Sustainability of Energy Systems

Question 1

Levelised costs

Answer 1

Levelised costs of electricity represent the revenue a plant owner must receive to make the investment worthwhile.

Uses discounted cash flow to account for:

• Opportunity cost of investment
• Risk to investor.

Question 2

Decommissioning and waste disposal

Answer 2

• Immediate dismantling: defuelling, dismantling and decontamination occur as soon as possible.
• Safe enclosure: defuelling and removal of some HLW followed by monitoring for 40-80 years so radioactivity decreases.
• Entombment: radioactive material gathered together and encased on site indefinitely.

Question 3

Ozone layer depletion

Answer 3

• Sources of halogen elements (CFCs, HFCs, freons, halons), photo-dissociate and cause catalytic destruction of stratospheric ozone.
• Ozone layer absorbs UVB, therefore depletion is harmful to organisms.
• Montreal protocol was successful in stopping production of CFCs but recycling of CFCs and HFCs still persists.

Question 4

Photochemical smog

Answer 4

• Complex mixture of compounds harmful to respiratory health.
• Created when emissions such as NOx and VOCs react with sunlight.
• Particularly problematic in areas of high traffic and industrial activity.

Question 5

Human toxicity potential

Answer 5

Human toxicity potential includes impacts of toxic compounds emitted to air, water and land.

Question 6

What is shale gas?

Answer 6

• Natural gas absorbed to shale rock, 500-5000m underground.
• Shale is cracked with high pressure fracking fluid
• UK resource

Question 7

Time horizon

Answer 7

This layer defines the time frame for the research, involving collection of data at a specific point of time or collecting data continuously over an extended period of time.

Question 8

Importance of time horizon

Answer 8

• Time horizon is important in the GWP of natural gas.
• In LCA we want to normalise emissions against reference substance in this case CO2.
• Methane is more potent than CO2 but to arrive at characterisation factor must assume a time horizon.
• Particularly important in gas sector due to methane leans/vents.

Question 9

What time horizon should be used?

Answer 9

• Long term climate stabilisation is the goal.
• Most climate impacts have consequences on long time scales (sea level rise, extinction events).
• But short term forcing does have an impact on climate effects.

Question 10

Shale gas unknowns

Answer 10

• Social repercussions: traffic, noise, house prices, public opposition.
• Industry practice and regulations- fugitive emissions, waste water treatment, solid waste disposal.