12 April 2012

Goin' Solar part 2

As an engineer by trade, I had lots of questions regarding the install.  Regretfully (but not surprisingly) these were questions the sales 'droid could not answer.  Specifically, I wanted to understand the calculation from panel efficiency and sub-optimal orientation to how many KW's would come out the other end.  They mount the panels flat to the roof rather than at the "latitude optimal" angle.  That simplifies the wind load calculations, and eases the HOA signoff.

Unfortunately the 'droid did not know and could not provide an answer.  I work in a similar environment.  But I'm the guy behind the scenes specifying/programming the calculation, not the 'droid.  And when our sales 'droids call me to understand how these things work, I get involved and answer all questions with complete transparency.  I am disappointed SolarCity could not do the same for me.

However by asking the right questions (rerun the numbers using these assumptions), and conferring with the local utility, we were able to reach the best answer.    The call to the utility also corrected some mal(latin for bad) data from the 'droid. 

Turns out our roofline runs ~200 degrees true.  That's 20 degrees tilted to the south east.  That means  the eastern facing roof is a little more optimal for sun orientation.  Unfortunately that also means our best generation hours are in the morning hours.  Since we are on a "time of use" plan, that would mean we are generating at a time of low cost and consuming during the higher cost hours.  Conferring with the utility confirmed this and recommended going back to the non-TOU plan.  Then the generation rates and consumption rates would match.

I still wonder if the TOU rates + suboptimal geometry wouldn't be a better solution still.  I'll bring this up at the engineering stage.  Even sticking with the current plan, it looks a good investment.  Even better so because the utility provider announced a new rate increase today.  That will improve our ROI.

I should also note, the utility's solar group concurre  with our calculations that shifting back to non-TOU would save us money.  I need to ask one more question - will the TOU + suboptimal geometry save us more?

BTW, one consideration to this is that both the SCSon and I are amateur radio operators and living in a HOA antenna restricted area.  Currently our antennae (VHF)  are hidden in the attic (J-pole for me, ground plane that he built for him).  But the solar panels on the roof will RF shade that.  OTOH, the solar panels could also provide cover for retractable mounts atop the roof.  I have ideas for antennas that would fold flat against the roof (now hidden by the solar panels) and easily erect as needed.

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