adminBy Takaendesa Denhere
Renewable energy refers to energy that comes from sources that are continuously replenished by nature – the sun, the wind, water, plants and the earth’s heat.
Renewable energy technologies turn these into usable forms of energy like electricity, heat and mechanical power.
Fossil fuel
On the other side, we also have non-renewable energy which is comprised of oil, coal and gas, collectively known as fossil fuels. They are formed from the fossilised remains of pre-historic plants and animals.
Fossil fuels are regarded as non-renewable energy sources as they take millions of years to form while the sources get depleted after extraction.
Demand for energy is continuously increasing with the increase in human population.
After World War II, much effort was put into the reconstruction of society, emphasis was directed on the growth and efficiency of mass production. As a result, energy demand grew tremendously during this period such that oil and gas became important energy sources.
Today; coal, oil and gas are the major sources of energy.
Developments in the second half of the 20th century have clearly illustrated that fossil fuels have an impact on man and his environment. The energy sources’ side effects are manifesting through global warming and climate changes.
According to the former UN Secretary General Koffi Anan as reported in the Africa Progress Panel Report of 2015, there is need to rethink about the relationship between energy and development because carbon-intensive energy systems that drive economies have set us on a collision course with our planetary boundaries.
This forces people to formulate the concept of a sustainable development to ensure that it meets the needs of the present without compromising the ability of future generations to meet their own needs.
The answer clearly lies in adoption of renewable energy which is clean and sustainable and friendly to the environment.
I am going to explore the available types of renewable energy.
Solar energy
First, we look at solar energy which is the most popularly used renewable source of energy. Solar energy comes from the sun and is converted into other forms of energy like heat and electricity.
Solar energy is classified under renewable energy because its supply is constant. Much of the world’s required energy can be supplied directly by solar power. A research by GENI revealed that the energy from the sun falls at a rate of 120 petawatts (1 petawatt = one billion million watts, or 10 to the power 15 watts) and therefore the energy received from the sun in one day can satisfy the whole world’s energy demand for more than 20 years.
Solar energy is mechanically harnessed for man’s use through photovoltaic panels or modules (commonly known as solar panels in Zimbabwe) and solar thermal systems or through solar water heating. Solar can be used on various applications in the home, offices or factories.
However, one of its limitation is that little or no solar energy is generated at night.
Wind energy
The wind is another source of renewable energy with zero emissions. Wind energy is generated using wind turbines that are mounted to trap the wind coming from any direction. The wind turbine technology looks simple – the wind spins turbine blades around a central hub which is connected to a shaft. This shaft then powers a generator to make electricity.
This equipment requires minimal maintenance and can last for a long time, onshore turbines for example have a lifespan of about 20 good years.
However, turbines are highly sophisticated power systems that capture the wind’s energy by means of new blade designs or airfoils. Modern, mechanical drive systems, combined with advanced generators, convert that energy into electricity. Wind turbines that provide electricity to the utility grid range in size from 50kW to 1 or 2 MW.
Large, utility-scale projects can have hundreds of turbines spread over many acres of land. Small turbines, below 50kW, are used to charge batteries, electrify homes, pump water for farms and ranches, as well as power remote telecommunications equipment.
According to Friends of the Earth, by the end of 2007 there were 169 onshore wind farms in the UK providing enough electricity for more than 1,4 million homes.
In Nyanga, we have a wind farm which was installed several years ago and it generates enough energy for the small community of Temaruni, thereby making it a success story.
Geothermal energy
This is another source of renewable energy. The earth’s core can reach temperatures of 4 983°C. This heat flows outward, heating the surrounding area and creating underground reservoirs of hot water and steam. These reservoirs can be tapped through geothermal heat pumps (GHPs) to generate electricity or heat buildings.
Geothermal power plants access the underground steam or hot water through wells that are drilled a mile or more into the earth. The steam or hot water is piped up to drive conventional steam turbines, these in turn power electric generators. The water is then returned to the ground to recharge the reservoir and complete the renewable energy cycle.
An international newspaper, Business Daily reported on August 11 that Kenya has the capacity to generate 10 000MW of geothermal power from the Rift Valley basin.
Biofuel
Biomass can be converted directly into liquid fuels – biofuel – which is easy to transport and possesses high energy density. It is commonly used to power vehicles.
The most common biofuel is ethanol which is made from the fermentation of biomass high in carbohydrates. The current largest source of ethanol in Zimbabwe is sugarcane. Flex-fuel vehicles are also now on the market, these can use a mixture of gasoline and ethanol such as E85 — a mixture of 85 percent ethanol and 15 percent gasoline.
Another biofuel is biodiesel, this can be produced from vegetable and animal fats. Biodiesel can be used to power vehicles or as a fuel additive to reduce emissions.
To increase our available supply of biofuel, researchers are testing crop residues such as cornstalks and leaves, wood chips, food waste, grass, and even trash as potential biofuel sources. Zimbabwe has already taken steps in this direction by building a jatropha fuel plant in Mt Hampden.
Hydro-power
Hydro-power plants convert flowing water’s energy into electricity, water is released through turbines to generate the power. The most common form of hydro-power uses a dam on a river to retain a large reservoir of water.
‘Run of the river’ systems, however, divert water from the river and re-direct it to a turbine through a pipeline. Hydro-power plants produce no air emissions but can affect water quality and wildlife habitats. Therefore, the plants are now being designed in a way that minimises their impact on the river’s ecosystem.
Tidal and wave energy
The last source of energy is still hdro in nature though it comes from the ocean. In this case, tidal energy generators are used to produce electricity. The turbines are placed under the water where there are high tidal movements to capture kinetic motion of the ebbing and surging of ocean tides in order to produce electricity. When wind blows across the sea surface, it transfers the energy to the waves. The energy output is measured by wave speed, wave height, wavelength and water density – the more the strong waves, the more power is produced.
Takaendesa Denhere is an independent researcher and he writes on renewable energy. For feedback contact him on his email: [email protected]
Bongani Ndlovu
Online Reporter