OFF GRID CASE
STUDY: Off-Grid Photovoltaic System
Vic Cooper, Big Sur, California
"We were very much satisfied. I thought
the job was professionally done. The components he
picked out seemed to work well together."
"Overall I enjoyed working with Farrel, which hasn’t
been the case with other people. I did call a few people
to ask about solar installation and did Web searches,
but because we were remote, a lot of people didn’t want
to work with us."
See a larger photo
Description of
Site:
The site is located in Big Sur,
California about one mile from the closest utility power
pole. The property is located on very steep terrain at
1800 feet above the Pacific Ocean with numerous scrub
oaks on site. Although the majority of the property is
steep, it does receive good southern exposure with no
obstructions.
Mr. Cooper purchased the property
with an existing solar electric power system in place,
but the system was underpowered and in poor condition.
The existing system was installed with a few low wattage
modules that were lying on the ground with exposed
wires. The system had used a low amperage charge
controller and a small bank of car batteries.
Customizing the System:
In our site analysis with Mr. Cooper, he
noted that he wanted a power system that could produce
both 120 and 240 volts. This would be necessary to power
a well pump. Mr. Cooper also noted that he wanted to be
able to run a standard electric (22 cubic foot)
refrigerator and a variety of office and household
appliances. The last consideration was his desire to
eventually construct a shop that would be at some
distance from the main house and would require a
substantial amount of power to run high-demand shop
tools.
Using a 120/240 volt system allowed Mr.
Cooper the option to operate high power equipment at a
longer distance from the power source than he would have
had with just a 120 volt system.
See a larger photo
Considerations:
The most appropriate site for the solar
array was located on a steep embankment that had good
southerly exposure. Due to the high winds in the local
area, Apex Solar chose a high-strength ground mount that
allowed the array to conform to the hillside. Also, at
Mr. Cooper’s request Apex Solar left extra racking space
on the array for additional modules to be placed there
at a later time if so desired.
Apex Solar chose
an Outback Power System which used a stacked pair of
3600 watt inverters. This allowed for a 120/240 volt set
up with an automatic generator start ability. Another
benefit of using an auto-start generator is that there
is little chance of damaging the battery bank due to a
deep discharge. This type of system requires very little
maintenance on the part of the homeowner.
The
power panel (the inverters, charge controllers, and
circuit breaker boxes) was mounted in a secure area of
the garage. The solar array was configured for a higher
voltage (100 volts) due to a distance of 250 feet, from
the array to the power panel. Because of the higher
voltage and lower amperage of the array, a small
diameter wire conductor was used without significant
loss of efficiency.
System Specifications:
-
2550 watt array using fifteen Sharp
170 watt modules
-
Sixteen 360 amp hour batteries (L16)
operating at 48 volts
-
Outback 7200 watt stacked inverters
operating at 120/240 volt
-
Mx 60 Charge controller
-
18 Kw diesel generator with auto
start on demand
Recommendations:
During the site analysis and design Apex
Solar made the following recommendations for Mr.
Cooper’s system:
-
Radiant Floor Heating.
The original home had been heated with a
wood-burning stove. Mr. Cooper wanted to update
this with a more modern heating system. Apex
Solar recommended a radiant floor system because
of the low energy demand of the radiant floor
water pumps and the ability to heat the water
with a solar thermal panel and a gas water
heater backup.
-
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.
-
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.
Results of
Installation:
This system was
installed in five days and has been operating
maintenance-free for over 8 months.
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