You can catch up on the first part: Renewable Energy: Providing Energy Security and Clean Environments (Pt1)
For centuries, the wind has served as a source of energy, and in the past, windmills (mounted on towers) were used to generate mechanical power, which was used for grinding grain and pumping water. The modern equivalent of the windmill is the wind turbine. The wind turbine is mounted about 30 m or more aboveground where the turbine is able to take advantage of the faster and less turbulent winds. The turbine’s propeller-like blades turn in the moving air and power an electric generator that supplies electric current. Thus, the wind turbine is the exact opposite of an electric fan, instead of using electricity to generate wind, it uses wind to generate electricity.
Just like other renewables, wind power emits no pollutants or greenhouse gases. The United States Department of Energy in 1990 reported that California’s wind power plants offset the emission of more than 1.13 billion Kg of CO2, and 6.8 million Kg of other pollutants that would have otherwise been produced. It would take a forest of 90 million to 175 million trees to provide the same air quality.
Wind Energy is growing rapidly and in 2013, the amount of electricity generated from wind energy reached 318,117 MW. It also accounted for 4% of total electricity usage in 2014. As of 2011, 83 countries around the world were using wind power on a commercial basis. Europe accounts for about half of the world total wind power generation.
The US, China and Australia also have high wind power generating capacities. In Australia, for example, by the end of 2011, wind power in South Australia reached 26% of the States electricity generation, edging out coal for the first time.
Wind energy is not without disadvantages, concerns have been raised over the noise produced by the rotor blades, aesthetic impacts, and birds and bats having being killed by flying into the rotors. Most of these problems have been resolved or greatly reduced through technological developments or by properly siting wind plants. The major challenge to using wind as a source of power is that it is intermittent and does not always blow when electricity is needed. Wind cannot be stored (although wind-generated electricity can be stored, if batteries are used), and not all winds can be harnessed to meet the timing of electricity demands. Furthermore, good wind sites are often located in remote locations far from areas of electric power demand (such as cities). Finally, wind resource development may compete with other uses for the land, and those alternative uses may be more highly valued than electricity generation. Nonetheless, wind turbines can be located on land that is also used for grazing or even farming.
Bioenergy is renewable energy made available from materials derived from biological sources. Bioenergy technologies can be put into three categories namely biofuels, bio-power and bio-products. Biofuels are liquid fuels made from biomass. These fuels can be used in cars, airplanes and trains. The two most common types of biofuels are ethanol and methanol. Ethanol is an alcohol made by fermenting any biomass high in carbohydrates (starches, sugars, or cellulose) through a process similar to brewing beer. Ethanol is usually used as a fuel additive to cut down a vehicle’s carbon monoxide emissions. Methanol on the other hand is often used to formulate biodiesel by combining it with vegetable oil, animal fat or recycled cooking grease. Biodiesel is also used as an additive to reduce vehicle emissions by 20%, and could be used as a renewable alternate fuel for diesel engines.
Bio-power is the use of biomass to generate electrical energy with six types of bio-power systems: direct-fired, cofiring, gasification, anaerobic digestion, pyrolysis, and small modular. The direct-firing system is the most used in the world which involves burning bioenergy feedstock (energy crops, such as fast-growing trees and grasses) directly to produce steam. This steam is usually captured by a turbine, and a generator then converts it into electricity. In some industries, the steam from the power plant is also used for manufacturing processes or to heat buildings. These are known as combined heat and power facilities. For instance, wood waste is often used to produce both electricity and steam at paper mills (More information can be found at Bio-power Systems).
Heat from the earth can also be used as an energy source in many ways, from large and complex power stations to small and relatively simple pumping systems. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of molten rock called magma.
The diagram above shows how geothermal energy is harvested and turned into electricity. The process is described below:
- Hot water is pumped from deep underground a well under high pressure.
- When water reaches the surface, the pressure is dropped, which causes the water to turn into steam.
- The steam spins a turbine, which is connected to a generator that produces electricity.
- The steam cools off in a cooling tower and condenses back to water.
- The cooled water is pumped back into the Earth to begin the process again.
The video below gives a better understanding of how geothermal pumps can heat and cool buildings
Other lesser forms of renewables include; ocean energy, hydrogen and fuel cells. Ocean energy comes in two forms; thermal energy from the sun’s heat, and mechanical energy from tides and waves. Like geothermal energy, ocean thermal and mechanical energy can be used to generate electricity.
Hydrogen, the simplest and most abundant element, is very high in energy and an engine that burns pure hydrogen produces almost no pollution. This is evidenced by the fact that NASA has used liquid hydrogen since the 1970s to propel the space shuttle and other rockets into orbit. Hydrogen fuel cells are also used to power the shuttle’s electrical systems, the process involves combining hydrogen and oxygen to produce electricity, heat and water (which the shuttle’s crew drinks). Hydrogen cells can be compared to batteries as both convert the energy produced by a chemical reaction into usable electric power. However, fuel cells will produce electricity as long as fuel (hydrogen) is supplied, never losing its charge. Fuel cells are a promising technology for use as a source of heat and electricity for buildings, and as an electrical power source for electric motors propelling vehicles. Fuel cells operate best on pure hydrogen but fuels like natural gas, methanol, or even gasoline can be reformed to produce the hydrogen required for fuel cells.
To conclude, if we are to be successful in meeting the rising energy needs and mitigating climate change, we need to focus our resources on developing technologies that will provide clean and sustainable energy. Developing and using renewables technologies will benefit the world a great deal, especially those of us in Africa. Renewables not only serve as sources of energy, they can be used as tools to address many other pressing issues, including; improving energy security; reducing the health and environmental impacts associated with fossil and nuclear energy; mitigating greenhouse gas emissions; improving educational opportunities; creating jobs; reducing poverty; and increasing gender equality. Countries, for example Ghana and Nigeria, that are facing acute energy crises would be better off investing in renewable energy technologies because this has the potential to provide lasting solutions to the energy problem which occurs almost every year. The development of a 225 megawatt capacity wind farm in Ghana’s east coast is a step in the right direction.