Pv tilt update

[bpulluta]

Please check if the PR fulfills these requirements

• CHANGELOG.md is updated
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce?

(Bug fix, feature, docs update, ...)

default update for 'PV tilt'.

• In core/pv.jl a change was made to make sure we are using the same assumptions as PVWatts guidelines, the default tilt angle for a fixed array should be 20 degrees, irrespective of it being a rooftop (0) or ground-mounted (open-rack)(1) system. By default the tilt will be set to 20 degrees for fixed ground-mount and rooftop, and 0 degrees for axis-tracking (array_type = (2), (3), or (4))

"The PVWatts® default value for the tilt angle depends on the array type: For a fixed array, the default value is 20 degrees, and for one-axis tracking the default value is zero. A common rule of thumb for fixed arrays is to set the tilt angle to the latitude of the system's location to maximize the system's total electrical output over the year. Use a lower tilt angle favor peak production in the summer months when the sun is high in the sky, or a higher tilt angle to increase output during winter months. Higher tilt angles tend to cost more for racking and mounting hardware, and may increase the risk of wind damage to the array."

What is the current behavior?

(You can also link to an open issue here)
The current default PV tilt angle for a rooftop is set to 10 degrees and for fixed ground-mount to 20 degrees.

What is the new behavior (if this is a feature change)?

The new behavior sets the tilt angle for fixed PV rooftop and ground-mount to 20 degrees and for axis-tracking to 0 degrees. This aligns it with the pvwatts defaults.

Does this PR introduce a breaking change?

(What changes might users need to make in their application due to this PR?)
Specify a PV tilt angle if they may need to use a lower tilt angle for their fixed arrays than the new default of 20 due to hardware cost, wind, or other consideration consideration

Other information:

[Bill-Becker]

Nice work! Just a suggestion to remove some excess description from the Changelog.

[bpulluta]

@adfarth, seems like all the test are passing now. Please let me know if its okay, once you've had a change to review. Thank you!

[adfarth]

Look great!