The reduced cost of solar photo-voltaic panel has created interest in households to opt for a solar panel on their roof top we have been getting various inquiries for roof top system sizing. Typically a house requires an average load of 2KW and 8 hours for operation. Hence the total energy requirement is about 16 KWh per day. Solar PV acts as back up to the grid and if we consider power back up requirements for 50% of this load, the energy requirement from Solar PV should be of the order of 8 units per day. Typical solar panels of 1 kW capacity produce about 5 unit (KWh) energy per day. Hence for this capacity about 2-3 KW solar panels are required. It is important to size the inverter and battery system accordingly hence in order to store 10 KWh. Inverter is available in 1 KW, 2 KW, 2.5 kW and 5 KW capacities . If future expansion plans are to be considered, 5 KW is an appropriate selection so that another 2.5 KW can be added to the same inverter in future. If the overall system is operating at 24 volts DC, a 2.5 KW DC system will produce about 10 Amp current at peak noon. This current needs to be charging the appropriate battery bank typically the modules that generate electricity at 18 volt or 36 volt. A 36 volt module is appropriate to charge a battery of 24 volt capacity, in order to assess the battery size, the battery is generally available in 12 or 24 volts and accordingly parallel and series combination is done.
Battery capacity is determined as follows:
Total Load= 2000 W
System voltage =24 volts
Operating hours = 4 hours
Battery capacity = (2000 ×4) ÷24= 333.33 A-h
Generally battery discharge is maximum upto 80%. Hence it is advisable to have 20% extra capacity to meet the required power back up.
Posted By: Prateek Sikka