[RE-wrenches] Tracker Benefits (was : Evergreen)

Sun Jan 3 14:59:15 PST 2010

David's cost benefit analysis is similar to the calculation I perform for any customer considering tracking.
The shading analysis is the sticker. No sight has perfect solar access, and every hour lost needs to be included in your analysis.
The new software that goes with the Pathfinder does a good job of this. (Pathfinder Assistant)
However, you not only need to account for various spots on the array, but you need to take Pathfinder readings at all the different locations of the array, through the day, and through the year.
For a 2 axis tracking unit like the Wattsun, you need to begin to imagine a cloud of locations, and accounting for the losses accurately 
gets harder, the more you think about it. How do you average all your points? (Calculus?) You have to do at least 2 sets of points (summer/ winter), 
with at least 4 points for each set.
I found that the "worst case scenario" readings done on a first site visit, (bottom array corners, winter tilt) are way too conservative for a fair cost evaluation of tracking.
I'll do an initial fixed array analysis, if that looks encouraging, there's enough space, and the customer really is wanting tracking,
I'll do the more sophisticated shading analysis, (which I'm still trying to fully develop, help please?)

Happy NEw YEar,

R. Walters
ray at solarray.com
Solar Engineer

On Jan 3, 2010, at 12:35 PM, David Katz wrote:

> Since modules are getting so inexpensive, the big questions is what is the best way to get 33% more power? Is it better to use 33% more modules on a fixed array, or use a tracker?  Which one costs less?  It costs $1.50 to $2.00 per watt for a tracker.   If modules cost $3 per watt and a fixed mount costs $.040 per watt , 33% of $3.40 per watt is $1.12 per watt.   And trackers don't come with a 25 year power output warranty.  I see tackers making sense when the array is powering a centrifugal pump in the summer or possible a time-of-use grid tie that pays more in the summer.  You are definitely better off with more modules on a fixed array in an off grid situation because you always need more power in the winter when the tracker is least effective.
> David
> 
> David Katz
> Chief Technical Officer
> AEE Solar
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> 
> Dana wrote:
>> 
>> You got it!
>>  
>> It boggles my mind to watch the two OB FM60s and see the difference each day and then to go back and see the data over time. It is a very good argument for tracking. We have a Durango client that we installed 12 KW GIT tracked and it is outperforming the expectations of our client too.
>>  
>> Dana Orzel
>>  
>> Great Solar Works, Inc
>> www.solarwork.com
>> E - dana at solarwork.com
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>> C - 970.209.4076
>>  
>> I will be the shift in how the world uses power! - Dana Orzel
>>  
>> From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Allan Sindelar
>> Sent: Thursday, December 31, 2009 8:13 PM
>> To: RE-wrenches
>> Subject: Re: [RE-wrenches] Evergreen
>>  
>> Dana,
>> Thank you for this information. I would like to clarify what you wrote. We have long accepted that trackers may be expected to increase daily output by about 35-40% in the summer and 10-15% in the winter, due to the differences in the sun's seasonal elevation and the resultant length of the solar day. It sounds as if you measured the effective increase from approximately summer solstice - winter solstice and got a 32% gain. You previously got the same gain (33%) measuring from last winter solstice to summer solstice. This makes sense, as it averages winter and summer gains over two roughly equal periods, with variations (summer monsoons, etc.) being within acceptable error. 
>> And whether grid-tied, grid-tied with backup, or off-grid is irrelevant as long as you can compare and record the outputs of the two otherwise identical arrays, one tracked and one fixed.
>> Do I understand this right? If so, it's good real-world data for design purposes.
>> Allan
>> 
>> Allan Sindelar
>> Allan at positiveenergysolar.com
>> NABCEP Certified Photovoltaic Installer
>> EE98J Journeyman Electrician
>> Positive Energy, Inc.
>> 3201 Calle Marie
>> Santa Fe, New Mexico 87507
>> 505 424-1112
>> www.positiveenergysolar.com
>> 
>> 
>> Dana Orzel wrote:
>> This is for a grid tied with battery backup Outback system.
>> The 32% increased gain for the tracker VS. fixed mount production is an average of the last 180 days and I checked it in the spring for the last 180 days [over the winter] and it was 33%. The 12 – Evergreen 180 watt modules produce about 65 -70% of our home and office’s electrical requirements.
>> Thanks,
>> Dana Orzel
>> Dana,
>> That 32% is a very useful number, and it matches with our experience as well. But I need to verify a couple of assumptions, please:
>> Does this represent average annual production, rather than peak seasonal? And is it a grid-tied system?
>> Thanks,
>> Allan
>>  
>> Allan Sindelar
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