---
title: "Major electricity sources and sustainability"
subject: "Power System Analysis I"
chapter: 1
key: "semester_4/power_system_analysis_i:electricity-sources-sustainability"
source: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/electricity-sources-sustainability
site: BCT Engineering
---

# Major electricity sources and sustainability

Power System Analysis I · Chapter 1: General Background

- Asked in: 2068 Bhadra, 2+4 marks
- Video: [Electricity – Sources and Uses](https://www.youtube.com/watch?v=ja8U4bFhEGQ) — Next Generation Science
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/power_system_analysis_i/electricity-sources-sustainability
- Whole chapter: https://www.bctengineer.com/md/semester_4/power_system_analysis_i/chapter-1

## Question

What are the major sources of electricity worldwide? Give reasons why the existing electricity supply scenario is not sustainable.

## Short answer

Major sources are coal (~35%), gas (~22%), hydro (~15%), nuclear (~9%), wind, and solar. Present supply is unsustainable because fossil fuels are finite, emit CO₂ causing climate change, cause air pollution, have low efficiency (30-40%), and create energy security risks. Transition to renewables is needed.

## Answer

#### Major sources of electricity worldwide (approximate shares, early 2020s)
| Source | Share of world generation |
|---|---|
| Coal | ≈ 35 % |
| Natural gas | ≈ 22–23 % |
| Hydropower | ≈ 15 % |
| Nuclear | ≈ 9 % |
| Wind | ≈ 7–8 % |
| Solar | ≈ 5–6 % |
| Oil, biomass, geothermal, others | ≈ 4–5 % |

So about 60 % of world electricity still comes from fossil fuels.

#### Why the present supply scenario is not sustainable
1. **Depletion of fuels:** Coal, oil and gas are finite; at current use, known reserves will last only decades (oil and gas) to about a century or two (coal).
2. **Climate change:** Burning fossil fuels emits large amounts of CO₂; the power sector is the largest single source of greenhouse gases, causing global warming.
3. **Air pollution and health:** SO₂, NOx, particulates and mercury from coal plants cause acid rain, smog and respiratory disease.
4. **Low efficiency:** Thermal plants convert only 30–40 % of fuel energy into electricity; the rest is wasted as heat.
5. **Energy security and prices:** Many countries depend on imported fuel; prices fluctuate with geopolitics (e.g. oil and gas price shocks).
6. **Nuclear issues:** Radioactive waste disposal, accident risk (Chernobyl, Fukushima) and high cost.
7. **Unequal access:** Many people (especially in rural areas) still lack reliable electricity.
8. **Water and land use:** Thermal plants need large quantities of cooling water; mining damages land.

A sustainable path needs more renewables (hydro, solar, wind), better efficiency, storage and smart grids. Nepal, with large hydro potential, can contribute by exporting clean hydropower.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The largest source of world electricity is
   A. Hydro
   B. Nuclear
   C. Coal
   D. Solar
   Answer: C. Coal is about 35 %. (Key point: Largest source)

2. About how much comes from fossil fuels?
   A. 60 %
   B. 20 %
   C. 10 %
   D. 90 %
   Answer: A. Coal plus gas plus oil is about 60 %. (Key point: Fossil share)

3. Why is the power sector a climate concern?
   A. Solar emits CO2
   B. Hydro emits SO2
   C. Wind emits ash
   D. Fossil burning emits CO2
   Answer: D. CO2 causes global warming. (Key point: Climate)

4. Thermal plants convert about
   A. 80 %
   B. 95 %
   C. 30-40 % of fuel energy
   D. 100 %
   Answer: C. The rest is wasted as heat. (Key point: Efficiency)

## Related in Power System Analysis I

- [Hydro and thermal power sources](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Ahydro-thermal-sources) — Power System Analysis I, chapter 1

## Related in other subjects

- [Nepalese electricity sector scenario](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Anepal-electricity-scenario) — Power Plant Design, chapter 1
- [Nepal electricity demand, supply and trend](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Anepal-demand-supply-trend) — Power Plant Design, chapter 1
- [Quarterly progress report: hydro-electricity supply centre (memo)](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Aquarterly-progress-report-hydro-supply-memo) — Communication English, chapter 7
- [Report on electricity demand-supply mismatch](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Areport-electricity-demand-supply-mismatch) — Communication English, chapter 9