Ground and pole mounted solar energy systems: More to know ... a few tools ....

[Information Technology and Solar Solutions]

Two person hand held hole digger - the two person would typically
provide the diameter required. If modules are mounted on a pole, the
diameter of the pole is greater. If modules are mounted on more than
one pole, the diameter of each pier decreases.

http://www.generalequip.com/prod_library/177-item.pdf
http://www.generalequip.com/category.php?id=9

In accordance with NEC 300.5 the the specific section with regards to
minimum cover requirements. Trench with a walk-behind pedestrian
trencher with at approximately 10-19 horse power at a depth of 2-3 ft
for in accordance to code. Although there are other trenchers,
consider what would be required.

http://www.ditchwitch.com/pdf/literature/english/1820_1330_1230_1030.pdf

The method would be to implement the array with the hole digger and
then perform the trenching. Remember, the size of the conduit, would
be based on the size of the conductors based on the distance from
point of connection or inverter input circuit. An for traditional
inverters the distance for AC < DC and for micro-inverters AC > DC.
And on the AC side the voltage drop would be approximately 1% or
less. On the DC side the factor would be power loss because MPPT is
provided by the inverter. As a result, the voltage drop calculations
on the DC would be administrative. Also, decreasing voltage drop on
both the AC and DC side would increase power of the array and increase
the derate factor.

Depending on the situation, the temperature of the conduit and
conductors underground would be less than the temperature on a rooftop
as indicated in NEC Table 310.15(B)(2)(c) Ambient Temperature
Adjustment for
Conduits Exposed to Sunlight On or Above Rooftops?

What do you think?