L23 - Feeding the world's energy demands: The role of biofuels Flashcards
How has global demand for energy and fuel risen between 1900 and today?
How much energy does the typical briton consume?
- 25 billion kWh/day in 1900
- 250 billion kWh/day today
- 125 kWh/day
How does the burning of fossil fuels cause global warming?
What agreement was made to limit warming?
- Release of CO2 gas alters radiative forcing, increasing incoming radiative energy
- UNFCCC agreed warming should be limited to 2˚C to avoid existential risk
- Paris Agreement
When are we likely to run out of cheap fossil fuel?
- Reserves run out in likely 75 years
- Production likely peaks by 2030
- Oil will become rarer and more expensive to extract
Define renewable energy
What are the three main applications we need renewable energy for?
Which application is coal almost exclusively used for now globally?
- Energy sources that are continually replenished by nature
- Power electrical devices
- Transport
- Heating homes
- Coal used for electricity production
What are first generation biofuels?
List the four main types of biofuels as well as which non-renewable energy they aim to replace
- Biofuels produced directly from food crops or other edible plant materials
1) Burning biomass to produce electricity + heat (coal substitute)
2) Carbohydrates extracted from seeds or sugar stores, converted to ethanol via fermentation (petroleum substitute)
3) Oils from seeds or algae converted to biodiesel by esterification (petroleum sub.)
4) Food for humans and animals
What are second generation biofuels?
Describe a specific example of a secondary biofuel which can potentially be improved by genetic modification
- Waste products from agriculture + forestry turned into alcohol or methane (petroleum or natural gas substitution)
E.g. Production of cellulosic ethanol from waste products e.g. wasteland straw or C4 grasses
- Lignin needs breaking up to make cellulose accessible for conversion to sugar
- Lignin hard to break up normally
- Hope for GM to engineer form of lignin that’s easier to separate
What three criteria must biofuels fulfil to become a viable energy source
1) Produce more energy than is consumed in growing + processing
2) Low impact on agriculture + nature
3) Be cost effective
Outline the challenge of efficiency in biofuels
What are the implications of this on whether biofuel alone could meet all energy needs?
- Photosynthesis only has 2% energy efficiency (10-20% efficient in solar)
- Life cycle analyses show efficiency of whole process «_space;2%
- E.g. 0.13% efficiency from solar to ethanol in sugercane
- Low efficiency increases land requirements greatly
- Insufficient land in the UK to meet energy requirements using only biofuels
- Globally, potentially enough land as less average energy use e.g. “wastelands” in US
What indirect effect can biofuels have on greenhouse gas emissions?
Give a case study of a biofuel power station that indirectly causes GHG emission through using biofuels
- Clearing of natural vegetation for biofuels releases C from plants + soil to atmosphere
- Only genuine emissions reductions after biofuel “benefit” repays “carbon debt”
- Also from indirect displacement of farmland to new land (+ higher food prices)
- Converting natural ecosystems has large carbon debt
- Converting waste biomass or degraded agricultural lands has little/no carbon debt
- Drax imports wood from US for wood pellets
- Largely not waste products but forest, so no better than coal!
- Still receives subsidies from UK for C reductions!
Give two main points on how certain biofuels are better than others
CAM metabolism plants more water efficient
- Could be grown over large “wasteland” arid regions
- E.g. planting agave in Australia
Using waste products
- No additional land use pressure
- E.g. straw, husk + food waste
What personal choices are available that can reduce energy consumption?
- Insulate home + control temperature
- Avoid flying
- Cycle/use public transport
- Push for more compact cities = less cars
