Observe the generated forecast over a period of time

Oct 13, 2025 by wbrum.org 78 views

Introduction

When the "Adjust solar forecast based on real production data" setting is enabled in the forecast settings, the forecasted values can sometimes be negative. This behavior is unexpected and seems to occur when using Open-Meteo as the data source with an efficiency setting of 78%. In this article, we will delve into the steps to reproduce this issue, the configuration details, log details, and the operating system or environment that evcc runs on.

Describe the Bug

The issue arises when the "Adjust solar forecast based on real production data" setting is enabled, and the forecasted values can sometimes be negative. This behavior is unexpected and seems to occur when using Open-Meteo as the data source with an efficiency setting of 78%. The negative forecast values can cause issues with the overall performance of the system, and it is essential to identify the root cause of this problem.

Steps to Reproduce

To reproduce this issue, follow these steps:

Enable "Adjust solar forecast based on real production data": Go to the forecast settings and enable the "Adjust solar forecast based on real production data" setting.
Use Open-Meteo as the solar forecast data source: Use Open-Meteo as the solar forecast data source.
Set the efficiency value to 78%: Set the efficiency value to 78%.
Observe the generated forecast over a period of time: Observe the generated forecast over a period of time.
Notice that some forecasted values may fall into the negative range on low forecast days: Notice that some forecasted values may fall into the negative range on low forecast days.

Configuration Details

The configuration details are as follows:

solar:
    - type: template
      template: open-meteo
      interval: 1h
      lat: 37.X
      lon: -122.X
      dec: 28
      kwp: 5.6
      az: -90
      efficiency: 78
    - type: template
      template: open-meteo
      interval: 1h
      lat: 37.X
      lon: -122.X
      dec: 27
      kwp: 2
      az: 90
      efficiency: 78
    - type: template
      template: open-meteo
      interval: 1h
      lat: 37.X
      lon: -122.X
      dec: 11
      kwp: 3.2
      az: 0
      efficiency: 78

Log Details

The log details are as follows:

[lp-1 ] DEBUG 2025/03/12 11:30:23 charge power: 0W
[lp-1 ] DEBUG 2025/03/12 11:30:23 charge currents: [0 0 0]A
[site ] DEBUG 2025/03/12 11:30:23 grid power: 0W
[site ] DEBUG 2025/03/12 11:30:23 pv 1 power: 613W
[site ] DEBUG 2025/03/12 11:30:23 battery 1 power: -10W
[site ] DEBUG 2025/03/12 11:30:23 battery 1 soc: 71%
[site ] DEBUG 2025/03/12 11:30:23 site power: 90W
[lp-1 ] DEBUG 2025/03/12 11:30:24 charge voltages: [2.1 2.1 2.1]V
[lp-1 ] DEBUG 2025/03/12 11:30:24 charger status: A
[site ] DEBUG 2025/03/12 11:30:24 solar forecast: accumulated 54.106kWh, produced -34.110kWh, scale -0.630

What Type of Operating System or Environment Does evcc Run On?

evcc runs on Linux.

External Automation

I have made sure that no external automation like HomeAssistant or Node-RED is active or accessing any of the mentioned devices when this issue occurs.

Nightly Build

I have verified that the issue is reproducible with the latest nightly build.

Version

The version of evcc is 0.200.9.

Conclusion

Q: What is the issue with the "Adjust solar forecast based on real production data" setting?

A: The issue arises when the "Adjust solar forecast based on real production data" setting is enabled, and the forecasted values can sometimes be negative. This behavior is unexpected and seems to occur when using Open-Meteo as the data source with an efficiency setting of 78%.

Q: What are the steps to reproduce this issue?

A: To reproduce this issue, follow these steps:

Enable "Adjust solar forecast based on real production data" in the forecast settings.
Use Open-Meteo as the solar forecast data source.
Set the efficiency value to 78%.
Observe the generated forecast over a period of time.
Notice that some forecasted values may fall into the negative range on low forecast days.

Q: What are the configuration details for this issue?

A: The configuration details are as follows:

solar:
    - type: template
      template: open-meteo
      interval: 1h
      lat: 37.X
      lon: -122.X
      dec: 28
      kwp: 5.6
      az: -90
      efficiency: 78
    - type: template
      template: open-meteo
      interval: 1h
      lat: 37.X
      lon: -122.X
      dec: 27
      kwp: 2
      az: 90
      efficiency: 78
    - type: template
      template: open-meteo
      interval: 1h
      lat: 37.X
      lon: -122.X
      dec: 11
      kwp: 3.2
      az: 0
      efficiency: 78

Q: What are the log details for this issue?

A: The log details are as follows:

[lp-1 ] DEBUG 2025/03/12 11:30:23 charge power: 0W
[lp-1 ] DEBUG 2025/03/12 11:30:23 charge currents: [0 0 0]A
[site ] DEBUG 2025/03/12 11:30:23 grid power: 0W
[site ] DEBUG 2025/03/12 11:30:23 pv 1 power: 613W
[site ] DEBUG 2025/03/12 11:30:23 battery 1 power: -10W
[site ] DEBUG 2025/03/12 11:30:23 battery 1 soc: 71%
[site ] DEBUG 2025/03/12 11:30:23 site power: 90W
[lp-1 ] DEBUG 2025/03/12 11:30:24 charge voltages: [2.1 2.1 2.1]V
[lp-1 ] DEBUG 2025/03/12 11:30:24 charger status: A
[site ] DEBUG 2025/03/12 11:30:24 solar forecast: accumulated 54.106kWh, produced -34.110kWh, scale -0.630

Q: What type of operating system or environment does evcc run on?

A: evcc runs on Linux.

Q: Is external automation involved in this issue?

A: No, external automation like HomeAssistant or Node-RED is not active or accessing any of the mentioned devices when this issue occurs.

Q: Is the issue reproducible with the latest nightly build?

A: Yes, the issue is reproducible with the latest nightly build.

Q: What is the version of evcc?

A: The version of evcc is 0.200.9.

Q: What is the solution to this issue?

A: The solution to this issue is to identify the root cause of the problem and provide a solution to prevent negative forecast values from occurring. This may involve updating the configuration settings, adjusting the efficiency value, or modifying the solar forecast data source.

Q: How can I prevent negative forecast values from occurring?

A: To prevent negative forecast values from occurring, you can try the following:

Update the configuration settings to use a different solar forecast data source.
Adjust the efficiency value to a higher or lower value.
Modify the solar forecast data source to use a different algorithm or model.
Monitor the system's performance and adjust the settings as needed to prevent negative forecast values from occurring.