Phase Shift: Why I Pulled The Plug On Solar Thermal Hot Water

Solar hot water panels going on my roof in 2013.

Two years ago, I ripped a perfectly functional solar thermal hot water system off my roof. It had been sitting there for a decade, dutifully heating about 70% of my water with the sun’s heat (the rest boosted by gas).

I removed it to use the precious north-facing roof space for something better — an array of high-efficiency REC solar panels.

Then, I removed the gas booster and swapped it for a Reclaim hot water heat pump. Why? With three EVs, I needed more cheap solar electricity, heat pump technology had improved to be quiet and reliable, and frankly, solar thermal hot water is on its way out.

Before: My roof with solar hot water and 6kW of Tindo panels (top)
After: 14kW of REC solar panels, Tindo relocated to E & S roof (bottom).

Solar Thermal Is Going Down The Drain

If you installed solar thermal hot water panels a decade ago, you probably felt pretty smug. It was the most efficient way to get hot water using the sun, and it made a big dent in your gas or electricity bills. But the economics have shifted dramatically.

A heat pump hot water system running on cheap solar electricity beats a solar thermal system in almost every way that matters. It’s 100% electric, easier to install and maintain, doesn’t dump hot water when it’s too sunny, can store solar energy to use at night, when powered by PV, or off-peak grid electricity, and is cheaper to run. It also lets you use your roof space for the most valuable real estate in Australian energy: more solar PV.

Heat Pumps Versus Midnight Showers

But heat pumps aren’t perfect.

I live with three teenagers, who all enjoy 45-minute showers. Usually around midnight. If I want a hot shower in the morning, I need to boost the hot water in the wee hours. The bad news? I can’t do this directly with solar electricity. The good news? The heat pump is so efficient that my battery can effortlessly boost it with stored solar.

If I had no battery, I’d program it to boost between 1 a.m. and 5 a.m., when I get off-peak grid electricity.

Standing next to my Reclaim heat pump, waiting for my teenagers to finish up in the bathroom.

Turn On The Tap, Turn Off The Gas

The shift wasn’t just about hot water. That old gas booster was one of the last things tying me to a gas connection. Replacing it with a heat pump meant I could finally scrap the gas meter. I also had to replace the gas hob with induction. That turned out to be a huge upgrade in itself — cooking on gas after experiencing an induction hob is about as much fun as driving on diesel after owning an EV.

Solar Thermal Will Slowly Evaporate

Solar thermal hot water isn’t disappearing overnight. Some systems will keep running for decades. But new installations? They’ll keep shrinking. When PV was expensive, solar thermal made sense. But now? Heat pumps + PV have won the battle to give you a hot shower.

I’m so sure of this that I not only shut down the solar thermal on my roof, but also an entire website I’d built dedicated to this once-pioneering technology.

SolarQuotes today instead offers a growing body of advice on hot water heat pumps, including video explainers. As of last week, we now offer up to three quotes for heat pumps from verified installers.

I pulled my solar hot water panels off the roof for the same reason I don’t use a fax machine anymore¹: technology has moved on. Fifteen years ago, both were essential technology. Today, they belong in a museum.

Phase Shift is a weekly opinion column from SolarQuotes founder Finn Peacock, in which he shares his views on all things home electrification.