Efficiency of Evacuated Tubes explained

Before delving into how and why Evacuated Tubes are so efficient, it's important to understand why efficiency is important, and what things affect the efficiency of a solar collector or solar panel (the bit that sits on your roof and gets hot).

After all, there is only a finite amount of sunlight that hits the surface of any solar collector and it is important to make sure that you catch and keep as much of it as you can.

Why is an Efficient Solar Collector important?

When you compare solar hot water systems, it is important to consider the efficiency of the collector, and how well it transfers heat into your water. The overall performance of your solar hot water system, and the amount of energy... and money that you will save is dependant on the performance of the collector right throughout the year.

For example, some types of solar collectors or panels might work really well in summer. However, some types of systems don't work well in winter when the weather is cold, the days are shorter and there is less sunlight.

Winter is also the time of year when you need hot water the most. This means that for half the year, solar panels with low efficiency don't do very much and your booster is doing most of the work... costing you money.

When you look at all the extra energy that a good quality, highly efficient solar collector will capture each year, and then mulitply this out over the entire life of the system - it can amount to thousands of dollars in savings. As energy costs continue to rise, the savings for you become even greater.

Don't worry, if you want year round hot water from the sun - whatever the weather - you can rely on an Evacuated Tube solar hot water system from Endless Solar.

How is solar performance calculated?

An accurate way to calculate the performance of a solar hot water system is by using a computer. Following the methodogies defined by Standards Australia - the performance is calculated in short intervals of throughout the whole year. Known performance and weather data for each geographic location, and household hot water usage patterns are used as input data for this simulation.

From start to finish, it's quite a complex process and involves a lot of computer processing! It's these calculations that are used by the Australian Federal Government Office of Renewable Energy Regulator (ORER) to define the savings that each system can produce... and the resulting Renewable Energy Certificates (RECs).

What affects solar thermal performance?

The thing to remember about efficiency is that it will always be different under different conditions. As you can imagine, on a day-to-day basis, there are so many things that change and consequently affect the performance of your system, for example:

• The temperature of the outside air
• The position of the sun in the sky relative to the collector
• The temperature of the water already in the storage tank
• The weather in general and the amount of sunlight available to the collector
• The amount of water being used by the household at any one time
• The temperature of the supply water

Keeping in mind the changing variables listed above, and considering that there there a still many additional things that affect the efficiency of the solar collector - you can imagine how complex the calculations must be to work out the savings throughout the whole year.

Why are Evacuated Tube collectors from Endless Solar more efficient?

Endless Solar has examined all the things that affect the efficiency of traditional 'flat plate' solar panels and other Evacuated Tube collectors. Some key improvements are:

• Vacuum: A high quality vacuum layer around the tube prevents heat loss when the outside air is colder than the tube. The tube captures the energy and keeps it inside like a thermos flask. This means that they work well in cold weather without losing energy.

• Surface: The tubes have a round surface which means that the sun's radiation is not reflected away when the sun is not directly above the collector. Evacuated Tubes from Endless Solar are designed to minimise reflection and take advantage of every last smidge of energy that hits them.

• Optimised for Australia: The tubes are spaced at a distance that is optimal for Australian conditions, allowing the collector to operate for longer in the day. Many 'generic' Evacuated Tube collectors do not incorporate this level of design and engineering.

• Tough: The collector is manufactured to withstand and retain very high temperatures without energy loss, thus allowing heat to be efficiently transferred to water that is already at at a high temperature.

• Refined: Premium quality absorber coating (the bit that catches the sun's energy) is designed to make the most of a broad spectrum of the sun's radiation and work effectively across a range of weather conditions.

• Heat Retention: High quality Rock Wool insulation in the manifold prevents heat loss.

Endless Solar Evacuated Tube Efficiency v Temperature

The graphs show the efficiency of two types of collectors as water is heated to a suitable delivery temperature. You will notice the effect of the vacuum (in the evacuated tubes) in retaining heat, especially in winter. Notice how inefficent a typical flat plate collector is as the collector starts to warm up in winter.

Sydney - Summer (Solar Radiation 879W/m2, Ambient Temperature 22°C)

Sydney - Winter (Solar Radiation 462W/m2, Ambient Temp 13°C)

Effects of collector orientation

The set of graphs below shows the advanced optical properties of Evacuated Tube collectors. You will notice that Evacuated Tubes collectors begin operating effectively earlier in the day, with higher outputs. They can also be placed on an east or west facing roof without a significant loss in performance.

Evacuated Tube Orientation in Sydney

Flat Plate Orientation in Sydney

What else is important?

Every component in a solar hot water system is important. Each component, and the way it is combined in the system, as well as how it is installed can affect the overall performance of that system.

At Endless Solar, we challenge ourselves everyday to further increase the performance of our solar hot water systems so that you can be confident that when you choose a system from Endless Solar, you'll be choosing one of The Best Water Heaters Under the Sun™.