Is there a thumbrule for the optimal spacing between pole-mounted tracking
arrays? No doubt there are a hundred variables to consider, but perhaps
there's a thumbrule.
Lets assume an reasonable US latitude - 40N, level ground, a straight line
of pole-mounted tracking arrays running due East-West, where each array atop
the pole is X' wide and Y' tall. Of course, the further apart the less
potential shading when the sun is low. At what angle relative to the
horizon to trackers typically start/stop?
Thanks,
WP
No rule of thumb, but there not a hundred variables.
I use two special tools. I have an old copy of PVCAD (no longer sold as
it is a DOS application) that can generate tables of irradiance by hour along
with sun elevation and azmiuth. It is a judgement call as to how much of the
available solar irradance you can afford to risk loosing due to shadows
from one part of an array on another. The loss of available energy in the
morning/evening is generally less than 6% for the first or last hour of the
day, so I try to set this as an acceptable loss. Depending on the array
design (number of series modules is the major consideration), shadows
can have varying effect on performance. Shadowing one module in a
series string may reduce the string voltage such that all the modules in
the string no longer contribute to the output. Bypass diodes are a
must on high voltage arrays.
The other major tool I use is Autocad. I build a three-dimentional model
of the proposed array, then look at it from the various sun angles to see
if there is shading. It can be difficult to find a spacing that works both
summer and winter. Dual axis trackers can be placed in staggered rows.
Between the two tools an acceptable design can generally be obtained.
The usual problem is how many modules are needed to support a
specific load. A related problem is to estimate the energy output with the
calculated shading, useful for utility connected systems.
Bill Kaszeta
Photovoltaic Resources Int'l
Tempe Arizona USA
[email protected]
