AC Degradation

The AC Degradation inputs allow you to model a decline in the system’s AC electrical output over time due, for example, to aging of equipment.

Note

When you specify degradation in each year, SAM ignores the value you specify for Year 1 (Row 1 of the input table) because it assumes degradation applies in Years 2 and later.

For systems with battery storage, the battery’s degradation depends on the inputs on the Battery Life page. For systems with fuel cells, the fuel cell degradation inputs are on the Fuel Cell page.

Annual Degradation for Single-year Simulation

Annual AC degradation rate

The annual reduction in the system’s AC output as a percentage of the system’s total annual AC output.

Value and Schedule Mode

For most situations where you want to model an annual reduction in the system’s output, you can use the “value mode” for a single annual degradation rate that applies to all years of the project cash flow. SAM applies the percentage to the system’s total annual electrical output value in years 2 and later.

Value Mode Example

An AC degradation rate of 1% for a system with a net annual AC output of 100,000 kWh in Year one results in annual output values of 100,000 kWh in year 1, 99,000 kWh in year 2, 98,010 kWh in year 3, 97,029.9 kWh in year 4, etc.

This example uses “compounding” degradation, where 1% is applied to the previous year’s output. Wind Power uses AC linear degradation, where the degradation is always applied to the year 1 nameplate value:

Linear Value Mode Example

An AC degradation rate of 1% for a system with a net annual AC output of 100,000 kWh in Year one results in annual output values of 100,000 kWh in year 1, 99,000 kWh in year 2, 98,000 kWh in year 3, 97,000 kWh in year 4, etc.

In some situations, you may want to assign a different degradation rate to different years of the project cash flow. To do that, you use the “schedule mode” to specify a table of degradation rate values. In Schedule mode, SAM applies the degradation rate for a given year to the annual output in Year one to calculate the annual output for that year.

Schedule Mode Example

For a system with a Year 1 AC output of 10,000 kWh, if you specify an AC degradation rate of 0.5% for Year 5, SAM would calculate the annual AC output in Year 5 as follows: 10,000 kWh × (1 - 0.005) = 9,950 kWh.

Because Year 1 is the first year of operation before degradation begins, you should set the degradation rate for Year 1 (the first row in the degradation table) to zero.

To enter an annual schedule of degradation rates:

1. Click the grey and blue Value/Sched button so Sched is highlighted in blue. SAM replaces the variable’s value with an Edit button.

   

2. Click Edit.

3. Change Number of values to the the analysis period from the Financial Parameters page. The number of rows in the table should be the number of years in the analysis period.

4. In the table of values, either type a value in each row, or click Paste to paste values from your computer’s clipboard. Row 1 is for Year 1.

To delete a value, select it and press the Delete key on your keyboard.

You must type a value for each year. If you delete a value, SAM will clear the cell, and you must type a number in the cell or SAM will consider the schedule to be invalid. Type a zero for years with no value.