Conventional, non-conventional sources and biomass

Conventional energy sources

Sources that have been in large-scale use for a long time, with mature technology. Most are non-renewable (except hydro and traditional biomass).

• Coal, petroleum, natural gas
• Large hydropower
• Nuclear energy
• Traditional biomass: firewood, cattle dung, crop residue burnt directly

Non-conventional energy sources

New or alternative sources, mostly renewable and environment friendly, still developing in technology and cost.

• Solar (PV, thermal)
• Wind
• Small/micro hydro
• Modern biomass: biogas, gasification, bio-fuels, briquettes
• Geothermal, tidal, wave, ocean thermal, hydrogen and fuel cells

Biomass energy

Biomass is organic matter of plant or animal origin. It stores solar energy by photosynthesis and releases it by burning or conversion. It is renewable if regrowth keeps up with use.

Conversion routes:

            +--> Direct combustion --> heat / steam power
 Biomass ---+--> Gasification -----> producer gas -> engine
            +--> Anaerobic digestion -> biogas (CH4)
            +--> Fermentation ------> ethanol
            +--> Pressing/esterify --> bio-diesel

Suitable examples:

1. Firewood in improved cooking stoves – the largest energy use in rural Nepal; improved stoves save about 30–50% of wood and reduce smoke.
2. Household biogas – cattle dung digesters supply cooking gas and slurry manure; hundreds of thousands installed in Nepal.
3. Bagasse cogeneration – sugar mills burn bagasse to make steam and electricity for the mill.
4. Rice husk gasifier – producer gas runs an engine-generator in a rice mill.
5. Briquettes – compressed sawdust, rice husk or forest litter (e.g. banmara weed) for clean household fuel.
6. Bio-ethanol – from molasses, blended with petrol.
7. Municipal waste to energy – biogas from organic waste of cities.

Advantages: renewable, carbon neutral, uses wastes, available locally, creates rural jobs. Disadvantages: low energy density, bulky to transport, smoke if burnt in open stoves, can cause deforestation if over-used.