Choosing a Renewable Energy System

WIND

Wind energy is harnessed when wind drives the rotation of the blades of a wind turbine, turning a generator to produce electricity.

Wind energy has a long history with agriculture in Australia, with many farmers using windmills to pump bore water.

Modern wind turbines range in size from small turbines that can produce a small amount of power for houses, boats and caravans, to large grid-connected turbines of over 2 megawatts capacity.

Wind power is generated when the wind blows, and is therefore considered a ‘variable’ source of energy and will be well suited to combining with energy storage to match generation with use.

When considering the potential for wind energy on-farm, growers should consider:

• the amount of energy used,
• the annual wind speed of the site
• A suitable site to locate a turbine (or more than one) and
• The potential to export power to the grid.

The Queensland Governments, MinesOnlineMaps website includes Renewable Resources maps which show the average annual wind speeds wind roses throughout Queensland along with suitable infrastructure.

Ground-Source Heat Pumps

Ground-sourced heat pumps transfer heat between the building and the ground, and make use of fairly constant year round sub-surface temperatures – typically between 10 and 15 degrees celcius.  They are well suited to heating and cooling applications.

This constant ground temperature means that the temperature difference between the condenser and evaporator can be reduced, requiring less energy.  For example, on a hot day of 40°C where a conventional system will need to provide a temperature difference of 16 degrees to get a target temperature of 24°C, a ground source heat pump will only need to provide a difference of 9°C.

The installation of ground-sourced heat pumps can be more expensive as the technology requires heat transfer pipes to be buried deep in the ground for the heat exchange to occur.

Solar Thermal Heat

Solar Thermal Heat is where the sun’s energy is harnessed to provide heat which can be used directly or used to drive a turbine to generate electricity.

The most common application of solar thermal heat in Queensland is the use of solar hot water systems to heat water for homes, pools and businesses.

For the generation of electricity, the sun’s energy is reflected by a number of mirrors onto heat collectors, which concentrates the energy to achieve high temperatures and pressures, hence the name Concentrating Solar Thermal Power (CSP).   The high temperature and pressure is used to drive a turbine, generating electricity.  The two main forms of CSP are:

• Power Tower: where light is reflected from thousands of ground-mounted mirrors to a collector at the top of a tall tower, generating very high temperatures and pressures.
• Parabolic Trough: where long mirrors, or highly polished metal troughs reflect sunlight to a solar collector at its focal line. The troughs can be six metres in diameter and hundreds of metres long.

Solar thermal heat requires direct sunlight to generate high heat.   As such, they are a ‘variable’ technology and extensive research and development is underway to develop cost-effective thermal storage solutions, such as molten salts to enable energy to be generated outside daylight hours.

CSP Aarlborg presented an outline of the Sundrop Farms project in South Australia, including how their solar thermal Power Tower technology will be used to provide electricity, steam and desalination to produce irrigation water for the site.  Also presented were smaller, scalable solar thermal and solar hot water technologies. Full presentation HERE.

The Queensland Governments, MinesOnlineMaps website includes Renewable Resources maps which show the average solar insolation including Direct Normal Irradiance (DNI) throughout Queensland along with suitable infrastructure.

Waste to Energy (Biogas)

Waste to Energy refers to a process where gas is captured from anaerobic digestion then either:

• used directly to generate heat
• burned in a turbine to produce electricity
• a combination of the above two, generating electricity and heat in a process called cogeneration;
• use of an absorption chiller to generate electricity, heat and cool in a process called trigeneration.

Utilitas outlined their technology to harness biogas, including a 200kWe Queensland case study, a 1.2MWe project in development and sought interest from farmers for a utility-scale plant in the Lockyer Valley. Full presentation HERE.

Qantum presented their biogas technology including an egg farm and abbattoir case study, including the potential to use biogas to manage peak demand, and its potential to combine with solar power and batteries for greater efficiencies and demand management. Full presentation HERE.