[RE-wrenches] SE or SW

[Jesse Dahl]

I did play around with numbers on there and came to that conclusion. Considering I'm only 50 miles from international falls, it's even a clearer choice then running the numbers in the cites. 

Verification is always nice!

Jesse

Sent from my iPhone

On May 15, 2013, at 5:59 PM, Kent Osterberg <kent at coveoregon.com> wrote:

> Jesse,
> 
> Running PVWatts for various tilt angles with an azimuth angle of 135° (or 225°) for locations in Minneapolis, shows that the optimum tilt angle for annual energy production is about 35°, that's almost the same as the optimum tilt with an azimuth of 180°. To maximize December energy production with the 135° azimuth, the optimum tilt angle is about 60° and that gives 12% more energy in December than the 35° tilt would (without considering how much better the steep tilt does at shedding snow). The SE roof with the steeper pitch is certainly the better choice.
> 
> Kent Osterberg
> Blue Mountain Solar, Inc.
> www.bluemountainsolar.com
> On 5/14/2013 8:23 PM, Jesse Dahl wrote:
>> Allan,
>> 
>> That is pretty much my thinking.  They have 0 interest in stepping foot roof and the SE give more tilt and easy ground access to clear the array during winter. 
>> 
>> I appreciate the advice. 
>> 
>> 
>> Jesse
>> 
>> Sent from my iPhone
>> 
>> On May 14, 2013, at 10:15 PM, Allan Sindelar <allan at positiveenergysolar.com> wrote:
>> 
>>> Jesse,
>>> Based only on the info you provided, I'd recommend the SE face. A low slope is best for maximizing annual gain, which is what a conventional grid-tie customer would want. But you are in essence giving them a system that will function as GT now, but as an off grid system if the grid goes down. Under that scenario, I would sacrifice annual spin-the-meter-backward production in favor of maximizing winter output, when days are shortest and loads are greatest. A steeper array pitch will maximize available charge during winter, while the shallow pitch will be great in summer but close to nothing in winter. Given their stated objective, explain the tradeoff as offering the best preparation for lack of grid.
>>> 
>>> I'd advise otherwise if they clearly want to seasonally adjust their array if there is an outage, and you install adjustable-tilt racks, and the owners are afraid of neither ladders, heights, or snow.
>>> 
>>> We just completed a 4 kW GTBB system for a customer with similar objectives. We used 16 240W modules on two 8-module pole-top racks, with the instruction to leave the tilt angle shallow as long as the utility is present, but tilt to 45-55 degrees in winter during an extended outage. (And a pair of Classic 200s to handle the 4-module series strings.)
>>> Allan
>>> 
>>> Allan Sindelar
>>> Allan at positiveenergysolar.com
>>> NABCEP Certified Photovoltaic Installer
>>> NABCEP Certified Technical Sales Professional
>>> New Mexico EE98J Journeyman Electrician
>>> Founder and Chief Technology Officer
>>> Positive Energy, Inc.
>>> 3209 Richards Lane (note new address)
>>> Santa Fe, New Mexico 87507
>>> 505 424-1112
>>> www.positiveenergysolar.com
>>> 
>>> 
>>> 
>>> On 5/14/2013 4:34 PM, Jesse Dahl wrote:
>>>> Hello,
>>>> 
>>>> I was asked to look at a site today for a homeowner looking for a grid-tie with battery-back up. They are Doomsday Preppers for lack of a better term and want certain loads if and when the grid goes down for good. Aside from parts selection, they have two roof lines, one facing SE one facing SW. the SW is very low slope and is only accessible with a ladder and climbing on the roof, the other is SE, much steeper slope and accessible from the ground or deck.  I mention the access because of snow removal. We had lots of snow last year and I spent lots of time on my roof removing 8" snow falls.  Both have good solar access.  
>>>> 
>>>> I'm inclined to chose the SE roof line, but I am interested in arguments for the SW. 
>>>> 
>>>> Thanks!
>>>> 
>>>> Jesse 
>>>> 
>>>> Sent from my iPhone
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