Storage

PV Storage

To view the PV Storage page, click PV Storage on the main window's navigation menu. Note that for the PV Storage page to be available, the technology option in the Technology and Market window must be Photovoltaics - Component-based Models or Photovoltaics - PVWatts Performance Model.

Note. Solar Advisor's PV storage feature is currently under development. The current implementation is intended for testing purposes. Feel free to experiment with the feature. If you have questions or feedback about modeling battery storage in Solar Advisor, please contact Solar.Advisor.Support@nrel.gov.

The PV Storage page allows you to specify the characteristics of a battery storage system for a grid-connected photovoltaic system with batteries and an electric load. When you model a system with batteries, you should also specify a load on the PV Loads page.Solar Advisor does not model stand-alone photovoltaic systems.

Solar Advisor's battery storage model is a simple representation of energy flows into and out of a "battery," which it models as a single device, whether your system uses a single battery or a bank of multiple batteries. The battery can store up to the maximum capacity of electric energy that you specify. When the battery's capacity in a given hour is less than its maximum capacity, either the grid or solar array can charge the battery depending on the dispatch control schedule that you specify on the PV Storage page. The photovoltaic array can only charge the battery during hours when the array output is greater than the electric demand, and the dispatch control schedule allows for the array to charge the battery. The battery discharges during hours when its state of charge is greater than the minimum value you specify, the array cannot meet the load, and the dispatch control schedule allows the battery to discharge. Each charge-discharge cycle of the battery incurs losses defined by the roundtrip efficiency value that you specify. The battery charges and discharges at the same rate, defined by the total capacity and hours to charge and discharge that you specify.

To model a system with no storage, set the total battery capacity to zero. When the capacity is equal to zero, the value of other parameters on the PV Storage page have no effect on the model's calculations.

The following information will help you experiment with the PV storage feature:

•	The battery parameters determine the basic charging characteristics of the battery system including its size, efficiency, and rate of charge and discharge.

•	The timing control options and schedule matrices determine how the battery operates: You must specify the times of day for each month that the battery can charge and discharge, and whether the battery is charged by the grid or photovoltaic array.

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You can visually explore the hourly results in DView to see how the model dispatches energy from the photovoltaic array, and to and from the grid and battery. Note that negative battery power values in the hourly results indicate battery discharging, and positive values indicate the battery charging. Negative grid power values indicate the grid delivering electricity to the battery or load, and positive grid power values indicate the system delivering electricity to the grid.

Battery Parameters

Total Battery Capacity (kWh)

The total battery bank storage capacity in kWh (kWh = Ah × V ÷ 1000). The default value is zero for a photovoltaic system with no storage.

Roundtrip Efficiency (%)

The battery's round-trip efficiency. Typically between 70% and 85% for batteries used in photovoltaic systems.

Initial Stored Energy (kWh)

Battery state of charge at the beginning of the simulation. A fully charged battery would have an initial stored energy equal to the total battery capacity. A fully discharged battery would have an initial value of zero.

Min. Allowable State of Charge (%)

The minimum battery capacity as a percentage of the total battery capacity.

Hours to Fully Charge/Discharge (hours)

The time to fully discharge the battery bank at the maximum discharge rate.

Max. Charge/Discharge Power (kWh/h)

The maximum charge and discharge rate. Calculated by dividing the total battery capacity by the hours to fully charge/discharge.

Solar Array Operation

Disable Solar Array Power Output

Choose this option to model a system with a load served by the grid and a battery, but no photovoltaic array. This option makes it possible to isolate the levelized cost of energy of the battery storage system.

Battery Dispatch Timing Control

The dispatch timing control options apply to each of up to four periods. See below for details.

Force charging from the grid

Energy from the grid charges the battery during hours when the battery capacity is less than 100% of the total battery capacity.

Allow discharging of the battery?

Energy can be drawn from the battery bank.

Allow charge (from excess solar)?

Energy can be delivered to the battery bank from the solar array during hours when the solar array power exceeds the load requirement.

The battery's operation is determined by the three timing control options and how you assign them to the dispatch schedule matrices. The following tips will help you experiment with the dispatch controls:

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For each of the four periods, you can assign any combination of the three timing control options, which are defined above. For example, you might only allow the battery to discharge during night hours, and allow the grid to charge the battery during early evening hours to ensure the battery is fully charged before it begins serving the load.

•	The two matrices allow you to define a separate battery dispatch control schedule for weekdays and weekends.

•	To assign a period to a month and hour of day, select cells in a matrix and type a period number. For example, to assign Period 3 to 6 am through 5 pm from June through July, select the cells in the June and July rows and 6 am through 5 pm columns and type the number 3.

•	When you assign a period to a matrix, Solar Advisor applies the timing controls that you checked for the period to the times indicated in the matrix.