Improve modeling of incentives that apply to part of the system

[cpaulgilman]

SAM's incentives ITC, PTC, IBI, CBI, and PBI generally apply to the system as a whole. In some cases, incentives may apply only to a component of the system, such as the storage component of an IPH system. In other cases, different incentives may apply to different components of the system, such as PV components and storage components in a PV+Storage system.

It is not possible in SAM to assign an incentive to a particular component. It is possible to approximate an incentive that applies to a component by estimating the incentive as a percentage of the total cost. However, this approach does not work well for analysis that involves scaling the size of the system or of different components.

Also, for front-of-meter (FOM) configurations, ITC qualification is defined on the Depreciation input page and is tied to depreciation classes. This is consistent with IRS rules, but because the ITC percentage is defined on the Incentives page, users often don't realize that the ITC amount is determined by the ITC qualification check boxes on the Depreciation page. This needs to be considered for any changes we make to allow the ITC to apply to components of the system.