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FOR IMMEDIATE RELEASE
Ft. Tuthill, Flagstaff, AZ Solar SuccessRESTROOM SOLUTIONS, INC. IS SUCCESSFUL IN TEAMING WITH PHOTOVOLTAIC RESOURCES INTERNATIONAL TO SOLVE COCONINO COUNTY'S SOLAR PROBLEMS AT FT. TUTHILL.April 21, 2003 After several concerns were expressed about the performance of the solar equipment at Ft. Tuthill's Amphitheater Solar Powered Composting Restroom, Kevin Mart, President of Restroom Solutions, Inc. and Bill Kaszeta, President of Photovoltaic Resources International piled into RSI's 4Runner and made it to the mountains. Seems the problem was "branches", "sap" and "shadows". See report filed by Bill below.
This
letter is a report of our site visit to the This
site has a photovoltaic (PV) power system that operates two composting toilet
fans. Power for the fans is supplied
by three pole mounted PV modules located about 25 feet south of the building.
To reduce the cost of the system, a speed (and power) reduction circuit
was designed into the controller. The
intention was to operate the fan at about half the normal current when the
temperature was below 50°F, as detected by a thermostat in the control
enclosure. The
inspection of the system determined the following: 1.
The PV
array was installed under a tree and as a result the branches of the tree were
casting shadows on the PV modules as shown below:
These shadows have a severe impact on system
performance because the current produced by each of the three PV modules is
determined by the least illuminated cell in the PV module.
In full sun we measured an output of about 5 amps with the shadows shown
above. There was also an area of sap over one of the solar cells (photo did not
record properly). After the branches
were trimmed back, the current increased to about 9.5 amps.
Cleaning the sap covered area increased the current to 10.5 amps, the
expected value for the three PV modules. 2.
There is
a large tree to the east of the PV array as shown below:
This tree casts a shadow on the array in the morning,
reducing the output substantially in addition to the closer shadows.
The presence of this tree was not known when the system was designed.
Proper operation of the system will require either removing the tree,
adding a PV module, or reducing the power required.
More about the options in the recommendation section of this report. 3.
The
system control assembly has an electronic speed control for the fan output that
was factory adjusted to reduce the current drawn by the fans in the winter when
sunshine is limited. This speed
reduction is set by a potentiometer on a printed circuit board in the control
enclosure and operation of the speed reduction is determined by a thermostat in
the control enclosure. The
thermostat was initially specified to be set at 50°F (its minimum setting).
The speed can be reduced in the winter because less air is needed for
composting in cold weather. The potentiometer was found to be in the full ccw
position and as such the fan would not operate when the temperature is below 50°F,
a common remark on the system log. If
the potentiometer had been left in the proper position, the fan would have
operated during many of the periods when it was recorded as not operating. 4.
Two of
the settings on the Trace C-12 PV system regulator were not in the specified
position, resulting in system low voltage disconnect/reconnect not functioning
as designed. These were reset to the
specifications indicated on the drawing inside the controller.
The settings were such that they increased the protection of the
batteries while reducing the operation of the fans. 5.
Because
of the shadows on the PV array, the batteries were at approximately 50% state of
charge. A short test of each of the
four batteries with a 7-amp load for 15 minutes indicated that the batteries
have not been damaged. 6.
No other
problems were noted. Recommendations: A.
Reliable
operation will require either removing the tree that shadows the PV array,
adding a PV module, or reducing the power required.
I recommend replacing the two 300 CFM fans with lower power 240 CFM fans.
This is relatively easy to do and will operate reliably in spite of the
tree shadow. Replacement fans are
$75 each from PVRI or Restroom Solutions. B.
Increase
the thermostat setting to 70°F so that a higher percentage of the winter
operation is at the lower power setting. Respectfully, William
J. Kaszeta President
For More Information Contact: |
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