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Posted by Josepi on April 8, 2010, 3:42 pm
 


Thanx for the info
My roof was designed by a truss company with the local climate factored in
(I hope...LOL). I put the house together myself and used to sit and worry
about all the weak points during these wind storms...many sleepless
nights...LOL We did have a shingle problem for a few years but have the
defect "ironed" out abd they stay put now.

How is the structure layering on your mounting brackets? I assume all metal
channelling with horizontal channels against the shingles with panels
directly bracketed to them = Two layers total


Is there a snow or rain catch problem with horizontal channels, first or
perhaps there is a vertical channel layer first??

Could the first layer of metal not be lagged directly into trusses or there
a reason to do otherwise?




My panels are also roof mounted, on a 45 angled roof.  They sit some
inches above the roof line.

We, too, have wind gusts in the range you mention; and this past winter I'm
told that there were even higher wind gusts -- someone said 90 mph (144
km/hr).  But I wasn't here that week so can't confirm that it really
happened at our site.

We've not had any damage to the panels or the roof.  And no roof leaks.

*BUT* there were specs that I obtained (from the architect who designed the
house, and his engineer) regarding the limits on the roof structure with
regard to weight and uplift force issues to ensure that the panels would be
OK in that location.

The panels are mounted on rails, with footings that penetrate the roof
(appropriately sealed with some kind of goop), and are anchored underneath
through wooden blocks that are tied to the roof support trusses.

I suspect that the structure of the roof will be the limiting factor for
you, in terms of putting panels up there.
--ron



Posted by Ron Rosenfeld on April 8, 2010, 6:10 pm
 




We have engineered trusses also, with hurricane clips added by the
architects.  We've had no shingle problems at all over the years (9 years
since we moved in) so I guess the carpenters did a good job with the
roofing.

If *I* had personally put the house together, it probably wouldn't be
standing today <g>.



There are two horizontal supports per row of panels.  

I have two rows of panels -- 6 wide oriented vertically.

Each support is on several "feet" that hold the support up 6-12" above the
roof.

I don't recall exactly how the PV Panels are attached to the horizontal
supports.



I've not seen any issues with regard to freezing around the supports.  I
suppose the roof pitch helps with that.


To me, the trusses seem fairly thin for that sort of application.  And, if
I recall correctly, the truss company recommended against that, feeling it
would weaken the structure.

--ron

Posted by Ron Rosenfeld on April 7, 2010, 12:49 pm
 



I think your calculations are off, both for the amount of electricity
generated and also for the assumption that $,000 will be lost every year.
The amount lost goes down with time as the debt gets paid off.

Initial Outlay:    $0,000

    I don't know how realistic this is, in Canada, including any
connection costs; but this is what the OP gave.

Pmt per kWh:    $.802

Annual Electricity Generation
     10  kW nameplate power
      4  Effective Sun Hours Day (average over the year)
    365  Days
     80% Efficiency    

Total Payments per year for generated electricity =
   10 x 4 x 365 x 80% x $.802 = $,367.36

Payback time = 11.4 years

The HOMER program, using Ottawa lat/long as the location, and the NASA
database for solar insolation (which averages about 3.6kWh/day), calculates
the PV (with 80% efficiency) to generate 12,449 kWh/year.  Figuring the
inverter at 90% efficiency, the funds generated by sale of electricity
would be  $,985.69 / year and the payback would be about 12 years.

The PVWATTS program, with a 72% derating factor, shows annual income of
$,724.96 and a payback of 12.6 years.

I don't know about maintenance on a grid-connected PV system.  The PV part
of my system at my off-grid location has required zero maintenance in the
six years since it's been installed.  The inverters have required zero
maintenance.  I updated my charge controller -- but that was under
warrantee and did not involve any cash outlay.

Definitely not the TEN years mentioned by the OP, but not terribly out of
line, depending on the various assumptions.
--ron

Posted by Josepi on April 7, 2010, 7:14 pm
 

Did you really think anybody would believe 4 hours of sun 365 days per year?
Where are you referring to where it never is overcast and never rains during
the prime +/- 2 hours from solar noon window ? Surely not in your maritime
weather out there. Geesh!

You,also, conveniently, left out the very modestly calculated (5% for Canada
and more for the US) interest payments.

You, also, indicate you are totally off-grid and had a charge controller for
six years. This indicate batteries. You, also, left out those maintenance
costs.

Adding in your forgotten factors I doubt you would ever, make your interest
payments on the money spent.


Me thinks you are involved in promotion of solar equipment, most likely in
battery sales, somewhat and it appears to be showing.



I think your calculations are off, both for the amount of electricity
generated and also for the assumption that $,000 will be lost every year.
The amount lost goes down with time as the debt gets paid off.

Initial Outlay: $0,000

I don't know how realistic this is, in Canada, including any
connection costs; but this is what the OP gave.

Pmt per kWh: $.802

Annual Electricity Generation
10  kW nameplate power
  4  Effective Sun Hours Day (average over the year)
365  Days
80% Efficiency

Total Payments per year for generated electricity =
   10 x 4 x 365 x 80% x $.802 = $,367.36

Payback time = 11.4 years

The HOMER program, using Ottawa lat/long as the location, and the NASA
database for solar insolation (which averages about 3.6kWh/day), calculates
the PV (with 80% efficiency) to generate 12,449 kWh/year.  Figuring the
inverter at 90% efficiency, the funds generated by sale of electricity
would be  $,985.69 / year and the payback would be about 12 years.

The PVWATTS program, with a 72% derating factor, shows annual income of
$,724.96 and a payback of 12.6 years.

I don't know about maintenance on a grid-connected PV system.  The PV part
of my system at my off-grid location has required zero maintenance in the
six years since it's been installed.  The inverters have required zero
maintenance.  I updated my charge controller -- but that was under
warrantee and did not involve any cash outlay.

Definitely not the TEN years mentioned by the OP, but not terribly out of
line, depending on the various assumptions.
--ron







Posted by wmbjkREMOVE on April 7, 2010, 7:45 pm
 

wrote:


Hey, it's raining strawmen again!

Wayne

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