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OFF GRID SOLAR POWER CASE STUDY
Off-Grid Residential Photovoltaic System
Vicki Reid, Descanso, California
“I shopped around our area for a solar
installer and couldn’t find anyone who would do a full
installation. We needed permits, solar power and a
generator. Basically we needed someone to take care of
all the details and follow through.
Apex Solar did a great job on the install and guiding us
through the whole process and I would recommend them
highly. “
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Description of Site:
The site is located in Descanso,
California, just east of San Diego. The site is in a
small valley and at an elevation of about 3,000 feet.
The site sees high summer temperatures of over 100
degrees and winter temperatures in the low 30s. The home
had a roof that was oriented perfectly for southern
exposure and was an ideal platform for the solar array.
Ms. Reid had purchased the property with the
understanding that utility power could be brought into
the site without any problems, as the nearest utility
pole was only a few hundred yards away. Upon completion
of the home, legal problems prevented her from accessing
a utility connection and she decided that going off-grid
was a better choice.
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Customizing the System:
In our site analysis with Ms. Reid, Apex
Solar noted that she would need a 120/240 volt system as
this would be necessary to power her well pump. In
addition, her home would have the normal household
appliances with an eye toward energy efficiency. Apex
Solar also recommended a generator back up for her
system and this would prove to be a major hurdle to
overcome as we started to work with local county code
requirements.
Considerations:
As Apex Solar started to develop a
system for Ms. Reid, it quickly became clear that
installing a generator in close proximity to the home
and solar array was not going to be feasible. The reason
for this was that the home was located close to the
property line and San Diego County has a noise ordinance
specifying, “…all generators shall not produce noise in
excess of 45 decibels at any property line.” (Department
of Planning and Land Use, Department of Public Works,
San Diego County.) Thus, the location for the generator,
batteries, and power panel had to be moved to the center
of the property and housed in a specifically engineered
noise-baffling structure.
Apex Solar worked directly with an acoustical engineer
to develop an enclosure that would allow for proper
ventilation of the generator and power equipment yet
reduce the perceived noise level at the property line to
less than 45 decibels.
By having the power panel at the center of the property
and the solar array at the house, this required a new
solution for delivering power from the solar array to
the batteries, which were 300 feet away.
See a larger photo
Apex Solar chose to use an AC coupled system, which
utilizes an SMA Sunny Boy inverter mounted on the house
and two (2) SMA Sunny Island inverters at the power
panel. This allowed all equipment to transfer power back
and forth on the AC side of the system, this allowed for
much longer distances with very low power losses.
An additional benefit of using the Sunny Islands was the
compact flash card that is plugged into the face of the
inverter and records all system parameters and errors.
If any errors or changes to the parameters of the system
need to be adjusted the compact flash card can be
removed and sent to a technician where a diagnostic
review of the information and adjustments to the
settings of the inverter can be made and the card
returned to the inverter where the information is
automatically downloaded and installed in the inverter.
This was especially beneficial to Ms. Reid as her
knowledge of the off-grid system was very limited and
this would allow Apex Solar to evaluate problems and
effect necessary changes without having to schedule a
site visit.
System Specifications:
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12 Evergreen ES 180 watt modules
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Unirac roof mounts\
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SMA Sunny Boy 3000U Inverter
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2 SMA Sunny Island 5000 watt
inverters
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Generac 18kW generator
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16 (L16) deep cycle batteries
Recommendations:
During the site analysis and design Apex
Solar made the following recommendations for Ms. Reid’s
system:
1. Pellet stove heating. The original home had
been heated with a central forced-air electric furnace.
Apex Solar recommended that the furnace not be used and
that it be replaced with another source of heat. Ms.
Reid chose a wood pellet stove.
2. Fluorescent light bulbs. This
included fixtures not normally associated with
fluorescent lights such as recessed can lights,
chandelier lights, and outdoor lighting. With new
advances in the availability of receptacles, bulb
shapes, and colors, the fluorescent bulb can match
almost all current incandescent bulb styles.
3. Other appliance recommendations.
Apex Solar recommended laptop computers over desk top
computers due to the significantly lower power draw.
Also, Apex recommended that all office equipment be
placed on power strips to allow for shut down of
“phantom loads” at the end of the day. In addition, the
electric kitchen stove and oven were replaced with an LP
gas stove.
Results of Installation:
This system was installed in five days
and has been operating maintenance-free since January
2008. The enclosure works incredibly well and the
generator noise was reduced to a low hum while standing
next to the generator enclosure. This installation
produced a very low maintenance system with an auto
generator start feature and the sophistication of the
SMA equipment.
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