CBSE · Class 10 · Science · Sources of EnergyWhat is a solar heating device? Explain the construction and working of a solar cooker with the help of a labeled diagram description. Also, mention its advantages and limitations.

Introduction to Solar Heating Devices\nA solar heating device is a gadget that uses solar energy directly to heat water or cook food. Among these, the box-type solar cooker is very popular and widely used for domestic purposes in regions with abundant sunlight.

Construction of a Box-Type Solar Cooker

• Insulated Box: A solar cooker consists of an outer box made of heavy-duty plastic or wood, which is thermally insulated to prevent heat loss.
• Inner Metal Box: Inside the outer box, there is an inner box painted completely black on its inner surfaces because black surfaces absorb the maximum amount of heat from sunlight.
• Glass Lid: The box is covered with a double-pane glass lid. The glass allows light to enter but traps the infrared heat inside due to the greenhouse effect.
• Plane Mirror Reflector: A plane mirror is attached to the outer box. It is adjusted at an angle to reflect extra sunlight into the interior of the box.
• Cooking Containers: Inside the black box, open containers made of aluminum or copper, painted black from the outside, are placed to hold the food.

Working Principle

1. The solar cooker is placed in direct sunlight for 3 to 4 hours.
2. Sunlight enters through the glass cover and also gets reflected by the plane mirror directly into the box.
3. The black interior of the box and the black-painted containers absorb this solar radiation and convert it into heat energy.
4. Due to the greenhouse effect, the temperature inside the box rises up to 100°C to 140°C, which is sufficient for boiling and cooking food items like rice, pulses, and vegetables.

Advantages of Solar Cookers

• Eco-friendly: They do not cause any pollution or release greenhouse gases, as they do not burn fossil fuels.
• Cost-effective: Sunlight is freely available in abundance, so there is no recurring fuel cost.
• Nutrient Retention: Food cooked in a solar cooker retains most of its essential nutrients because the temperature does not rise uncontrollably.
• No Attendance Required: Unlike cooking on a gas stove, it does not require constant monitoring.

Limitations

• Weather Dependent: They cannot be used on cloudy, rainy, or gloomy days.
• Time Consuming: Cooking takes much longer compared to conventional LPG stoves or induction cooktops.
• Limited Temperature: They cannot be used for frying or making chapatis as high temperatures (above 150°C) cannot be attained.