The new solar PV system was connected 24 days ago and I’ve been taking readings from the electricity meter and the inverter for 22 of those days and recording the whole lot on a spreadsheet.
For the first 7 days, I was tweaking the system, e.g. by turning off the hot water system and doing a daytime water heating boost, but I gave that away and went back to normal, i.e. normal daytime/evening use in the house and off-peak water heating at night (although I am being more careful with hot water use (shorter showers…ugh…do love my hot shower).
So the results that follow are for the next 15 days of normal use.
OK, first up—last years usage figures, which have been fairly typical over the years. I’ve calculated this at current supply charges for comparison (there were 2 cost increases last year and another one at the beginning of this year).
Average consumption per day (2012):
House 5 kWh costing $1.26 per day
Hot water 5 kWh costing $0.83 per day
Total consumption = 10 kWh per day, costing $2.09 per day
Add in supply cost of $0.92 per day = $3.01 = total cost per day
15 days on solar panels:
Average consumption per day:
House 2.0 kWh costing $0.50 per day
Hot water 4.6 kWh costing $0.76 per day
Total consumption = 6.6 kWh per day, costing $1.26 per day
Add in supply cost of $0.92 per day = $2.18 = total cost per day
You can see that consumption in the house has dropped by more than half—that’s energy coming from the sun—and water heating is marginally lower (shorter showers).
(Note that heating hot water at night, even though on the off-peak rate, is now more expensive than powering the house—how can I get the sun to shine at night?)
Now, here’s where it gets interesting.
The solar panels have generated an average of 13.3 kWh per day (just over twice what I used), meaning I exported an average of 6.7 kWh per day to the grid. The inverter gives me this reading at the end of every day, before it shuts down.
The current feed-in tariff (what I get credited for exporting to the grid) is (a lousy) $0.08 per kWh. Yes, you read that correctly—8 cents per kWh! And they sell it back to me at 25 cents per kWh. My electricity! Nasty them!
So I earned the magnificent sum of 6.7 x $0.08 = $0.54 per day for the electricity I exported to the grid.
54 cents per day credit. Not exactly an overseas holiday in there.
Take that off the daily usage cost ($1.26) and you have $0.72 per day
Add in the supply charge ($0.92 per day) and the all-up cost is $1.64 per day.
Go back to the 2012 figures and compare that to $3.01 per day.
Savings of $1.37 per day. ($3.01 minus $1.64)
Is that good? Well…
It’s worth $500 per year. Still no overseas holiday, but better than nothing (an iPad maybe?).
The catch is in that supply charge. No matter how much energy I save or how much energy I export to the grid, I can’t avoid that supply charge and I can’t afford to go off-grid.
Here’s another way I looked at it.
Express the daily export value (54 cents) as a percentage of the daily supply cost (92 cents).
54/92 x 100 = 59%. So what I’m exporting to the grid is saving 59% of my daily supply charge.
That’s not including what I’m saving in powering the house by the sun (in the daytime).
Oh, well, that’s better…..
I should mention that I’m calculating the daily export to the grid by subtracting what I’m still taking from the grid from what the panels generate. The meter isn’t actually reading this yet. I’m waiting for the energy supplier to come out and reconfigure the meter to read the export. Until then, I’m not actually getting that 54 cents credit—they’re getting the power for free. Nasty them again!
I’ve got a nominal 40-day wait from the time my energy retailer puts in the request to the energy supplier to reconfigure the meter, until they actually come out and do it. It’s day 33 and I’m counting down. If nothing happens in the meantime, when I get to day zero, angry phone calls will ensue.
I should also mention that when the meter IS reconfigured, it looks like I will lose the night-time water heating and go onto a time-of-use tariff. I’m still not sure about this, so I’m waiting to see what the Powers That Be will say. I really WANT the water to be heated by the sun anyway, it’s just that there will surely be a change in the tariff and it certainly won’t be downwards.