Marc Hausstaetter, Managing Director, Ecotherm Middle East on how solar water heaters are meeting the hot water demand of Palm Jumeirah's Shoreline Apartments. One of the leading players in Austria in solar thermal energy, Ecotherm has successfully adapted its solar water heaters to the GCC region.
During the past 20 years, the use of solar energy has become widespread in Central Europe. However, it is only in the last two years that the United Arab Emirates (UAE) has started exploiting the benefits of solar energy, This is not suprising given the availability of abundant and cheap fossil energy in the GCC region, which made renewable energy an unattractive option. However, the rise of energy prices globally is slowly but surely altering this picture even if the current slowdown lowered the prices of fossil fuels for a while. A single constant power source available is the sun's energy, delivered free of charge and with zero carbon emission certificate attached. Solar energy is clean energy with no CO2 emissions - a point well worth remembering in congested cities.
In the emirate of Dubai, Nakheel has completed a major solar energy project utilising solar thermal energy at the Shoreline Apartments, located on the trunk of Palm Jumeirah. The system produces hot water for the apartments and has the capacity to harness 80% of the annually available solar energy required for hot water demand. This ambitious target was set by the client, while past studies show that a solar system has its highest efficiencies at 50-60% coverage of the total annual hot water demand.
System specification
While every supplier of solar system has developed his or her own recipe for success, some fundamentals remain. The sun provides approximately 1,000W per m2. The task of the thermal solar panel and its system is to capture this energy and transfer it to domestic water with as few losses as possible. A normal solar panel has around two m2 net area and supplies around 1.8kW. Around five to 10% is lost through panel dissipation, depending on insulation thickness and design. A further loss of 10% has to be considered due to heat loss of the piping system. The calorifier and buffer tank capacities must then be specified. The storage capacity should ideally match the total capacity of the solar panel per day. If the system needs to supply hot water in the morning, the whole system has to sized and designed accordingly.
The shoreline apartments comprises approximately 156 apartments. For this project, we used three stainless steel tanks of 4,000 litres capacity and special internal flat coil heat exchangers of 100-120 kW. Stainless steel was used because it is hygienic and long lasting and is also the best material to transfer and store hot water.
However, where does the remaining 20% energy requirement come from? There are very few days with shadow and rain in the Gulf, and on these days, hot water supply must be maintained using an automatic backup system. Electric heating elements are the most common way to generate this energy but on the Palm Jumeirah, special stainless steel condensing boilers with 109% thermal efficiency were installed. These boilers are re-using the 'waste' heat of the flue gas to pre-heat the water. The flue gas cools down to around 600°C and no insulation of the chimney is necessary.
An innovative and 'green' boiler system was installed by ECOTHERM on the Burj Khalifa too.
Overall, solar thermal system represents a higher initial investment than a common gas fired heating system, but due to very low running costs, the actual return of investment is between four to seven years (depending on system requirement). This will be further reduced in the future when the prices of electricity, oil and LPG will rise.
© H2O 2010
