---
title: "Why biomass is a renewable source"
subject: "Power Plant Design"
chapter: 1
key: "semester_8/power_plant_design:biomass-renewable-claim"
source: https://www.bctengineer.com/q/semester_8/power_plant_design/biomass-renewable-claim
site: BCT Engineering
---

# Why biomass is a renewable source

Power Plant Design · Chapter 1: Energy Sources and Electric Power Generation

- Asked in: 2074 Magh, 4 marks; 2078 Kartik, 4 marks (asked 2 times)
- Video: [Biomass: How clean is energy from waste and plants really?](https://www.youtube.com/watch?v=XXu15NlOuGo) — DW Planet A
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/power_plant_design/biomass-renewable-claim
- Whole chapter: https://www.bctengineer.com/md/semester_8/power_plant_design/chapter-1

## Question

How do you claim that biomass is renewable sources of energy?

## Short answer

Biomass is renewable because plants regrow within human time scales using solar energy via photosynthesis, forming a closed carbon cycle. Waste streams (dung, crop residue) are continuously produced. Sustainability requires harvest not exceeding regrowth.

## Answer

Biomass is called a renewable energy source because it is **continuously replenished by nature within a human time scale**, using solar energy through photosynthesis.

#### Reasons
1. **Regrowth** – trees, crops and grasses grow again in months or years after harvest; fossil fuels take millions of years to form.
2. **Solar origin** – biomass stores sunlight as chemical energy:
$$
6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2
$$
   As long as the sun shines, new biomass forms.
3. **Closed carbon cycle** – the CO₂ released when biomass is burnt was taken from the atmosphere during growth, so the net addition of CO₂ is nearly zero (carbon neutral).
4. **Continuous supply of wastes** – animal dung, crop residue, food and municipal organic waste are produced every day and can be used in biogas plants.
5. **Can be managed** – plantation, energy crops and community forestry keep the stock constant.

#### Condition
```text
  Plant growth  --->  Biomass  --->  Combustion / digestion
       ^                                   |
       |          CO2 to atmosphere        |
       +-----------------------------------+
```
Biomass remains renewable **only when harvesting does not exceed regrowth**. Over-cutting of forests (deforestation) makes it non-renewable in practice and releases stored carbon permanently.

## Check yourself

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

1. Why is biomass renewable while fossil fuel is not?
   A. Biomass regrows in months or years; fossil fuels take millions of years
   B. Biomass is cheaper
   C. Biomass has no carbon
   D. Fossil fuels grow faster
   Answer: A. Biomass is replenished by nature within a human time scale using solar energy. (Key point: Replenished on human time scale)

2. How does biomass store energy?
   A. By nuclear reactions in soil
   B. By photosynthesis storing sunlight as chemical energy
   C. By absorbing heat from the earth's interior
   D. By compressing water
   Answer: B. 6CO2 + 6H2O + light gives glucose and oxygen, storing solar energy. (Key point: Solar origin)

3. When does biomass become non-renewable in practice?
   A. When harvesting exceeds regrowth, e.g. deforestation
   B. When it is dried
   C. When used in biogas plants
   D. When it is replanted
   Answer: A. Over-cutting breaks the cycle and releases stored carbon permanently. (Key point: Condition of renewability)

## Related in Power Plant Design

- [Conventional, non-conventional sources and biomass](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aenergy-sources-biomass) — Power Plant Design, chapter 1
- [Biomass compared with geothermal energy](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Abioenergy-vs-geothermal) — Power Plant Design, chapter 1
- [World renewable energy scenario](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aworld-renewable-scenario) — Power Plant Design, chapter 1
- [Is firewood in Nepal renewable?](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Afirewood-renewable-nepal) — Power Plant Design, chapter 1, asked 4×
- [Energy sources in Nepal and wind scope](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aenergy-sources-nepal-wind) — Power Plant Design, chapter 1, asked 2×
- [Energy sources and solar power generation](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aenergy-sources-solar-power) — Power Plant Design, chapter 1

## Related in other subjects

- [Types of renewable energy sources](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Arenewable-energy-types) — Power System Analysis I, chapter 1
- [Renewable sources and least suitable for Nepal](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Arenewable-sources-least-suitable-nepal) — Power System Analysis I, chapter 1
- [Renewable energy and trapping solar energy](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aenergy-renewable-solar-066j) — Building Technology, chapter 1
- [Conventional vs renewable energy for generation](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Aconventional-vs-renewable-generation) — Power System Analysis I, chapter 1, asked 2×