Why biomass is a renewable source

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

  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.