Solar water heater

 

Solar water heating systems use free heat from the sun to warm domestic hot water. It absorbs the energy from the sun in the collector panels located on the roof of home.

The sun's energy is then transferred either directly or indirectly (depending on the system) to the water stored in the hot water cylinder. When there is not sufficient energy from the sun to heat the water in the cylinder a booster system (either electric, gas or wetback) is used to heat the water to the required temperature.

A solar water heating system consists of three main parts:

1. Solar hot water collector - which are located on the roof

2. Hot water tank which can be also located on the roof or on the ground (a split system)

3. Pumps and controller

There are two types of solar water heating systems:

1. Active system which have circulating pumps and controls (Forced flow type)

2. Passive system, which don't have circulating pumps and controls (Thermosyphon type)

Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.

There are two main types of solar water heater collectors, either flat panel or evacuated tube. Flat panel systems collect the suns rays via a metal plate with a dark coating. They work best with direct sunshine. Evacuated tube systems collect the suns rays in glass tubes with a vacuum inside. They are generally more efficient than flat panel systems because they trap heat even in low sunlight.

 

 

Geographic location, sunshine hours, home orientation and roof angle must be taken into account when choosing a suitable solar water heating system.

1. Active System

Active systems use electric pumps, valves, and controllers to circulate water or other heat-transfer fluids through the collectors. They are usually more expensive than passive systems but are also more efficient.

2. Passive system

Passive systems move water through the system without pumps. Passive systems have no electric components to break. This makes them generally more reliable, easier to maintain, and possibly longer lasting than active systems. Passive systems can be less expensive than active systems, but they can also be less efficient.

A thermosiphon system relies on warm water rising, a phenomenon known as natural convection, to circulate water through the collectors and to the tank. In this type of installation, the tank must be above the collector. As water in the collector heats, it becomes lighter and rises naturally into the tank above. Meanwhile, cooler water in the tank flows down pipes to the bottom of the collector, causing circulation throughout the system. The storage tank is attached to the top of the collector so that thermosiphoning can occur.