Stand Alone Power Systems

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Relationship between WTG size & Time, EWEA (click to enlarge)
Relationship between WTG size & Time, EWEA (click to enlarge)
Wind resource of Australia (click to enlarge)
Wind resource of Australia (click to enlarge)
Wind speed versus height (www.brighton-webs.co.uk) (click to enlarge)
Wind speed versus height (www.brighton-webs.co.uk) (click to enlarge)
Solar resource of Australia (click to enlarge)
Solar resource of Australia (click to enlarge)
Concentrating PV (click to enlarge)
Concentrating PV (click to enlarge)
Thin film PV technology (click to enlarge)
Thin film PV technology (click to enlarge)
Photo bioreactors, Arizona State University (click to enlarge)
Photo bioreactors, Arizona State University (click to enlarge)

Renewable Energy

Wind Power

Wind energy conversion is the process of converting kinetic energy from the wind into useful electrical energy via a wind turbine. Wind turbines are a clean and renewable energy source which makes an environmentally friendly method of generating electricity. Wind power is generally one of the lower cost renewable energy generation methods, this is one reason why there has been considerable growth in the wind power market.

How big are wind turbines?

Wind turbines comes in a variety of sizes from very small 1-2 m rotor diameters with rated power of kilowatts up to very large wind turbines with 120+ m rotor diameters and up to 5+ megawatts.

Why are wind turbines so large?

The energy extracted from the wind is proportional to the wind speed and the swept area of the wind turbine rotor, in other words the larger the wind turbine the more energy is extracted from the wind for a given wind speed. The following formula gives the relationship for the theoretical power in the wind.

Power = 0.5 x Swept Area x Air Density x Velocity3

Why are wind turbines so high?

The hub heights of wind turbines range from 10 m up to 100 m above the ground.  The higher the wind turbine hub height generally the faster the average wind speed, this is due to the decreasing effects of terrain and vegetation on the wind flow. The following formula can be used to determine the wind speed at a specific height given a known height and average wind speed.

Solar Energy

Solar energy is ‘generated’ by converting solar radiation from the sun into electrical energy utilising photovoltaic (PV) panels. When solar radiation incidents a piece of silicon an electrical charge is created this is the process by which PV panels can be used to generate renewable electricity. Solar energy is an intermittent renewable energy that fluctuates with the cloud cover and exhibits seasonal changes.

PV orientation

PV panels are mounted in a north facing direction in the southern hemisphere to capture the suns rays as it moves from east to west. To maximise the solar radiation incident on the PV panel a ‘tracker’ is used, this is either a single or two axis mechanism that allows the PV panel to track the sun.


Dual axis tracking at Nellis Air Force Base

Dual axis tracking at Nellis Air Force Base

Types of technology

There are three main types of PV panels, traditional flat plate silicon cells, thin film technologies and concentrating PV where optics are used to concentrate solar radiation onto a small area of highly efficient PV cells. The efficiency or how well PV panels convert solar radiation into electrical energy varies from 6 % through to 22 %. Over the past few years, production capacity is thought to have grown at an average of 48% each year and cumulative global production is now at 12.4 Giga Watts (GW).

In attempting to reduce the cost of solar energy concentrated PV uses low cost lenses and mirrors to focus solar radiation onto a more costly but small and highly efficient PV cell.

Concentrating PV

Thin film solar cells use layers of semiconductor materials only a few micrometers thick, this potentially allows more price competitive systems because they can be manufactured with dramatically less material, shorter supply chains and cheaper, faster processes. Thin film technologies can satisfactorily operate across Australia with specific advantages for locations with higher ambient temperatures, more varied weather and cloudy locations.

Biodiesel

Biodiesel is a significantly lower carbon intensity substitute for traditional hydrocarbon based diesel fuels, such as oil. 

How is biodiesel created?

Biodiesel is produced from a variety of organic feed stocks either from plant matter, animal products or algae. Biodiesel can be created from virgin oil crops such as soya bean, canola, jatropha or palm oil. Biodiesel can also be created from animal products including tallow, lard and fish oils. The third source often referred to as a second generation biodiesel comes from algae processes. This approach can produce at least 15 times more oil per hectare than plant based alternatives like jatropha, canola and palm, and are 20 times as productive as corn and soy. Producing biofuels from algae has the advantage of not competing with arable land needed for the production of edible crops.

Biodiesel can be used as a substitute for ordinary fuels, to run automobiles, aircraft and as fuel to generate electricity in conventional diesel generators.

Energy Storage

Energy storage technologies give a power system the ability to store excess energy and recover at a later, preferably peak time.

Why does energy need to be stored?

Energy needs to be stored to allow energy supply at all times of the day regardless of weather conditions that affect renewable energy generation. For example solar power is available only when the sun is shinning and having energy storage would allow this power to be used when needed. Energy storage potentially allows greater penetration of renewable sources into the electricity grid instead of limiting wind farm output this excess energy can be diverted to storage.

What are the major types of energy storage?

In addition to batteries there are a range of storage technologies all which have there own advantages and limitations. All storage technologies suffer some losses in the system for example flywheels lose energy from friction and batteries lose energy from the conversion from electrical – chemical – electrical energy.  Pumped hydro is currently the world’s largest source of energy storage. The main types of energy storage are:

  • Chemical, such as Hydrogen and Biofuels
  • Electrochemical, such as ordinary lead-acid batteries and flow batteries like the VRB on King Island
  • Electrical, such as supercapacitors
  • Mechanical, such as flywheels and pumped hydro storage
  • Thermal, such as molten salt used in solar thermal energy plants or chilled water storage used in building cooling systems