Power bills
We received our power bill from AGL the othr day. How does your power bill compare with the same time last year. If you have photovoltaic panels on the roof it will likely be a lot lower than last year. The reason is simple. When the sun is shining strongly the photovoltaic panels produce much more power. Remember how wet and overcast and rainy last summer was month after month from October onwards. There just weren’t sunny days. This year has been an absolute contrast with sunny days and blue skies day after day after day. For a while there we could be forgiven for thinking it would never rain no matter what the Southern Oscillation Reading said to the contrary.
So we have been rebated for a lot more input power this year than last (46 kwh for our bill with a 1kw photovoltaic panel). But that is not the end of the story.
Photovoltaic panels only input power into the mains grid when you are using less power than you are producing. Up until that point any power you produce is used directly not input into the grid. You don’t get rebated for it at the high rate but you don’t get charged for it either on your power bill.
How much power do the photovoltaic panels produce that we use directly rather than inputting into the mains grid?
One way to get an estimate is to compare our mains usage power this year with the same period last year. We used 298kwh more mains power last year than this year.
It is also a good idea to think of any major differences that occurred between the two comparision periods. Well last year we were away for 10 days and things were generally turned off. This year we were away but we had a house sitter so thing weren’t turned off. So that would be a reason to less power last year than this year but in fact we used a lot more.
In total if we take the power we produced away from the power we consumed from the mains power in the same period we used nearly 50% more power per day last year than this year (13.0kwh/day compared to 8.8kwh/day this year for a home with 2 people)
It makes an even bigger % difference in cost because the rate for input power is so much higher than the rate for power drawn from the mains.
Since we installed our photovoltaic panels we have produced 3819kw in 11670 hours.
Doing the sums that means that since we installed photovoltaic panels one third of the power we produced by photovoltaics was input into the mains grid and two thirds was used directly by us instead of drawing power from the mains.
So what proportion of our total consumption of power is solar generated by the photovoltaic panels? 19% of the power we consume is PV generated and more is input into the grid.
12% of our power drawn from the mains is offset by the power we input into the mains.
If we think of the power we put into the mains as offsetting what we consume then 29% (or nearly a third) of the power we consume is offset by our 1kwh photovoltaic panel system.
What does that translate into in terms of cost? I’ll leave that for another day. It is made more complex because AGL have been steadily changing their charging system for power to load the charges on fixed costs.
Another point to note too is this doesn’t include the power saved by a solar hot water system which is a big saving. We’ll look at that another time too.