What is Solar Water Heater?
Solar water heater (SWH) or solar hot water (SHW) systems comprise several innovations and many mature renewable energy technologies that have been well established for many years. SWH has been widely used in Greece, Turkey, Israel, Australia, Japan, Austria and China.

In a “close-coupled” SWH system the storage tank is horizontally mounted immediately above the solar collectors on the roof. No pumping is required as the hot water naturally rises into the tank through thermosiphon flow. In a “pump-circulated” system the storage tank is ground or floor mounted and is below the level of the collectors; a circulating pump moves water or heat transfer fluid between the tank and the collectors.

SWH systems are designed to deliver hot water for most of the year. However, in winter there sometimes may not be sufficient solar heat gain to deliver sufficient hot water. In this case a gas or electric booster is normally used to heat the water.

How does solar water heater work?
Solar water heaters do three basic operations before the hot water comes out of your faucet:

1. Energy Collection: Sunlight, short wave energy, is collected and converted to heat which is long wave energy energy.

The solar collector is mounted on or near your home facing south. As the sunlight passes through the collector’s plastic or glass “glazing,” it strikes a metal or rubber absorbing material. This material converts the sunlight into long wave heat, and the glazing prevents the heat from escaping like a greenhouse. It is like leaving a car parked in the sun with its windows rolled up. The temperature inside a glazed solar collector on your roof can easily reach 300°F when there is no heat transfer fluid flowing through it.

The most common types of solar collectors used in solar water heaters are glazed flat plate collectors. A glazed flat plate collector consists of a shallow rectangular box with a transparent plastic or glass “window” covering a flat black plate or selective “Chrome” coating. The black plate is attached to a series of parallel tubes or one serpentine tube through which water, or other heat transfer fluids pass.

2. Energy Transfer: Circulating fluids like water in an “Open Loop” or Propylene Glycol in a Closed Loop” transfer the collected energy in the form of heat to a storage tank.

Heat energy is transferred from the collector to the water storage tank. In some water heaters, hot fluid is pumped from the collector to the storage tank. The pump is powered by electricity that either comes from an electrical wall outlet or a small photovoltaic module located beside the collector.

3. Energy Storage

Solar-heated water is stored in an insulated tank until you need it. Hot water is drawn off the tank when tap water is used, and cold make-up water enters at the bottom of the tank.

Solar water heaters tend to have a slightly larger hot water storage capacity than conventional water heaters. This is because solar heat is available only during the day and sufficient hot water must be collected to meet evening and morning requirements.