First Electricity Bill

I've just received my first Synergy bill that is totally under the regime of the new Solargain solar power system.

It's probably most accurate to compare like with like, i.e. my June 2017 bill vs the June 2016 bill, bearing in mind the following variables:

1. The minor fact that the June 2016 bill covers 61 days whereas the (latest) June 2017 bill covers 63 days

2. The supply charge has increased from $0.429/day to $0.448/day

3. The electricity tariff has increased from $0.234/unit to $0.241/unit (where 1 unit = 1 kwh)

4. This winter I am heating the house more, now that I have the use of the split system reverse cycle air conditioners.  (The impact of this may not be as large as it may appear because last year I was using fan heaters to do some heating, particularly in the middle of winter.)

5. The WA Government assistance payment (subsidy) has gone up from $34.42 to $36.71

With those caveats dealt with, the following is a summary of the outcomes:

Bill for June 2016: $156.05

Bill for June 2017: $ 55.20

Reduction:             $100.85

There are two elements to this reduction:

1. My usage of power from the grid was reduced by the extent to which I could directly use solar power.  I maximized this direct use by, for example, running the washing machine (with its concomitant use of hot water) at my prime solar time (10AM-12PM) on sunny days.

2. I received a credit of $55.54 for 778 kWh that I sold back to the grid.

Extrapolating from this one data point indicates a current saving of over $600 pa in my electricity bills, likely to increase as the Synergy electricity tariff increases (forecast to increase by 15% during the next 3 years), placing a greater value on my solar power.

This $600 pa is comfortably higher than the $414.50 pa that was required to make the investment of $8290 worthwhile under the assumption that the opportunity cost of the investment at a generous 5% pa.

Reports from the Fronius inverter data logger (available to me via the web) indicates an average production of 13.4 kWh per day for the month of May, not far off the 14 kWh predicted in the Solargain's proposal last January (below).  Note that June will be the nadir of production, which will increase as we progress into the summer.  That coupled with the fact that I will use less electricity in the summer means that I'll be expecting smaller electricity bills than the $55.20 for Apr-May.