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Evacuated Tubes Solar Hot Water Systems

There are many ways to heat the water in your home, and evacuated tube solar hot water systems are one of the most sustainable ways to do it. Although they can be seen around the world, many people overlook evacuated tube solar hot water systems when it comes time for a home upgrade. 

To educate home and building owners throughout Australia and beyond, we’ve developed this complete guide to evacuated tube solar hot water systems, for answers, clarifications, and green energy inspiration. 

What is Evacuated Tube Solar Hot Water? 

While the sun has been used to naturally heat up swimming pools since the dawn of man (and is still the best policy for natural swimming pools), evacuated tube solar hot water systems have been developed and optimized for just the past few decades.

Evacuated tube solar was pioneered at the University of Sydney, and University of NSW. Sydney University began work on evacuated tube technology in 1975, and by 1980, the first ‘Sydney tubes’ were in commercial production in Japan. So, far from being ‘new technology’, evacuated tubes have been on the market for over 30 years in both Japan and Europe.

Since that time, all around the globe different types of systems have been built around the basic principle that the heat from direct sunlight can be transferred onto a hot water supply.

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Why use an Evacuated Tube Solar Hot Water System?

Evacuated tube solar hot water systems are designed to utilize the abundant and free energy of the sun to maintain a hot water supply in a home or commercial building. When compared to traditional hot water heating methods, evacuated tube solar hot water systems are able to mitigate utility costs, and thus save on monthly energy bills while utilizing a source of renewable energy. 

Evacuated Tube vs Flat Plate Thermal Solar Collectors

Evacuated tube collectors and flat plate solar collectors are the two most common ways to harness thermal solar energy on a roof or property space. The systems serve the same purpose, each with pros and cons depending on local resources and weather conditions.  

It is easy to distinguish between evacuated tube and flat plate solar collectors. Evacuated tubes can be recognized as a series of metal cylinders installed next to one another. They are a newer technology, developed first in the 1970s.

Flat plate solar collectors more closely resemble photovoltaic solar panels and usually do not appear to be more than a black or dark-colored rectangle on the roof of a building. Technology that resembles modern flat plate collectors dates back over a century, as a tried and true method for harnessing thermal solar energy

Which is better? 

  • When considering between evacuated tube and flat plate solar collectors, the verdict typically comes down to cost. As a newer and generally more efficient technology, evacuated tube systems are almost always more expensive to purchase and install than their flat plate counterparts.
  • Evacuated tube solar collectors are generally better performing than flat plate collectors in cloudy or cold conditions and also work efficiently throughout the day, rather than just during peak sun hours.
  • Flat plate collectors are also limited to water temperatures up to 140 degrees Fahrenheit, while evacuated tube systems can heat water up to 200 degrees Fahrenheit for use in hospitals, car washes, laundromats, and other special purposes. 

In short, evacuated tube systems are superior to flat plate collectors, if the upfront money is available. 

Common Issues with Evacuated Tube Solar Thermal Systems

Despite their superiority to flat plate collectors, there are some disadvantages of evacuated tubes and solar thermal energy systems as a whole. In snowy conditions, thermal flat plate solar collectors heat up with the sun, always melting and sliding off of the panels at quicker rates than the rest of the roof. Because evacuated tubes use a vacuum glass seal to keep heat in, the collectors do not radiate and therefore snow will melt at ordinary rates as the rest of the roof. 

Beyond this, all kinds of thermal solar collectors are always going to be limited by local sun conditions. In areas of excessive cloud coverage or frequent dips below freezing temperatures, an evacuated tube system may not provide enough energy for a home’s hot water. To mitigate this, many solar hot water systems are installed with a gas or electric boost to reliably heat the water in the absence of solar thermal energy. 

How Does an Evacuated Tube Solar Hot Water System Work?

Evacuated tube solar hot water systems come in all shapes and sizes, but the basic principles behind the technology generally always remain the same. To help you quickly understand how a system works, we will now outline the evacuated tube solar hot water process in three easy steps, as visualized in the image below. 

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Step 1: Solar Thermal Energy is Collected in the Evacuated Tubes

When the sun peaks over the horizon in the morning, solar thermal collectors get to work all over the world. The process begins when sunlight (both ambient and direct) hits the evacuated tube system and warms the specialty heat transfer fluid encased inside. Within each sealed tube, the fluid cycles back and forth, sending the kinetic energy to a heat exchanger, which is typically a copper manifold. During step 1, the collectors will create solar thermal energy at any time of day when the sun’s radiation is present. 

Step 2: The Heat is Transferred to a Hot Water System

In the second step of an evacuated tube solar hot water system, the heat is transferred to the building’s water supply. In some systems, the hot water tank is located directly above the evacuated tube collector, while other standalone tanks may be installed on the roof or within a structure.  

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In the schematic diagram above, the heat transfer is represented with the number 5. Within the tank, you can see that the piping from the energy generation side and distribution side are separate. Here, it is easy to see how hot transfer fluid from a solar thermal system heats the water within a tank, without directly interfering with the home’s water supply. 

If solar thermal energy is not available, heat is transferred to a water tank is possible with a boost from gas or electric power (the sensors and systems are represented by numbers 2, 3, and 4 above). In warm climates, some evacuated tube solar systems are built without additional boosts, as the cost of the materials and installation may not be warranted for only a few sunless days per year.  

Step #3: Hot Water is Used Throughout the Home

Once the water is heated in the tank, it can then be used throughout the home or building. Hot water tanks are typically heavily insulated so as to keep hot water inside for long periods of time. Sufficient insulation allows solar thermal hot water to be available throughout the night when the sun is not radiating heat. 

From the inside of a home, it is essentially impossible to tell the difference between a solar and a traditionally powered hot water system. With an evacuated tube solar hot water system, you may simply turn the knobs, fire up your dishwasher, and use your home’s hot water just as you currently do. 

The Basic Components of an Evacuated Tube Solar Hot Water System 

Now that we’ve covered the basic principles of how an evacuated tube solar hot water system works, we will break down some of the most important components to bring a broader understanding of the inner workings of the technology. Part for part, the components of an evacuated tube solar system must be fine-tuned in order to find the perfect solution for any particular building’s location and water demands. 

The Tubes / Solar Collectors

Obviously, the most important and variable part of an evacuated tube solar hot water system is the evacuated tube system itself. The size of your evacuated tube solar system directly relates to the amount of hot water potential that can be generated on any given day of sunlight. Typically, systems are sized and identified by the diameter and quantity of the tubes that are installed. Multiple sets of collectors may be necessary for large and multi-unit buildings.

In direct solar hot water systems, the rooftop tubes are not filled with a heat transfer fluid, but rather contain the building’s constantly flowing water. Here, the tubes are shaped, sized, and connected to a home’s hot water system much differently than in heat pipe transfer systems.  

The Controller 

Most evacuated tube solar hot water heater systems operate passively with adjustments easily made on a controller installed within the home. Solar thermal controllers resemble basic thermostats and can be used to optimize the temperature of your hot water tank and configure system boosts or operating modes. 

Controllers may be installed at the same time as your evacuated tube system, or purchased aftermarket. Many units can also integrate into a building’s existing smart controls. 

The Boost 

In the absence of available solar energy, most hot water systems are equipped with a boost mechanism attached to the system’s controller. Boosts are either gas or electric-powered, the choice of which is up to the consumer.

If you have an existing (or plan to build a) PV solar energy system, then we recommend using an electric-powered boost system to assist your evacuated tube solar hot water system. Although it is true that sunlight is less available at the same time for both the electric and heating components of a system such as this, lower overall electricity costs from PV solar make an electric system more attractive for those with multiple arrays installed.

On the other hand, gas-assisted systems may be favored in areas with readily available utility lines and low energy rates. While gas-boosted hot water systems are typically more expensive to install, their utility running costs are typically lower than grid tie electricity rates when incorporated into an evacuated tube hot water solar system.

The Tank

A well-insulated tank is the heart of an evacuated tube solar hot water system. Tanks are sized appropriately to accommodate the approximate water demand of a home or commercial building. While bigger tanks do allow for more water storage, larger capacity reserves also take longer to heat up initially. Once at the desired temperature, the tank’s insulation and outside conditions determine how long the hot water supply will be available. 

In modern evacuated tube solar hot water systems, the tank is either directly connected to the collector itself, or completely modular, located somewhere else on the property. While interconnected rooftop solar tanks help save space and improve efficiency, they are typically limited to only meet small hot water demands. In these instances, multiple units must be installed to accommodate a capacity that could only be held by a larger, standalone tank. 

In our case studies below, you will see examples of both water tank locations for evacuated tube solar hot water systems, with attached and modular tank system designs. 

Evacuated Tube Solar Hot Water Case Studies

If you would like to see an evacuated tube solar hot water system at work, it may be as easy as going outside and looking up. Evacuated tube solar hot water systems are used all around the world to heat the water of homes, apartment buildings, businesses, hotels, and more. With installations in remote jungles and crowded urban areas throughout the globe, we will highlight some of the most common and practical uses of evacuated tube solar hot water systems below. 

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Residential Solar Hot Water in Australia

At home down under, residential buildings throughout Australia are covered in solar hot water systems, with evacuated tube collectors available to purchase in every populated area of the country. There are many reputable domestic and international evacuated tube solar hot water system manufacturers, with installation and delivery available to accommodate any Australian home’s hot water system.

According to the Clean Energy Council of Australia, solar water heaters are very effective in both saving Australian’s money on utility expenses and lowering local carbon emissions. With the help of nationally and locally available financial incentives, nearly 2 million solar thermal systems have been installed by Australian homeowners to date. 

In the image above, you can see a typical residential evacuated tube solar hot water system. Look familiar? If you’ve ever looked down upon the rooftops of a residential area in Australia, then chances are that you have seen a collector such as this before. 

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International Evacuated Tube Solar Hot Water 

Of course, the sun shines in more places than just Australia, so plenty of countries have caught on to the evacuated tube solar revolution. Pictured above, solar thermal collectors are placed in a backyard of a home in Spain, adding green energy generation to the ambiance of the outdoor space. With a door that opens to the covered space beneath the collectors, the system is most likely designed for easy access to the water tank, valves, and controls. 

Today, solar water heating markets are emerging in nearly every country in the world, with most of the global share split between China, the United States, and Turkey. The Australian market is large and growing, with some of the most practical and forward-thinking national standards and policies already in place. In terms of per capita solar water heating, top producing nations include Greece, Israel, Austria, Cyprus, and Barbados. 

Commercial Uses: Hotels, Laundry, and Other Businesses

There is an old saying that basically claims that any good thing can be monetized. Evacuated solar hot water heating is no exception, as systems are constantly being developed and installed to lower commercial businesses’ bottom lines. 

While it is something you may not think about every day, a large portion of our economy is based around the production and use of hot water. From manufacturing plants and treatment facilities to hotels and laundromats, hot water demand is actually much higher in the commercial and industrial sectors than in typical residential areas. 

Obviously, modern businesses will typically choose to install an evacuated tube hot water system to reduce their operating costs. Today, many businesses can lower the cost of an installation with renewable energy incentives and rebates, while also meeting environmental goals for local standards or investor and customer expectations. 

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Low-Cost Housing and Public Health

As the sun shines the same on every living soul, it also powers evacuated tube hot water systems equally around the world. Thanks to their ability to generate long-term, free sustainable energy, thermal solar hot water systems are frequently used as part of public health projects and low-cost housing facilities. 

Often installed alongside a PV electrical solar energy system, evacuated tube solar hot water systems can be quickly installed to provide decades of hot water with very little maintenance required. With access to hot water, previously unsuitable living conditions can be dramatically upgraded with an evacuated tube solar hot water system. 

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Evacuated Tube Solar Hot Water for Swimming Pools

Before we wrap up this guide, we would like to make a note that some evacuated tube solar systems can also be used to heat the water in a pool, rather than a home’s faucets and appliances. In the image agave, a thermal solar collector is placed adjacent to a swimming pool and connected to a conventional pool heater, filter, and pump. 

Although the sun naturally heats a pool’s water, adding an evacuated tube solar collector helps to rapidly raise the pool temperature and maintain regular conditions throughout the entire season. With solar energy, thermal collectors drastically reduce the energy consumption and operating costs with traditional pool heating systems. 


In summary, evacuated tube solar hot water systems are a new take on an old technology that has firmly established its place in the green revolution. We hope that this guide has helped you understand the science behind the technology and inspired you to adopt solar thermal energy in your own life. For additional information, feel free to check out our guide on the best Solar Hot Water Systems in Australia to find the perfect evacuated tube or flat plate system for you. 

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