Jawaharlal Nehru Technological University Hyderabad B.Tech III NON-CONVENTIONAL POWER GENERATION Previous Question Paper (November/December - 2018 - R16)

The fundamental difference between active and passive solar heating systems lies in their reliance on mechanical or electrical devices to circulate heat.

Active Solar Heating Systems utilize mechanical and electrical equipment, such as pumps, fans, and controllers, to collect, store, and distribute solar energy. These systems actively move a heat transfer fluid (like water or air) from collectors to storage and then to the point of use. Examples include solar water heaters with pumps and forced-air solar heating systems.

Passive Solar Heating Systems rely on the building's design and materials to collect, store, and distribute solar energy without the use of mechanical or electrical devices. They use natural processes like convection, conduction, and radiation. Key elements include south-facing windows for solar gain, thermal mass (like concrete floors or brick walls) to absorb and release heat, and proper insulation to retain heat. The design itself manages the solar energy flow.

A solar pond is a body of water that collects and stores solar energy. It is essentially a large, shallow pond lined with a dark material to absorb sunlight. The key feature of a solar pond is its ability to create a temperature gradient within the water column, with the bottom layer being significantly hotter than the top layer. This is achieved by establishing a salt concentration gradient, where the bottom layer has a high salt concentration, and the top layer has a low salt concentration. The salt gradient suppresses convection, allowing the absorbed solar heat to be retained in the lower, hotter layers.

Applications of Solar Ponds:

• Low-Temperature Industrial Process Heat: Solar ponds can provide heat for various industrial processes that require temperatures up to around 80-90°C, such as drying, pasteurization, and chemical processing.
• Electricity Generation: The hot brine from the bottom of the solar pond can be used as the heat source in an Organic Rankine Cycle (ORC) or other low-temperature thermal power cycles to generate electricity.
• Water Desalination: Solar ponds can be used in solar stills to desalinate water, producing potable water from saline sources.
• Space Heating and Cooling: In some applications, the heat from solar ponds can be used for heating buildings in winter and, with absorption chillers, for cooling in summer.
• Aquaculture and Agriculture: The heated water can be used to extend growing seasons for fish farming (aquaculture) or in greenhouses for agriculture.