Renewable sources of energy

What are infinite energy sources

• Energy sources that can last indefinitely without a reduction in their supply

Why are infinite energy technologies necessary

• To provide energy for the current generation and future generations

What process produces the Sun’s energy

• Nuclear fusion reactions

How much energy do the Sun’s nuclear fusion reactions release

• About 3,800 million million million million units of energy

How much of the Sun’s energy output does Earth receive

• 1/200,000,000,000 of the Sun’s total energy output

How much of the solar energy reaching Earth could meet global human energy needs

• Just 1% of the energy reaching Earth

What limitation prevents solar energy from being collected at all times

• It cannot be collected at night

What factors cause sunlight to vary on Earth

• Geographic location, time of year, time of day, and weather conditions

What technological improvement is needed to make solar energy more effective

• More efficient harnessing techniques, particularly in battery storage

How do solar heat collectors work

• Black tubing absorbs heat from the Sun, heating water moving through it

What is a common use of solar heat collectors

• Warming swimming pool water

To what temperature can water be heated by flat plate collectors

• Up to 100°C

Where are solar heat collectors commonly used

• For hot water supply in homes, hospitals, industry, and agriculture

What happens when solar radiation is insufficient to maintain water temperature

• Another energy supply (e.g., electricity) is used to maintain temperature

What do photovoltaic cells (PVs) do

• Convert solar energy into electricity

What are photovoltaic cells primarily made of

• Silicon, a semiconductor

What is a semiconductor

• A material that will conduct electricity only under certain conditions

How are semiconductors made conductive in PV cells

• By incorporating two types of impurities into silicon

What impurity creates an n-type semiconductor in silicon

• Arsenic or phosphorus, which provide extra electrons for conduction

Why are n-type semiconductors able to conduct electricity

• They have free electrons available to participate in conduction

What impurity creates a p-type semiconductor in silicon

• Boron or aluminium, which have a shortage of outer valence electrons

What happens when n-type and p-type silicon are in contact

• A p-n junction is formed

What happens in a p-n junction in the dark (away from sunlight)

• Excess electrons from the n-type silicon drift across to fill spaces in the p-type silicon

What charge does the n-type side of a p-n junction develop and why

• Positive charge, because it loses electrons

What charge does the p-type side of a p-n junction develop and why

• Negative charge, because it gains electrons

What does the charge separation across a p-n junction produce

• An electric field across the junction

What happens when solar energy hits a photovoltaic cell

• Energy excites electrons in the p-type silicon, moving them across the junction to the n-type silicon

How does a photovoltaic cell generate electricity for an external device

• If a wire is connected across the junction, the moving electrons create an electric current that powers the device

How does the consumer cost of generating electricity from photovoltaic (PV) cells compare to power stations

• It is quite high, but some costs are offset by reduced electricity bills

What is the cost trend for photovoltaic cells

• Costs are falling, making them more viable for future generations

How are PV cells used in many Melbourne houses

• Houses use PV cells while staying connected to the grid, exporting excess electricity and drawing from the grid at night or on cloudy days

What is a major environmental advantage of operating photovoltaic cells

• They produce zero pollution while operating

What are two environmental concerns linked to photovoltaic cells

(1) Energy use and pollution during manufacturing

(2) Sand mining for silicon

What is the efficiency range of photovoltaic cells

• 15%–40%

How is wind created on Earth

• Sunlight heats air unevenly; warm air rises, cooler air moves in to replace it, creating circulation

Give a local example of wind formation

• Cool sea breezes moving over land as it heats up

Give a global example of wind formation

• Hot air rises at the equator, and cooler air is drawn in from the poles

What factors influence global wind patterns

• Earth’s rotation, ocean currents, and different land masses

How much potential energy could wind produce compared to humanity’s needs

• Up to 10 times more energy than humanity uses per year

What are wind turbines used for

• For mechanical tasks (e.g., wind pumps) and to generate electricity

What are the two main types of wind turbine designs

• Vertical axis and horizontal axis

How do wind turbines generate power

• Wind spins propeller blades, which drive a shaft connected to a mechanical device or electric generator

What conditions are required for efficient wind electricity generation

• An unobstructed, steady flow of wind

Which country leads the way in electricity generated by wind

• Denmark

What percentage of Denmark’s renewable and total electricity is from wind

• About one-third of its renewable energy, and 4.9% of total electricity

How many wind turbines did Australia have in 2015, and where were most located

• 2,062 turbines in 76 locations; over half in South Australia, and 25 in Victoria

How is hydroelectric energy produced

• Water stored in dams flows through a turbine, spinning a shaft connected to an electric generator

What factors affect electricity generation in hydroelectric systems

• The volume of water flowing through the turbine and the vertical distance the water falls

How is energy converted in a hydroelectric dam

• Gravitational potential energy of stored water → kinetic energy as it falls → electrical energy via the generator.

What is an operational advantage of hydroelectric power

• It can be brought into operation quickly and easily, and can be turned up or down quickly

What is the efficiency rate of hydroelectric power

• Approximately 70%

How much of the world’s electricity production comes from hydroelectric power

• About 19%

What percentage of total global energy comes from hydroelectric power

• About 10%

What is a major environmental advantage of hydroelectric power

• It is clean and emits no particulate pollution

What is a social disadvantage of hydroelectric dams

• Humans may be displaced when the initial dam is built, and large areas of occupied land are flooded

How do hydroelectric dams impact wildlife habitats

• Storage, diversion, and release of water disrupt natural water flows, affecting aquatic and terrestrial habitats

How does diverting rivers and lakes for hydroelectric dams affect the environment

• Water is often diverted from its natural course to maintain optimum levels for turbines, disrupting ecosystems

How does dam water release affect downstream aquatic species

• Release water is usually cold and from the bottom of the dam, disrupting natural temperature and affecting species downstream

How is tidal energy similar to hydroelectric power

• Both use moving water to spin turbines that generate electricity

How is electricity generated from tides

• A dam wall is built across a bay or inlet; moving water passes through turbines to generate electricity

Can tidal energy use both incoming and outgoing tides

• Yes, electricity can be generated from both incoming and outgoing water

What is required to generate large amounts of tidal power

• Large volumes of water

What are the main disadvantages of tidal power

• Few suitable sites, expensive to build, and massive disruption to aquatic ecosystems

What factors determine the power a wave can produce

• The wave height and period (time between successive wave fronts)

How do wave energy systems generate electricity

• Using floats that move with the waves to compress air or lift fluid, driving generators

What are the main disadvantages of wave energy systems

• They can be damaged by storms and corroded by salt water

Where does geothermal energy come from

• High pressures and temperatures deep within the Earth

Why do some areas have high geothermal activity

• The Earth's crust is thin, with cracks and faults allowing heat to approach the surface

How is geothermal energy extracted

• Water seeps down cracks, is heated, and re-emerges as hot water or steam, which drives turbines to generate electricity

Can geothermal energy be used without water reaching the surface as steam

• Yes, the heat can be extracted without steam emerging

Give an example of high geothermal energy use globally

• In Iceland, 95% of buildings use geothermal energy

Give a local example of geothermal energy use in Australia

• Portland, Victoria: heats public swimming pool complex and 14 buildings

Is geothermal energy considered renewable or non-renewable

• Locally non-renewable (removal can deplete the source); globally renewable due to extensive availability

What are the environmental advantages of geothermal energy

• Clean source of energy

What are the main environmental disadvantages of geothermal energy

• Local depletion of resource, possibility of land subsidence, potential ecosystem damage

What is a limitation of geothermal energy in Australia

• High-grade sources are rare and expensive to exploit

What is biomass energy

• Energy derived from material produced by living things, such as plants and animals

Give examples of biomass materials

• Waste from agriculture

• Forestry products

• Industrial human

• Animal wastes

How can biomass be used directly

• Wood can be burnt for heating

How can biomass be used to produce fuels

• It can be converted into biofuels for transport or biogas for heating and electricity

Where does the energy in biomass originally come from

• Solar energy, converted into biomass through photosynthesis

What is biogas and how is it produced

• Gas produced from the breakdown of plant and animal waste in the absence of oxygen, usually containing ~60% methane

How can biogas be used

• Burnt in power furnaces, heaters, engines, or used to generate electricity

Who relies on biomass for heating and cooking

• About 30% of the world’s population, mainly in developing countries

What are the disadvantages of using wood for energy

• Low efficiency; ~90% of heat lost in open fireplaces; smoke can cause air pollution; unsustainable use can lead to deforestation, soil erosion, and soil salting

What determines if biomass is renewable

• The rate of deforestation—if used sustainably, it is renewable; otherwise, it is not

What is ethanol and how is it produced

• A biofuel made from materials containing sugars, starch, or cellulose, produced via fermentation and distillation

How is ethanol used in transport

• Blended with petrol to reduce petroleum use; in Australia, a 10% ethanol blend is available for most cars

What are the disadvantages of ethanol as a biofuel

• Production can lead to photochemical smog, reduced tropospheric ozone, high costs, and competition with food production

How abundant is hydrogen on Earth

• It makes up 90% of Earth’s atoms and about 75% of its mass

How much hydrogen exists as gas in the atmosphere

• Very little—only about one part per million. Most hydrogen is bound in water or carbon dioxide

What type of reaction occurs when hydrogen combusts

• An exothermic reaction, releasing heat energy

How does hydrogen compare to natural gas in density and energy content

• Hydrogen gas is about 1/8 the density of natural gas and has about 3 times the energy content per unit mass

What is the byproduct of burning hydrogen in air

• Water, which removes air pollution problems

How is hydrogen gas commonly produced

• By electrolysis of water, which splits water into hydrogen and oxygen

What is a limitation of producing hydrogen via electrolysis using electricity from fossil fuels

• It does not solve the environmental problems associated with fossil fuel use

Why is hydrogen energy currently expensive and challenging

• Generating electricity for electrolysis via renewable sources (wind or solar) is costly, and fossil-fuel-derived electrolysis does not reduce environmental impacts