[RE-wrenches] Array spacing for optimum performance

[Kent Osterberg]

Carl,

As you posed your question, with the array fixed at the angle optimized 
for annual energy production, you've forced a solution that cannot meet 
the goal of harvesting the maximum energy from the site.

To get the most energy from any site,  the array will be horizontal with 
no spacing between rows. The intuitive way to see this is to consider 
the question: how do you get every photon that hits the site to land on 
a PV module? Horizontal is not a very practical solution. To wash clean 
with rainfall, the modules need to have some slope; 10° to 15° is 
usually considered minimum. If someone is to clean the modules by hand, 
or inspect the modules, there must be access space between the rows.

Also, the horizontal solution isn't the most cost effective solution, 
except perhaps near the equator. To get the most energy per money unit 
(insert your choice: dollar, yen, ...), more information needs to be 
considered. If the value of the land or roof surface is ignored, the 
lowest cost per kWh will probably occur when the modules are spaced far 
enough apart that there is virtually never any shading from the rows in 
front and the optimum angle is a little less than the latitude. This 
solution produces much less energy the maximum possible. And, of course, 
ignoring the value of the land or roof space isn't practical either.

Ultimately, you have to look at what limits apply to the problem and 
work from there.

Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com


On 4/15/2012 4:44 PM, Michael Welch wrote:
> Carl is having sending issues, so I am posting this on his behalf. He 
> will be able to receive your responses on the list, though.
>
> *From:* Carl Emerson <Carl at solarking.net.nz>
> *Sent:* 15 April 2012 10:16 p.m.
> *Subject:* Array Spacing for optimum performance.
>
>  Hi there,
>
> Can I raise a design issue with large grid-tied arrays.
>
> Using William's spreadsheet for array spacing leaves me with several 
> questions unanswered.
>
> Assuming the array is inclined for max year round performance, one 
> could then space the array for no shading for a certain sun Elevation 
> and Azimuth.
>
> The question I have is what is the sweet spot when compromising 
> shading for array spacing in large arrays.
>
> Narrower spacing means more panels in the array and better output in 
> summer.
>
> Wider spacing means better winter performance with less panels and 
> less annual power production.
>
> Is there a guideline available to optimise these factors...
>
> Thanks for your help.
>
> Carl Emerson
> Freepower Co.
> Auckland N.Z.
>
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