Current year, investment year and forecast year

[tsmbland]

There's a lot of confusion about this, so I wanted to clarify things (for myself and others) with a couple of examples.

This is what MUSE is currently doing, not what it's necessarily supposed to be doing:

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Example 1:
Time framework: [2020, 2025, 2030, 2035]
Forecast: 5
Objective: Lifetime LCOE
Maximum iterations: > 1 (endogenous mode)

In 2020, the agent makes investment decisions for the year 2025, aiming to meet known demands in 2025 (and other constraints), choosing the technology with the lowest LCOE over its lifetime. Decisions are based on technology parameters in 2025, and endogenously calculated commodity prices for the year 2025, both of which are assumed to be constant over the lifetime of the technologies.

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Example 2:
Time framework: [2020, 2025, 2030, 2035]
Forecast: 10
Objective: Lifetime LCOE
Maximum iterations: > 1 (endogenous mode)

In 2020, the agent makes investment decisions for the year 2025, aiming to meet known demands in 2030 (and other constraints), choosing the technology with the lowest LCOE over its lifetime. Decisions are based on technology parameters in 2030, and an estimate of commodity prices for 2030 (based on linear extrapolation of the current price and the endogenously calculated price in 2025), both of which are assumed to be flat over the lifetime of the technologies.

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There's already discussion in #466 and #196 about how we might change this, but just wanted to clarify how things are currently working before changing anything