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.”
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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.
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.
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
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.