Evacuated tube vs flat plate solar collectors: which suits your roof?
Both collect heat from the sun and pass it to your water. The difference shows up in cold weather, in hail country and in what can be repaired.
A flat plate collector is a glazed, insulated panel, while an evacuated tube collector is a row of glass tubes with a vacuum around each one. Both turn sunlight into heat for a solar hot water system. Neither is better everywhere.
For most Australian homes, the climate and the roof decide it, not the brochure. Here is how to think it through.
How does each type collect heat?
A flat plate has a dark metal absorber under a sheet of glass, inside an insulated frame. Water or fluid runs through pipes fixed to the absorber. It looks like a skylight lying on the roof.
An evacuated tube has a vacuum between two layers of glass, like a thermos flask. The vacuum cuts heat loss. Each tube works on its own and plugs into a shared header.
Which one copes better with cold weather?
The tube, in general. Its vacuum holds heat when the air is cold and windy, so it keeps working on cool, clear days. That matters in the alpine areas, Tasmania and the cooler southern inland.
On the warm coast, the gap shrinks. A flat plate does very well where frost is rare. Do not pay for cold-weather performance you will never use.
What about hail, frost and damage?
Ask about this before you sign. Glass tubes are individually thin, and hail can break them in a bad storm. A flat plate has one toughened glass sheet, which usually takes hail better.
Frost matters for the pipes inside the collector. Systems in frost areas use a protected closed circuit, and that is a design choice for the installer. Our guide to solar hot water explains the loop and the booster.
Which is easier to repair?
A broken tube can often be swapped on its own, if the maker still sells that size. A damaged flat plate usually means replacing the whole panel. Both can fail at the pipe connections, and that is plumbing work.
Evacuated tube vs flat plate at a glance
| Question | Flat plate | Evacuated tube |
|---|---|---|
| Cold, windy days | Loses more heat | Holds heat better |
| Hail | One toughened sheet | Many thin tubes |
| Repair | Replace the panel | Often swap one tube |
| Roof look | Low, flat profile | Rows of tubes, more visible |
| Best fit | Mild and warm areas | Cold or low-sun areas |
Does one make the booster unnecessary?
No. Neither type removes the need for a booster on cloudy runs. The booster, gas or electric, is what keeps you in hot water in a bad week. Whichever collector you choose, check that the booster suits your household.
My view: do not overpay for tubes on a mild coast
If you live where frost is rare and winters are short, a flat plate is usually enough. Tubes earn their place when winters are cold or the roof gets little direct sun. If an installer pushes tubes with no reason given, ask for one.
What should you ask the installer?
- Which climate zone is my address in, and why does that suit this collector?
- What happens in hail, and what does the warranty say about it?
- Can a part be replaced on its own, and for how long will it be stocked?
- Is the system certified, and who issues the compliance certificate for the plumbing?
This far you can go yourself
You can compare brochures, note which way your roof faces, check for shade and read the warranty. You can also look at the collectors from the ground for cracks or dirt.
Climbing on the roof, handling the pipe connections, the tempering valve and the booster is work for a licensed plumber. And any gas booster is work for a licensed gasfitter. Your state or territory plumbing regulator lists licensed tradespeople.
How to choose a collector for your own roof
Work through these in order. Each step narrows the choice, and the last two stop you signing too early.
- Ask about frost first. Frost decides how the collector circuit has to be protected, and that is the installer's design call, so get it in writing.
- Check the winter sun on your roof. Tubes earn their place when the roof gets little direct sun. On a sunny, mild coast a flat plate usually does the job.
- Think about hail. One toughened sheet usually takes a bad storm better than many thin glass tubes. Ask what the warranty says about hail damage.
- Look at what you will see from the street. A flat plate sits low. Rows of tubes are more visible, which matters if the roof faces the front.
- Ask which parts can be replaced alone. A single tube can often be swapped, but only while the maker still sells that size. A flat plate usually means a whole new panel.
- Check the booster. Neither type removes the need for one, so confirm it suits your household before you compare collectors.
If two quotes give different advice, ask each installer for the reason behind the collector they chose. Our solar hot water comparison covers the tank side of the same decision.
Warning signs in a solar collector quote
A good quote explains why it fits your address. These are the gaps to watch for before you say yes.
| Warning sign | Why it matters | What to ask |
|---|---|---|
| Tubes pushed with no reason given | Tubes pay off in cold or low-sun areas, not everywhere | Which climate zone is my address in, and why does that suit this collector? |
| Nothing said about hail | Glass tubes are individually thin and a bad storm can break them | What happens in hail, and what does the warranty say? |
| Only a headline warranty figure | Terms can differ for the collector, the tank and the booster | What is the warranty on each part, in writing? |
| No mention of spare parts | A broken tube is only a cheap fix if the size is still sold | Can a part be replaced on its own, and for how long will it be stocked? |
| Compliance not mentioned | The plumbing side must be certified by a licensed plumber | Who issues the compliance certificate for the plumbing? |
| Booster left out of the talk | The booster keeps you in hot water in a bad week | Which booster is included, gas or electric, and who fits it? |
A gas booster is licensed gasfitter work, and the roof pipework is licensed plumbing work. Your state or territory regulator lists licensed tradespeople.
Frequently asked questions
Is an evacuated tube better than a flat plate?
In cold or low-sun areas, often yes, because the vacuum holds heat. In mild and warm areas a flat plate usually does the job and is tougher in hail.
Which solar collector lasts longer?
It depends on the make, the water and the climate. Ask the installer for the warranty terms for each part, not just the headline figure.
Can hail damage solar hot water collectors?
Yes, in a severe storm. Glass tubes are more exposed than a single toughened flat plate sheet. Ask what the warranty covers before you buy.
Do I still need a booster with solar hot water?
Yes. On cloudy runs the booster, gas or electric, keeps the water hot. Fitting it is licensed work.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Australian Government, energy.gov.au. Hot water systems: types, installation and energy performance
- Clean Energy Council. Solar water heating
- NSW Fair Trading. Plumbers, drainers and gasfitters: licensing