Comparing Types of Solar Water Heating Systems

There are three main types of solar water heating systems commercially available.

Sealed Solar Heater

The first system and most basic is a sealed solar heater. This is a whole heater combining gathering heat and accumulating heat into one, which is generally made up of two to three round tubes painted black. The black coating absorbs heat, which warms the water.

Advantages: simple structure and lower cost of construction.

Disadvantages: very quick to loose heat, and cannot be used in winter or cloudy and rainy days.

This product is only used for the most basic of needs as it is inefficient and has been technologically superseded.

Flat-panel Solar Water Heater

The second type of system is flat-panel solar water heater. It is made up of a panel and heat collecting water tank, and generally runs in natural circulatory style. The flat-panel heat collector consists of the panel for absorption of heat, a transparent cover, an insulating layer for back and side face, and the framework.

The flat panel solar system has a lower cost of construction, high rate of heat, it can produce hot water when sunny; but it looses heat too quickly. Also on cloudy or rainy days the flat panel systems are not as efficient as vacuum tubes.

Vacuum Tube Water Heater

The third type of system is vacuum tube water heater. It usually adopts natural convection for exchanging heat, which is made up of several glass vacuum tubes for heat collection inset directly into the water tank. There is silica gel band between each vacuum tube for collecting heat and the hole of water tank. The vacuum tube transfer heat through super conductor in the copper heat tube rather than water, so the rate of heating is high.

NZ Solar products use this glass tube system for heat collection, which is made out of the concentricity sleeved pipes of high borosilicate glass. The space between the two tubes is drawn to be a vacuum of 5*10-3pa, and the outside of the inner tube deposits some gradating aluminium nitrogen/aluminium. The solar spectrum absorbs the coating selectively (the rate of absorption is a=0.90~0.92, the rate of emission is b=0.06~0.1). The heat consumption rate of the vacuum tube is small (U=0.55~1.2W/m2.0C), so you can use the heater both in rainy and varied weather.

The features of this system are:

• High heating rate
• Quick heat absorption
• Slow heat loss
• Small heat consumption: can be used in winter and rainy days