically great looking and compact
  4. Solis – efficient Grid-Tied options
  5. Steca – solid German engineering, compact and innovative

Resources:

https://en.wikipedia.org/wiki/Solar_inverter

SolarAdvice Rating
Overall
4.7
  • Return on Investment
  • Affordability
  • Energy Saving
  • Overall Cost
  • Installation (Speed)
  • Installation (Cost)
Sending
User Review
4 (3 votes)

Solar Inverter Review Summary

Depending on what type of inverter you choose the experience can differ greatly, for such an important component it’s safe to say that we rate the Solar Inverter high.

Inverters have improved over the years and they’re only getting more reliable, cheaper, easier to install with improved monitoring features.

Consult with a technician before purchasing your inverter just to make sure it suits your needs.

Pros

Enables system monitoring

Affordable

Expandable (Micro-inverters)

Long lasting

Cons

Expensive for larger systems

Can vary depending on manufacter

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  1. Pingback: Reduce your electricity bill with solar inverters | MFLI Home July 28, 2017

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