Forecast UI: Dynamic yMin value for dynamic price forecast

[deadrabbit87]

The minimum value on the Y-axis is always set to 0. This makes it harder to visually interpret smaller price fluctuations.

I’ve attached two screenshots that show what I mean:

It would be great if there were a similar option to yMax — for example, a dynamic yMin value calculated as:
yMin = minimum forecasted price + small buffer.

This would make the chart easier to read and more informative when prices vary within a small range.

[naltatis]

A few considerations:

Scope: Not only affects the forecast modal. Is also relevant for charge plan and grid-charging views.

Tech: For historical reasons we use different techniques (chart libs) in the above mentioned scopes. If we change the behavior, we need to be consistent across all.

Combined chart: the forecast chart shows grid, co2, feedin (PR) and production values in one chart. The 0-axis of all datasets is aligned. Negative prices are supported. If we introduce non-0 based scales we'll have to split this chart in to multiple separate ones (which might be a good idea for other reasons anyways - dedicated page).

Axis: Our co2/price/production charts dont have an y-label axis but the min/max labels provide context. Using non-0-based y-axis can lead to a distorted sense of saving potential, especially if we daily adjust the scale dynamically based on data. The Tibber chart addresses this partly by introducing an avg. price axis and color coding. We have to make the context very clear if we do this. In general I'm a fan of showing absolute values to not create false incentives or urgency, but I understand the appeal of this request and am not fundamentally against it. This video describe the considerations and tradeoffs quite well https://youtu.be/14VYnFhBKcY?si=-6yP3TlN5IC4XuZs

TLDR
Yes, we should to this, but it's not a trivial change with a couple of prerequisites to be addressed.