General Sizing Instructions
The design of any PV system requires certain basic calculations. First,
This method was first developed by experienced PC system designers and published in 1988 as "Stand-Alone Photovoltaic Systems - A Handbook of Recommended Design Practices". The worksheets developed in this handbook can be completed to give the size of the PV array and battery that are needed to produce and store the energy needed by the load. Other worksheets can be used to determine the size of wires, fuses, switches, etc. (the BOS) required to install your system. The blank worksheets in each section may be copied and saved.
Calculate the Load
Design Current
Battery Size
PV Array Size
Hybrid Needed??
Use Worksheet #1 to calculate the power (current) requirements of the load
You must estimate the amount of power required by the load. This is done by listing each load and making an estimate for how energy it will consume in a day. The worksheet calculations will yield the total daily load given in Amp-hours. If the load demand varies widely from month-to-month (or season-to-season), you must fill out Worksheet #1 for each month. Usually the system size will be dictated by the worst-case month&emdash;the month with the largest load and the lowest solar insolation. Consider this month first.
Each box in the worksheet is numbered. The instructions below tell you how to fill in each box.
1 Load Description: List each load (i.e., fluorescent lamp, pump, radio). Enter the dc loads at the top and the ac loads, if any, at the bottom part of the worksheet. 2 QTY: Enter the number of identical loads in the system. 3 Load Current (A): Enter an estimate of the current required by each load when operating. Use the manufacturer's rated current, or measure the current. 4 Load Voltage (V): Enter the voltage of the load, i.e., 120 volt ac, 24 volt dc, etc. The operating voltage is usually listed on the appliance. 5A DC Load Power (W): Calculate and enter the power required by the dc load. Power equals the product of voltage and current. 5B AC Load Power (W): Calculate and enter the power required by the ac load. Ignore the power factor for this calculation. 6 Daily Duty Cycle (hrs/day): Enter the average amount of time per day the load will be used. (Enter fractions of hours in decimal form, i.e., 1 hour, 15 minutes would be entered as 1.25.) 7 Weekly Duty Cycle (days/wk): Enter the average number of days each week the load will be used. 8 Power Conversion Efficiency (decimal): This factor accounts for power loss in systems using power conditioning components (converters or inverters). If the appliance requires ac power or dc power at a voltage other than your system voltage, you should enter the conversion efficiency of the device. If you do not have the actual efficiency of the converter being used, use the default values given below for initial sizing. Power Conversion Efficiency Default DC to AC 0.85 DC to DC 0.9 9 Nominal System Voltage (V): Enter the desired system voltage. The system voltage is normally the voltage required by the largest loads. Common values are 12 or 24 volts dc and 120 volts ac. 10 Amp-Hour Load (Ah/day): Calculate the average energy requirement per day in ampere-hours by performing the calculations as indicated by the mathematical symbols across the page. 11 Total DC and AC Load Power (W): Enter the individual ac and/or dc loads. 11A Total dc load in Watts. 11B Total ac load in Watts. 12 Total Ampere-Hour Load (Ah/day): Calculate the daily average system load in ampere-hours. 13 Total DC Load Power (W): Enter value from Block 11A. 14 Total AC Load Power (W): Enter value from Block 11B. 15 Nominal System Voltage (V): Enter value from Block 9. 16 Peak Current Draw (A): Calculate the maximum current required if all the loads are operating simultaneously. This value is used for sizing fuses, wiring, etc. 17 Total Ampere-Hour Load (Ah/day): Enter value from Block 12. 18 Wire Efficiency Factor (decimal) (1 - wire loss): Enter the decimal fraction accounting for loss due to wiring and switchgear. This factor can vary from 0.95 to 0.99. Wire size should be chosen to keep wire loss in any single circuit to less than 3 percent (>0.97). Wire Efficiency Factor Default Value = 0.98 19 Battery Efficiency Factor (decimal): Enter the battery efficiency which is equal to ampere-hours out divided by ampere-hours in. Use manufacturer's data for specific battery. Assume constant voltage operation. Battery Efficiency Factor Default Value = 0.90 20 Corrected Amp-Hour Load (Ah/day): Calculate the energy required to meet the average daily load plus losses.
1 Load Description: List each load (i.e., fluorescent lamp, pump, radio). Enter the dc loads at the top and the ac loads, if any, at the bottom part of the worksheet.
2 QTY: Enter the number of identical loads in the system.
3 Load Current (A): Enter an estimate of the current required by each load when operating. Use the manufacturer's rated current, or measure the current.
4 Load Voltage (V): Enter the voltage of the load, i.e., 120 volt ac, 24 volt dc, etc. The operating voltage is usually listed on the appliance.
5A DC Load Power (W): Calculate and enter the power required by the dc load. Power equals the product of voltage and current.
5B AC Load Power (W): Calculate and enter the power required by the ac load. Ignore the power factor for this calculation.
6 Daily Duty Cycle (hrs/day): Enter the average amount of time per day the load will be used. (Enter fractions of hours in decimal form, i.e., 1 hour, 15 minutes would be entered as 1.25.)
7 Weekly Duty Cycle (days/wk): Enter the average number of days each week the load will be used.
8 Power Conversion Efficiency (decimal): This factor accounts for power loss in systems using power conditioning components (converters or inverters). If the appliance requires ac power or dc power at a voltage other than your system voltage, you should enter the conversion efficiency of the device. If you do not have the actual efficiency of the converter being used, use the default values given below for initial sizing.
Power Conversion Efficiency Default
DC to AC
0.85
DC to DC
0.9
9 Nominal System Voltage (V): Enter the desired system voltage. The system voltage is normally the voltage required by the largest loads. Common values are 12 or 24 volts dc and 120 volts ac.
10 Amp-Hour Load (Ah/day): Calculate the average energy requirement per day in ampere-hours by performing the calculations as indicated by the mathematical symbols across the page.
11 Total DC and AC Load Power (W): Enter the individual ac and/or dc loads.
11A Total dc load in Watts.
11B Total ac load in Watts.
12 Total Ampere-Hour Load (Ah/day): Calculate the daily average system load in ampere-hours.
13 Total DC Load Power (W): Enter value from Block 11A.
14 Total AC Load Power (W): Enter value from Block 11B.
15 Nominal System Voltage (V): Enter value from Block 9.
16 Peak Current Draw (A): Calculate the maximum current required if all the loads are operating simultaneously. This value is used for sizing fuses, wiring, etc.
17 Total Ampere-Hour Load (Ah/day): Enter value from Block 12.
18 Wire Efficiency Factor (decimal) (1 - wire loss): Enter the decimal fraction accounting for loss due to wiring and switchgear. This factor can vary from 0.95 to 0.99. Wire size should be chosen to keep wire loss in any single circuit to less than 3 percent (>0.97).
Wire Efficiency Factor Default Value = 0.98
19 Battery Efficiency Factor (decimal): Enter the battery efficiency which is equal to ampere-hours out divided by ampere-hours in. Use manufacturer's data for specific battery. Assume constant voltage operation.
Battery Efficiency Factor Default Value = 0.90
20 Corrected Amp-Hour Load (Ah/day): Calculate the energy required to meet the average daily load plus losses.
Use Worksheet #2 with estimates of the solar energy available at (or near) your site to determine the Design Current and the optimum tilt angle for your PV array. An array set at the same angle as the latitude of the site will receive the maximum annual solar radiation. If the load demand is high in the winter (northern hemisphere), set the array tilt at latitude plus 15°. For a predominant summer load, set the array tilt angle at latitude minus 15°. Calculate the design current for all three tilt angles if the load demand varies widely throughout the year. Completing the calculation on the worksheet will yield the optimum tilt angle for your array. The numbered instructions correspond to the numbers in the boxes in the worksheet. The worksheet may be copied and saved.
21 System Location/Insolation Location: Enter the latitude and longitude of the system site and the location of the insolation data used. See Appendix A. 22A, B, & C Corrected Load (Ah/day): See Block 20 Worksheet #1. Enter the corrected load for each month for each tilt angle. 23A, B, & C Peak Sun (hrs/day): Enter the average number of hours each day when insolation was 1,000 watts per square meter. Enter the value for each month for each tilt angle. Weather data for selected sites is given in Appendix A. NOTE: Peak sun hours are equal to the average kilowatt-hours/m2-day. 1 kwh/m2 = Langley/85.93 = 316.96 Btu/ft2 = 3.6 MJ/m2. 24A, B, & C Design Current (A): Calculate the current required to meet the system load. NOTE: The recommended tilt angle for the array is selected by first determining the largest design current for each of the three tilt angles; then selecting the smallest of those three values. 25A + 26A Peak Sun (hrs/day) and Design Current (A): Select and enter the largest monthly design current and corresponding peak sun hours from columns 24A, 24B, and 24C. 27 & 28 Peak Sun (hrs/day) and Design Current (A): Select and enter the smallest of the three design currents and the corresponding peak sun hours from 25A, B, or C and 26A, B, or C.
21 System Location/Insolation Location: Enter the latitude and longitude of the system site and the location of the insolation data used. See Appendix A.
22A, B, & C Corrected Load (Ah/day): See Block 20 Worksheet #1. Enter the corrected load for each month for each tilt angle.
23A, B, & C Peak Sun (hrs/day): Enter the average number of hours each day when insolation was 1,000 watts per square meter. Enter the value for each month for each tilt angle. Weather data for selected sites is given in Appendix A.
NOTE: Peak sun hours are equal to the average kilowatt-hours/m2-day. 1 kwh/m2 = Langley/85.93 = 316.96 Btu/ft2 = 3.6 MJ/m2.
NOTE: Peak sun hours are equal to the average kilowatt-hours/m2-day.
1 kwh/m2 = Langley/85.93 = 316.96 Btu/ft2 = 3.6 MJ/m2.
24A, B, & C Design Current (A): Calculate the current required to meet the system load.
NOTE: The recommended tilt angle for the array is selected by first determining the largest design current for each of the three tilt angles; then selecting the smallest of those three values.
25A + 26A Peak Sun (hrs/day) and Design Current (A): Select and enter the largest monthly design current and corresponding peak sun hours from columns 24A, 24B, and 24C.
27 & 28 Peak Sun (hrs/day) and Design Current (A): Select and enter the smallest of the three design currents and the corresponding peak sun hours from 25A, B, or C and 26A, B, or C.
Use Worksheet #3 to calculate the size of the battery needed for the PV system. This will depend largely on the value you select for storage days. This value depends on many factors such as site accessibility, type of batteries selected, and variability of the load. For more information see the discussion on batteries.
29 Corrected Amp-Hour Load (Ah/day): Enter value from Block 20 Worksheet #1. 30 Storage Days: Choose and enter the consecutive number of days the battery subsystem is required to meet the load with no energy production by the array. System availability is defined as critical (99 percent available) or non critical (95 percent available) and directly affects the number of storage days. Use the chart below to find the recommended number of storage days if no better estimate can be made. 31 Maximum Depth of Discharge (decimal): Enter the maximum discharge allowed for the battery. This depends on size and type of battery. Consult the battery manufacturer or use default values below. Maximum Depth of Discharge Battery Type Default Value Lead Acid Shallow Cycle 0.25 Lead Acid Deep Cycle 0.75 Nickel Cadmium 0.90 32 Derate for Temperature (decimal): Enter a factor that derates the battery capacity for cold operating temperatures. Ask the battery manufacturer for this information. If no better information is available derate a lead acid battery's capacity one percent for each degree Celsius below 20°C operating temperature. Temperature Correction Factor Default = 0.90 33 Required Battery Capacity (Ah): Calculate the battery capacity required to meet the daily load for the required number of days. NOTE: Select a battery for your system and record the specifications in the battery information block. 34 Capacity of Selected Battery (Ah): Enter the manufacturer's rating of battery storage capacity in ampere-hours. Batteries are normally rated at optimum test conditions; 20°C, and discharge rates of C/20 or lower. 35 Batteries in Parallel: Calculate the number of parallel connected batteries required to provide the storage capacity. 36 Nominal System Voltage (V): Enter the value from Block 9, Worksheet #1. 37 Nominal Battery Voltage (V): Enter the rated voltage of the selected battery, i.e., 2, 6, or 12 volts. 38 Batteries in Series: Calculate the number of series connected batteries required to provide the system voltage. 39 Batteries in Parallel: Enter the value from Block 35. 40 Total Batteries: Calculate the total number of batteries in the system. 41 Batteries in Parallel: Enter the value from Block 35. 42 Capacity of Selected Battery (Ah): Enter the value from Block 34. 43 System Battery Capacity (Ah): Calculate the battery system storage capacity. 44 Maximum Depth of Discharge (decimal): Enter the value from Block 31. 45 Usable Battery Capacity (Ah): This is the amount of ampere-hours that can safely be used from the installed batteries.
29 Corrected Amp-Hour Load (Ah/day): Enter value from Block 20 Worksheet #1.
30 Storage Days: Choose and enter the consecutive number of days the battery subsystem is required to meet the load with no energy production by the array. System availability is defined as critical (99 percent available) or non critical (95 percent available) and directly affects the number of storage days. Use the chart below to find the recommended number of storage days if no better estimate can be made.
31 Maximum Depth of Discharge (decimal): Enter the maximum discharge allowed for the battery. This depends on size and type of battery. Consult the battery manufacturer or use default values below.
Maximum Depth of Discharge
Battery Type
Default Value
Lead Acid Shallow Cycle
0.25
Lead Acid Deep Cycle
0.75
Nickel Cadmium
0.90
32 Derate for Temperature (decimal): Enter a factor that derates the battery capacity for cold operating temperatures. Ask the battery manufacturer for this information. If no better information is available derate a lead acid battery's capacity one percent for each degree Celsius below 20°C operating temperature.
Temperature Correction Factor Default = 0.90
33 Required Battery Capacity (Ah): Calculate the battery capacity required to meet the daily load for the required number of days.
NOTE: Select a battery for your system and record the specifications in the battery information block.
34 Capacity of Selected Battery (Ah): Enter the manufacturer's rating of battery storage capacity in ampere-hours. Batteries are normally rated at optimum test conditions; 20°C, and discharge rates of C/20 or lower.
35 Batteries in Parallel: Calculate the number of parallel connected batteries required to provide the storage capacity.
36 Nominal System Voltage (V): Enter the value from Block 9, Worksheet #1.
37 Nominal Battery Voltage (V): Enter the rated voltage of the selected battery, i.e., 2, 6, or 12 volts.
38 Batteries in Series: Calculate the number of series connected batteries required to provide the system voltage.
39 Batteries in Parallel: Enter the value from Block 35.
40 Total Batteries: Calculate the total number of batteries in the system.
41 Batteries in Parallel: Enter the value from Block 35.
42 Capacity of Selected Battery (Ah): Enter the value from Block 34.
43 System Battery Capacity (Ah): Calculate the battery system storage capacity.
44 Maximum Depth of Discharge (decimal): Enter the value from Block 31.
45 Usable Battery Capacity (Ah): This is the amount of ampere-hours that can safely be used from the installed batteries.
Use Worksheet #4 to calculate the size of the photovoltaic array. This should be large enough to provide energy to the load during the Design Month and to fully recharge the batteries during periods of sunny weather. For information on PV modules click here. The blank worksheet may be copied and saved.
46 Design Current (A): Enter the value from Block 28, Worksheet #2. 47 Module Derate Factor (decimal): Enter a factor to adjust module current from standard operating conditions (SOC) of 1,000 w/m2 and 45°C temperature to field conditions, i.e., dust accumulations, mismatch loss between modules, degradation over time, etc.) Ask the module distributor or use the default values below. Module Derate Factor Default Value Module Type Default Value Single or Polycrystalline Silicon 0.90 Amorphous Silicon 0.70 48 Derated Design Current (A): Calculate the minimum array current necessary to supply the average daily load at the chosen site. NOTE: Select a PV module and record the specifications in the module information block. Be sure to determine the module voltage when it is operating at the highest temperatures expected for your site. 49 Rated Module Current (A): Enter the rated module operating current at 1,000 w/m2 and 45°C operating temperature as given by the manufacturer. 50 Modules in Parallel: Calculate the number of parallel connected modules required to provide the array current. 51 Nominal Battery Voltage (V): Enter the value from Block 37 Worksheet #3. 52 Batteries in Series: Enter the value from Block 38 Worksheet #3. 53 Voltage Required to Charge Batteries (V): Calculate the minimum voltage required to charge the batteries. 54 Voltage at Highest Module Temperature (V): Enter this value from the manufacturer's specifications. 55 Modules in Series: Calculate the number of series connected modules required to produce the system voltage. You must not round down. Round up or select another module with a higher operating voltage. 56 Modules in Parallel: Enter the value from Block 50. 57 Total Modules: Calculate the total number of modules in the array. 58 Modules in Parallel: Enter value from Block 50. 59 Rated Module Current (A): Enter the module current when operating at 1,000 w/m2 and 45°C temperature. 60 Rated Array Current (A): Calculate the rated array current when operating at 1,000 w/m2 and 45°C temperature. 61 Module Short Circuit Current (A): Enter module short circuit current when operating at 1,000 w/m2 and 45°C temperature. 62 Array Short Circuit Current (A): Calculate the array short circuit current when operating at 1000 w/m2 and 45°C temperature. 63 Modules in Series: Use the value from Block 55. 64 Rated Module Voltage (V): Enter module voltage when operating at 1,000 w/m2 and 45°C temperature. 65 Array Rate Voltage (V): Calculate array voltage when operating at 1,000 w/m2 and 45°C temperature. 66 Open Circuit Module Voltage (V): Enter module open circuit voltage when operating at 1,000 w/m2 and 45°C temperature. 67 Array Open Circuit Voltage (V): Calculate array open circuit voltage when operating at 1,000 w/m2 and 45°C temperature.
46 Design Current (A): Enter the value from Block 28, Worksheet #2.
47 Module Derate Factor (decimal): Enter a factor to adjust module current from standard operating conditions (SOC) of 1,000 w/m2 and 45°C temperature to field conditions, i.e., dust accumulations, mismatch loss between modules, degradation over time, etc.) Ask the module distributor or use the default values below.
Module Derate Factor Default Value
Module Type
Single or Polycrystalline Silicon
Amorphous Silicon
0.70
48 Derated Design Current (A): Calculate the minimum array current necessary to supply the average daily load at the chosen site.
NOTE: Select a PV module and record the specifications in the module information block. Be sure to determine the module voltage when it is operating at the highest temperatures expected for your site.
49 Rated Module Current (A): Enter the rated module operating current at 1,000 w/m2 and 45°C operating temperature as given by the manufacturer.
50 Modules in Parallel: Calculate the number of parallel connected modules required to provide the array current.
51 Nominal Battery Voltage (V): Enter the value from Block 37 Worksheet #3.
52 Batteries in Series: Enter the value from Block 38 Worksheet #3.
53 Voltage Required to Charge Batteries (V): Calculate the minimum voltage required to charge the batteries.
54 Voltage at Highest Module Temperature (V): Enter this value from the manufacturer's specifications.
55 Modules in Series: Calculate the number of series connected modules required to produce the system voltage. You must not round down. Round up or select another module with a higher operating voltage.
56 Modules in Parallel: Enter the value from Block 50.
57 Total Modules: Calculate the total number of modules in the array.
58 Modules in Parallel: Enter value from Block 50.
59 Rated Module Current (A): Enter the module current when operating at 1,000 w/m2 and 45°C temperature.
60 Rated Array Current (A): Calculate the rated array current when operating at 1,000 w/m2 and 45°C temperature.
61 Module Short Circuit Current (A): Enter module short circuit current when operating at 1,000 w/m2 and 45°C temperature.
62 Array Short Circuit Current (A): Calculate the array short circuit current when operating at 1000 w/m2 and 45°C temperature.
63 Modules in Series: Use the value from Block 55.
64 Rated Module Voltage (V): Enter module voltage when operating at 1,000 w/m2 and 45°C temperature.
65 Array Rate Voltage (V): Calculate array voltage when operating at 1,000 w/m2 and 45°C temperature.
66 Open Circuit Module Voltage (V): Enter module open circuit voltage when operating at 1,000 w/m2 and 45°C temperature.
67 Array Open Circuit Voltage (V): Calculate array open circuit voltage when operating at 1,000 w/m2 and 45°C temperature.
NOTE: In some applications you may wish to know the highest voltages that might be produced by the array. This will occur when the array is operating at its lowest temperature. Use manufacturer's data to determine module voltage for the coldest temperatures expected.
Use Worksheet #5 to determine if your application would be a candidate for a hybrid power system. This type of system uses more than one power generator and may be the cost-effective alternative for specific systems. Completing this worksheet will give an indication of whether a hybrid power system should be considered for this application. This blank worksheet may be copied and saved.
68 Total Amp-Hour Load (Ah): Enter the value from Block 20 Worksheet #1. 69 Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1. 70 Watt-Hour Load (Wh/day): Calculate the average daily load power of the system. 71 Conversion Factor: Multiplying by this factor converts watt-hours per day to kilowatt hours per year. 72 Annual Kilowatt-Hour Load (KWH/YEAR): Calculate the average annual load power. This value is helpful if a hybrid system is required. 73 Derated Design Current (A): Enter the value from Block 48 Worksheet #4. 74 Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1. 75 Design Array Power (W): Calculate the average daily power required by the load. 76 Watt-Hour Load (Wh/day): Enter the value from Block 70. 77 Array to Load Ratio (decimal): Calculate the factor used to determine if a hybrid design should be considered. 78 Hybrid Indicator: Plot a point on the graph using values from Blocks 76 and 77. NOTE: If the hybrid indicator suggests a hybrid system, complete the hybrid worksheets, HY#1 and HY#2. Compare life cycle cost analyses of both designs and make a decision as to which would be the optimum system. Otherwise: Use the Component Specification Worksheets to complete the design Top of page
68 Total Amp-Hour Load (Ah): Enter the value from Block 20 Worksheet #1.
69 Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1.
70 Watt-Hour Load (Wh/day): Calculate the average daily load power of the system.
71 Conversion Factor: Multiplying by this factor converts watt-hours per day to kilowatt hours per year.
72 Annual Kilowatt-Hour Load (KWH/YEAR): Calculate the average annual load power. This value is helpful if a hybrid system is required.
73 Derated Design Current (A): Enter the value from Block 48 Worksheet #4.
74 Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1.
75 Design Array Power (W): Calculate the average daily power required by the load.
76 Watt-Hour Load (Wh/day): Enter the value from Block 70.
77 Array to Load Ratio (decimal): Calculate the factor used to determine if a hybrid design should be considered.
78 Hybrid Indicator: Plot a point on the graph using values from Blocks 76 and 77.
NOTE: If the hybrid indicator suggests a hybrid system, complete the hybrid worksheets, HY#1 and HY#2. Compare life cycle cost analyses of both designs and make a decision as to which would be the optimum system.
Otherwise: Use the Component Specification Worksheets to complete the design
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Designing a hybrid power system is not a simple matter. You are considering at least two independent power sources that must be controlled and synchronized. Most controllers for hybrid systems are custom-designed. Still this should not discourage you from completing the Hybrid worksheets. This exercise will help you learn about your application and cost-effective methods of providing energy.
Use Hybrid Worksheet #1 HY to calculate the Battery Capacity, Generator Size, and Percent Contribution of the PV Array and Generator. The blank worksheet may be copied and saved.
1Y Corrected Amp-Hour Load (Ah/day): Enter value from Block 20 Worksheet #1.
2Y Storage Days for Hybrid System: Enter the number of days of storage for the hybrid system. This value is usually smaller than for a stand-alone system because the generator is available for backup.
Days of Storage Default for Hybrid System = 3 Days
3Y Maximum Depth of Discharge (decimal): Enter the value from Block 31 Worksheet #3 if the same battery will be used. If another battery is selected, use the manufacturer's specifications to select a safe depth of discharge.
4Y Derate for Temperature (decimal): Enter the value from Block 32 Worksheet #3 if the same battery will be used.
Allowance for Temperature Derate of Battery = 0.90
5Y Hybrid Battery Capacity (Ah): Calculate the required hybrid battery capacity.
6Y Peak Current Demand (A): Enter the value from Block 16 Worksheet #1.
7Y Battery Discharge Time (HOURS): Calculate the battery discharge factor&emdash;this is the number of hours the battery can supply the peak current to the load. This factor should be greater than 5 to prevent damage to the batteries. If less than 5, increase the number of storage days and recalculate 1Y through 7Y.
8Y Hybrid Battery Capacity (Ah): Enter the value from Block 5Y.
9Y Battery Charge Time (HOURS): Enter the minimum time that will be used to charge the battery. Determine the maximum charging current that should be used for the chosen battery from the manufacturer's specifications.
Charge Time Default Value = 5
10Y Maximum Battery Charge Rate (A): Calculate the maximum battery charge rate.
11Y Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1.
12Y Nominal Charging Power (W): Calculate the charging power required.
13Y Efficiency of Battery Charger (decimal): Determine and enter the battery charger efficiency. See manufacturers' specifications
Battery Charger Efficiency Default Value = 0.80
14Y Generator Derate (decimal): Generator power output should be derated for high altitude operation because the thinner air reduces combustion efficiency. Ask your generator supplier what derate factor should be used. If no other information is available, use a default of 3 percent per 1000 feet of elevation above sea level for gasoline, diesel, and propane fueled generators. Use 5 percent for natural gas generators. For example, a 5000 Watt diesel generator operating at 9000 feet elevation should be considered as a 3650 Watt generator.
[5000 * (1 - 9 * 0.03)] = 3650
15Y Generator Size (W): Calculate the generator size to the nearest whole number.
16Y Hybrid Array to Load Ratio (HAL): Determine the split between generator and PV power using the graph provided on the next page. Start with the HAL factor calculated in Block 77, Worksheet #5 and determine the amount of load provided by the PV array. In most cases this will indicate a high percentage of PV power and therefore a high initial cost for the system. System designers adjust the HAL to change the PV array size depending on the application and the budget available. The percentage of the load provided by PV power, and thus the initial cost, increase as you move up the curve. The shape of this curve will change slightly with weather patterns. For areas with long periods of inclement weather, the slope of the curve will decrease, indicating a smaller PV array for a given HAL value.
17Y Load Provided by Array (decimal): Enter the number selected from the left axis of the graph that corresponds to the HAL ratio chosen.
18Y Load Provided by PV Array (decimal): Enter the value from Block 17Y.
19Y Load Provided by Generator (decimal): Calculate the percentage of load provided by the generator.
20Y Annual Kilowatt-Hour Load (kWh/yr): Enter value from Block 72 Worksheet #5.
21Y Annual Generator Output (kWh): Calculate the annual generator output.
22Y Annual Generator Output (kWh): Enter the value from Block 21Y.
23Y Conversion Factor: This factor converts kilowatt-hours to watt-hours.
24Y Nominal Charging Power (W): Enter the value from Block 12Y.
25Y Annual Generator Run Time (hr): Calculate the time the generator will run in a typical year.
26Y Oil Change Interval (hrs): Select and enter number of operating hours between oil changes for your generator. Some typical intervals are given in the following table along with suggested intervals for more thorough cleaning and maintenance and engine rebuild.
Generator Maintenance Interval Default Values - Hours
Oil Change
Engine Tune-up
Rebuild Engine
Gasoline Engine (3600 rpm)
50
300
5,000
Gasoline Engine (1800 rpm)
100
Diesel
400
1,200
7,200
27Y Services Per Year (number): Calculate the recommended number of service calls per year.
Use Hybrid Worksheet #2 HY to calculate the number of PV modules and batteries for your hybrid system. These will differ from the calculation you made using Worksheets 3 and 4. The blank worksheet may be copied and saved.
28Y Hybrid Array to Load Ratio: Enter the value from Block 16Y Worksheet #1HY.
29Y Watt-Hour Load (Wh/day): Enter the value from Block 70 Worksheet #5.
30Y Hybrid Array Power (W): Calculate the hybrid array power.
31Y Nominal System Voltage (V): Enter the value from Block 9 Worksheet #1.
32Y Rated Module Current (A): Enter the value from Block 59 Worksheet #4.
33Y Modules in Parallel: Calculate the number of modules connected in parallel required to provide the array current. Rounding down will mean more generator operating time.
34Y Nominal System Voltage (V): Enter the value from Block 31Y Worksheet #1HY.
35Y Nominal Module Voltage (V): Enter the nominal module voltage from Block 64 Worksheet #4.
36Y Modules in Series: Calculate the number of series connected modules required to produce the system voltage.
37Y Modules in Parallel: Enter the value from Block 33Y.
38Y Total Modules: Calculate the total number of modules required.
39Y Hybrid Battery Capacity (Ah): Enter the value from Block 5Y Worksheet #1HY.
40Y Capacity of Selected Battery (Ah): Enter the rated capacity for the selected battery from manufacturers' specifications.
41Y Hybrid Batteries in Parallel: Calculate the number of parallel connected batteries required to provide the storage capacity.
42Y Nominal System Voltage (V): Enter the value from Block 31Y Worksheet #1HY.
43Y Nominal Battery Voltage (V): Enter the nominal battery voltage from Block 37 Worksheet #3.
44Y Batteries in Series: Calculate the number of series connected batteries required to provide the system voltage.
45Y Batteries in Parallel: Enter the value from Block 41Y.
46Y Total Hybrid Batteries: Calculate the total number of batteries in the system.
47Y Hybrid Batteries in Parallel: Enter the value from Block 41Y.
48Y Capacity of Selected Battery (Ah): Enter the value from Block 40Y.
49Y Hybrid System Battery Capacity (Ah): Calculate the battery subsystem storage capacity.
50Y Maximum Depth of Discharge (DECIMAL): Enter the value from Block 3Y Worksheet #1HY.
51Y Usable Battery Capacity (AH): Calculate the usable battery capacity of the hybrid system.
Note: Use the Component Specification Worksheets to complete the design
Acknowledgment and Disclaimer
