Energy Transformation and Renewable Sources

Forms of energy

Energy is the ability to do work, measured in joules (J). Forms include kinetic, potential (gravitational, elastic), chemical, thermal, electrical, light, sound, nuclear.

Conservation of energy

Energy cannot be created or destroyed. It changes from one form to another. In every conversion some energy becomes wasted heat.

Examples:

• Electric kettle: electrical -> heat.
• Solar panel: light -> electrical.
• Battery torch: chemical -> electrical -> light.
• Hydro dam: gravitational potential -> kinetic -> electrical.
• Cooking on a jiko: chemical -> heat and light.

Efficiency

Efficiency = (useful energy output / total energy input) x 100%.

Worked example: A motor takes 800 J and produces 600 J of useful work. Efficiency = 600 / 800 x 100 = 75%. The wasted 200 J is lost as heat and sound.

Renewable and non-renewable

• Renewable: replaced naturally in a short time (solar, wind, hydro, geothermal, biomass, tidal).
• Non-renewable: finite (coal, petroleum, natural gas, uranium).

Kenya's energy mix

Kenya generates a large share of electricity from renewables:

• Geothermal: Olkaria in Naivasha, the largest in Africa; steam turns turbines.
• Hydro: Seven Forks on River Tana, Turkwel Gorge, Gitaru.
• Wind: Lake Turkana Wind Power at Loiyangalani, Ngong Hills.
• Solar: Garissa solar plant, home solar systems and solar water heaters.
• Biogas and biomass: cow dung digesters in rural homes; bagasse in sugar factories.

Advantages of renewables

• Do not run out and produce little pollution.
• Reduce dependence on imported fuel.
• Suitable for off-grid rural homes.

Disadvantages

• High installation costs.
• Weather dependent (solar at night, wind calm).
• Hydro depends on rainfall and affects ecosystems.

Biogas

Animal waste ferments without air in a digester producing methane. Gas is used for cooking and lighting; slurry is good fertiliser. It reduces firewood use and deforestation.

Energy saving

Use energy-saving bulbs and LEDs, improved cooking stoves, insulate homes, switch off unused appliances and use public transport.

Impact of fossil fuels

Burning fuels releases carbon dioxide that increases global warming, and causes air pollution and acid rain. Kenya's climate commitments aim to expand clean energy.

Try it

• Draw an energy flow chart for a wind turbine powering a lamp.
• Find the efficiency of a charcoal stove that gives 1,200 J useful from 6,000 J.
• Suggest how your school can use solar power and save energy.