The United States Census Bureau estimated that the world population was 6.772 billion as of 18th July 2009. According to population projections, the world population is growing and will continue to grow until around 2050. With the increasing number of people there is a mounting concern of how to effectively replace non-renewable resources with renewable resources to produce energy that will match or exceed the rate of consumption by humans.

The Sun yearly transports more than ten thousand times the energy that humans currently use. Photovoltaic cells can convert sunlight directly into electricity. Solar heating systems make use of heat from the sun and, in some cases, only the light for heating water, swimming pools and even used for central heating and air conditioning. With continuous advancement in solar technology, solar energy promises to be one of the most effective ways to replace non-renewable energy.

Solar water heaters have gained popularity throughout the world and are slowly replacing the conventional water heating systems in most part. They are proven to have many advantages over the conventional system.

A solar water heater consists of storage tanks and solar collectors. In most water heating systems cold water is passed into the collector where it is heated and then the heated water is flown to the storage tank. There are two types of solar water heating systems: active and passive. In the active system the water is pumped into the collector. The passive system makes use of natural convection to drive the water into the collector. For this to be possible the storage tank needs to be placed above the collector, as hot water rises and cold water sinks, and hence the cold water will flow from the storage tank into the collector which then heats it and in turn the heated water rises to the storage tank. This means that the roof is supposed to be designed as such that it can accommodate the heavy storage tank. Passive systems are not as efficient as active systems however; they are less expensive, more reliable and have a longer lifetime.

There are many advantages of using a solar water heater over the standard water heater. The biggest advantage is that it makes use of energy from the sun which is free and though it may have a much higher initial cost, the operating cost is significantly lower than that of a standard water heater. Also, a solar water heater has a much higher life expectancy than the standard. Apart from these, the solar water heater also has a larger storage capacity compared to the standard. It does not pollute the environment. Using a solar water heater reduces carbon dioxide emission significantly.

Solar water heaters can be effectively operated in any climate these days at reasonable prices. Different systems have been specifically designed to suit different areas and climates. These systems have been proven reliable and efficient and therefore the number of people using solar water heating systems throughout the world is increasing greatly.