Finally!

Good things come to those who wait!

Early January finally delivered the payoff, my spreadsheet indicating that, for three months running, Oct to Dec '14, my solar credit exceeded my charged consumption, meaning there was every prospect of an issued bill in credit. It's worth noting the figures I've calculated and track in my spreadsheet ignore my hot water ("J" tariff) and daily connection charges, so the final, actual bill result, may not be as significant as my figures suggest. I decided to ignore those items in my calc's as there's no direct involvement in the solar/consumption relationship. The hot water is charged at a lower rate and is only consuming at night so my solar production can't contribute to any overall change to that cost. Similarly the connection charge can't be affected by my solar production.

The Bill!

So my official issued bill summary looked like this:

My Calculations

My spreadsheet summary, based on my "scheduled" readings (first day of each month) looks like this:

Legend:

1.   Total Cons.                 actual electricity in kWh used in house (calculated**)

2.   Charged Cons.            kWh I paid to buy from the grid (from the meter)

3.   Total Solar                  kWh my panels produced

4.   Exported                    kWh sent to grid

5.   Charged Cost              the cost of 2. @ approx 36c/kWh (incl GST)

6.   Solar Credit                the value of 4. @ 23.6c/kWh

7.   Total Cost                   what it would have cost me to buy all the electricity used at 1.

8.   Billing                         the difference between 5. and 6.

9.   Actual Savings            the difference between 7. and 8.

10. Export:Prod                the proportion of solar exported (lower is better)

11. Accumulated savings   the progressive sum of 9.

12. Solar Surplus?            the difference between 3. and 1. (more is better)

13. Prog. Surplus             the progressive sum of 12. Shows cons/prod profile

** to calculate my actual consumption the following formula using the above figures is used:
1. = 2.+(3.-4.) 

i.e. Total consumption=Charged Cons. + (Total Solar-Exported)

Consumption Strategy

As I'm a "Customer Group 4" participant in the (SA Gov.) "Solar Feed-in Scheme" I only receive 23.6c/kWh for any electricity exported to the grid. As this is less than (cheaper) the electricity I purchase (~36c/kWh) it's to my benefit to use as much of my (cheap) solar electricity as possible, hence I monitor the "Export:Prod" figure. In order to reduce this figure I take steps to ensure appliances are used during the day ("solar time") rather than at night, these include power tools, dishwasher, washing machine and electric vehicle charging, etc.

When the actual (SA Gov.) "Feed-in" subsidy ceases at the end of September 2016, I'll only get the "Minimum Retailer payment" which is a mere 5.3c/kWh (I appear to be getting 7.6c/kWh ATM). This will have a significant impact on my financial model, reducing my savings(!!), and means I'll have to take steps to minimize the Export:Prod figure further, possibly adapting storage strategies I'm currently evaluating and will elaborate in future posts.