The White Lily (![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
thewhitelily) wrote2010-09-02 09:16 pm
thewhitelily) wrote2010-09-02 09:16 pm
S Day
So Tuesday was the big day when 30 solar panels made their way onto our roof. So far, we've been pretty happy. Yesterday was the first full day in operation and Brisbane really turned on the weather which was, aside from smoky haze from some bushfires and some afternoon cloud cover, a clear and sunny day.
So: let's see some real figures. Sunrise was at 6am, sunset at 5:30. At 8am, the system was generating 1.9kW. By about 9am, it was generating about 2.9kW. Presumably this peaked somewhere closer to its theoretical maximum of 5.4kW around midday, but we didn't get the opportunity to check. Over a period of eleven hours and twenty minutes of operation (according to the inverter logs) yesterday, the panels generated at total of 24.8kWh of power. It won't be properly connected up to the grid for another two weeks (it is going into the grid, but it's just making our meter go backwards and thus saves us 17c pkWh rather than the full 50c feed in tarriff).
Thus the solar panels subtracted $4.22 off our power bill, yesterday alone. If it had been properly connected to the grid already, it would theoretically have been $10.54. (Waiting just two weeks for the rewiring of our meter, if the weather is consistent, will cost us around $88 in lost profits! Ack!) The theoretical cost of the panels to us, simply calculated as a increase in the interest we needed to pay on our home loan over that one day period was $3.57. (Although again, technically, we managed to pay on a credit card and so we won't be paying this extra interest for another two weeks; I guess it all comes out in the wash.) Assuming a 35 year depreciation period costs us another $1.57.
Thus, technically, yesterday we made a profit of $2.92. Theoretically, the profit should have been more like $5.40. If yesterday was an average day, that is every day, for which even a small amount adds up very quickly for something that requires no additional work on our part.
In other terms, at the current rate it's just under an eight year payoff including the interest for the outlay, and anything it generates (ie. the whole $10.54 per day) from June 2018 to the end of its lifetime is gravy. Definitely worth it.
So was yesterday an average day? It was the first day of spring - roughly three quarters of the days in the year are longer. It was hazy from a bit of smoke in the air, and there was light cloud cover in the afternoon. Nonetheless, I certainly would have described it as a clear day, which is not always the case even in Brisbane. According to the BOM, yesterday's solar exposure was somewhere between 15 and 19MJ/m2 (Figures more accurate than the colour map are on a subscription basis only). Brisbane's mean daily solar exposure annually is 19.5MJ/m2. So, essentially, yes. Yesterday was an indicative, likely to be slightly conservative, day for what the future holds for our solar array.
We've yet to see what the next electricity bill actually brings, we've yet to see how long the government rebate lasts (if it went away tomorrow and electricity prices didn't rise, we would pay off the panels in 28 years rather than 8), and we've yet to see how the panels last the test of time. For the next 10-15 years (depending on the part) they're simply under warranty. Research suggests we shouldn't expect any problems for significantly longer than that. Accidental damage (hail/storm/etc) is covered on home insurance. Zombie attack doesn't seem to be covered anywhere. I suppose we shall just have to wait and see.
But for the moment, I am very pleased indeed.
Edit: Figures updated when I realised I had the feed-in tarriff wrong - it's 50cpkWh, not 40.
So: let's see some real figures. Sunrise was at 6am, sunset at 5:30. At 8am, the system was generating 1.9kW. By about 9am, it was generating about 2.9kW. Presumably this peaked somewhere closer to its theoretical maximum of 5.4kW around midday, but we didn't get the opportunity to check. Over a period of eleven hours and twenty minutes of operation (according to the inverter logs) yesterday, the panels generated at total of 24.8kWh of power. It won't be properly connected up to the grid for another two weeks (it is going into the grid, but it's just making our meter go backwards and thus saves us 17c pkWh rather than the full 50c feed in tarriff).
Thus the solar panels subtracted $4.22 off our power bill, yesterday alone. If it had been properly connected to the grid already, it would theoretically have been $10.54. (Waiting just two weeks for the rewiring of our meter, if the weather is consistent, will cost us around $88 in lost profits! Ack!) The theoretical cost of the panels to us, simply calculated as a increase in the interest we needed to pay on our home loan over that one day period was $3.57. (Although again, technically, we managed to pay on a credit card and so we won't be paying this extra interest for another two weeks; I guess it all comes out in the wash.) Assuming a 35 year depreciation period costs us another $1.57.
Thus, technically, yesterday we made a profit of $2.92. Theoretically, the profit should have been more like $5.40. If yesterday was an average day, that is every day, for which even a small amount adds up very quickly for something that requires no additional work on our part.
In other terms, at the current rate it's just under an eight year payoff including the interest for the outlay, and anything it generates (ie. the whole $10.54 per day) from June 2018 to the end of its lifetime is gravy. Definitely worth it.
So was yesterday an average day? It was the first day of spring - roughly three quarters of the days in the year are longer. It was hazy from a bit of smoke in the air, and there was light cloud cover in the afternoon. Nonetheless, I certainly would have described it as a clear day, which is not always the case even in Brisbane. According to the BOM, yesterday's solar exposure was somewhere between 15 and 19MJ/m2 (Figures more accurate than the colour map are on a subscription basis only). Brisbane's mean daily solar exposure annually is 19.5MJ/m2. So, essentially, yes. Yesterday was an indicative, likely to be slightly conservative, day for what the future holds for our solar array.
We've yet to see what the next electricity bill actually brings, we've yet to see how long the government rebate lasts (if it went away tomorrow and electricity prices didn't rise, we would pay off the panels in 28 years rather than 8), and we've yet to see how the panels last the test of time. For the next 10-15 years (depending on the part) they're simply under warranty. Research suggests we shouldn't expect any problems for significantly longer than that. Accidental damage (hail/storm/etc) is covered on home insurance. Zombie attack doesn't seem to be covered anywhere. I suppose we shall just have to wait and see.
But for the moment, I am very pleased indeed.
Edit: Figures updated when I realised I had the feed-in tarriff wrong - it's 50cpkWh, not 40.
Inspired
(Anonymous) 2010-09-05 11:54 pm (UTC)(link)TPWFL
Re: Inspired
obsessedinclined, I'm sure we'll keep you updated on the ongoing practical output. Of course, in a few years time the tech will likely be better, too!