Today, solar water heating applications are mainly used in residential and commercial settings to heat both water and space. However, the use of evacuated glass has enabled thermal collectors to reach very high water temperatures within the vacuum glass tube. This makes possible the use of solar thermal for solar air-conditioning, which will open up a broad market for new solar thermal applications.

Solar Lord combined German design and The University of Sydney’s coating technology to manufacture an efficient U tube collector, which achieved 98.4 per cent absorber efficiency in test results performed by the Fraunhofer Institute for Solar Energy Systems.

Stagnation test results also showed that the collector can withstand a wide spectrum of climatic conditions, without losing efficiency, making it well suited to the varied Australian climate. This achievement was recognised by a Housing Industry Association GreenSmart Product of the Year award in 2007.

Key contributors to the high performance of U tube collector solar thermal water heaters

Limited heat loss

The design of the collectors, which have an evacuated space between the two glass tubes, creates the best possible insulation available – a vacuum jacket.

Sunlight passes freely through the clear tube, is absorbed and then transfers this solar energy into heat energy. The vacuum between the tubes virtually eliminates convective heat loss even in lower ambient environmental temperatures, making these collectors particularly useful in areas susceptible to frosts and cold winters. This technology enables the collectors to perform in overcast, cloudy or even rainy days.

Strong sun performance

The simple cylindrical construction of the evacuated glass tubes allows for passive sun tracking.

While flat panel collectors rely on the sun’s heat and are only able to perform at their maximum when the sun is perpendicular to the collector, a cylindrical collector maximises collection of the sun’s rays.

Solar selective coatings

Advanced solar selective coatings employ two exclusively licensed patent technologies invented by the University of Sydney – material of coating AlN/AIN-SS/CU.

An interference absorptive coated with novel sputtering deposition of trivalent element technology allows for absorption 12 per cent higher than ordinary vacuum tubes, and 30 per cent lower emissions. The coatings can remain stable up to 400° Celsius, while stagnation temperatures can exceed 270° Celsius.

Operating in extreme conditions

Built using borosilicate glass, the collector tube is resistant to hail impact, and the construction of evacuated tubes provides a natural barrier against frost damage. In recent laboratory tests, the Solar Lord open loop systems were accredited level two frost protection – allowing them to work effectively down to -25° Celsius. There is no need for a closed loop system in Australia and no ongoing maintenance required.

The system comes with a stainless mounting kit and frame, and the collectors can be installed on a low pitched roof or horizontally. The U tube collector is more versatile when it comes to installations, and compliments home design. Because the U tube requires substantially less roof space, the remaining roof space can be utilised for other solar application like solar photovoltaic (PV) or skylights.

While the manufacture of evacuated tubes is more labour intensive than simply producing flat plate collectors, this initial difference in end cost is quickly offset by the system’s long term savings.

Solar hot water vs PV

By absorbing the full spectrum of solar radiation, solar thermal collectors are more efficient at collecting energy than PV panels.

PV panels convert between 13 and 18 per cent of the sun’s energy into electricity, while solar thermal panels are able to transfer more than 70 per cent of the solar heat they absorb into heating water.

The total cost of a solar hot water system depends on many factors, including their location and the system that is currently in use. A typical installation for a family of five in a metropolitan area will cost between $4,000 and $6,000. Current federal and state rebate incentives, along with deduction of RECs value can bring the cost down significantly. Dollar for dollar, Solar Lord says a solar hot water system is a lot cheaper than a PV system.

However, the company says that despite the greater cost effectiveness, solar hot water systems have received a lot less political and business attention than PV.

The introduction of the Federal rebates program focused on PV, drawing attention to the dollar amount of the rebate rather than focusing on what system would actually provide for greater value. PV systems may also be more desirable to invest in rather than solar hot water systems because PV makes the meter spin backwards, giving consumers the impression that they can sell this power back to the power companies. Moreover, customers are reluctant to replace the existing hot water if it is still in a good condition.

Solar Lord says that a recent report shows Australia is the world’s worst in per capita carbon dioxide emissions . With too much energy used in Australia to heat water, the use of solar water heating nation-wide and funding for products offering higher efficiencies, are simple and effective solutions to lower the nation’s energy use and reduce emissions.