Fixed Tilt vs. Solar Tracking PV Arrays
data from NREL's PVwatts calculator
OEES 265 Alt. Energy Construction
- Download the fixed vs. tracking spreadsheet.
- Go to NREL's PVwatts calculator for Albuquerque.
Leave the DC rating at 4 kW.
as the array type, use a tilt angle of 46 degrees, and click Calculate.
- (They don't have data for Grants.)
In the fixed tilt
column of the spreadsheet, type in the energy values (dollars)
for October through March.
Click the browser's Back
Change the tilt angle to 24 degrees, and click Calculate.
- 46 degrees is an average tilt angle that will yield
the most energy for the winter half of the year.
In the fixed tilt column of the spreadsheet, type in
the energy values for April through
Click the Back
Change the array type to 1-axis, specify a tilt angle of 46 degrees, and click Calculate.
In the 1-axis column
of the spreadsheet, type in the energy values (dollars) for October through March.
Click the Back
Change the angle to 24
degrees, click Calculate,
and record the energy values for April
Click the Back
Change the array type to 2-axis and click Calculate.
- 24 degrees is an average tilt angle that will yield
the most energy for the summer half of the year.
In the 2-axis column
of the spreadsheet, type in the energy values for all twelve months.
- The tilt angle is irrelevant for a 2-axis
which is more cost effective: fixed tilt, 1-axis, or 2-axis.
| When comparing fixed vs. tracking PV
systems, you'll want to be sure that they are all grid-tie or all
stand-alone. Also, if batteries are needed, make sure that batteries
are either included or not included for the all the systems you're
comparing. Same goes for inverters. (You don't want to be comparing
apples and oranges, as the saying goes.)
Near the bottom of the fixed vs. tracking spreadsheet,
type in the wattage and cost for this system.
If you wish, do the same for a 2-axis system, or do a
2-axis system instead of a 1-axis system.
Find a low-cost-per-watt fixed tilt system, and type
in it's data also.
- Search the Internet to find a 1-axis photovoltaic
system with a low cost per watt.
- You could either buy a system that includes a
mounting rack, or you could plan on building your own mounting rack.
- If you're going to build your own mounting rack,
make a guess as to how much lumber and hardware is needed, and estimate
You'll want the fixed tilt system to have a higher wattage rating than
the tracking system in order to end up with roughly the same annual
amount of energy.
By trial and error, adjust the fixed-tilt DC wattage ratings (in the
blue-shaded box near the bottom of the spreadsheet) to get an annual
energy value roughly equal to that for a 1-axis or 2-axis system. Then,
calculate the cost of the additional panels needed to supply the
necessary wattage rating.
You can now tell which is more cost effective, a fixed-tilt system or a
To be fair to tracking systems, they are able to supply more energy
than fixed-tilt systems during the morning and afternoon hours. I would
think that NREL simply used an average amount of sunlight for each day.
If this is the case, a tracking system might perform better during July
and August than what is indicated by NREL's PVwatts calculator. The
afternoon thunderstorms we get during these months would greatly reduce
energy production while they are occurring. A tracking system would be
able to harvest more energy during morning hours than would a
fixed-tilt system. Thus, a tracking system might produce more energy
per day than what the PVwatts calculator predicts.
and error, adjust the fixed tilt DC rating to give the same annual
energy value as the 1-axis or 2-axis system.