Design criteria

DESIGN CRITERIA BEFORE DESIGN A SYSTEM

Precaution to consider before start designing

• Before designing,check the components rating availability. 
• According to the availability of market standard products,make the design simple and easy. 
• 4main considerations to take into account:

           >load requirement

           >inverter standard ratings(power,std.voltage ranges of DC input/AC output)

           >battery capacity

           >SPV module Wattage

Efficiency factors to be consider while designing the system

• Overall system efficiency from panel output to terminal loadpoint,which terminated as 77%to82%. 
• Solar panel-take output as 90 to 95% of the STC(standard Testing condition)rating 
• Inverter-consider 95to98% for transformer less inverters,and 80to85%nfor inverter with built-in-transformer. 
• Battery-efficiency due to internal battery losses80to85% 
• Derating factor for the DOD(depth of discharge)60to70% 
• Charge controller 15-25% increase in ampere ratings(overload capacity)
• Cable-consider sizing 115%of the operating current(amperes)in circuits 
• DC and AC circuit breakers-125% of overload current for over load protection and upto 250% of short circuit current in the system 
• And the circuit breakers to be designed and specified for the maximum AIC(ampere interrupting capacity)rating equal to the potential fault current that may flow into the specific circuit section.

Inverter design and sizing:

• Input of the inverter rating which should not be less than the total demand load in watts of the system and care should be taken that the inverter capacity covers the maximum demand/peak load device. 
• For stand alone system-inverter size should be 25-30%larger than the demand load 
• Grid-tie system-the input rating should be same as the PV modules 
• Total demand watt of the system is raised by the inverter efficiency 
• Inverter input DC voltage range:12v,24v,48v,96v,144v,192v,240v,400v…..upto 960v

Solar charge controller and sizing:

• It is typically rated against ampere and voltage capacities. Select cc to match the voltage of pv array and batteries and identify which type of cc is right for your application.make sure that cc has enough capacity to handle the current from PV array.

• For series cc type ,the sizing of cc depends on the total PV input current which is deliverd to the cc and also depend upon PV panel configuration.(series and parallel configuration).

• The ampere is increased by the 15% upto 25% to avoid the losses and overloading

• Ranges in market:10A,15A,82A,85A……250A ans voltage upto 600volts.

• According to standard practice,the sizing of cc is to take the short circuit current(Isc)of the PV array,and multiply it by 1.25(125%) ,CC rating=total short circuit current of PV array*1.25

Battery sizing with backup:

• Determine the total watt-hour energy storage and multiply with the number of days storage requirement.

• Raise such arrived capacity by inverter efficiency,battery efficiency and battery DOD factor and divide by system nominal voltage,to arrive battery capacity in Ah

• Nominal voltage which chosen according to panel output and inverter input voltage

• 12v battery available ranges:25Ah,40Ah,70Ah,100Ah,135Ah,150Ah,185Ah,200Ah

• Req.installed battery capacity=(total watt-hour of energy required for storage)/(batt.effi*batt.DOD*batt.bank operating DC voltage)