A typical solar water heater comprises of two parts – a solar collector and a storage tank. Depending on whether they have circulating pumps, the systems are categorized as either active or passive.
There are two types of active solar-powered water heaters:
- Direct circulation systems
Direct circulation systems are best suited for areas without hard or acidic water and climates without long periods of freezing temperatures. This system works by sending pressurized potable water directly through the collectors.
- Indirect circulation systems
Indirect circulation systems, on the other hand, send heat transfer fluids through their collectors. Heat exchangers then transfer heat from the fluids to the potable water. These systems are best used in climates that have long periods of freezing temperatures. Some indirect systems also come with overheat protection. When the solar intensity is too high, this feature prevents the transfer fluid and collector from being damaged.
There are two different types of passive systems:
- Integral collector-storage (ICS) passive systems
An Integral Collector Storage (ICS) system is the simplest form of solar thermal system because the storage tank is also the collector. They're also extremely efficient, though they are climatically limited.In the same way as a collector box, an ICS box is insulated on three sides and has one glazed side that faces the sun. However, the hot water tank itself sits in the box. The tank is painted black or with a selective paint for heat transfer. The sun's radiation passes through the glazed side of the box and warms the tank directly, which warms the water inside it. Simple. Integral collector-storage passive systems work efficiently in homes that need significant amounts of hot water during the day and evenings. The heaters are used in areas that rarely experience freezing temperatures.
- Thermosyphon systems.
Thermosyphon systems are more expensive and reliable compared to integrated collector-storage systems. This type of heaters requires professional installation as the collector needs to be installed at a spot below the storage tank. The design allows water to flow through when warm water rises to the top of the tank, and cold water sinks to the bottom. The water heaters are best installed by experts because the storage tanks are heavy, and the design of the roof has to be considered. Although they cannot be used where freezes occur, thermosiphon systems are more efficient than a basic ICS because the tank can be better insulated, thus retaining more heat during cooler hours.
Solar water heater
Flat-plate Panels are the most common in the domestic sector. This type of collector consists of an insulated and weather-proof box with a dark absorber plate. The insulation is crucial since it helps prevent heat loss in the system. On the other hand, the absorber ensures there is maximum absorption of heat energy from the sun.
Evacuated-tube solar collectors contain rows of transparent glass tubes that are placed parallel to each other. Each tube features an outer tube and absorber made of metal, and a fin coated with solar energy-absorbing material.