What do beer, inverters and the aardvark have in common?

I like beer and I like aardvarks. So that’s a start. But inverters can be confusing in that the rated capacity is not the usable capacity. 

When I order a pint, I’m pretty sure I’ll get a pint. I prefer it in an English style pint glass. Called Nonic glasses, they were patented in 1913 and called Nonic because the ‘no-nick’ bulge prevents damage if the glass is knocked over. The British, forever inventive, also tried it with a battleship, HMS Nonic, but it capsized. . . 

Where was I?

Beer. Part of that pint is golden nectar and the other is a white cap sealing in its sublime goodness. Especially if it’s a Doombar amber ale brewed in Cornwall PL27, and is the single strongest argument for immigrating to the UK. 

I am struggling this morning sticking to the bar top. I mean pint. I mean, point . . .

It’s the quantity and flavour that matters most, right? Right.

Inverters. Whether its blue, red, orange, green and black or silver, it’s like the glass. The number written on it promises the quantity. But is the quantity poured into our AC glass, what we ordered? Its not. Heiner explains why. 

Understanding Inverter Power Ratings: The Beer Glass Analogy

When comparing inverters, one of the most common sources of confusion is the way power output is rated. Inverter specifications often list values in kVA, while users are typically more interested in how many kilowatts (kW) of usable power they can actually draw. While many people are aware that kVA and kW are not the same thing, the reason behind this difference is often not understood.

This is where the beer glass analogy, and drinking helps.

Imagine a beer glass filled right to the top. The glass has a fixed size, just like an inverter has a fixed electrical capacity. In the glass however, not everything is drinkable because some of the volume is taken up by the head. The foam still occupies space in the glass, but it doesn’t make you want a second. Only the amber nectar does.

In electrical terms, the size of the glass represents apparent power, which is measured in kilovolt-amperes (kVA). This is the total electrical power that flows through the inverter’s components. It includes both usable power and non-usable power. The drinkable beer represents real power, measured in kilowatts (kW). This is the power that actually performs useful work, such as running appliances, charging devices, or powering tools.

The ratio between usable power (beer) and total power (beer plus foam) is called the power factor. A power factor of 1.0 would mean a glass full of pure beer with no foam — every bit of power flowing through the inverter is converted into useful output. In the real world, most AC loads do not behave that perfectly. Motors, compressors, and many electronic devices cause current and voltage to fall out of phase, creating what we can think of as electrical “foam”.

For example, an inverter rated at 5 kVA with a power factor of 0.8 can deliver:
5 kVA × 0.8 = 4 kW of real, usable power.

Even though the inverter is working at its full capacity, only 4 kW is available to your appliances. The remaining 1 kVA is effectively foam — it takes up capacity inside the inverter but does no useful work.

This distinction is critical when sizing an inverter for a vehicle or off‑grid system. If you only look at the kVA rating without understanding the power factor, you may assume you have more usable power than you actually do. In practical terms, that can lead to nuisance shutdowns, overloaded systems, or inverters running closer to their limits than expected.

The key takeaway is simple: kVA tells you how big the glass is, but kW tells you how much beer you can actually drink. When comparing inverter specifications, always look for the real power rating and understand the assumed power factor behind it. That understanding leads to better system design, more reliable performance, and fewer surprises once everything is installed. 

Finally, the Aardvark in the story.

A curious creature from south and central Africa, in a way like Doombar – rare, mostly nocturnal, amber in colour and provides a real thrill when one is sighted.

 

The end.