Solar hot water panels: flat-plate or evacuated tubes?

There are two options when it comes to choosing between the types of solar hot water systems. These are flat plate collectors and evacuated tubes. Let us show you which of the solar hot water panels for sale on the market are the best…

Flat plate collectors are most commonly used for domestic solar hot water heating. They are shallow rectangular boxes made from aluminium with a glass lid topping it. Their dimensions are generally between 1 and 1.15 wide by 2 and 2.5 metres long.

solar hot water flat plate collector system

The aluminium box holds the copper pipes that carry the water through the collector to absorb the sun’s heat, and is topped by a glass lid. The copper pipes are usually made in the style of a grate, as shown below.

solar hot water panels copper pipes flat panel system

The pipes as they are inside the box will still heat the water, but their efficiency is lowered. To maximise the panels’ efficiency, the surface area of the panel needs to be maximized so that it can get the best amount of benefit from the sun’s rays. To achieve this, horizontal fins are welded in between the pies, with insulation placed at the bottom of the aluminium box. These factors help to maximize the heat absorbed into the panel, therefore getting the highest possible amount of heat into the panel itself, which directly affects how much hot water is collected.

This is what a finished panel looks like beneath the glass panel.

solar hot water panels copper pipes in glass system flat panel system

And with the glass panel added.

solar hot water panels copper pipes glass casing flat panel system

As you can see, the flat plate collector is a relatively simple device, which means that they’re cheaper to manufacture and very reliable. Another great feature of the flat plate panel is that they are very resilient, meaning that they are well suited to the harsh Australian environment.

Evacuated Glass Tube Collector

The evacuated glass tube collector is the best option for solar hot water systems in colder parts of Australia. The more complex operating system and design varies widely depending on its use. However, its operating system means that it can appeal to the need for solar powered hot water in areas that have less direct contact with the sun.

evacuated tube glass collector solar hot water system

Evacuated tube glass collectors operate in a way similar to a greenhouse. The tube glass collectors draw heat from the sun through a number of annealed tubes that have individual heat-absorbing plates built within them. The tubes work like small greenhouses as they trap the heat from the sun inside the glass tubes, which are then used to heat water either directly or through a heat transfer system.

The name of the evacuated glass tubes comes from the vacuum that is created between the inner and outer tubes during the manufacturing process. The insulation provided by the vacuum makes the glass tubes an extremely efficient solar heater. The roundness of the tubes means that it can collect heat from the sun throughout the day, which differs from the flat plate system as it can capture the sun’s rays only in direct light. This means that the evacuated glass tubes are more efficient as they can absorb more sunlight for a longer time.

The evacuated tube glass collector system is a lot more complex and, as such, more expensive to manufacture than the flat plate collectors. As they are also made predominantly with glass, they can also be quite fragile. Despite these drawbacks however, the evacuated glass tube collector is a very beneficial system. The improved performance of their tubes is more noticeable during the colder months and in colder climates when more water is heated through the collected solar hot water panels rather than from the booster, showing it to be a much more efficient alternative.

So, although the evacuated tube collector is more costly initially, it delivers great results for colder climates making it a brilliant option to save you money in the long run, while also being environmentally friendly.

What’s the best option for you?

It really depends on the climate where you live. Both the flat plate collectors and the evacuated glass tube collectors have their own individual benefits that work better for different climates. This diagram shows the percentage of heat that is collected from flat plate collector systems in each state.

solar hot water panels australia regions

The flat plate collector system works better in states where the amount of sunlight during the day is a lot higher. So for Queensland, the Northern Territory, and Western Australia, the flat plate systems are ideal. However, in places with a colder climate where there might not be as much exposure to sunlight, the evacuation tubes are the more efficient option.

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