From the Canyon Edge -- :-Dustin

Wednesday, September 9, 2009

Solar Installation - Part 4

As of September 1, 2009, all 38 panels are now on the roof, and hooked up to the inverter, thought it's not yet turned on.

I had my inspection with Craig of Texas Solar Power Company, and David of Austin Energy today.

We spent about an hour going over the entire system. They turned it on for a few minutes, verifying the functionality. David went over every aspect of the design and installation. He noted a couple of things he wants to see updated in the CAD drawings and documentation. Craig is supposed to send those over to David as soon as possible, at which point my installation should be approved.

Now, I'm waiting 2 weeks for Austin Energy to come back out to my house to replace my current electric meter with one that can handle the PV junction. At that point, Austin Energy will actually turn on my system, and I will be generating Solar Power!

And then my rebate will be submitted for processing. I hope to see that rebate check in 6-8 weeks.

Many people have asked for more details about how the system works, and how my electric bill will be calculated.

The PV system will only generate electricity when the sun is out. Many factors will affect how much electricity is generated, including cloud cover, cleanliness of the panels, ambient temperature, length of the day, and the time of the year.

My system consists of 38 panels that are rated at 175 Watts apiece, for a theoretical maximum of 6650 Watts of output. The 38 panels are divided into two separate arrays. The Southwest-facing array consists of 3 strings of 9-panels apiece. These strings generate 357 Volts, 356 Volts, and 355 Volts apiece. Note the subtle difference in voltages. This ensures the direction of the flow (electricity always flows from higher voltage to lower voltage).

The amperage varies with the quality of the sunshine, and affects the output wattage. More sun yields more Amps, and thus more Watts. The other, Southeast-facing array consists of a single 11-panel string, which generates 439 Volts.

It is the job of the inverter to combine these two arrays and produce an AC current. My particular inverter is rated at 96.5% efficiency, so during the best hours of the day, I should see somewhere around 6400 Watts of electricity. During yesterday's test around Noon, with partial cloud cover, the system was generating 5550 Watts -- and this was far more electricity than I was consuming at that time.

The inverter is tuned to produce an AC voltage that is slightly higher than the power coming from Austin Energy's utility pole. This ensures that I use my solar generated power first, and any remaining flows back into the city's grid.

Now 6400 Watts is far more energy than I will be consuming during the daytime. However, at night, I won't be collecting any sunlight. During the day, the surplus will be used by others on the energy grid, and Austin Energy only buy that electricity from me at 40% of the price that I pay them for the electricity I use at night ;-) Such are the breaks... They pay the rebate, and thus they get to make the rules.

So we'll need to adapt our electrical usage model in order to maximize our savings. It will be in our best interest to run our laundry, dishwasher, and hot water heater during the daytime.

On a separate note, I'm quite eager to play with the serial data output on the Aurora inverter. Of course, my inverter came with a CDROM of Windows software that is worthless to me. Thankfully, someone out there has written a GPL application that communicates with the inverter's interface. I can't wait to play with it, once my system is turned on. Assuming it work's, I'll get it packaged and included in Ubuntu Karmic+1!

For other articles in this series, see:



  1. Wow Awesome!
    How much that cost you. Doing a calc with $4 per watt I guess it is $26,600

    Really is it?


  2. Nice post and interesting practical information.


  3. From photos you recently posted of your solar panel project, you appear to be blessed with having a clear view of the sky all day long. For folks who aren't so fortunate, National Semiconductor, under their SolarMagic brand, recently introduced "shadow mitigation" technology to compensate for panels that get shaded by chimneys, tree branches, and so on. The technology will soon get even better with National's acquisition of a Silicon Valley startup called Act Solar.

  4. Cool, seems like your getting screwed by the power company though. Is it possible for you to power a battery backup for when you need energy at night then draw from the grid only when absolutely necessary? Seems like thats a better way to go then buying back the same energy you just sold for a higher price from a .. (and I'm only assuming as it's the same everywhere) .. greedy bastard of a Government forced monopolistic very uncool dare I say evil .. power company.


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