Science & Technology in Action

6th Edition

Sustainability in the Pipeline

Bord Gáis Networks

Many micro generation resources e.g. solar, wind and hydro, are free and sustainable. This lesson describes significant micro generation technologies. It describes how Bord Gáis Networks is exploring using such technologies in combined heat and power systems in order to maximise efficiency and reduce the environmental impact.”
Download

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

Lesson excerpt

What is Micro Generation?
Micro generation is the generation of electrical or thermal energy by individuals, businesses and communities from a low carbon source. The term does not have an exact defnition but generally refers to relatively small-scale systems with outputs in the range 2.5 to 50 kW. A particular advantage of many forms of micro generation is that the resources are free and sustainable, e.g.solar, wind and hydro. This lesson describes signifcant micro generation technologies.

1. Wind Technologies
For micro generation, average wind speeds of approximately 5 m/s are required over an unobstructed landscape to commence power production. This is known as the cut-in wind speed. In any wind turbine, kinetic energy (Ek) (the energy of movement) of air is converted into rotational movement by the blades of the turbine. This turning moment (torque) causes a generator within the turbine housing to rotate to produce electricity:

For micro generation, average wind speeds of approximately 5 m/s are required over an unobstructed landscape to commence power production. This is known as the cut-in wind speed. In any wind turbine, kinetic energy (Ek) (the energy of movement) of air is converted into rotational movement by the blades of the turbine. This turning moment (torque) causes a generator within the turbine housing to rotate to produce electricity:

Kinetic energy (Ek) = ½ mv2 (joules)
where:
m = mass of air in kg
v = velocity in m s-1
Ek = kinetic energy in joules

The total wind power in the area swept by the turbine rotors is given by
the following equation:
P = ½ × ρ × A × v3

where:
P = power in watts (1,000 watts = 1 kilowatt)
ρ = air density at sea level (approx. 1.2 kg m-3)
A = rotor swept area, exposed to the wind (m2)
v = wind speed in m s-1

The theoretical maximum efficiency of any design of wind turbine is 59.3%; this is known as Betz's Law.

Quiz questions

  1. Micro generation systems have a maximum output of 50 kW. true
  2. PV (photovoltaic) panels have an average efficiency of about 45 %. false
  3. The Sun’s energy is generated by nuclear reactions true
  4. Every 100 units of input a CHP (Combined Heat and Power) plant typically produces an output of 50 units of electricity true
  5. CHP is more efficient than separate heat and power. true
  6. CHP has more heat losses than separate heat and power false
  7. Separate heat and power plants use different fuel sources false
  8. Every MW of traditional power generation that is replaced by CHP reduces annual CO2 emissions by 1000 tonnes true
  9. PV requires a greater area of panels than solar thermal to capture the same amount of energy true