Rooftop PV

With the increase in electricity prices, mainly due to the building of excess poles and wires, it is now cheaper to install PV cells on your roof. However the rules are designed to protect the coal industry, so any excess power you export to the grid, you will be paid only 6-8 c/kWh. PV wil cost you 14-17 c/kWh.  So because of the rules, you cannot afford to put in a system bigger than you need. However when battery storage is cheap enough the game will change completely, so leave room for expansion.

To work out the economics of PV on  your roof, you need to know how much sunlight you will be receiving.  

Sunlight energy

The Clean Energy Council gives the performance of PV cells in various locations, and the Bureau of Meteorology give data and charts for the insolation (sunlight energy) for any location in Australia in any year. 

They do not correlate exactly.

 Go to BOM and select "Solar exposure" and a location by text or map, then select the weather station.

The table produced gives the daily sunlight energy in MJ or kWh/sq m. for a day, month or year. Choose kWh and multiply by 0.85. This calculation will give the average daily energy in kWh/day from a 1 kW rated PV installation. 

The accuracy of this conversion factor is puzzling. The table to the right shows the figures for the capital cities according to the BOM and Clean Energy council. They vary from 0.75 for Darwin, to 0.92 for Hobart. Why would the warmest cities have the lowest efficiency?

Different experts give different figures:

So be aware of the accuracy of this calculation. + or - 10%.

Real output from PV 

The website shows various PV installations around the world

  Bureau Of Meteorology Clean Energy Council
All years Mean daily Ave daily

kWh/sq m

(flat plate)

kWh/1kW system

(Inclined cells)

Adelaide 4.8 4.2
Brisbane 5.2 4.2
Canberra 4.8 4.3
Darwin 5.9 4.4
Hobart 3.8 3.5
Melbourne 4.2 3.6
Perth 4.8 4.4
Sydney 4.6 3.9