1. Evaluating the Budget
2. Evaluating the Space required for Installation
3. Estimate the Site Annual energy production
4. Sizing the array and Selection of array
4.a Determine annual Energy consumption
5. Looking contract options
6. Getting ready to match the inverter to an array
6a. Power value to inverter of PV
6b. DC Voltage value to inverter of PV
6c. AC Voltage value to inverter of PV
6d Temperature coefficient of the module
7. Inverter Maximum current input
1. Evaluating the Budget
The Budget of the system whould be estimated based on kW, Area of installation, Technology etc
2. Evaluating the Space required for Installation
Space required for the installation will be evaluated based on few factors.
A. Area:-
1. Conduct site survey for available space for installation of modules
2. Consider site clearance for safety of installation and future maintenance and clearance from other services.
Make sure you have considered dead spaces (the space around the panel)
3. Run shade analysis for the space.
4. The Power Density of the module will be quick way to analyse the area, power relation.
5. Finalize the type of installation
B. Location (Based on Step-3):-
3. Estimate the Site Annual energy production
Step-1 Evaluate the agreement with the utility
tep-2 Estimate the annual energy production based on modeling programs like PV-Syst
Step-3 For quick analysis, use PV Watts to measure the energy production
Step-4 Finalize Tilt, orientation and shading effects of the array
Step-5 Don't treat this as a promised value
4. Sizing the array and Selection of array
4 A
- Collect the utility Bill for 12 months
- Make a load analysis chart
- Make sure there is no addition or deletion of load in the system
5. Looking contract options
Net Metering Agreement:-- Extra Energy produced by the client may not be en cashed
- The client will produce energy and will back up his loads, if any extra energy required, that will be taken from the utility
The time at which Extra energy produced by PV uploaded to utility
TOU - (Time of use Metering Method)
Utility charges the client based on the time of the day he consumes or produces. usually the day time energy cost may be high comparing to night time, hence its advisable to reduce the consumption and increase the power uploading
FIT (Feed in Thariff Method)
Energy produced will be connected will be through separate meter and will be considered as a separate entity. Hence the load details will not have any relation between the PV sizing.Working Steps:-
- Calculate the energy consumption of client (from step4)
- If client may need 5000kWh/Yearly
- If Solar PV produces 2000kWh/Yearly
- Remaining power can be loaded from utility
- Also cross check the maximum demand
6. Getting ready to match the inverter to an array
Matching the PV with inverter will be subdivided to three steps
Power --> Voltage --> Current
The Calculation should be submitted to electrical inspector if necessary
6a. Power value to inverter of PV
- Options of using multiple inverter should be considered
- The array output losses to be considered (temp cof, resistivity of the cable, efficiency of the system,)
- Industrial standard for Eff. is 80% for array
- Maximum rated power input of the inverter be taken from the spec sheet of the inverter
- If you connect more number of PV modules to inverter, inverter may not take that power
- If inverter handle more power for a long run, the life of the inverter may come down
5000W array x 87% Eff. = 4350W ( Inverter rating) next available size is 4.5kW inverter
Advantage of selecting next higher rating inverter
- If in a sunny day the irradiance is more than 1000W, the array produce more energy and we may not utilize that power, if the next size selected, we can utilize this additional power.
- The life span of the inverter will increase, (its not fully loaded)
- Also check the efficiency of the inverter at different loading (like losses @ 25%, 50% & 75% Loading.
Voltage window - Minimum and maximum values of the voltage in the incoming and outgoing side of the inverter
- Make sure that the array designed for the voltage within the window of the inverter voltage
- If the input voltage is higher, the inverter will trip
- If the input voltage is lower, the inverter will shut down
- Make sure the protection for the DC input side of the inverter
- Maximum DC voltage willl be recorded by the inverter, if inverter fails due to high input DC vge, the warranty may not be applicable for the inverter.
Check the line voltage
Match it with inverter output voltage
Eg: - If the grid voltage is 120/240V we cannot select an inverter is with 210/208V
6d Temperature coefficient of the module
The Voltage and temperate of the module will have inverse characteristic, make sure , array voltage will not exceed the inverter's input value
Temperature coff. of crystalline module is 0.35%/'C (for general calculation)
Temperature coff. of thin filim module will be crosschecked in technical spec.
The temperature coff. value of the inverter will always depends on the type of module.
Calculate Module's Maximum Voltage
How to calculate the change in voltage due to temp in a PV Module
- Collect the temperature coefficient of the PV module
- Collect the record cold temperature for client location in degree celsius
- calculate how many degree Celsius less than STC (25'C) in the site on the record cold day
- multiply the temperature coefficient of he module by the number of degree calculated in step-3
- add the value with Voc of the module STC
Voc- 45V
Temp Coefficient (+-0.35"C)
Step-(1) temp coff (-0.35"C)
Step-(2) record cold temperature for client location in degree Celsius 15"C
Step-(3) 15'C - 25"C = -10"C Step-(4) -10 x 0.35% = 3.5% rise in voltage (of -ve value fall in voltage, +ve rise in voltage)
Step -(5) add the value with Voc of the module STC
Voc- 45V
Temp Coefficient (-0.158V/"C)
Step-(1) temp coff (-0.158V/"C)
Step-(2) record cold temperature for client location in degree Celsius 15"C
Step-(3) 15'C - 25"C = -10"C Step-(4) -10 x -0.158V/"C = +1.58Volt rise in voltage (of -ve value fall in voltage, +ve rise in voltage)
Step -(5) add the value with Voc of the module STC
Case Study
Voc - 45V
Temp Coefficient (-0.158V/"C)
Step-(1) temp coff (-0.158V/"C)
Step-(2) record cold temperature for client location in degree Celsius -5"C
Step-(3) -5'C - 25"C = -30"CStep-(4) -30 x -0.158V/"C = +4.7Volt rise in voltage (of -ve value fall in voltage, +ve rise in voltage)
Step -(5) add the value with Voc of the module STC --> 45V + 4.7V = 49.7V
Taking the vaule from NEC
The Temperature coff can be taken from the NEC table 690.7
Execptions-
When the information provided by manufacturer, you shall calculate the new voltage.
The table is applicable for only crystalline, (if you are using thin film , this table may not be applicable)
NEC values are more conservative, that may not work in the system.
Calculate Module's Minimum Voltage
The Voltage may go down if the temperature of the stalled will be higher than STC
If the voltage come down below the window, the inverter may shut down
Long Term performance of the system
Over the course of 25 years, the power produced by the PV module may decrease by 1% in every year.
This factor should consider while we calculating the DC voltage and selection of inverter
Calculating Minimum DC Voltage in PV module
Step-1 Collect the temp coff. of PV module in Volt/'C
This value can be taken from Spec sheet
Step-2 Collect 2% design temp for your client location i "C
From ASHRAE
Step-3 Determine how may "C to add to (2) based on type of mounting array
Step-4 Add (3) + (2)
Step-5 (4) - STC =(5)
Step-6 (5) x Temp Coefficient = (6)
Step-7 (6) + Vmp @ STC = (7)
Case Study
Vmp - 37.2
Step-1 Temp coff. of PV module in Volt/'C -> -0.5%/"C
37"C x -0.5%/"C = 37"C x -0.005V%/"C = -0.186Volt / "C
This value can be taken from Spec sheet
Step-2 2% design ambient temp for your client location --> 33"C
Step-3 Determine how may "C to add to (2) based on type of mounting array
Panel mounted within 6' from ground hence consider --> 35"C
Step-4 Add (3) + (2) --> 35"C + 33"C = 68"C
Step-5 (4) - STC =(5) --> 68"C - 25"C = 43"C
Step-6 (5) x Temp Coefficient = (6) --> 43"C x 0.186Volt / "C = -8Volt
Step-7 (6) + Vmp @ STC = (7) --> 37.2Volt + (-8Volt) = 29.2Volt
Minimum No of Modules needed
Inverter DC window min - 250Vlot DC
250Volt DC / 29.2Volt = 8.56Modules or 9 Modules Minimum
