My 4400 Watt
Battery Backup Utility Interactive Photovoltaic System
This system is a grid-tied, PV system with battery back-up, with PV generation consisting of 22 PV modules with a combined STC rated dc output power of 4400 watts. The modules are mounted on a custom-designed mounting structure, engineered to withstand winds exceeding 150 mph, and are connected into 11, 3-module, source circuits. I be source circuits feed two Maximum Power Point Tracking Charge Controllers to maximize energy capture by the PV modules, The charge controllers feed the system batteries and the inverters, which are connected to supply 120/240 volt ac emergency loads and also to the electric utility grid. The system is provided with a visible, lockable, load break utility disconnect switch and all disconnects and labels required by the National Electrical Code. Optional system performance metering and optional bi-directional utility’ kWh meters are also available. The system batteries are sized tor either 216, 258, 400 or 512 ft amp hours at 48 V for providing approximately 8, 8.6, 16 or 20 kWh of emergency power from the inverter to emergency (uninterruptible) loads.
When the sun is shining, power from the PV array is used to keep the batteries fully charged. After charging the batteries, the PV power is made available to the emergency loads. If PV power meets the requirements of the emergency loads, any remaining PV power is then directed to the interruptible loads of the occupancy. If any PV power remains after the interruptible loads have been powered, it is delivered to the utility. When utility power is available, but if PV power is not available, emergency loads are supplied by the utility . If neither utility nor PV power is available, emergency loads are supplied by the batteries. Thus, the batteries are only cycled if utility power is lost. The batteries used are specially designed, deep cycle, maintenance free batteries that arc capable of undergoing approximately 3.000-4,000 charge-
discharge cycles. Designing the system to minimize battery cycling extends the life of the batteries.
The inverter meets the requirements of IEEE 929 and UL 1741. This means that if it detects a loss of utility power, it will automatically disconnect from the utility. When this happens, only the uninterruptible loads arc powered by the inverter. When utility voltage is restored, the inverter automatically reconnects to the utility grid after verifying utility voltage and frequency stability.
Note that the two Outback GVFX3648 Inverters will supply a maximum of 7200 watts when the utility grid is down. When the utility grid is up, the inverters will pass through 60A @ 120V, or 7200 VA each. for a total of 14,200 VA.
Note also that the PV system can be expected to generate approximately 27kWh per day as long as the day is mostly sunny. Run times of loads may need to be adjusted on a daily basis to avoid having the inverter shut down if the battery state of charge reaches the minimum allowable limit of 44 volts. The estimated daily kWh loads in the table are based on assumed emergency operation.
When the utility is in operation, the kWh consumption is no longer limited by battery capacity, since the grid will supply 11,520 VA continuously (60A C.B) via the inverters if necessary.