Photovoltaic Systems Engineering Session 17 Solar+Storage Systems SEC598F18 Photovoltaic Systems Engineering Session 17 Solar+Storage Systems Grid-tied Systems, part 2 October 31, 2018

Session 17 content Battery Enhanced Systems Design Example Battery Purposing Inverter and Battery Selection Required programming

Battery-Enhanced PV Systems – Example Part 1: Standby Loads

Battery-Enhanced PV Systems – Example Part 2: Inverter Selection Characteristics Pout = 3600W @ 120V This power level is less than the highest possible load (5044W), so at some point the inverter will shut down until the load drops. In other words, not all the loads could be operated simultaneously Ipass = 60A (continuous) The load current maximum is 42.4A, and if it is viewed as a continuous flow, then the design current is: Idesign = 1.25 * 42.4A = 53A < 60A

Battery-Enhanced PV Systems – Example Part 3: Battery selection Daily load: Eday = 7.35kWh/day Energy supplied to inverter: Esupply = 7.35kWh/(0.98*0.94) = 8.0kWh Charge to be supplied by batteries: Qsupply = Esupply/Vbatt = 8000Wh/(48V) = 166Ah To account for 80% depth of discharge QF = Qsupply/DoD = 166Ah/0.8 = 208Ah wire loss CC loss

Battery-Enhanced PV Systems – Example Part 3: Battery selection, cont. Autonomy: Battery choice: Vbatt = 6V Qbatt = 200-250Ah Number of batteries: Eight 6V batteries in series yields 48V outage t < 1 day Grid on Grid on

Battery-Enhanced PV Systems – Example Part 3: Battery selection, cont. Choosing Pb-acid batteries: Flooded batteries are lower cost, but typically have lower DoD allowances AGM and Sealed batteries are more expensive, can discharge faster, but have fewer O&M troubles A faster discharge rate reduces capacity: 6V @ 208 Ah with C/24 rate derates to 6V @ 186 Ah with C/8 rate

Battery-Enhanced PV Systems – Example Part 4: Array sizing On a daily basis, charge to be supplied by the array: Qarray = Qsupply/hbatt = 166 Ah/0.9 = 185 Ah This charge must be supplied at 48V Earray = Qarray * Vbatt = 185 Ah * 48 V = 8.88 kWh To account for array losses Earray, daily = Earray /(hmismatchhwirehMPPT) = 8.88 kWh/(0.85*0.98*0.98) = 10.9 kWh

Battery-Enhanced PV Systems – Example Part 4: Array sizing, cont. On a monthly basis Earray, monthly = Edaily*30 = 327 kWh Using PVWatts A system of 4kW seems perfectly suitable Upon reflection A system of 4kW would over-produce most of the year, so it is prudent to calculate a size that matches the need in the month most likely to have power failures So, 4kW can be reduced to 2.8kW

Battery-Backup PV Systems – Example Part 5: Charge Controller and Inverter considerations PV Battery Charging

Battery-Backup PV Systems – Example Part 5: Charge Controller and Inverter considerations PV Battery Charging Complete

Battery-Backup PV Systems – Example Part 5: Charge Controller and Inverter considerations No PV

Battery-Backup PV Systems – Example Part 5: Charge Controller and Inverter considerations No Grid