Old equipment is most commonly decommissioned immediately (i.e., Decommissioning Proportion = 1.0). However, it might be more realistic to model delayed decommissioning, reflecting operational delays due to focusing on new equipment, or keeping old equipment as a contingency or for repurposing elsewhere.
If Decommissioning Proportion = 1.0 then old equipment is decommissioned as fast as transition occurs if Decommissioning Mode is set to Annual Proportion (default) or Instantaneous Proportion (legacy). The new options for Decommissioning Mode allow you to be much more prescriptive about how decommissioning occurs, as they can be set independently of the same modes for Churn Mode, as shown in the following example.
Relative Profile
Following on from the example in Figure 4 in 1.6.1.3 Churn Mode, in which 200 customers transition from Resource 1 to Resource 2 each year over 5 years, from Y3 to Y7 (Churn Mode = Absolute Profile), you can set Decommissioning Mode = Relative Profile, with straight-line inputs as shown in Figure 1 below.
Figure 1: Modelling decommissioning using Decommissioning Mode = Relative Profile
These inputs mean that decommissioning will not start until end of Y7, at which point the transition of customers from Resource 1 to Resource 2 should be complete. The decommissioning will occur at a rate of 50% of the original number of Resource 1 units per year, so it will take 2 years to complete.
Figure 2: Decommissioning of Resource 1 after transition of customers from Resource 1 to Resource 2
Essentially, these new inputs allow you to be much more ‘hands on’ when modelling the transition and decommissioning of resources.