As the mercury climbs and solar yields improve around the Summer solstice, spare a thought for your inverter, steadfastly sweating away on the wall. High temperatures aren’t just an inconvenience, they’re an electronic health hazard, shortening the lifespan of your inverter. Read on while I explain how heat saps your inverter’s efficiency—and your wallet.
Electronics Hate Heat
Anything electrical doesn’t cope well with heat.
Solar inverters detect when they’re getting too hot and throttle back, converting less solar DC into AC electricity, which is a shame when you need that energy to run the air conditioning.
This is called ‘temperature derating’ and is smart design because it saves this expensive piece of kit from burning itself out1.
Fan-Forced Cooling Is Best
There is much to be said for proper thermal management with a fan, so I have always been keen on Selectronic and Fronius inverters. Even when the competition likes to market their devices as being practically silent by comparison, the roar of a Fronius fan reassures me there’s some work being done by a machine that will last longer because it runs cooler. Best of all it means more yield harvested.
Fan-forced cooling means more energy than passive cooling, according to Fronius. Image credit: Fronius
If you look under the bonnet of a modern car, you’ll find that the radiator they use to manage the heat from a combustion engine is broad, thin, lightweight and fan-forced. They don’t just hang a big heavy hunk of finned aluminium on the front and hope there’s a quiet breeze to cool the inefficient heatsink.
Fun fact: According to a Fronius whitepaper the fans for a Fronius inverter never run at full speed in Australia. The scorching Aussie heat de-rates the output of solar arrays enough that the inverter doesn’t have to deal with really high solar inputs found in Austria’s snowy alpine regions.
A Fronius “snapinverter” series inverter partially opened to reveal the cooling fan that makes all the racket.
The latest Gen24 Fronius inverters have a bigger, slower and much quieter fan than their ‘snapinverter’ predecessors, plus enough recycled aluminium to account for 328 beer cans, I’m assured.
The internals of a Fronius Gen24 inverter.
Perhaps it’s telling that after years of solid alloy silence, the Sungrow inverter (3 phase 15kW) I installed recently has a fan stuck quietly on the back, too.
Real-world conditions are displayed on an app in Darwin vs the instructions. Note 71°C internal temperature causing “Power Limitation Mode”. This customer ran an oscillating fan on hot days to keep the inverter online.
Small Spaces Need Ventilation
Electric motors are often specified to have 20°C temperature rise so on a 40° day it’s perfectly normal for say a pool pump to run at 60°C. That’s too hot to lay your hand on comfortably. Some solar inverters are much the same. They’re obliged by law to put “hot surface” warning stickers on them.
I have seen first hand where wall paint has been discoloured by hot heat sinks, while inverters have led short lives because they’ve been kept like naughty children in a cupboard under the stairs. In that particular instance we replaced the inverter and gave it a bathroom exhaust fan, plugged into a home brewers thermostat, to keep the cupboard fresh.
Like a bathroom heat lamp shut in a box, at 96% efficiency, this 30kW machine can throw off a lot of energy. The exhaust fan should keep the cheap replacement inverter cool, though.
How To Keep The Sun Off Your Inverter
For many years, the rules for solar (Clause 8.1.1.2) have dictated inverters can’t go on the North side of the house in full sun. Radiant heat from outside and electrical heat from inside just bakes them.
Better installers resort to a “hammerbarn awning”, which is better than nothing. Realistically, they offer patchy protection, especially if your inverter calls for 500mm of clearance from what’s supposed to protect it.
This awning would want a gap against the wall to let the hot air out.
There are many better options available, which are more durable than a cardboard box, however they’ll add $300 – $450 to the cost of your system. If you’re just a little handy, grabbing a $30 shade sail, screwing it to the eave or wall above the inverter & then pegging it to the ground or fence is a great idea.
You get what you pay for with inverter covers
I’ve done this experiment, and shade cloth can easily lower the wall temperature by 10°C. Just stopping rain strikes is surprisingly good for the longevity of the inverter, labels & more importantly, DC isolators if you have them.
That flaming mess was a DC isolator, an item worth having checked by qualified people. These days, inverter makers build them for much better quality & safety.
A Cool Garage Is Best
Installing complex electrical equipment out of the weather is also a good idea. Most grid-connect inverters are pretty robust, but some aren’t. Even if it’s sealed to IP66 ratings, though, exposure to the elements simply doesn’t do things any good. I’ve always advised people that putting your inverter where it will be seen regularly is also a great way to ensure it keeps working.
Heritage rules are sometimes genius.
Dos And Don’ts
- Don’t wrap an inverter with insulation or keep it in a sealed box
- Do Put it in the shade
- Do keep an eye out for dirt, dust, wasps, geckos and other wildlife.
- Remember that professional servicing can identify problems before they become a disaster.
- Many network connection agreements actually oblige you to have an electrician test your system and issue a compliance certificate every five years.
Boiled eggs, anyone?
Footnotes
- For comparison, when the generator on my 100-year-old car has a minor malfunction, it’s more likely to toast the hand-wound armature, burn the insulation from the fields and, in a final act of self-immolation, throw molten solder everywhere. It’s a lot of heartache for a machine that’s only ever good for about 200 watts. ↩
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