Solar thermal systems harness solar energy by utilising solar radiations to generate heat- as hot water, hot air, steam etc. that can be deployed for meeting numerous applications in different sectors such as power generation on a large scale, space heating, space cooling, community cooking, process heating etc. These applications make use of solar energy collectors as heat exchangers that transform solar radiation energy to internal energy of the transport medium (or heat transfer fluid, usually air, water, or oil). The solar energy thus collected is carried from the circulating ﬂuid either directly to the hot water or space conditioning equipment, or to a thermal energy storage tank from which can be drawn for use at night and/or cloudy days. Solar thermal systems can be either non-concentrating or concentrating types. They may also be either stationary or with sun-tracking mechanisms, depending on the application, temperatures required, and economic viability.
Working of a Solar Water Heater
The system is generally installed on the roof or open ground, with the collector facing the sun and connected to a continuous water supply. Water flows through the tubes, absorbs solar heat and becomes hot. The heated water is stored in a tank for further use.
Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don't.
Active Solar Water Heating Systems -
There are two types of active solar water heating systems:
Direct circulation systems Pumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.
Indirect circulation systems Pumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.
Passive Solar Water Heating Systems -
Passive solar water heating systems are typically less expensive than active systems, but they're usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:
Integral collector-storage passive systems : These consist of a storage tank covered with transparent material to allow the sun to heat the water. Water from the tank then flows into the plumbing system. These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.
Thermosyphon systems Water is heated in a collector on the roof and then flows through the plumbing system when a hot water faucet is opened. The majority of these systems have a 40-gallon capacity.