Questions and Answers About Renewables

Renewable Energy

- Wind
- Hydro
- Hydrogen
- Solar
- Wave and tidal
- Energy efficiency

Renewable Energy Policy

Renewable Energy 

- Economic factors involved in electricity developments
- The Mandatory Renewable Energy Target (MRET)
- Emissions trading

Basslink

What is renewable energy?

Energy obtained from sources that are essentially inexhaustible, unlike, for example, the fossil fuels, of which there is a finite supply. Renewable sources of energy include water, wood waste, geothermal, wind, photovoltaic, and solar thermal energy.

Wind electricity

What is a wind farm?

A wind farm is a collection of wind turbines all in the same location and used for the generation of electricity.

What is wind energy?

Wind is a form of solar energy, created by the rotation of the planet, uneven heating of the atmosphere by the sun and irregularities of the Earth’s surface.

How does wind convert to electricity?

Wind energy spins the blades of a wind turbine. The blades are connected via a shaft to generator where the spinning motion is converted to electrical energy. The generator and gearbox sits on top of the tower inside a structure called a nacelle. A cone shaped hub, supporting the turbine blades, is attached to the nacelle at one end, and the nacelle revolves horizontally to allow the blades to face into the wind regardless of wind direction. The nacelle has a steel frame and fibreglass shell.

How big are modern wind turbines?

Modern wind turbines can be very large structures. Tubular steel towers, about 4 meters in diameter at the base and 2 meters at maximum height. Towers range from 66 meters to 90 meters and are usually assembled in 3 stages.

Substantial concrete foundations are required to ensure the structures are stable.

The blades can be very large spanning greater than 66 meters in diameter, which is larger than the span of a jumbo jet. There are 3 blades per tower and they are made from fibreglass and epoxy resin. Blades spin at 21 revolutions per minute.

Where are wind farms located?

The first step in developing a wind farm is to asses and understand the available wind resource. This involves taking detailed measurements over an extended period to establish the average wind speed on the proposed site. The power output of a turbine is a function of the cube of the wind speed. This means that small increases in average wind speed produce large increases of power output. Area’s with an average wind speed of about 7 meters per second (25 kilometres per hour) or higher can be potential wind sites.

Typical elements of a wind farm include:
· Access roads, fences and associated infrastructure;
· A control room and other buildings such as maintenance shops;
· Wind turbines placed on towers of suitable height to generate electricity;
· An electrical substation located adjacent to wind turbines;
· Underground cables from the wind turbines to the substation.

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Hydro electricity

What is a dam?

Dams are the most recognisable features of hydro electric schemes. They are constructed to create water storages that provide a continuous fuel to spin the turbines.
The type of dam to be built depends on a range of factors:
- Height (or head) of water to be stored
- Shape and size of the valley at the proposed construction site
- Geology of the valley walls and floor
- Availability, quality and cost of construction materials
- Availability and cost of labour and machinery.

How is a dam constructed?

Dams can be grouped into 2 major categories on the basis of their composition – embankment dams (rockfill and earthfill) and concrete dams.

Engineers must first de-water the section of river valley in which they wish to place the dam. This is usually achieved by diverting the river through a tunnel. 

Work on diverting the river starts in summer when river levels are low. Earth-moving equipment is used to build a small dam (called a cofferdam) upstream of the main construction area. This acts as a barrier to the river and causes it to flow through the diversion tunnel.
Another cofferdam is built downstream of the main damsite to prevent water flowing back into the construction area.
Pumps are used to remove any water that seeps through the cofferdams.

Concrete-faced rockfill dams require a footing (or plinth) to be constructed around their upstream edge. The plinth is made from concrete and serves as a foundation or connection between the dam and the valley walls and floor. It has an important role in preventing water leakage around the edges of the dam. The area under the plinth is waterproofed by drilling holes and pumping cement grout into cracks in the rock. The thin concrete face on the upstream side of the dam is connected to the plinth via stainless steel and rubber seals called waterstops.
During dam construction the associated power station and intake works are also being built. When the dam is completed the diversion tunnel is closed and the lake begins to fill. The closure of the diversion tunnel has two phases. During low flow a large re-usable steel gate is lowered across the entrance. The diversion tunnel is then permanently blocked off by the construction of a concrete plug.
In some instances dewatering outlets are built into the plugs so water can be released during an emergency.

How is water transferred to the power station?

Water is transferred to the power station from nearby storages via long overland tubular pipes called Penstocks, or, intakes down vertical shafts and or inclined tunnels. In some instances water is transferred via Flumes or open air channels whose floors and walls are made from re-inforced concrete. As water enters the power station it passes through a large inlet valve that can be quickly opened or closed. Each valve opens to a large spiral casing made of steel. These direct water onto the blades or buckets of the turbine. Water leaves the turbine and flows out of the station via the tailrace. 

What is hydrogen?

Hydrogen is the most abundant element in the Universe. The hydrogen atom is the simplest building block of all molecules. In its normal gaseous state, hydrogen is colourless, odourless and tasteless.
For transport, heat and electricity, hydrogen is zero – emission alternative to fossil fuels and can be created using renewable energy. Hydrogen is establishing a foot hold through out the world with renewable based countries like Iceland aiming to become a hydrogen society by 2030.
A distinct advantage of hydrogen is that it can be stored. As a storage medium, it can be incorporated with renewable energy to power transport and produce electricity without emitting greenhouse gases, the only by product being water.

What is Solar Power?

Solar power describes a number of methods of harnessing energy from the light of the Sun. It has been present in many traditional building methods for centuries, but has become of increasing interest in developed countries as the environmental costs and limited supply of other power sources such as fossil fuels are realized. It is already in widespread use where other supplies of power are absent such as in remote locations and in space.

What is wave and tidal power?

Wave power refers to the capture of (ocean) wave energy to do useful work including electricity generation, desalination, and filling a reservoir with water. Wave Power is renewable energy and is a form of solar energy transferred to water by the wind. Though often co-mingled, wave power is physiologically distinct from the diurnal flux of tidal power and the steady gyre of ocean currents which are powered by the earth's rotation.

Tidal power is a means of electricity generation achieved by capturing the energy contained in moving water mass due to tides. Two types of tidal energy can be extracted: kinetic energy of currents due the tides and potential energy from the difference in height (or head) between high and low tides.

Energy Efficiency

What is energy efficiency?

Refers to programs that are aimed at reducing the energy used by specific end-use devices and systems, typically without affecting the services provided. Such savings are generally achieved by substituting technically more advanced equipment to produce the same level of end-use services (eg lighting, heating, motor drive) with less electricity.

What are some examples of energy efficiency?

Businesses have introduced energy efficient measures to reduce the consumption of fossil fuels and increase the efficiency of their use of electricity. Battery and hybrids vehicles are part of the solution and a variety of energy efficient measures have been introduced in Australia via a building management program.

What is Basslink?

Basslink is an undersea power cable that will link Tasmania to mainland Australia’s electricity network – National Electricity Market (NEM). The nearly 300 klm long cable will transmit direct current (DC) electricity with electrons flowing in one direction. A smaller cable (known as metallic return) will be laid along side the main cable to allow completion of the circuit via a return current.
Basslink will have an average power transfer capacity of 480MW but will be able to be operated for short periods up to 600MW.
Connection to the NEM will allow Tasmania to export its renewable energy to mainland consumers and prevent Tasmania form exhausting its water levels during times of prolonged drought.

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