Home solar update

The 1.5 KW solar system on our roof has just passed a good round number in its total output – 12 000 kWh, or 12 MWh – and that’s a good enough excuse for another update.

We installed the system in May 2011 so it has produced an average of 6.26 kWh per day for five years. That’s a useful percentage of a household’s consumption: according to Ergon’s figures on the back of our power bill, the average consumption for a household like ours is about 20 kWh per day, so our panels are producing nearly a third as much as we use.

Of course, we use some of our solar power during the day and export the rest of it, and then use Ergon’s power all night, so our net benefit doesn’t quite reflect those numbers. I did the sums a year after the installation and came up with a figure of $700 p.a., with the expectation that that would increase if power prices increased. Using the same logic now for the five year period, we find:

  • Total produced = 12 000 kWh (6.26 kWh/day)
  • Total exported to grid ~ 5200 kWh, for ~ $2300 income
  • Total PV power used at home ~ 6800 kWh, for ~ $1700 savings
  • Total benefit ~ $4000

In 2011 I said:

All in all, making the best guesses I can for the unknowns, pay-back time for the whole project (PV system and switchboard) looks like being in the 5 – 8 year range. That’s perfectly acceptable … Of course, if the electricity tariff rises (hands up everyone who thinks it is going to fall? No, my hand didn’t go up either), pay-back time will drop accordingly.

The cost for the system was $3500. Even if my new figures on exports and savings are on the optimistic side, it looks like our system has paid for itself, just a few months ahead of the earliest date I anticipated.

That’s pleasing, of course. The thought that it will continue to  bring us that $800 p.a. benefit indefinitely is even more pleasing. So is the thought that we have done our little bit to reduce CO2 emissions, and that it has basically cost us nothing to do so.

Was there any downside?  Maintenance costs? Repair costs after the cyclone? None at all. It just sits there quietly on the roof, collecting photons and turning them into useable electricity, day after day.

For the record, the general tariff was 19.4 c/kWh when we installed the system five years ago, had risen to 30.8 c/kWh by July 2014 and has now (surprisingly) dropped back to 22.3 c/kWh. In May 2011 the “service fee” or “daily supply charge” was only $23 per quarter, whereas by May 2014 it had risen to 55 cents per day ($49 per quarter). It has continued to rise and is now $1.07 per day, closing in on $100 per quarter. The supplier is simply trying to maintain revenue in the face of flat or falling demand and the service fee is a favoured strategy – but that’s a topic for another day.

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