Factors to be taken into account in the use of solar water heaters as a sustainable energy option

Abstract

Solar water heating is a possible sustainable energy option for thermal applications. Hotel industry, as it requires hot water for day to day operations makes use of this option in order to reduce their electricity consumption. A major motivation for the hotel industry to adopt the technology is for the financial savings that it is supposed to bring in. However due to various lapses in installation and operation the full potential of the solar water heater is not harnessed leading to unexpected excessive use of electricity for the purpose.

The most widely used solar water heater in the hotel industry is the passive direct convection storage unit with a flat plate collector that also comes with a backup electrical heater to ensure a steady supply of hot water at anytime of day. It was observed that in almost all of the hotels that had solar water heaters in operation, the units were conveniently installed on roof tops without due attention to the proper orientation of the flat plate collector. Hence it is very common to find flat plate collectors facing the east or west in hotels along the coastal regions. Improper orientation means that the amount of solar energy falling onto the collector is not optimized. A further complication of this practice is that in some cases the roof casts a shadow on the flat plate collector for a few hours during sunrise or sunset further reducing the time that the flat plate collector is exposed to solar radiation. Lack of attention to the flat plate collectors is widely evident from the dirt and dust on the panels.

In some of the hotels, the importance of water quality on the performance of the solar water unit is not well understood. The water in these units is practically heated by the backup electrical heater. Data logging on such units show that the electric heater is in constant operation.

A study was carried out aiming at finding out the impact of the above issues on the proper functioning of a solar water heater and their effects on the solar water heater as a sustainable energy option.  A 300 litre solar water heater was used for the study as it is the most widely used size in the hotel industry. Measurements revealed that a total wastage of 6 kWh of electricity occurs due to a combination of the above factors. The study also looked at the financial implications to the user if factors such as correct orientation, maintenance and water quality are overlooked.