As you may be aware, solar water heaters absorb electromagnetic energy (sunlight) to heat the water.  In order to absorb this energy, the solar water heater must be equipped with components that can focus this energy into heating water, these components together make up a collector.

The Evacuated Tube System (ET-SWH) has multiple collectors arranged in parallel rows. Each collector is made up of a pipe inside two glass walls, and the air between these two walls is removed to create a vacuum to effectively prevent heat lost, virtually zero. This is especially evident when touching an evacuated tube collector and noticing its cold temperature while the heating medium inside might be boiling.  Nearly 94% of the sun’s energy that hit the collector is absorbed and captured by this type of system. Besides being the most efficient at absorbing the sun’s energy, it also offers other advantages as compared to the flat plate system. The evacuated tube collector absorbs energy the moment the sun brakes over the horizon until it sets again.  This is because the sun’s light is always striking each collector at a 90 degree optimum angle throughout the day.

The Flat Plate (FP-SWH) is comprised of a plate that collects the diffused sunlight which surrounds a pipe traversing in a snake-like pattern, and an insulated metal box to retain the heat. Although the flat plate is widely used in the US and slightly less expensive than the evacuated tube system, the insulated metal box looses heat through the glass cover and thus higher cost per BTU.  Nonetheless, the flat plate is the oldest type of collector and readily available in the United States; this is because the flat plate system is easier to manufacture and simpler to design. However, the flat plate collector may not be able to supply hot water in winter months and may need decommissioning to protect its components from freezing. Due to their design, the flat plate collector receives optimum sunlight only during midday, therefore they need a carefully calculated location and angle facing the sun.

Performance:  Due to its efficiency, the evacuated tube collector heats water faster and can provide hot water up to 200 degrees Fahrenheit (93 degrees Celsius), which translates to an efficiency range of 70% to 80% and as such, the difference in efficiency is more pronounced when operated in cloudy days or colder regions as compared to the flat plate collector. Thus, due to their heating efficiency the evacuated tube system is suitable for commercial applications that require hot water in larger quantities. The flat plate collector, on the other hand, may take longer to heat water and can supply hot water up to 140 Fahrenheit (60 degrees Celsius).  Thus, limiting the amount of hot water available in a given day.

Durability: Both ET-SWH & FP-SWH are expected to last about ten (10) to fifteen (15) years.

Installation: Both need to face South (in the northern hemisphere), and have a slanting position. However, the evacuated tube collector receives sunlight at 90 degree optimum angle throughout the day for maximum production. The flat plate collector must be carefully position for best production results.

Versatility: The most significant advantage of the evacuated tube system offered by FMZ Devices is that the hot water production capacity can be scale down by simply unplugging collectors. Since the collector pipe is independent of the overall system, a collector can simply be removed without affecting the system as a whole. This key feature of the evacuated tube system offered by our company allows for seasonal control, which is not an option in other solar collector systems. This means that in months of high hot water production, the evacuated tube system allows for the removal of a few collectors to store away for months when demand exceeds production.

Conclusion: Due to the high efficiency of the evacuated tube collector (ETC) system, and its versatility, the ET-SWH is therefore the superior choice, especially when it comes to cloudy days or colder areas which may experience snowfall for the most part of the year.

Have questions?  Contact us, we’re ready to answer any questions you may have, we are here to help!