The dawn of a new era in renewable energy?

The need to develop renewable energy is widely seen as a futuristic technological challenge. In reality, some of the most effective ways of harnessing horsepower from nature are based on concepts that have existed for donkey’s years. The wind turbine is an obvious example. Another – less well known, but conceived almost a century ago – is the solar tower or solar chimney. And if the Australian company EnviroMission completes an ambitious solar tower project in the New South Wales desert, the technology could capture not just the sun’s rays but the public’s imagination worldwide. The firm is planning to construct a tower a colossal one kilometer high. If built, it will be the world’s tallest structure by a huge margin.

    How it works

A large glass enclosure is built, with a chimney at its centre. The sun heats the enclosure, causing expansion of the air inside. At the top of the chimney, the lower temperature and lower pressure due to the higher altitude create a pressure differential known as stack effect. This causes air to flow up the chimney. Electricity is generated by turbines at the bottom of the chimney, which are driven by the flow of air. The bigger the area of glass and the taller the chimney, the greater the airflow and the higher the generating capacity.

b) Label the diagrams using the forces in a box.

bending, centrifugal force, compression, contraction, expansion, friction, pressure, shear, tension, torsion/torque

1.                              2.           3.                    4.

 

5.                    6.                    7.                              8.

 

9.                              10.

 

c) What physical forces would act on a solar tower 1 km high?

 

d) Listening 7. Su, a structural engineer specializing in the design of very tall structures, is giving a talk to a group of engineering students. Listen to the talk. Which of the forces in Exercise 9b doesn’t she mention?

E) Complete the following sentences from the talk using the forces in Exercise 9b. Listen again and check your answers.

1) So that downward force means the structure is in _________, especially near the bottom.

2) … a horizontal load, exerted by air ________ against one side of the structure.

3) Because the structure is fixed at the ground level, and free at the top, that generates ________ forces.

4) …when elements bend, you have opposing forces: ________ at one side, _______ at the other.

5) … the wind effectively tries to slide the structure along the ground, and the foundations below the ground resist that. The result of that is _______ force…

6) … the foundations need to rely on _______ with the ground to resist the pull-out force, …

7) The action of the wind can also generate _______. You get a twisting force…

8) When concrete absorbs heat from the sun, you get _________; as soon as the sun goes in, there’s ________.

 

You and your partner specialize in designing structures for electrical transmission grids. You are currently working on a cable support concept for power lines near wind farms exposed to severe weather. You have come up with the following design. In pairs, hold a short meeting to evaluate your design concept. Explain the forces acting on the structure.