From the Canyon Edge -- :-Dustin

Wednesday, September 15, 2010

My First Year of Solar Power

I've posted a few times now about the 6.7KW photo-voltaic (solar) power system we have on our roof in Austin, Texas. It was activated one year ago, today.

Many, many people ask me about it. It has been operational for about a year, so I can finally analyze it's performance each month out of the year. This is important because the energy produce depends greatly on the position of the sun in the sky, the length of the days, and the weather. Different amounts of power are produced at different times.

I'm currently using Curt Blank's aurora program to gather data from my inverter. I have packaged this for Ubuntu, by the way. You can find it in Ubuntu 10.04 and beyond.

My current inverter reading as of today looks like this:
Current date/time: 15-Sep-2010 11:30:02

Daily Energy = 7.314 KWh
Weekly Energy = 91.434 KWh
Monthly Energy = 366.448 KWh
Yearly Energy = 7123.188 KWh
Total Energy = 9433.281 KWh
Partial Energy = 1537.161 KWh

Current date/time: 15-Sep-2010 11:30:05

Input 1 Voltage = 244.048767 V
Input 1 Current = 9.157255 A
Input 1 Power = 2234.816895 W

Input 2 Voltage = 255.783203 V
Input 2 Current = 3.767791 A
Input 2 Power = 963.737732 W

Grid Voltage Reading = 239.640839 V
Grid Current Reading = 12.036012 A
Grid Power Reading = 3196.468750 W
Frequency Reading = 59.966419 Hz.

DC/AC Coversion Efficiency = 99.9 %
Inverter Temperature = 54.750835 C
Booster Temperature = 49.749878 C

The most important number above (for this post) is:

Total Energy = 9433.281 KWh

In the last 365 days, this system has produced 9.4 Megawatt-hours of power.

What does this mean in terms of cost savings? Roughly, I know that electricity in Austin is about $0.115/KWh, so that's approximately $1,085 in savings on my electric bill. The real formula is actually a far more complicated differential equation, as I buy and sell electricity at two different rates, the rates change slightly every month, etc. But this is a reasonable ballpark figure.

Austin Energy actually has a web application where I can view and analyze my usage online. Here's a screenshot of my last 2 year's usage. Note the "Solar kWh" row, as well as the year-to-year difference in "$ Billed".

I can also download these stats in a CSV format, drop it into a spreadsheet and print some pretty cool charts. Analyzing the data directly, I can see that my solar investment has saved me exactly $1,210.71 over the last 12 months -- about $100/month, which is what I expected when I purchased the system.

Accounting for both the Austin Energy PV Rebate, and the Federal Tax Credit, our system is well on its way to paying itself off in just a few short years.

Once again, thanks to the outstanding individuals at Texas Solar Power Company in Austin for their outstanding service and timely installation.

As George Harrison wrote, "Here comes the sun!"

Doo do doo doo,


  1. If it weren't for the rubbish British weather, I'd follow suit. Trouble is we have more cloud and rain than sun!!

  2. @Ted Simth: Despite the British weather it's probably still worth it financially because of the feed-in tariff of 41.3p/kWh. Sunniest area is Cornwall, getting progressively less sunnier the further north. If you've got a decent bit of roof you can get a good return on investment from this.

  3. When i sum it up and interpreted correctly you needed around 24000kWh a year ???
    Are you running a greenhouse with lamps, or a server farm?
    I use around 2000kWh a year and my appartment is even heated by electricity.

  4. First, it's a house and not an apartment.

    Second, heating the place isn't the problem, in Austin, TX... It's cooling.

    My winter electric bills are very low. It's the rest of the year, when it's 100F/40C, and electricity is cranking hard on the air conditioner.


  5. I keep thinking I'd like to go solar, not because I'm a green-nut, but it's just plain techno-cool. Everytime I look at my paycheck and see how much I've paid in taxes this year, I can't help but think I could have bought a SWEET array this year... We get descent sun here at 42 Deg North, it would be worth it.

    Is your array static or does it track the sun? I'm assuming static, based on some of your fluctuation remarks. I wonder what sun tracking would do to your breakeven point?

  6. Definitely static; does not track the sun.

    And yes, the tax benefit was nice. Nice to get a little of my hard earned dollars back :-)

  7. What about uploading aurora to Debian too?

  8. I'd love to. I need to get my Debian maintainership... High up on my to-do list.


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