Lecture 7: Renewable Energy

Question 1

What are the renewable sources of energy?

Answer 1

Solar, wave, tidal, hydro, geothermal, wind

Question 2

What are the non-renewable sources of energy?

Answer 2

Fossil (oil, gas, coal), Nuclear (fission, fusion), Bio-derived

Question 3

What is the order of rate of replenishment for energy sources?

Answer 3

Solar, Wave (constant)

Wind, Hydro (daily)

Tidal, Geothermal (weekly)

Bio-derived (yearly)

Fossil (millions of years)

Nuclear (never)

Question 4

What are the most to least influential factors behind the level of solar energy a point on Earth receives?

Answer 4

Latitude - Time of Day - Time of Year - Cloud Cover - Topography - Air Pollution

Question 5

What are the two mechanisms for harnessing solar energy and what are their efficiencies?

Answer 5

• Solar thermal (50% efficient) - solar radiation heats water in pipes
• Photovoltaic panels (10-20% efficient) - incident photons transition free electrons and holes over depletion region which causes a flow of charge and a current, gradually breaks down which decreases efficiency

CASE STUDY: To power the whole UK, we would need solar panels only to cover 0.73% of the country.

Question 6

What methods are there to harness wind energy?

Answer 6

• Sailing
• Windmills
• Wind turbines (large on-shore, micro, off-shore, vertical axis)

Question 7

What causes wind?

Answer 7

• Differences in atmospheric pressures
• Difference between pole and equator heating and rotation of the planet (Coriolis effect) are major factors of large scale winds
• Near Earth, frictional forces causes wind to be slower

Question 8

How would you calculate the energy from a wind turbine?

Answer 8

Consider a mass M of air passing through an area A in time T.

Mass = density x volume = density x area x distance = pAv*t

Kinetic energy = 0.5mv2 so 0.5pAvtv2 = 0.5pAt*v3

Maximum energy from a windmill given by Bertz’s law is 0.59 so assuming wind speed of 6m/s and p to be 1.5kg/m3 and 25m dia. Turbine,

Power = Energy/Time = 0.59(0.51.3pi12.5^26^3*t)/t= 40.6kW

Question 9

How much of the UK would need to be wind turbine farms to meet energy demand?

Answer 9

• Must split up wind turbines to ensure maximum efficiency and avoid wind shadows
• Would need 10% of uk to be wind farms

Question 10

How does hydro create energy?

Answer 10

• Needs altitude and rainfall, so suitability depends on precipitation and topology
• Water falls with a potential energy due to gravity which creates kinetic energy
• Turbine is submerged and energy depends on the head of water above the turbine and volume flow rate going through it
• Penstock (large pipe) can be used to deliver water whilst maintaining the head

Power = rhoVhg (efficiency factor *load factor L for electricity generation)

• Loughborough has about 660mm rainfall a year which is 0.013W/m2 a year :(

Question 11

How much of energy consumption does global manufacturing account for?

Answer 11

25%

Question 12

How do you calculate direct energy?

Answer 12

Sum of Theoretical Energy (minimum energy required for a process) and Auxiliary Energy (energy required by supporting activities while carrying out that process eg. Control systems, cooling)

Question 13

How do you calculate indirect energy?

Answer 13

Sum of energy within each zone, a zone being an area with similar activities and intensity in energy consumption.

Question 14

How do you calculate the Embodied Product Energy?

Answer 14

Sum of direct and indirect energy.