Sign convention for time series

Intro

Question:

How does IESopt interpret positive and negative values in a Profile connected using node_from?

Answer:

When modeling energy systems in IESopt, you might have a fixed Profile representing both energy demand and supply — the proper sign of generation / consumption then depends on the way it is configured and connects to other components. Understanding how to correctly connect this Profile to a Node is crucial for accurate results.

Details

Understanding node_from and node_to

Generally the following intuition applies:

  • node_from: Indicates that the component draws energy from the specified Node.

  • node_to: Indicates that the component injects energy into the specified Node.

Example: node_from

If you connect your fixed Profile (mode: fixed, which is the default) to a Node using node_from, here’s how IESopt interprets the values:

  • Positive Values: The Profile draws energy from the Node (consumption).

  • Negative Values: The Profile effectively injects energy into the Node (generation).

Why does this happen?

In IESopt, drawing a negative amount of energy from a Node (-x kWh) is mathematically equivalent to injecting a positive amount of energy (+x kWh) into it. This means, the following are equal:

  • A negative value in a node_from-configured Profile

  • A positive value in a node_to-configured Profile

  • Injecting x > 0 units of energy into a Node

  • Withdrawing a negative amount of energy from a Node

Practical example

Suppose you have a fixed Profile connected to an electricity grid Node:

myprofile:
  type: Profile
  carrier: electricity
  node_from: elec_grid_node
  value: [100, -50, 150, -75]  # in kW

  • At time step 1: The Profile draws with a power of 100 kW from the Node (consumption).

  • At time step 2: The Profile injects with a power of 50 kW into the Node (generation).

  • And so on.

Alternative approach with node_to

If you prefer to handle injections explicitly, you can use node_to:

  • Connect your Profile using node_to.

  • Positive values will inject energy into the Node.

  • Negative values will draw energy from the Node.

Summary

  • Using node_from:

    • Positive values = Draw from Node.

    • Negative values = Inject into Node.

  • Using node_to:

    • Positive values = Inject into Node.

    • Negative values = Draw from Node.

By correctly setting up your Profile and understanding the sign conventions, you ensure that your model accurately reflects the intended energy flows.