Thermal Solar Tubes vs PV Solar + a Good Old Electric Cylinder

There’s a certain type of solar salesperson who gets very excited about thermal solar tubes.

They’ll talk about “direct heat transfer efficiency.”
They’ll mention “superior thermal capture.”
They might even dramatically point at a shiny evacuated tube array like they’ve just discovered fire.

And technically?

They’re not wrong.

Thermal solar tubes are extremely efficient at turning sunlight into heat.

The problem is that efficiency, on its own, is a pretty useless metric if it solves the wrong problem.

Because when most New Zealand homeowners ask us whether they should install thermal solar tubes or just go with photovoltaic (PV) solar and keep their standard electric hot water cylinder, they’re usually asking a much simpler question:

What gives me the best real-world value?

And for most homes in 2026, the answer is surprisingly straightforward.

PV solar wins.

Pretty comfortably.

First: What’s the Difference?

Thermal Solar Tubes (aka evacuated tubes / hybrid hot water systems)

These are purpose-built to heat water.

They collect solar heat directly and transfer it into your hot water cylinder.

That’s it.

They do one job.

And when conditions are ideal, they do it very well.

PV Solar Panels + Traditional Electric Cylinder

This setup uses standard solar panels to generate electricity.

That electricity can then:

• Run your home

• Charge a battery

• Export to the grid

• Heat your hot water cylinder via a timer or smart diverter

In other words:

It’s flexible.

And flexibility matters far more than theoretical peak efficiency.

The “Thermal Is More Efficient” Argument

Yep.

It is.

A thermal tube setup can produce the equivalent heat output of roughly 3–4 PV panels using less roof space.

That sounds impressive.

And if this were 2012, that’d be a killer argument.

But here’s the awkward little detail thermal sales brochures tend to mumble into their shoes:

Roof space usually isn’t the problem anymore.

Modern homes often have room for plenty of panels.

And panel prices have dropped dramatically.

So the old “but thermal is more efficient per square metre” argument is a bit like insisting your fax machine is more efficient than email because it uses less screen space.

Technically interesting.

Practically irrelevant.

Summer: Thermal Wins (Sort Of)

Let’s give thermal tubes their due.

In peak summer, thermal systems absolutely crank.

Blue skies. Warm ambient temperatures. Long daylight hours.

This is their happy place.

They can outperform the equivalent PV array for raw hot water production.

But here’s the issue.

Summer is when solar energy is already abundant.

If your home has a properly sized PV system — say 10–14 panels or more — you’ll typically have so much excess daytime generation that heating water becomes trivial.

Your hot water cylinder is already full of free solar-powered heat.

So yes, thermal might produce more.

But more of something you already have plenty of isn’t exactly revolutionary.

It’s like adding a second dessert after you’re already full.

Nice.

Unnecessary.

Winter: This Is Where It Falls Apart

This is the bit that matters.

And it’s where thermal solar starts sweating.

(Which is ironic, given the topic.)

Thermal tube systems rely heavily on ambient conditions.

When it’s cold, overcast, and miserable — which is exactly when you want hot water most — performance drops hard.

Why?

Because thermal systems collect heat.

And when the outside environment is cold, collecting and retaining useful heat gets much harder.

PV panels, on the other hand, generate electricity from light.

They don’t need warm air.

In fact:

PV panels often perform slightly better in cooler temperatures.

So during winter:

• Thermal tubes are fighting cold air and reduced heat gain

• PV panels are happily converting available light into usable electricity

And that electricity can still heat your cylinder.

This is why thermal systems often look fantastic on paper and a lot less magical during an actual New Zealand winter.

The Cost Conversation

This is where things usually get awkward for thermal advocates.

A thermal hot water setup typically means:

• More specialised hardware

• Additional plumbing complexity

• Pumps / controllers

• More maintenance points

• Fewer installers with deep expertise

• Harder future servicing

And all of that costs money.

Often quite a bit of it.

Meanwhile, adding a few extra PV panels to cover your hot water load is usually:

• Simpler

• Cheaper

• Easier to maintain

• More future-proof

If one system can only heat water, and another can heat water plus run your house, charge batteries, support EV charging, and potentially provide backup functionality...

Why would you pay more for the less versatile option?

That’s not innovation.

That’s expensive nostalgia.

The Future-Proofing Problem

This is the thermal industry’s biggest challenge.

Homes are electrifying.

Fast.

We’re seeing:

• EV chargers

• Home batteries

• Smart load control

• Dynamic tariffs

• Energy management software

• Grid-interactive systems

PV plugs into all of it.

Thermal doesn’t.

Thermal is a single-purpose tool trying to compete in a multi-purpose energy ecosystem.

And that’s a tough sell.

So… Is There Ever a Case for Thermal?

Actually, yes.

Thermal tubes can make sense if:

Your roof space is extremely limited

And every square metre matters.

Your hot water demand is unusually high

Think large households with massive daily usage.

You specifically want dedicated water heating

And don’t care about broader energy flexibility.

For those edge cases?

Thermal can still be a legitimate option.

But for the average Kiwi household?

It’s usually overcomplicating a problem that modern PV solves beautifully.

Equity Solar Brokers’ Honest Take

We’re not anti-thermal.

We’re anti-paying extra for marginal gains that don’t materially improve your life.

That’s the distinction.

For most homes, a well-designed PV system paired with your standard electric cylinder will:

• Cost less

• Perform better through winter

• Offer greater flexibility

• Deliver stronger long-term value

And perhaps most importantly…

It avoids turning your roof into a museum exhibit for solar technology’s awkward teenage years.

Sometimes the smartest energy solution isn’t the fanciest.

It’s the one that quietly works, year after year, without demanding applause.

And right now?

That’s PV.