Support configurable fallback powers in formulas for components or component categories

[shsms]

What's needed?

Actors/apps should be able to specify what kind of estimate should be used as a fallback when a (non-meter) component is missing data, and for how long. Currently we always fallback to 0, assume that it is not producing data.

Actors/apps also need to know when something is based on estimates and not actual measurements. They can change the prediction mechanism, and how long it is applied before settling on 0 or None or another value.

Proposed solution

No response

Use cases

No response

Alternatives and workarounds

No response

Additional context

cc: @thomas-nicolai-frequenz @cwasicki

[thomas-nicolai-frequenz]

should be used as a fallback when a (non-meter) component

@shsms why wouldn't we apply this to meters as well?

[shsms]

should be used as a fallback when a (non-meter) component

@shsms why wouldn't we apply this to meters as well?

This is how I see it:

if a meter doesn't have a fallback component based on the component graph (maybe because it is a dangling meter or consumer meter), and if it is missing data, we have to treat it as unmeasurable and stream None.

If a meter has fallback (maybe an inverter), then when the meter is not streaming, we fallback to the inverter, and when the inverter is not streaming, we can customize the next level fallback.

So there's only one case where we want to support configurable fallbacks, although it is a very common case.

---

This is assuming our formula generators are considering meters as primary components and inverters/etc as fallback:

| category | has fallback | operational mode | data | effect                  |
|----------|:------------:|------------------|:----:|-------------------------|
| meter    |      No      | has telem        | yes  | stream data             |
| meter    |      No      | has telem        |  no  | stream None             |
| meter    |      No      | inactive         |  -   | invisible (≈ 0)         |
| meter    |     yes      | has telem        | yes  | stream data             |
| meter    |     yes      | has telem        |  no  | use fallback            | <-- [1]
| meter    |     yes      | inactive         |  -   | use fallback as primary |


| category |       is primary        | operational mode | data | effect              |
|----------|:-----------------------:|------------------|:----:|---------------------|
| inverter |     no (has meter)      | has telem        | yes  | stream data         |
| inverter |     no (has meter)      | has telem        |  no  | configured fallback | <-- [2]
| inverter | yes (no/inactive meter) | has telem        | yes  | stream data         |
| inverter | yes (no/inactive meter) | has telem        |  no  | stream None         |


[1]: Delegate to fallback component, whether configured fallback behaviour gets used or not
[2]: Only case where configured fallback would get used.