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Energy and Industry: Sources, CO2 and Life Cycles

Factories need energy. It comes from fossil fuels, nuclear power, hydro, wind and solar. To judge a source we compare CO2 per kWh, reliability, cost and other effects. A life cycle looks at a product from raw material to making, use, disposal and recycling, because energy and waste appear at every stage.

đŸŽŦ Step-by-step story

  1. A factory needs energy to run its machines. The bolt on the left stands for the energy supply. Where should it come from?
  2. There are six common sources: coal, natural gas, nuclear, hydro, wind and solar. Each tower is one source.
  3. Now the towers grow. The height shows the CO2 given out for each kWh of electricity, counted over the whole life of the plant. Coal is highest. Wind and nuclear are lowest.
  4. Pick a source with the buttons. Three bars show CO2, reliability and cost. No source is best at all three, so we have to judge.
  5. Now look at a product life cycle: raw material, making, use, disposal and recycling. The yellow dot travels round. Every stage needs energy and makes waste.
  6. Free play. Choose a source and set how many kWh the factory uses. The red tower shows the CO2 produced.

Tip: drag the 3D scene to turn it. Use two fingers to zoom.

🤔 Common doubts, cleared

Why does a factory need so much energy?

Heating, melting, driving machines and making chemical reactions go all need energy. The bolt in step 0 stands for all of this.

Are all renewables the same?

No. Hydro is steady, wind and solar vary. Each has different cost and land use.

Why is nuclear so low in CO2 but still debated?

It makes little CO2 but leaves radioactive waste and needs strict safety. So CO2 is only one yardstick.

Which source is the best?

None wins on all three bars. Change the picked source in step 3 and watch the bars move in different directions. That is why countries use a mix.

Does recycling always save energy?

Often yes, for metals and glass, but it also takes energy to collect and process. The ring in step 4 shows recycling feeding back into raw material.

Why is the CO2 for solar not zero?

Making the panels uses energy. Switch the source in step 5 and compare solar with coal at the same kWh.

Energy from different sources

Industry uses energy for heat, motors and chemical reactions. The main sources are:

Chemistry link: burning a fuel is a reaction with oxygen. For methane, CH4 + 2 O2 → CO2 + 2 H2O + energy.

Comparing and judging sources

To compare sources fairly, use the same unit and the same yardsticks:

No source is best at everything, so countries use a mix. A good judgement states the criteria first and then weighs them. Note: the numbers are rounded and vary between studies and places.

Life cycles of products

A life cycle follows a product through all its stages: raw materials (mining, farming, drilling), making (factory processes), transport and use, disposal (landfill, burning) and recycling or reuse. A life cycle assessment (LCA) counts the energy, raw materials and waste at every stage.

Why do this? A product can look green in use but be costly to make, or the other way round. A lamp uses most of its energy in use, but a phone uses most in making. LCA shows where to improve: use less material, make with clean energy, make it last longer, or recycle.

Cradle to grave is the whole line from raw material to disposal. Cradle to cradle means the old product becomes raw material for a new one: a loop.

Industry goal: do more with less energy, and reuse waste heat and by-products.

Try it: count the stages of your phone or bottle

Take a plastic bottle or a phone. Write the stages of its life cycle. For each stage, write where energy is used. Which stage do you think uses the most? Then pick it in the 3D step 4 and compare.

Key formulas and definitions

Worked examples

1. A factory uses 500 kWh. How much CO2 is given out if the electricity comes from coal (820 g/kWh)?

500 × 820 = 410 000 g = 410 kg of CO2.

2. The same 500 kWh come from wind (11 g/kWh). What is the CO2, and how many times lower than coal?

500 × 11 = 5500 g = 5.5 kg. Ratio = 820 Ãˇ 11 ≈ 75 times lower.

3. Convert 2 kWh to MJ.

2 × 3.6 = 7.2 MJ.

4. A kilogram of natural gas gives 50 MJ and coal gives 25 MJ per kilogram. How much coal gives the same energy as 10 kg of gas?

Gas energy = 10 × 50 = 500 MJ. Coal needed = 500 Ãˇ 25 = 20 kg.

5. A solar plant gives power only 20% of the time (it works 4.8 hours per day on average). How many hours per week is that?

4.8 × 7 = 33.6 hours per week (about 20% of 168 hours).

6. A product uses 10 units in raw materials, 30 in making, 5 in use, 5 in disposal and recycling saves 8. What is the net energy, and which stage dominates?

Total = 10 + 30 + 5 + 5 = 50. After recycling: 50 − 8 = 42. Making dominates (30 of 50 = 60%).

Common mistakes

Practice quiz

1. Which source has the highest life-cycle CO2 per kWh among these?
2. Wind and solar are:
3. 1 kWh equals:
4. A life cycle assessment looks at:
5. Cradle to cradle means:

Practice: answer these yourself

Type or choose your answer, then press Check. Use a hint if you are stuck; the full solution appears after you answer.

Frequently asked questions

Which energy source gives the least CO2 per kWh?

Over the whole life, wind, nuclear and hydro are lowest, around 10-25 g CO2 per kWh. Coal is highest, around 800-1000.

What is a life cycle assessment?

A method that adds up energy, materials and waste for every stage of a product, from raw material to disposal.

How do I convert kWh to MJ?

Multiply by 3.6. So 1 kWh = 3.6 MJ.

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