|I was disappointed that my adjustable
declination feature may not provide much energy gain. So I devised
this simple reality check to see if the tilt angle equation was anywhere near
accurate. This procedure was based on power delivered during the period April
through April 23, and on April 21 in particular.
This exercise will attempt to show reasonable alignment of predicted performance with observed performance. Some justifiable approximations and assumptions must be made, so it is not a formal proof - just a reality check.
|When the system was activated on
April 11, the array tilt angle was set to 23.6 degrees. And there it
stayed. From the
daily angle chart, this would be the optimum setting for day 98 - about
|Based on the daily energy chart we might expect about 0.6377 kWh per sq. ft. incident on the
array during day 98. We might expect 0.6350 on day 110, or
perhaps slightly less due to departure from the optimum tilt
angle that was set for day 98.
|Between April 18 and April 23 (days 101 and
112) we had six nearly perfect cool, clear days during which the
system delivered an average of 42.1 kWh per day. The best day was
April 21 (day 110), cloudless from dusk to dawn, on which 43.5 kWh was
delivered. Energy delivery is measured by a private kWh meter.
|The active area of a KC-120-1 PV panel is 8.41 sq. ft.,
and 72 of them present a 605.52 sq. ft. target. From the day 110 prediction of
0.6350 kWh per sq. ft.
total incident energy, we should have been exposed to 385 kWh. Applying
conversion efficiencies of 13.53% for the
PV panels and 88% for the inverters, we might expect
slightly less than 45.80 kWh to be delivered.
This is remarkably close to the 43.5 kWh actually recorded on day 110.
From the foregoing, the tilt angle equation seems to be aligned with the PTC power rating and measurements of actual energy produced. This gives credibility to the equation, but does nothing to ease my disappointment with the minimal effectiveness of seasonal elevation adjustment.