Solar Advisor applies the annual performance factors to the total annual electric output calculated by the hourly simulation model.

System Degradation

The system degradation represents an annual reduction in system output due to equipment aging. It applies to the gross total annual electric output in year two and subsequent years. When you enter the degradation rate as a single value, the degradation for each year is compounded.

Availability

Entering Values as an Annual Schedule

You can also define the system degradation or availability using an annual schedule, which allows you to manually assign a different degradation rate to each year. One application of this approach is modeling the effect of replacing equipment within the system lifetime: You can set the system degradation to zero for the year equipment is replaced. To define an annual schedule, right-click the system degradation variable and choose Annual Schedule in the Input Type window. Note that for system degradation rates entered on an annual schedule, degradation rates are not compounded annually: Solar Advisor multiplies each year's degradation rate by the first year annual output. For step-by-step instructions for entering variables in an annual schedule, see Entering year-by-year O&M costs.

Fig 1. Diagram of derate and degradation factors

The graphs below show the effect of different combinations of a system derate factor of 5% and system degradation factor of 1% on the annual output of a residential, grid-connected PV system.

Fig 2. Graphs showing effects of different combinations of system derate and degradation factors

Availability

Power Plant Availability describes plant downtime due to forced and scheduled outages. Availabilities of 94% are typical for parabolic trough systems.

Solar Advisor applies System Availability to the system's total annual output. The availability factor represents the percentage of time in a year that the system does not produce energy. Note that the factor is applied to the annual output, not to particular hours of the year.