Build a Solar Updraft Tower

The Sun is a very powerful source of heat and energy. In fact, in less than 15 seconds, it can provide as much energy to Earth as humans use in one day! Most of this energy reaches Earth in the form of light and heat. It’s no wonder people have long considered how this energy can be harvested and put to good use! Over the last two centuries, scientists researched and developed technologies to convert the Sun’s energy directly into electrical energy. Today, many different methods of solar power generation exist, such as solar cells, solar thermal collectors, and solar concentration systems.

One of these systems, called the solar updraft tower, is a solar thermal collector technology. A solar updraft tower can generate electricity from low-temperature solar heat. The science concepts behind this idea are based on the greenhouse effect and the chimney or stack effect. These power plants consist of a large collector structure and a very tall and slender tower. The collector structure resembles a gigantic greenhouse and consists of a massive, transparent canopy that is suspended 6 to 65 feet (2 to 20 meters) off the ground. The tower is located in the middle of the canopy structure and has large air inlets at its base. Inside the tower are big wind turbines to produce electricity.

When the sun shines onto the collector structure, the heat of the sun gets trapped underneath like in a greenhouse, which heats the air and ground underneath the canopy structure. As hot air is less dense than cold air, it starts to rise, causing an air flow also called thermal convection. The air has no other way to escape than through the tower. The rising air in the tower creates low pressure at the bottom of the tower, and more hot air from the collector is sucked inside the tower through its air inlets at its base. As a result, solar radiation causes a constant updraft in the tower. The wind turbines installed inside the tower convert the energy contained in the updraft into mechanical energy by moving its blades. In the next step, this energy is converted into electrical energy by generators. Although the technology seems pretty simple and can generate lots of energy, no full-scale units are in operation, yet. However, several prototype models have been built and studied.

• To understand that heat from the sun can also be turned into electrical energy.
• To understand that a solar updraft tower uses the sun to heat up air, which then powers a turbine within a large tower.
• To understand that a propeller can spin with just hot air.

1. What happens to the propeller resting on top of the needle? Does it move?
2. What happens when you switch on the lamp?
3. What do you notice about the temperatures? Did they change? If yes, how? Can you explain why?