Community solar subscriber cost of participation omits up-front costs

[cpaulgilman]

Describe the bug

The Community Solar model calculates a subscriber NPV for each subscriber class. The NPV is the present value of each subscriber class cost of participation. In the current implementation, the cost of participation for each subscriber class is set to the project owner revenue from that subscriber class. However, up-front payments are treated as a reduction in the Year 0 cost, similar to an investment based incentive and therefore not included in the annual revenue that starts in Year 1. This results in the subscriber up-front payment not being included in the subcriber NPV.

See https://sam.nrel.gov/forum/forum-general/4651.

To fix this, the subscriber cost of participation should be calculated separately from the owner revenue.

To Reproduce

1. Create a PVWatts / Community Solar case.
2. Run a simulation for the default case and note the Subscriber 1 NPV.
3. Change the Subscriber 1 Up-front cost to $5000.
4. Run a simulation and note that the Subscriber 1 NPV does not change.

Expected behavior

Subscriber NPV should change with up-front cost

Operating System and Version

• SAM 2023.12.17 r2