Solar update

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.

10 Responses to “Solar update”

  1. rabidlittlehippy Says:

    Solar hot water system in your future maybe?
    Our hot water is heated totally off grid. Our system is a first nd foremost solar hot water system, any water is always first heated by the sun, even in winter. When there is no sun it still goes through the SHW system. Then it goes via the wood heater we have (not applicable in Summer of course), thirdly it goes to the gas boost if needed (we are yet to connect the gas) and finally to electric boost, again if needed (which we switched off at the meter box). We have had 2 days in nearly 12 months where the water has been less than hot. Both days were heavily overcast but not cold enough for the fire to be lit (days like today with more cloud cover). It was still hot enough for a shower although not worth standing under long to enjoy (warm but not bone soaking hot) so I call that a win. It’s the Autumn and Spring where we are more likely to need to boost systems. It’s a great system. 🙂
    I’ve sent in my details today for our solar electricity quote. Even though it’s unlikely to happen for quite some time it’s still worth looking int to find out what we can fit on the roof and what system we might need.
    I love reading your updates as it excites me to think that maybe one day I might be out there hovering in front of my power box, pencil and paper in hand taking notes to analyse. And knowing that it’s one step closer to damning the electric man… 😉


    • foodnstuff Says:

      I’ve always said that if my electric hot water system conked, I would get a solar heated one. Now that I’ve got the PV I’ll see how things go if and when I get the water heated by the panels.

      Reading the meter is certainly addictive. I’m glad that, unlike chocolate, it doesn’t put weight on 😉


  2. Chris Says:

    Whatever profit you make, will also have to factor in costs for servicing or parts which are not part of the manufacturers/installers guarantee. This may not impact in the first year or two, but from five years onwards, the clock for replacing parts starts ticking and then you’ll be up for perhaps a full panel re-install at 10-15 years.

    We’ve had our solar hot water system running without flaw for six years. This winter it decided not to heat our water, so we’re looking at having a service person take a look at it.

    One of the things which hasn’t had me buy on-grid solar yet, is the fact we’d make little money for the money invested plus 100% operational costs return to us. In effect, we’d be paying the regular service charges for the power company to keep the grid operational, plus money from our own pocket should the solar need repair.

    In theory, I like the idea of solar but it hasn’t won me on the cost effectiveness of it. Like you, we live out of town so we have to pay for electricity to our water pump and septic to the house. So we’re looking at tweaking how the septic works, to save on drawing electricity. It’s a bit of a juggling act though, isn’t it?

    I hope your solar panels work out for you in the end though. 🙂


    • foodnstuff Says:

      Thanks for the comments, Chris. I guess I haven’t given too much thought to the future. After a full year of operation, I’ll be able to see how cost effective it is—for that time anyway—and worry about the future when it happens.


  3. L from 500m2 in Sydney Says:

    Sounds like you need some batteries 🙂


  4. narf77 Says:

    My head hurts after all of that computation! It’s good to see that you are, in fact, saving money and $500 is still $500. Our aim is to go off grid but in order to do that we are going to have to rob a bank methinks. Any banks you don’t particularly like? Let us know 😉


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