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. “
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.
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.
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.
