Some Myths and Surprises

about energy and carbon emissions

Nicola Terry

Energy and Carbon Emissions: the way we live today

This presentation was prepared using s5. Type 't' for outline mode with explanations.


  • Some interesting facts from my book: A Fact Book of Energy and Carbon Emissions (published May 2011)
  • Wide range of topics, mainly personal activities in the UK

Glass v. Plastic Bottles

Myth: Glass bottles are better than plastic

Energy (in kWh) for a 1 litre bottle:

a plastic bottlePlastic a glass bottleRecycled a milk bottleReused
Make bottle (1 litre) 1.1 1.4
Washing 0.2
Transportation - guess 500km 0.0 0.4 0.4
Total 1.1 1.8 0.6

  • It takes more energy to make a 1 litre bottle from recycled glass than from plastic - and more carbon emissions
  • Glass is heavy - adds to transport costs
  • Washing and reusing the glass bottle is better - as long as the distance travelled is less than 1200km
  • Wouldn't it be easier if we all used standard shapes and sizes so you could reuse for different products by changing the label?

Tidal/Wave/Wind energy resource

Myth: We don't need ugly wind turbines because there is plenty of power in the tides, or nuclear ...

graph showing energy resources
Data from DECC 2050 pathways analysis - limit of practicability, regardless of cost.
  • Nuclear limit is how much can be built by 2050
    • 146 GW = 120 Sizewell B's
    • potential longer term uranium supply issues
    • and still waiting for disposal facility for radioactive waste
  • Tidal energy dissipated globally is 3.75 TW. World energy usage is 15 TW.
    • Friction means the moon is receding from the earth and day length is increasing.

Being a veggie(1)

Myth: Becoming a vegetarian will help save the planet

grammes CO2e per 100g except 2 eggs or 50g cheese

780 560 550 440 90
pork chicken eggs cheese lentils

Cheese, milk, cream and eggs are just as bad as meat because animals are inefficient protein concentrating machines. To help save the planet: Eat less animal products of all kinds.

Being a veggie(2)

Myth: Becoming a vegetarian will help save the planet

grammes CO2e per 100g

30 100 240 60 460
a lorry a lorry a lorry a lorry a lorry
Fresh Frozen Local Madrid Nairobi

  • Exotic fruit and vegetables can be just as bad as meat if imported by air.
  • Importing by road, train or ship is not nearly so bad.
  • Frozen and canned vegetables are roughly similar in carbon emissions depending on distance travelled (heavy can) and time frozen.

Organic is good

Myth: Organically grown food is more sustainable

Wheat needs less energy Tomatoes need more energy
Lamb generates less GHGs Beef generates more GHGs
Green manure crops 'mine' earth minerals

Sustainability requires using only renewable inputs and recycling all the nutrients.

  • Wheat needs lots of fertiliser - chemical fertiliser has lots of energy
  • Organic tomatoes (grown in greenhouses) have lower yield per unit area so higher heating cost
    • Bigger differences in yield from different varieties
  • Organic sheep and cattle both need less energy
  • Organic cattle grow more slowly

Energy payback for Solar Panels

Myth: Solar PV panels take as much energy to make as they generate in their lifetime

house with solar panels Solar panels: 3-6
power station CCGT power stations: 2-5
wind turbines Wind turbines: 9-34
power station Nuclear power: 14-16
  • The payback for solar panels is not great but definitely positive and coming down. The Sahara Solar Breeder project would reduce carbon emissions for PV.
  • For CCGT, the energy payback is just as bad as for solar panels if you count the energy used to locate, extract, process and transport the fuel.
  • The energy payback for wind turbines is similar to nuclear power but the wind farms probably have lower carbon emissions than nuclear.
Sources for energy payback: Hydro Quebec 2005 and Energy Enviro Finlad 2006 Sources for Carbon emissions: getme. Sources for Sahara Solar Breeder New Scientist. It is a joint project by Algerian and Japanese universities. <--!>

Roof insulation

Myth: From an uninsulated house you will lose 25% of your energy through the roof.

True but irrelevant. Only applies to 1 in 30 houses!

Every house is different.

  • For Victorian house with solid walls and 50mm insulation
    • walls lose heat 4 times as fast as the roof (per unit area)
    • more roof insulation saves perhaps 7% overall.
  • The first 50mm of insulation cuts heat loss by 75%.
  • The first 100mm of insulation cuts heat loss to about the same as a filled cavity wall.


Surprise: Buying an eco kettle can pay back embodied carbon emissions in days

a kettle
  • Modern kettle has low minimum fill and accurate measures
  • Avoiding 1 extra mug full (0.25 litres) saves 16g CO2
  • Embodied emissions in kettle say 2000 gCO2
  • Payback after 2000/16 = 125 uses
  • 5 times a day: 125/5 = 25 days


Surprise: A new eco-car will take years to pay back embodied carbon emissions (Unless you drive an awful lot)

Toyota Prius Hybrid
  • Manufacturing 5,700 kg CO2
    • says Toyota - How Bad are Bananas says 13-17 tonnes
  • Running: 89 gCO2/km - cf 190 for oldish diesel
  • Payback 5,700/(.190-.089) km
    = 57,000 km

TV vs. Book

Surprise: Watching TV generates less carbon emissions than reading a book

Book TV
Embodied CO2 2.5 kg (Penguin) 220kg (How Bad are Bananas)
Time used 10 hours 2 hours/day 5 years = 3650 hours
Embodied CO2/hour use 250g 60g
Usage CO2/hour 0 Assume 80W -> 40g
Total CO2/hour use 250g 100g
If 2 people watching 250g 50g
If read book 5 times 50g 50g
Library books are read on average 4.6 times per year.

Horse vs. Van

Surprise: For the same useful energy, a horse needs 150 times as much space as an electric van

Area needed to generate 1 kWh/day (square metres)
Solar PVHorse pulling cart
First approximation (horse generates 750W for 8 hours, needs 2 hectares) 2.1 3370
Payload efficiency (van 1.0/3.5, horse 0.72/1.0) 7.2 4700
Electric motor is only 80% efficient 9.3 4700
Allow for embodied energy (van 42 MWh over 10 years, horse working life 5-15 years) 33 5400

  • The van is powered by solar pv panels. 2.1 m2 supplies 1 kWh/day
  • Payload efficiency:
    • The unladen van is 2.5t and it can carry 1t load.
    • The horse can pull 1t of which 280kg is cart and driver.

What does this tell us?

  • Beware extravagant claims
  • Don't jump to conclusions
  • Do look at the figures - you might be surprised
  • Use your imagination
  • Look forward rather than back

Your thoughts?