General
Variable |
Description |
Name |
Name your storage component. |
Abbreviation |
Give the component an abbreviated name. |
Manufacturer |
State the storage manufacturer. |
Chemistry |
Provide information on the chemistry of the storage component. |
Notes |
If desired, provide further information. |
Requires One Minute Timestep |
Select if the BESS requires a 60 second time interval. |
Max. Charge Rate |
The maximum charging current allowed, defined as amps of charging current per Ah of the remaining headroom in the battery. |
Max. Charge Current |
The maximum allowable charging current, in amps. |
Max. Discharge Current |
The maximum allowable discharging current in amps. |
Calculate End of Life by |
If you choose "Sum of Calendar and Cycling Degradation," the battery is replaced when the sum of these values reaches the degradation limit you specify. If you select "Calendar or Cycling Degradation, Whichever is Greater," the battery is replaced when either the calendar degradation or cycling degradation reaches the degradation limit. |
Cycling Degradation Uses Battery Capacity |
Select if the cycling degradation uses nominal or degraded battery capacity. |
Functional Model
The Functional Model dictates how the battery behaves in simulation. Enter the power-capacity discharge data in the table.
Variable |
Description |
Nominal Voltage |
The no-load voltage of the battery model. You can generally set this to the manufacturer's nominal voltage of the battery. |
Maximum Capacity |
The combined capacity of both tanks in the kinetic model, in amp-hours. |
Rate Constant |
The rate constant parameter specifies how quickly or slowly the two tanks equalize, in units of 1/hr. |
Capacity Ratio |
The capacity ratio specifies the relative size of the two tanks of the kinetic battery model. |
Effective Series Resistance |
The series resistance that is added to the model, in ohms. |
Capacity Curve Graph |
Specify power and capacity discharge data in the adjacent table to visualize the trend on the graph. |
Temperature vs. Capacity
Enter the nominal capacity for each temperature into the table on the left side of the page.
Variable |
Description |
Ignore Capacity Changes with Temperature |
If you do not want to include temperature effects on capacity in the battery model, check the box. Checking this option sets the d0 term to 1.0, and d1 and d2 to zero, which makes the temperature 100% of nominal at all points. |
Fitted d0 |
Constant term in quadratic fit. |
Fitted d1 |
Coefficient of temperature in quadratic fit. |
Fitted d2 |
Coefficient of temperature squared in quadratic fit. |
Cycle Lifetime
The number of charge and discharge cycles that the storage component can complete before losing performance.
Variable |
Description |
Depth of Discharge |
The amount of a battery’s storage capacity that is utilized. |
Cycles to Failure |
The number of cycles a battery will go through before failing. |
Degradation Limit for Model Fitting (%) |
This value is used to calculate the values for A and Beta. You can set the actual value used in the simulation in the defaults tab. |
Model Parameters Fit from the Data |
1/N = A*DOD ^ beta |
Fitted A |
degradation in decimal format per 100% DOD cycle
Example: 0.00014423*100 = 0.014423% degradation per 100% DOD cycle Looking for 2% cycling degradation per year? .02/0.00014423 = 139 100% DOD cycles per year Looking for 20% degradation limit before replacement? .2/0.00014423 = 1388 100% DOD cycles to failure |
Fitted Beta |
Fitted Beta tells you how partial cycles impact degradation. Set beta to 0 for a set number of cycles to failure, with no dependence on DOD. When beta = 1, The impact of a kWh throughput on the lifetime and degradation is the same, regardless of how it is cycled. HOMER doesn’t look at State of Charge in absolute terms; it looks at SOC swing to calculate the lifetime impact.
Note:
HOMER doesn’t treat degradation from micro cycling differently if the BESS is cycled between 20- 30% vs if the BESS is cycled between 90 -100% (at beta =1); the degradation in both cases will be equivalent. Beta = 1 means constant throughput. |
Estimated Lifetime Throughput (kWh) |
Estimated amount of stored and released energy a battery contains in its lifetime. |
Temperature vs. Lifetime
Some data sheets or manufacturers can provide data for shelf life versus temperature. It is common for battery "shelf life" to decrease at higher temperatures. Enter years and temperature data into the table and click Recalculate. HOMER fits an Arrhenius type equation to the data. Alternately, to choose a fixed lifetime in years, check the box at the top "Use constant shelf life regardless of temperature (years)" and enter the number of years to the right.
Variable |
Description |
Fitted B |
Coefficient of the model. Conceptually equal to the inverse of the shelf life (in hours) times the Capacity degradation Limit as a fraction. |
Fitted d |
Coefficient of the exponential term in the model. A large value of d indicates a stronger temperature dependence. Tip: The fit HOMER computes when you click Recalculate depends on the value of the Capacity degradation Limit input in the Default tab. If you change the value of the Capacity degradation Limit, you may want to Recalculate again. |
Thermal
HOMER tracks the battery bank's internal fixed temperature, or runs a simple lumped-capacity model to estimate at each time step. The lumped thermal model tracks the battery's internal temperature based on ambient temperature, losses converted to heat, conductance to ambient, and heat capacity.
Variable |
Description |
Maximum operating temperature |
Above this temperature, the battery turns off, meaning that neither charging nor discharging is allowed |
Minimum operating temperature |
Below this temperature, the battery turns off, meaning that neither charging nor discharging is allowed |
Conductance to ambient (W/K) |
The rate at which heat is exchanged between the component and ambient. Note - If this is set to a large value, the component follows the ambient temperature (defined in the temperature resource) very closely. |
Specific heat capacity (J/kgK) |
The amount of heat energy the component absorbs, per kilogram of mass, before increasing in temperature by one degree Celsius. |
Fixed bulk temperature |
Fixes the battery internal temperature to the specified value when “Consider temperature effects?” is not selected. |
Augmentation
The energy capacity of batteries inevitably decreases with time and usage. Augmentation is the process of supplementing the Battery Energy Storage System (BESS) capacity throughout the project lifetime.
Variable |
Description |
Augmentation ($/kWh) |
Cost to augment the storage component in ($/kWh). The Augmentation price will be interpolated based on what day of the year the augmentation takes place. |
Augmentation Degradation Limit (%) |
The point at which the storage will be augmented. The storage capacity may degrade up to the augmentation degradation limit, at which point the augmentation expense incurs and the storage system is brought back up to the original installed capacity as if new. For example, if the Aug deg is set to 10%, the battery will degrade down to 90% before being augmented back up to 100% capacity. If the battery were 5mwh, the capacity degrades down to 4.5, then the storage is augmented with 0.5 |
Converter
A dedicated Storage DC/DC converter is optional and can be included to account for inefficiency, costs, and total capacity. Select the check box to enter associated values.
Variable |
Description |
Size |
The sizing entry allows you to test different numbers of units of these modules. For example, you may enter 100 units of 1MW/4MWh modules for a total system size of 100MW/400MWh. Enter multiple sizing options to test which configuration may lead to the best economics. |
Cost |
Specify costs such as Capital Expenses ($/kW-yr), Operating Expenses ($/kW-yr), and Replacement ($kW). Direct costs are specified separately from indirect capital costs so that you may add additional expenses that reference a percentage of direct costs. |
Storage DC/DC Converter Efficiency |
The efficiency with which the inverter converts DC voltage from one power level to another, in %. |
Lifetime |
The expected lifetime of the inverter, in years. |
Efficiency |
The efficiency with which the inverter converts DC electricity to AC electricity, in %. |
Relative Capacity |
The rated capacity of the rectifier relative to that of the inverter, in %. |
Size Relative to Storage Capacity (C-Rate or 1/hr Rate) |
A measure of the rate at which a battery is charged or discharged relative to capacity |
Defaults
In the Defaults tab, you can set the default values for all of the inputs that are displayed on the Design page when a user adds the component to a HOMER model, including cost options and Site Specific Inputs. You can modify any of these values on the Design page after you add the component to the model.
Variable |
Description |
Cost |
Cost Sensitivity Analysis is the total installed costs for storage including Capital Expenses ($/kWh) and Operating Expenses ($/kWh/yr). You may assign a sensitivity (different values) to this parameter. Cost Breakdown allows you to specify Direct and Indirect Capital as well as Operating Expenses. |
Electrical Bus |
The conducting pathway that allows the flow of current in either Alternating Current (AC) or Direct Current (DC). |
Initial State of Charge |
The state of charge of the storage bank at the beginning of the HOMER simulation, in %. |
Consider Temperature Effects? |
Allows you to consider the effects of temperature on storage. For example, many batteries show a decrease in available capacity at cold temperatures. |
Minimum State of Charge |
A lower limit on the state of charge of the storage bank, in %. |
Use Minimum Storage Life |
Allows you to set a lower limit on the lifetime of the storage bank. |
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