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,