Wind Power

Energia

Physics
Jnr Science Cert
This lesson examines the principles of conversion of wind energy to electrical energy and the factors that must be taken into account when connecting generator outputs to the national grid.

Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

Exploiting the wind
Global reserves of fossil fuels are becoming more costly to exploit and less accessible. With the demand for energy growing at an ever increasing rate there are valid concerns about the availability and sustainability of energy supplies for future generations. As an alternative to fossil fuels, sources of renewable energy like wind power are becoming increasingly popular in many countries. Wind power is one of the cleanest sources of energy available. It involves very low emissions of greenhouse gases and the ‘fuel’ is free. As Ireland is one of the windiest countries in Western Europe there is great potential for making use of this resource.

Energia, a leading supplier of electricity to the Irish market is busy expanding its renewable energy portfolio. In effect this clean energy supply reduces our output of CO2 by 150,000 tonnes of per annum – the equivalent to removing 40,000 cars. In this lesson we look the fundamental physics underlying the generation of electricity using the wind.

Basics
In comparison with water air seems to have no appreciable mass. However it is relatively easy to show that a litre of air under ordinary conditions has a mass of about 1.2 grams. A cubic metre of air is therefore about 1.2 kg. The large classroom of say 12 × 7 × 3 m would have about 300 kg of air – about a third of a tonne. The kinetic energy of such a mass of air moving at say 100 km/h would be over 100 kJ.

Kinetic energy
If a force acts on a body it accelerateaccelerates it. For example if a force of a newton acts on a kilogram for 6 seconds then the kilogram gains a velocity of 6 m/s. If it starts from rest (zero velocity) then its average velocity during the 6 seconds would be 3 m/s and so it would travel 18 m while being accelerated.

True or False?

1. A kilogram of still air has a kinetic energy of 1000 joules.
2. If a force of one newton acts on a body it gains velocity.
3. Work = force × mass
4. The energy of the wind is proportional to its velocity cubed.
5. To extract all the kinetic energy from the wind, wind speed would have to be reduced to zero.
6. Changing the pitch of a blade can increase its efficiency.
7. The average of an alternating current is zero.
8. Batteries connected in series can produce a higher maximum current.