Inverter Oversizing

Getting the most for your money

In general terms, inverter oversizing, is the concept of installing more solar panels than your inverter is rated for.

But shouldn’t your solar panels and inverters match in terms of the energy they can handle?Well, it’s a little bit more complicated than that since there are so many different factors to consider when installing solar panels, and this is one that we believe is often overlooked.

Here’s an explanation of what oversizing solar inverters actually entails, how it works, and whether it’s the right choice for your solar installation.

What is an inverter?

An inverter is at the heart of your solarsystem. It’s a central unit that makes it all work. The inverter is the part of your system that transforms the DC energy (Direct Current energy) created by your solar panels, into AC (Alternating Current energy) which powers your home, business or any other premises.

Without an inverter, there’s no way to use the energy that’s produced by your solar panels. So it’s important that we make the most of what it does.

There are many makes and kinds of inverters in the market, but they can be narrowed down to 3 main types of inverters. One type of inverter might work for your situation but may not work for others, and vice versa, so it’s vital that you opt for an inverter that is suited to your specific needs.

What is a solar array?

Simply put, a solar array (or PV array) is the technical term for a group of solar panels. The panels on your roof will be called a  ‘solar array’. The number of panels required and therefore the size of your array will depend on your particular solar needs.

Another important factor is how much sun you get during the day and how that impacts the average efficiency of the solar panels. This is where inverter oversizing comes in!

What exactly is Inverter Oversizing?

As mentioned earlier, oversizing solar inverters refers to when you install a solar array (a group of solar panels) that collectively have a higher energy capacity than the rated size of your inverter. Basically, you install more solar panels that your solar inverter capacity is meant to handle.

For example, say you have a 5kW Inverter, a very common size for homes in the UK since most energy providers cap the electricity export for homes at 5kW. At any period in time, your solar system won’t be able to export more than 5kW of ‘sbare’ energy to the National Grid. ‘Exporting’ excess energy to the grid is what happens when you don’t self-consume the energy yourself.

In theory, it sounds sensible to match a 5kW Inverter with 5kW worth of panels – and many people do this. For a 5kW system we would install  15 panels at 330Watt each, a total 4.95kW. But when you opt for inverter oversizing, you install more than 5kW worth of panels instead.

At first this might sound a bir strange and possibly a  ‘waste’ of all that extra energy if you can’t use it or put it back into the Grid. Bu it actually a reasonable thing to do since it boils down to solar panel efficiency.

Solar panel efficiency 

The truth is that solar panels don’t stay fully efficient throughout their useable livespan. Individual solar panels almost never produce exactly the amount of energy that they are rated to. So a 330Watt panel will rarely (most likely never) produce exactly 330Watt at any one time.

So why are the solar panels rated to that number when it’s practically impossible to reach it?

Well, that’s because a solar panel’s capacity is rated under controlled Standard Test Conditions, which are generally the absolute perfect conditions to maximise their output. Conditions which, unfortunately, are rarely experienced in the UK!

So how efficient can solar panels get?

The graph below is an example of the energy yield for a ‘matching’ solar array and inverter. It is apparent how the 5kW of panels never quite reach the 5kW maximum of the inverter, even at its most efficient point at midday.

Graph 1 – Avg. daily solar production for a non-oversized system

Why should we oversize solar inverters?

Those who have been installing inverters for a long time know that they your can actuallyhandle a lot more energy than you would think – around 133% or more.  So to get more energy early on and throughout the day, your solar array should add up to much more than 5kW.

Using the example of the 5kW inverter, instead of matching it up with 5kW worth of solar panels, you can go all the way up to 6.6kW of solar panels.

This amounts to adding only 5 extra solar panels, an extra expense, but it can greatly increase your daily energy yield. Here’s the proof:

The graph below depicts the energy yield of 10 customers, each with a 6.6kW system, over a period of 7 days. As you can see, the inverter reaches its maximum capacity early on in the day and continues to produce that much power well into the afternoon. In fact, some tests have shown an increase of up to 28% daily energy yield with an oversized inverter.

Simply put, the extra panels do wonders for the environment, your power usage, and your running costs!

Graph 2 – Avg. daily solar production for an oversized system

Is it safe to oversize solar inverters?

Pretty much every inverter on the market is designed to safely manage one-third (133%) of additional energy from an associated solar array. As long as the solar system is designed and installed by a reputable company, there should be no safety concerns with oversizing your inverter.

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