Brett,
I would first of all seriously recommend looking at your power consumption habits BEFORE going down the path of a grid-tie solar system. You need to know how much power you are typically using, and during what time of the day.
To do this, I would recommend installing one of these -
http://www.jaycar.com.au/productView.asp?ID=MS6155
... it's a household Power Monitor, which also stores all the power useage data so that you can plug it into your computer and see WHEN you are using your electricity throughout the day/week/month/year.
If you have a pool, then your typical pool pump ALONE will chew through the power that a 1.5kW solar system will produce each day.
To work out how much electricity a solar system produces on average each day, you need to multiply the power of the system by the number of "peak sun hours" you get in your location - which in the gold coast is 4.5 hours on average (less in winter, more in summer).
So - a 1.5kW system will produce around about 6.75kWh per day.
A typical home, without a pool, and only occasionally using aircon, will use about 20kWh per day on average.
In queensland, you dont yet have "GROSS METERING".... which is where every single watt your solar system produces is fed back into the grid, and you get a credit for all of it. You then buy all your electricity as per normal
Queensland currently only has "NET METERING".... which is where the power produced by the solar system powers your house first, and then anything left over is fed back into the grid, and you only get a credit for what is left over. You only buy electricity when your solar system is unable to meet the power needs of the home.
With GROSS metering, you would get credited for the full 6.75kWh per day, and still buy the typical 20kWh per day.
With NET metering, you would only get credited for around 3kWh per day (depending on how much power your home is using during sunlight hours, i've assumed the house uses around 3.5kWh during the daytime), and would buy only 16-17kWh per day (the missing 3-4kWh has been supplied by the solar system).
.... so from this you can start to work out the savings.
To do this you need to know the rate at which your electricity provider gives you credits for feeding power back into the grid.
Currently, the highest credit provided in QLD is $0.52/kWh from AGL.
So... with a NET metered, 1.5kW grid tied solar system, on a typical household which uses around 20kWh per day.... your power bill would be reduced by:
- 3.5kWh credited at $0.52/kWh = $1.82
- 3.5kwh in reduced normal power usage at $0.19/kWh = $0.62
=== total saving approximately $2.43 per day, or $220/quarter.
.. based on QLD, net metered 1.5kw system, $0.52/kwh credits from AGL.
... in NSW, because we have gross metering and $0.60/kWh credit from our providers... that saving would be ~$370/qtr for a 1.5kW grid tied solar system.
Yeah all of that is pretty confusing, i know.... but at least it can help you work out the savings you might get based on each sized solar system.
... i just noticed you've given your quarterly power useage of 1800kWh. This is around 19kWh/day, so you are a pretty average power user, and my calculations above will work relatively well for you.
I would still recommend installing the household power monitor first, so that you can work out how much power your house is using each week during the daylight hours when a solar system would be producing power... you can then use these figures to work out how much credit a solar system would provide you with.
However - my rough estimate is that you would reduce your power bill by around $800per year.
BUT - the big thing to remember is that these savings all assume that you dont change your power useage habits after installing the solar system. The problem MANY users have is that after installing a grid-tied solar system, they think they have free power - and so they start leaving things turned on all the time and wasting electricity, thus reducing the savings they wouldve otherwise had.
