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The front-of-meter (FOM) battery model assumes that the battery is used to maximize revenue for a power generation project. The battery in a PV-battery front-of-meter application may be connected either to the AC or DC side of the inverter as shown in Figures 1 and 2.
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Figure 1: PV-battery DC-connected Front-of-meter
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Figure 2: PV-battery AC-connected Front-of-meter
The battery in a generic front-of-meter application is connected to the AC side of the system as shown in Figure 3.
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Figure 3: Generic-battery AC-connected Front-of-meter
Battery Cell and System
Chemistry
@@ -125,8 +125,25 @@ Flow Batteries
The all iron redox flow battery model available in SAM shares the same input field framework as the vanadium flow battery, but relies on tabular voltage vs. depth-of-discharge in place of a voltage model. Default iron flow battery values are based on preliminary manufacturer data and feedback for an all-iron hybrid-redox flow battery.
•AIFB: All Iron Redox Flow (Fe2+, Fe3+) Battery Bank Sizing
The two battery bank sizing options allow you to either automatically size the battery bank based on desired size, or to specify the number of cells and their configuration in the bank yourself. The automatic option is suitable for an initial preliminary design. It uses the basic equations described below to determine numbers of cells and strings or stacks, but does not take into account real-life design considerations that are outside of the model's scope. If you use the automatic sizing option, you should refine the bank sizing parameters by specifying your own values after analyzing the initial results.
+Set desired bank size
+Choose this option to have SAM calculate a number of cells in series and strings in parallel based on the desired bank capacity and power values you enter.
+If you choose this option, be sure to verify the values under Computed Properties to make sure SAM was able to calculate values close to the desired values.
+Specify cells
+Choose this option to manually specify the number of cells in series, strings in parallel and C-rates of charge and discharge.
+Desired bank capacity, kWh
+For the Set Desired Bank size option, the size of the battery bank in kWh. Compare this to Nominal bank capacity under Computed Properties to verify that SAM calculated a nominal value close enough to the desired value to meet your requirements.
+Desired bank power, kW
+For the Set Desired Bank size option, the maximum discharge rate in kW. Compare this to Maximum discharge power under Computed Properties to verify that SAM calculated a discharge power close enough to the desired value to meet your requirements.
+Number of cells in series
+For the Number of Cells in Series option, the number of cells in series in the battery bank. The number of cells in series determines the maximum discharge power.
+Number of strings in parallel
+For the Specify Cells option, the number of strings of cells in parallel in the battery bank. The number of strings in parallel determines the nominal bank capacity.
+Max C-rate of charge, 1/hour
+For the Specify Cells option, the maximum charge rate relative to the nominal bank capacity, determines the maximum charge current shown under Computed Properties.
+Max C-rate of discharge, 1/hour
+For the Specify Cells option, the maximum discharge rate relative to the nominal bank capacity, determines the maximum discharge current shown under Computed Properties.
To automatically size the battery bank:
-1.Click Set desired bank size. 2.Enter values for Desired bank capacity in kilowatt-hours and Desired bank power in kW. Choose either DC or AC as appropriate for your battery ratings. 3.The default desired battery bank voltage is 500 VDC. If you want to change the nominal DC voltage of the battery bank, expand the Battery Voltage panel, and change the Desired bank voltage in DC Volts under Voltage Properties. 4.Under Computed Properties in the Current and Capacity group, check the Nominal bank capacity and Nominal bank voltage to make sure they are close enough to your desired values. Also check that Maximum discharge power (DC) is close to your desired bank power. You can estimate the nominal battery bank hours of autonomy by dividing the capacity in kWh by the maximum discharge power in kW, which is shown as Time at maximum power.
+1.Click Set desired bank size. 2.Enter values for Desired bank capacity in kilowatt-hours and Desired bank power in kW. Choose either DC or AC as appropriate for your battery ratings. 3.The default desired battery bank voltage depends on the battery chemistry. When you choose the battery type, SAM sets the nominal DC voltage of the battery to a default value for each battery chemistry. If you want to change the value to a different voltage, expand the Battery Voltage panel, and change the Desired bank voltage in DC Volts under Voltage Properties. 4.Under Computed Properties in the Current and Capacity group, check the Nominal bank capacity and Nominal bank voltage to make sure they are close enough to your desired values. Also check that Maximum discharge power (DC) is close to your desired bank power. You can estimate the nominal battery bank hours of autonomy by dividing the capacity in kWh by the maximum discharge power in kW, which is shown as Time at maximum power.
If you use AC ratings for the capacity and power values, SAM converts them to DC using the DC to AC conversion efficiency you specify under Power Converters.
See Calculations for Automatic Bank Sizing for details about how SAM determines the bank size based on the values you enter.
To manually size the battery bank for conventional batteries:
@@ -178,9 +195,9 @@ Computed Properties
Stacks in series
For flow batteries, the number of stacks in series.
Max C-rate of discharge
-Either calculated from Maximum Discharge Power ÷ Nominal Bank Capacity, or user input.
+Either calculated as Maximum Discharge Power ÷ Nominal Bank Capacity, or value input under Battery Bank Sizing.
Max C-rate of charge
-Either calculated from Maximum Charge Power ÷ Nominal Bank Capacity, or user input.
+Either calculated as Maximum Charge Power ÷ Nominal Bank Capacity, or value input under Battery Bank Sizing.
Maximum discharge power, DC kW
The maximum discharge power, calculated from the nominal bank capacity and maximum C-rate of discharge. This is also the nominal DC power of the battery bank.
Maximum charge power, DC kW
@@ -192,32 +209,32 @@ Computed Properties
Time at maximum power
The nominal bank capacity divided by the maximum power, or 1 divided by the maximum C-rate of discharge.
Maximum discharge current
-Calculated from the maximum C-rate of discharge: Max Discharge Current = 1000 × Max C-rate of Discharge × Nominal Bank Capacity ÷ Nominal Bank Voltage.
+Calculated from the maximum C-rate of discharge: Max Discharge Current = 1000 × Max C-rate of Discharge × Nominal Bank Capacity ÷ Nominal Bank Voltage.
Maximum charge current
-Calculated from the maximum C-rate of charge: Maximum Charge Current = 1000 × Maximum C-rate of Charge × Nominal Bank Capacity ÷ Nominal Bank Voltage.
+Calculated from the maximum C-rate of charge: Maximum Charge Current = 1000 × Maximum C-rate of Charge × Nominal Bank Capacity ÷ Nominal Bank Voltage.
Power Converters
For photovoltaic-battery systems, SAM can model a battery that is connected to either the DC or AC side of the photovoltaic inverter.
Notes.
-The Power Converters inputs are only available with the PV Battery configuration. They are not available with the Generic Battery configuration, which assumes that the battery is the only DC component in the system.
+The DC connected option is only available with the PV Battery configuration. The Generic Battery configuration assumes that the battery is the only DC component in the system.
-The Power Converters inputs account for electrical losses associated with converting between DC and AC power for the batteries in the system. For all power converters except the photovoltaic inverter, SAM models the converter performance using the fixed conversion efficiency values you provide.
+The Power Converters conversion efficiency inputs account for electrical losses associated with any battery power converter equipment except for the photovoltaic inverterfor the batteries in the system. SAM models each battery converter as a fixed conversion efficiency.
-The photovoltaic inverter is a separate component from the power converter equipment specified here and uses a more sophisticated model with an efficiency curve that varies with the inverter load. You specify the photovoltaic inverter model and parameters on the Inverter page.
+The photovoltaic inverter is a separate component from the battery power converters specified here and uses a more sophisticated model with an efficiency curve that varies with the inverter load. You specify the photovoltaic inverter model and parameters on the Inverter page.
DC Connected
-Choose the DC Connected option for a battery connected to the DC side of the photovoltaic inverter through a battery management system (BMS) so that the same inverter converts DC power from the BMS and photovoltaic array to AC power. This configuration also requires a DC power optimizer or DC/DC converter to connect the photovoltaic array to the BMS and inverter as shown in the diagram above.
-To account for electrical losses from the DC power optimizer, be sure to assign an appropriate value to the DC power optimizer loss on the Losses page.
+Choose the DC Connected option for a battery connected to the DC side of the photovoltaic inverter through a battery management system (BMS) as shown in the diagram above.
+To account for electrical losses from the DC power optimizer between the photovoltaic array and inverter, be sure to assign an appropriate value to the DC power optimizer loss on the Losses page.
For a DC-connected battery, during time steps when the total power from the photovoltaic array and battery is greater than the inverter's nameplate capacity, the inverter limits its output power to the nameplate capacity. For the automated dispatch options with Battery can charge from clipped system power enabled, if the battery is not fully charged and is not discharging, the excess power from the array charges the battery.
DC to DC conversion efficiency, %
For the DC-connected option, the electrical conversion efficiency of the battery management system (BMS). SAM applies this loss to power into or out of the battery BMS as energy enters and leaves the battery. SAM disables this input for the AC Connected option.
Inverter efficiency cutoff, %
-For the DC-connected option, the inverter efficiency cutoff is an inverter efficiency threshold below which the battery is not allowed to charge or discharge through the inverter.
+For the DC-connected option, the inverter efficiency cutoff is the photovoltaic inverter operating efficiency threshold below which the battery is not allowed to charge or discharge. SAM reports the inverter operating efficiency in the time series results.
AC Connected
-Choose the AC-connected option for a battery connected to the system between the inverter and grid interconnection point. Power conversion equipment is required to convert DC power from the battery to AC power before it can serve the load or be sent to the grid, and to convert AC power from the inverter or grid before it can charge the battery.
+Choose the AC-connected option for a battery connected to the system between the inverter and grid interconnection point as shown in the diagram above. Power conversion equipment is required to convert DC power from the battery to AC power before it can serve the load or be sent to the grid, and to convert AC power from the inverter or grid before it can charge the battery.
AC to DC conversion efficiency, %
-For the AC-connected option, the electrical conversion efficiency associated with the equipment that converts the AC power from either the photovoltaic inverter or grid to DC power for the battery. SAM disables this input for the DC Connected option.
+For the AC-connected option, the electrical conversion efficiency associated with the equipment that converts AC power from either the photovoltaic inverter output or grid to DC power for the battery. SAM disables this input for the DC Connected option.
DC to AC conversion efficiency, %
-For the AC-connected option, the electrical conversion efficiency associated with the equipment that converts the DC power from the battery to AC power for either the AC load or grid, or both. SAM disables this input for the DC Connected option.
+For the AC-connected option, the electrical conversion efficiency associated with the equipment that converts DC power from the battery to AC power for either the AC load or grid, or both. SAM disables this input for the DC Connected option.
Charge Limits and Priority
Minimum state of charge, %
Sets a limit on the quantity of energy that can be drained from the battery. Battery lifetime is highly dependent on depth of discharge, so this value should be set based on your battery chemistry and desired performance over time. For example a value of 15% would prevent the battery from discharging below a 15% state of charge.
@@ -229,35 +246,41 @@ This setting only applies to subhourly simulations. You can ignore it for hourly simulations. For sub-hourly simulations, there may be periods of time where the photovoltaic output varies above and below the load causing rapid cycling of the battery. This kind of cycling, especially if the cycles are deep, may degrade battery performance over time. The minimum time at charge state prevents the battery to change between charging and discharging within the number of minutes that you specify.
Battery Lifetime
SAM's battery lifetime model considers battery cycling and age as the primary causes of capacity degradation.
+Note. To control the frequency of battery replacements as they degrade over time or to remove battery replacements from your analysis, expand the Battery Replacements panel to change the replacement options, and change the battery replacement costs shown under Operation and Maintenance Costs on the System Costs page as appropriate.
Cycle Degradation
-Cycle degradation is a reduction in the battery's capacity at 100% charge as the battery is charged and discharged. The cycle degradation model relies on information about capacity fade at the number of cycles elapsed at an average depth of discharge. If you enter your own cycle degradation data, you should enter at least two or three sets of data for two or three different depths of discharge.
-You must provide at least three rows of data. For a table with more than one depth-of-discharge value, SAM uses bilinear interpolation to consider both the average depth-of-discharge and cycle number when applying the capacity fade. If the table contains data for a single depth-of-discharge value, then SAM only considers the cycle number in the capacity fade calculation using a rainflow counting algorithm.
-For example, given the following graph from a battery's datasheet:
+Cycle degradation is a reduction in the battery's capacity at 100% state of charge as the battery experiences many charge/discharge cycles. The cycle degradation model relies on information about capacity fade at the number of cycles elapsed at an average depth of discharge in the Cycle Degradation table.
+SAM assigns default values to the table appropriate for the given battery chemistry when you choose a battery type. You can use the default values unless you have better data from a manufacturer data sheet or other source.
+If you decide to use your own cycle degradation data, you must provide at least three rows of data in the table. For a table with more than one depth-of-discharge value, SAM uses bilinear interpolation to consider both the average depth-of-discharge and cycle number to determine the available capacity. If the table contains data for a single depth-of-discharge value, SAM only considers the cycle number in the capacity fade calculation using a rainflow counting algorithm.
+For example, given the following graph from a battery's data sheet showing a curve for three different depth-of-discharge levels:
You might enter the following data in the table:
-Some battery data sheets do not report this kind of information. For these batteries, you can use the default values in the table.
Calendar Degradation
-Calendar degradation is a reduction in capacity over a battery's life that occurs over time. This degradation may be a function of time, temperature and state of charge, or simply a function of time.
+Calendar degradation is a reduction in capacity over a battery's life that occurs over time, regardless of the number of charge/discharge cycles. This degradation may be a function of time, temperature and state of charge, or simply a function of time.
+None
+Choose None to ignore calendar degradation. SAM will calculate capacity degradation using only the data in the Cycle Degradation table.
Lithium-ion model
+Choose Lithium-ion model to use the equations shown to calculate calendar degradation for Lithium-ion batteries. The Calendar Degradation graph shows the degradation curves resulting from the equations.
The Lithium-ion model accounts for how a Lithium-ion battery's capacity degrades with time, temperature, and state-of-charge. For a description of the model, see Smith, K.; Saxon, A.; Keyser, M.; Lundstrom, B.; Cao, Z.; Roc, A. (2017). Life Prediction Model for Grid-Connected Li-ion Battery Energy Storage System. 7 pp. 2017 American Control Conference, Seattle, USA.
-Custom degradation
-The custom degradation option allows you to enter your own degradation curve. To enter the curve, click Custom degradation, and for Rows, type the number of capacity as % of nominal full capacity and battery age in days data points on your degradation curve. Then type the values in the table, and check the curve for the correct shape.
+Custom Degradation
+Choose Custom to use the Custom Degradation table to specify degradation curves. The Calendar Degradation graph shows degradation curves from the data in the table.
+To enter custom data in the table, click Custom degradation, and for Rows, type the number of data points in your degradation curve. Each capacity value should be a percentage of the battery nominal full capacity. The battery age should be in days. For example, the table below shows that the battery degrades to 80% of its nominal capacity after 10 years (365 days × 10 years = 3650 days), and to 50% of nominal capacity in after 20 years.
Battery Replacements
-Battery degradation as a reduction in available storage capacity over time caused by battery cycling (charge and discharge cycles) and age. If you model battery replacements, SAM calculates an annual replacement cost in the project cash flow based on the replacement options specified here and the and replacement cost on the System Costs page.
+When you enable battery replacements, SAM determines when batteries need to be replaced based either on battery degradation as determined by the Battery Lifetime inputs or a fixed replacement schedule that you specify. It also calculates an annual replacement cost in the project cash flow based battery replacement cost specified as an operation and maintenance cost on the System Costs page.
No replacements
-Use this option if you do not want to account for battery replacement costs, or if you want to account for them using one of the Operation and Maintenance cost categories on the System Costs page.
+Use this option if you do not want to account for battery replacement costs, or if you want to account for them using one of the general Operation and Maintenance cost categories on the System Costs page.
If you choose the No replacements option, SAM operates the system with no battery after the available storage capacity is depleted.
Replace at specified capacity
Use this option if you want SAM to calculate the year(s) in which batteries are replaced based on degradation of the battery's capacity caused by battery cycling as determined from the Battery Lifetime parameters.
-Set Battery bank replacement threshold as percentage of the battery's rated capacity that triggers a replacement. When the battery's available capacity has degraded to this percentage, SAM replaces the battery and applies the battery replacement cost from the System Costs page to the project cash flow. If you set the threshold to less than 2%, SAM sets the value internally to 2% to avoid simulation issues as the battery's available capacity approaches 0% of its original capacity.
+Set Battery bank replacement threshold as percentage of the nominal battery capacity that triggers a replacement. When the battery's available capacity has degraded to this percentage, SAM replaces the battery and applies the battery replacement cost from the System Costs page to the project cash flow. If you set the threshold to less than 2%, SAM sets the value internally to 2% to avoid simulation issues as the battery's available capacity approaches 0% of its original capacity.
Replace at specified schedule
-Use this option to specify the years when batteries are replaced and the percent of battery capacity that is replaced in those years.
-Use the Battery bank replacement schedule option to force all batteries to be replaced in a given year or years, regardless of degradation. Click Edit array to specify the percentage of total battery capacity to be replaced in each replacement year. In the Edit Array window, click Number of values, and enter the analysis period from the Financial Parameters input page. Then in the table, type a percentage for each year in which the batteries will be replaced. The rows for the remaining years should be zero.
+Use this option to specify the years when batteries are replaced and the percent of nominal battery capacity that is replaced in those years, regardless of the battery's degradation.
+Click Edit array to specify the percentage of total battery capacity to be replaced in each replacement year. In the Edit Array window, click Number of values, and enter the analysis period from the Financial Parameters input page. Then in the table, type a percentage for each year in which the batteries will be replaced. The rows for the remaining years should be zero.
Battery Voltage
The voltage properties are technical specifications available on most battery manufacturer data sheets.
+Note. When you change the battery type, SAM changes the voltage properties inputs to default values appropriate for the battery chemistry you selected. You can use these default values unless you have better information from a manufacturer's data sheet or other source.
Battery voltage varies with state of charge as the internal open circuit potential decreases or increases. When a battery charges, positive ions travel from the cathode to the anode, lowering the open circuit potential of the anode and increasing the open circuit potential of the cathode, resulting in a net increase of potential between the anode and cathode. Similarly, as a battery discharges, ions flow back from the anode to the cathode, reducing the net potential. Battery manufacturer data sheets typically report a voltage-discharge curve of some kind to illustrate this behavior. SAM uses a dynamic voltage model, which specifies how to extract information from a data sheet to populate the voltage discharge curve.
Voltage variations in charging and discharging affect the battery's round-trip efficiency. During charging, voltage increases, requiring more power to charge the cell. During discharge the voltage decreases and less power can be extracted. The round-trip efficiency is computed as the net amount of energy discharged from a cell divided by how much energy it took to charge the cell.
Voltage Properties Common to All Chemistries
@@ -274,14 +297,16 @@ Electrochemical PropertiesThe electrochemical model properties apply to the lead acid and Lithium-ion battery types. They are disabled for the flow battery types.
SAM displays the Voltage Discharge graph based on the electrochemical properties you specify.
C-rate of discharge curve
-Battery manufacturer data sheets typically include a set of curves like the one below that show cell voltage as a function of charge removed for different discharge rates. The "C-rate" is the current used to discharge the battery. It is defined as the current divided by the rated capacity. In this example, if the discharge current is given at the 20-hour discharge rate, the C-rate would be I20 ÷ q20 × C = 0.05 × C (C/20).
+Battery manufacturer data sheets typically include a set of curves like the one below that show cell voltage as a function of charge removed for different discharge rates. The "C-rate" is the current used to discharge the battery. It is defined as the current divided by the rated capacity.
+In this example, if the discharge current is given at the 20-hour discharge rate, the C-rate would be I20 ÷ q20 × C = 0.05 × C (C/20).
Fully charged cell voltage
-The voltage at the given C-rate when a cell is at its maximum charge
+The cell voltage (Vfull) at the given C-rate when a cell is at its maximum charge.
Exponential zone cell voltage
-The cell voltage at the end of the exponential zone, as shown in the Nominal Current Discharge Characteristic graph below. The cell charge removed at this point is  .
+The cell voltage (Vexp) at the end of the exponential zone, as shown in the Nominal Current Discharge Characteristic graph below. The cell charge removed at this point is .
Nominal zone cell voltage
-The cell voltage at the end of the nominal zone, as shown in the Nominal Current Discharge Characteristic graph below.. The cell charge removed at this point is 
+The cell voltage (Vnom) at the end of the nominal zone, as shown in the Nominal Current Discharge Characteristic graph below.. The cell charge removed at this point is .
+Note. The voltage inputs must satisfy Vfull > Vexp > Vnom.
Charge removed at exponential and nominal point
Voltage vs discharge curves show that cell-voltage typically undergoes several distinct regions depending on charge.
@@ -290,23 +315,50 @@ Voltage Table
To use the voltage table to define the voltage curve:
1.Choose Voltage table. 2.For Rows, type the number of pairs of voltage - depth of discharge pairs you want to use to define the voltage. The table will expand to the number of rows you type. You can also click Import to import data from a text file. Try clicking Export to create a template file to see what the text format should be.
3.Type values in the depth of discharge and cell voltage columns. The Voltage Discharge graph will update as you type. Battery Losses
-Some battery systems have additional losses not captured by the conversion losses in power electronics components above. For these losses, SAM offers the ability to generically specify power losses when the battery is charging, discharging, or at an idle state. If a detailed loss profile is available, it can be entered as a time series.
+Some battery systems have losses that are not accounted for by the conversion losses specified under Power Converters above. You can use the ancillary equipment losses to account for these additional losses. By default, these losses are set to zero, which is appropriate for most analyses.
+Ancillary Equipment Losses
+These are losses to account for electrical losses or consumption by equipment in the battery system such as for heaters and pumps for temperature control equipment.
+For DC-connected batteries, the losses are applied the system's DC power. For AC-connected systems, they are applied to the AC power.
+Losses by operating mode
+Choose this option to specify losses by month that apply when the battery is charging, discharging, or idle.
+Charging mode losses
+Losses that apply when the battery is charging.
+Click Edit values to specify the loss in kW by month. SAM will apply the loss in each time step of the month. For example, if the expected loss in January is 500 W, enter 0.5 for January, and SAM will reduce the available power by 0.5 kW for each time step in January.
+Discharging mode losses
+Losses that apply when the battery is discharging.
+Idle mode losses
+Losses that apply when the battery is neither charging, nor discharging.
+Time series losses
+Choose this option to specify hourly or subhourly time series losses.
+Time series losses
+Click Edit array to enter or import kW loss values for each time step of the simulation
Battery Thermal
-The thermal model calculates the battery temperature, which modifies the battery capacity. The system configuration assumes that the battery is stored in a conditioned room at a fixed temperature and is not exposed directly to heat from the sun. The two main heat-transfer terms are transfer between the battery and the room, and internal energy generation via resistive heating. The battery internal resistance input is under "Battery Voltage."
+The thermal model calculates the battery temperature affects battery capacity and lifetime. The model's two main heat-transfer terms are transfer between the battery and its environment, and energy generated by resistive heating inside the battery. The battery internal resistance input is under Battery Voltage.
Thermal Properties
Specific heat Cp (J/kg-K)
Estimated specific heat capacity for the battery.
Heat transfer coefficient h (W/m²-K)
Estimated heat transfer coefficient for heat transfer from the battery to the room.
The default value for behind-the-meter applications is 7.5 W/m²-K, and for front-of-meter applications, the default is 15 W/m²-K.
-Room temperature (°C)
-Temperature of the room where the battery will be stored. The default value is 25.
+Environment temp option
+Choose how to represent the temperature of the battery's environment.
+
+Use weather file ambient temperature
+Choose this option to use temperature data from the weather file as the battery environment temperature. This would be appropriate for a battery installed outdoors. Note that SAM does not account for the effect of solar heating for a battery exposed to direct sunlight.
+Enter single fixed temperature
+Choose this option to model the battery environment temperature as a single constant value throughout the year. This would be appropriate for a battery installed in a conditioned room or building.
+Enter time series temperature
+Choose this option to provide your own time series temperature data.
+Single environment temperature
+For the Enter Single Fixed Temperature option, the temperature of the battery environment in degrees Celsius. This is disabled for the Use Weather File Ambient Temperature and Enter Time Series Temperature options.
+Time series environment temperature
+For the Enter Time Series Temperature option, click Edit array to enter or import hourly or subhourly temperature data in degrees Celsius. Note that the number of time steps must match the simulation time step determined by the weather file. This is disabled for the Enter Single Fixed Temperature and Use Weather File Ambient Temperature options.
Capacity fade with temperature
The manufacturer data sheet may include battery capacity versus temperature data showing how the battery's capacity decreases with ambient temperature.
Temp (°C)
-Ambient temperature
+Battery environment temperature in degrees Celsius.
Capacity (%)
-The discharge capacity as a percentage of rated capacity at the given temperature.
+Battery discharge capacity as a percentage of rated capacity at the given temperature.
Physical properties
In order to scale battery mass and surface area as the battery bank is sized, properties are entered on a per Watt-hour basis.
Specific energy per mass (Wh/kg)
diff --git a/deploy/runtime/help/html/edit_parametric_values.htm b/deploy/runtime/help/html/edit_parametric_variables.htm
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- The Edit Shading Data window is where you define beam and sky diffuse shading losses.
-Each shading loss is a percentage that represents the portion of the solar radiation component (either beam or diffuse) that is prevented from reaching the array by a nearby shading object:
-•SAM reduces the plane-of-array beam irradiance (direct normal irradiance) in each hour by the beam shading loss for that hour. Beam irradiance is solar energy that reaches the array in a straight line from the sun. For example, for a beam shading loss of 10% for the 8 a.m. hour of December 20, SAM would reduce the beam radiation value in the weather file by 10% for that hour, and use that reduced value to calculate the total incident radiation on the array for that hour.
-•SAM reduces the incident sky diffuse irradiance for each hour by the sky diffuse shading loss. Sky diffuse radiation is radiation that reaches the array from the sun indirectly after being reflected by clouds and particles in the atmosphere. Sky diffuse radiation does not include diffuse radiation reflected from the ground. Note that you can only specify a single constant value that applies to all hours of the year for the sky diffuse shading loss.
-
-SAM allows you to import shading data from the following software:
-•PVsyst, photovoltaic system design software, http://www.pvsyst.com •Solmetric SunEye, shading analysis device, http://www.solmetric.com •Solar Pathfinder, shading analysis device, http://www.solarpathfinder.com Importing Data from PVsyst
-You can import a "Near Shadings" table generated by PVsyst into SAM. SAM automatically imports data from the text file generated by PVsyst into the Solar Azimuth by Altitude Shading loss table and the diffuse shading loss value.
-Notes. We have tested the following procedure with Version 5 of PVsyst.
-The "Near Shadings" table in PVsyst looks like this:
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-The "Near Shadings" data exported to a text file looks like this (in this example with semicolon delimiters):
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-To import a "Near Shadings" table from PVsyst:
-1.In PVsyst, follow the procedure to create and export a "Near Shadings" table. The table in PVsyst should look similar to the one below. SAM will recognize any of the delimiter options: tab, comma, or semicolon. 2.In SAM, click Edit shading (on the Detailed Photovoltaic model Shading and Layout page or PVWatts System Design page) to open the Edit Shading Data window, and click the PVsyst near shading and navigate to the folder containing the shading file. When SAM imports data from the file, it displays the message "Azimuth-Altitude Table and Diffuse loss update" and populates the azimuth-altitude shading table, the sky diffuse shading loss, and enables both options.
-3.Disable any shading options that do not apply to your analysis. Importing from Solmetric SunEye
-The Solmetric SunEye software generates shading data in two formats: The obstruction table, which characterizes shading using an altitude-azimuth angle table to indicate solar positions that are blocked by nearby obstructions, and the hourly shading file, which lists hourly beam radiation shading factors. SAM can read data from both tables.
-Use the obstruction table if you plan to model the system for different locations (assuming the same shading obstructions). Use the hourly shading loss table if you plan to model the system for a single location.
-Note. If you use the hourly shading loss table, be sure that the weather data specified on the Location and Resource page is for the same location as the one where the SunEye measurements were made.
-To import a SunEye obstruction table:
-1.In the Solmetric SunEye software (not the PV Designer software), on the File menu, click Export Session Report and Data. The SunEye software creates a set of files, and assigns a default name like Sky01ObstructionElevations.csv to the obstruction data file. By default, the files are in a folder named ExportedFiles in the exported report folder.
-2.In SAM, click Edit shading (on the Detailed Photovoltaic model Shading and Layout page or PVWatts System Design page) to open the Edit Shading Data window, and click Suneye obstructions table, and navigate to the folder containing the file you want to import. 3.Open the obstruction data file for any of the available skies (Sky01ObstructionElevations, Sky02ObstructionElevations, etc.). If the average or worst case obstruction data from multiple skylines will be used, then an extra step is required. In a spreadsheet program, open the ObstructionElevation file containing the average and maximum values as well as all skylines in the SunEye session. Make sure that the desired data (average or maximum) is in the third column, delete the other columns, and save the file as .csv with a name like ObstructionElevationsAVG.csv. Use this file as the obstruction data file in SAM.
-SAM displays the message "Azimuth-Altitude Table updated," populates the azimuth-altitude shading loss table, and enables the Enable solar azimuth by altitude beam irradiance shading loss option.
-4.Be sure to enable and disable the other shading options as appropriate. To import a SunEye hourly shading file:
-1.In the Solmetric SunEye software (not the PV Designer software), on the File menu, click Export Session Report and Data. The SunEye software creates a set of files, and assigns a default name like Sky01Shading.csv to the hourly shading file. By default, the files are in a folder named ExportedFiles in the exported report folder.
-2.In SAM, click Edit shading (on the Detailed Photovoltaic model Shading and Layout page or PVWatts System Design page) to open the Edit Shading Data window, and click Suneye hourly shading, and navigate to the folder containing the shading file. 3.Open the shading file for any of the available skies (Sky01Shading, Sky02Shading, etc.). To use average shading for multiple skylines, open AverageShading.csv. SAM displays the message "Hourly Shading Factors for Beam Radiation updated," populates the hourly shading loss table, and enables the Enable Hourly Beam Shading Factors option.
-4.To see the hourly data, click Edit Data under Hourly Shading Factors for Beam Radiation. 5.Be sure to enable and disable the other shading options as appropriate. 6.On the Location and Resource page, choose a weather file for the same location represented by the SunEye shading data. Importing from SolarPathfinder Assistant
-The SolarPathfinder Assistant software generates shading data in two formats: The obstruction table, which characterizes shading using an altitude-azimuth angle table to indicate solar positions that are blocked by nearby obstructions, and the hourly shading file, which lists hourly beam radiation shading factors. SAM can read data from both tables.
-Use the obstruction table if you plan to model the system for different locations (assuming the same shading obstructions). Use the hourly shading loss table if you plan to model the system for a single location.
-Note. If you use the month-by-hour shading loss table, be sure that the weather data specified on the Location and Resource page is for the same location as the one where the Solar Pathfinder measurements were made.
-To import a Solar Pathfinder obstruction table:
-1.In SolarPathfinder Assistant, on the File menu, click Export, Horizon Angles. 2.In the Save window, specify the location and name of the data file. 3.In SAM, click Edit shading (on the Detailed Photovoltaic model Shading and Layout page or PVWatts System Design page) to open the Edit Shading Data window, and click Solar Pathfinder obstructions, and navigate to the folder containing the file you want to import. 4.Open the obstruction data file you saved in Step 2. SAM displays the message "Azimuth-Altitude Table updated," populates the azimuth-altitude shading loss table, and enables the Enable Azimuth-Altitude Shading Factors for Beam Radiation option.
-5.Be sure to enable and disable the other shading options as appropriate. To import a Solar Pathfinder Month by Hour shading file:
-1.In SolarPathfinder Assistant, on the File menu, click Export, Shading Data. 2.In the Save window, specify the location and name of the data file. 3.In SAM, click Edit shading (on the Detailed Photovoltaic model Shading and Layout page or PVWatts System Design page) to open the Edit Shading Data window, and click Solar Pathfinder month by hour shading, and navigate to the folder containing the shading file. 4.Open the shading file you saved in Step 2. SAM displays the message "Hourly Shading Factors for Beam Radiation updated," populates the hourly shading loss table, and enables the Enable Hourly Beam Irradiance Shading Losses option.
-5.To see the hourly data, click Edit Data under Enable hourly beam irradiance shading losses. 6.Be sure to enable and disable the other shading options as appropriate. 7.On the Location and Resource page, choose a weather file for the same location represented by the Solar Pathfinder shading data. |
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-SAM provides the three options described below to specify beam irradiance shading loss: Hourly, month by hour, and solar azimuth by solar altitude.
-Typically, you would enable only one of the three options. However, if you enable more than one option, SAM combines the losses you enabled for each hour to calculate a total shading loss.
-Tip. If you plan to import hourly, month-by-hour, or azimuth-by-altitude shading data from text files, you can see the correct file format by exporting existing data (even if it is all zeros). You can use the exported file as an example for your data.
-Hourly Beam Irradiance Shading Losses
-The Hourly option allows you to use a set of hourly (8,760 hours/year) beam shading losses.
-The data's time convention should follow that of the weather file. For the standard TMY files, Hour 1 is the hour ending at 1 a.m. on Monday, January 1.
-To specify hourly beam shading factors:
-1.Check Enable hourly beam irradiance shading losses to show the Edit Data button. 2.Click Edit Data to open the Edit Data window. 3.To copy data from a spreadsheet, select and copy a column of 8,760 beam shading factors in the spreadsheet and click Paste in the Edit Data window. To import data from a text file, click Import and navigate to the file. The file must contain a single column of 8,761 rows: A header in the first row followed by 8,760 beam radiation values.
-To see an example of the correct file format, click Export to export the default shading table to a text file and open it with a text editor.
-Once you define a table of hourly shading losses, you can clear the Enable hourly beam irradiance shading losses to run a simulation with no losses without losing the shading losses data.
-Month by Hour Beam Irradiance Shading Losses
-Note. You can use the 3D shade calculator to automatically generate month-by-hour shade factors from a three-dimensional drawing of the array and nearby objects.
-To specify month by hour shading factors:
-1.Check Enable month by hour beam irradiance shading factors. 2.Type shading data into the table, or import it from a text file. To the month-by-hour shading loss matrix is a 24-by-12 table containing a set of 24 hourly shading losses for each month of the year. The shading loss in a cell applies to a given hour for an entire month.
-•The data's time convention should follow that of the weather file. For the standard TMY files, the value in the first row and column is for the hour ending at 1 a.m. for all days in January. •A red cell indicates a value of 100%, or full shading (beam radiation completely blocked). •A white cell indicates a value of zero, or no shading. •A dark shade of red indicates more shading (less beam irradiance) than a light shade of red. To define a shading loss for a single cell:
-•Click the cell and type the shading loss percentage. •To replace the value in a cell, click the cell and type a replacement value. •To delete the value from a cell, double-click the cell and press the Delete key. To define a single shading loss for multiple cells:
-•Use your mouse to select the cells to which you want to apply the shading loss percentage. •Type a value between zero and one. •Press the Enter key or click Apply to selected cells. To import or export month-by-hour beam shading factors:
-SAM allows you to import and export the shading loss matrix as a comma-delimited text file that contains 12 rows of 24 hourly shading factors separated by commas. The file should not have row or column headings.
-To see an example of the correct file format, export the default shading table to a text file and open it with a text editor.
-•To export the shading matrix as a text file, click Export. SAM saves the file with the .csv extension. •To import a data from a comma-delimited text file, click Import. You can open a correctly formatted text file with any extension, although SAM expects a .csv file by default. Solar Azimuth by Altitude Beam Irradiance Shading Loss Table
-The solar azimuth-by-altitude table is a two-dimensional look-up table of beam irradiance shading losses. For each hour in the simulation, SAM calculates the position of the sun as a pair of solar azimuth and altitude angles and looks up the shading loss to use for that hour based on the solar position. SAM uses linear interpolation to estimate the value of the shading loss for solar angles that fall between values in the table row and column headings.
-•Azimuth angle values use the following convention: 0 = north, 90 = east, 180 = south, 270 = west. To define the azimuth-altitude shading loss table by hand:
-1.Click Enable solar azimuth by altitude beam irradiance shading loss table. 2.In Rows and Cols, type the number of rows (solar altitude angle values) and number of columns (solar azimuth angle values) in the table. Specify a number of rows that is one greater than the number of altitude values: For example for a table with nine rows of altitude values, specify a Rows value of 10. Similarly, specify a Cols value that is one greater than the number of azimuth values.
-3.In the top row (highlighted in blue), type a set of solar azimuth angle values in degrees between zero and 360 and increasing monotonically from left to right. 4.In the leftmost column (highlighted in blue), type a set of solar altitude values in degrees between zero and 90 and increasing monotonically from top to bottom. 5.Type a beam shading loss percentage (between zero and 100%) in each cell of the table. A value of 100% indicates that beam irradiance is fully blocked by a shading object. A value of zero indicates that beam irradiance is not blocked. To import or export azimuth-by-altitude beam shading factors:
-SAM allows you to import and export the azimuth-altitude lookup table as a comma-delimited text file that contains shading percentages separated by commas. The file should also include the row and column headings indicating the solar azimuth and altitude values.
-To see an example of the correct file format, export the default shading table to a text file and open it with a text editor.
-•To export the shading table as a text file, click Export. You can save the file with any file extension, including .txt or .csv. •To import data from a comma-delimited text file, click Import. |
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-SAM provides a single input for a constant sky diffuse loss that it applies to every hour in the year. It represents portion of the sky that is obstructed. A value of zero is for no shading loss, a value of 100% completely blocks sky diffuse irradiance from the array.
-To define a sky diffuse shading loss:
-1.Click Enable sky diffuse shading loss (constant). 2.Type a value for the shading loss as a percentage. |
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