Alternative energy sources


Co-generation system means a system that simultaneously produces power (electrical or mechanical) and cogeneration heat (for example to heat water) from the same fuel in a single thermodynamic process.

By harnessing more energy from one generation process, cogeneration increases energy efficiency and can reduce greenhouse gas emissions when compared to other power systems. The generator can be located close to where the energy is needed, enabling local or building-based systems to control their own power.

BASIX assesses co-generation systems based on:

  • Fuel that the co-generation system will use
  • Electrical output of the co-generation unit in kW
  • Efficiency of fuel to electricity conversion in %

Co-generation has been applied around the world in a variety of industrial and commercial settings. In some larger applications, the heat can be used for space cooling as well as for water and/or space heating (tri-generation).

In addition to proving the effectiveness of a simple cogenerated hot water supply in a multi-unit residential setting, Australian building designers and developers have been able to use the technology to provide a wider range of energy services to residential development, including low greenhouse emission air-conditioning. Tri-generation is already being considered for a number of major mixed-use development sites in Sydney.

Find out more about co-generation sizing and fuel types in relation to BASIX. 

How to measure efficiency of fuel to electricity conversion

Obtain this information from the supplier of your co-generation system. As a rule of thumb, efficiency of systems generally ranges from between 20% and 45%.

Diagram showing typical set up for Multi-unit co-generation system as well as energy outputsDiagram showing typical set up for Multi-unit co-generation system as well as energy outputs 


BASIX assesses photovoltaics as an alternative energy source based on the total rated output of all panels, expressed in kW. The rated output of an individual photovoltaic panel can be found written on the back of the panel. If the rating is not shown on the panel, the manufacturer or supplier of a system should be able to advise you of the rated output for the particular system.

A photovoltaic system (PV) is a type of energy system consisting of flat panels, typically made from silicon, which are installed in an unshaded location. These panels capture sunlight and convert this into electricity which can be used in your home.

Photovoltaic system size is generally limited by both cost and availability of suitable unshaded space. It is common to install a smaller photovoltaic system that meets only part of the total electricity demand of the building.


Before installing a photovoltaic energy system, ensure your home is designed as efficiently as possible. Many energy efficiency measures will be more cost-effective in reducing greenhouse gas emissions than a photovoltaic system.

Ensure that the area where the PV panels will be located is completely unshaded – shading of even part of a panel can greatly reduce output. Also ensure the panels are sloped at an appropriate angle and correctly orientated – the wrong slope or orientation can reduce annual output of power. Check the development controls relevant on the land neighbouring your house. It may be possible that your neighbour is permitted to construct a taller dwelling, which may overshadow your photovoltaic panels. Speak to your neighbours to see if they have any plans to redevelop their property in a way which may affect your solar access.

Aesthetic considerations are usually important when installing a photovoltaic system, and it is common for a system to be installed flush to the roof at a non-optimal slope, and even incorporated directly into the building fabric as roof tiles, in order to ensure the panels as unobtrusive as possible and do not detract from the appearance of the building.

Consult with your photovoltaic system supplier to determine the most appropriate system for your needs.

Fuel type

Fuel types for co-generation systems available in BASIX:

  • Biodiesel (an alternative fuel or fuel additive for diesel engines, which is renewable, biodegradable and has low greenhouse gas emissions)
  • Gas
  • Diesel

These fuel types are ranked in order of greenhouse efficiency, with biodiesel the most greenhouse efficient fuel type, followed by gas, then diesel.

If you are selecting the biodiesel option, the calculations assume that B60 biodiesel will be used (a blend of 60% biodiesel, 40% diesel). If the system is designed to take B100 (100% biodiesel), please apply through the BASIX Alternative Assessment process.


How do I size my cogeneration system?

A cogeneration unit produces electricity at an efficiency generally in the range of 20% to 45%, depending on the technology used. The input energy that is not converted to electricity is converted to heat, a large portion of which may be harnessed for such uses as hot water or space heating.

Typically in a commercial situation, a cogeneration unit should be sized and operated to match the actual heat requirement – so it is likely to run for longer periods in colder weather and shorter periods in hot weather. If it is oversized to produce more electricity, there may be excess heat which will be dumped because there is nowhere for it to be used.

A cooling system that can use heat (e.g. an absorption or desiccant cooling system) can be installed to increase the hours of operation in summer, when it is often more profitable to generate electricity.

It may be cheaper and simpler to size a cogeneration unit so that all of its electricity output is used within the development: negotiating contracts to sell power to an electricity retailer can add to complexity and costs.

Rated output

What is Peak kW output?

The rated electrical output of a photovoltaic system refers to the nominal peak watt rating of approved modules under standard test conditions (as identified by international standard IEC61215). This is not a 'per hour' rating of the system when installed at your project, but refers to the system's output under standard test conditions, which is an illumination level of 1000 W/m² (bright sunshine), a spectrum equivalent to AM1.5, and 25 degrees Celsius module temperature at the test.

BASIX assesses photovoltaic systems according to the electrical 'size' of the system (the rated electrical output expressed as peak kW) and the location of your proposed development.

A system's rated electrical output as stated by the manufacturer may be shown as peak kW, W, kW, Wp or Wpeak. If the rating is not shown on the panel, the manufacturer or supplier of a system should be able to advise you of the rated output for the system. This rating, expressed in kW, should be entered in the BASIX interface.

Converting from W to kW and from Peak kW to kWh

If the rated output of a system is expressed in watts (W), this figure will need to be divided by 1000 and entered as kilowatts (kW) in the BASIX interface. There is no need to provide BASIX with the average daily or kilowatt-hour (kWh) output of the system. BASIX will make this calculation for you based on the geographic location of the PV system.