input / output power need to be discussed

[sfluegel05]

Description of the issue

This originally came from #736 and was about axioms connecting artificial objects to power wrongly (see section Original issue). However, the discussion shifted to a possible distinction between input power and output power.

• Do we need this distinction?
• How would this affect our current concept of power?
• How should we connect power to energy transformations?

Original issue

• gas turbine, hydrogen turbine, PV panel, steam turbine, water turbine and wind rotor all have physical output some power
• gas turbine, hydrogen turbine and water turbine use has physical input despite not being processes
• generator and heater use has physical output despite not being processes

All of these axioms have in common that they relate an artificial object to some power, energy or fuel via has participant-subproperties. has participant is defined as a relation between a process and a continuant, in which the continuant is somehow involved in the process. Therefore has participant-subproperties cannot be used for artificial objects.

Ideas of solution

The idea behind the axioms was probably that, for example, a gas turbine is used in a process that needs gas as an input and gives power as an output. If we change the axioms to reflect that, we have to do changes like gas turbine has physical output some power --> gas turbine participates in (energy transformation and has process attribute some power) The general pattern would be object participates in (process related to some energy / fuel / power)

We could also add new classes for all the processes in which the objects participate. Then we could say, for example, gas turbine participates in some gas combustion process and gas combustion process has process attribute some power. I would prefer not to do this and to use anonymous classes like above, because these classes seem to be very specific and have no use case despite being the process the object participates in. But maybe someone from @OpenEnergyPlatform/oeo-domain-expert-energy-modelling sees this differently.

Workflow checklist

• [ ] I discussed the issue with someone else than me before working on a solution
• [ ] I already read the latest version of the workflow for this repository
• [ ] The goal of this ontology is clear to me

I am aware that

• [ ] every entry in the ontology should have a definition
• [ ] classes should arise from concepts rather than from words

[l-emele]

has output some power is simply wrong in that cases. I think that comes from a state of the OEO when we did not yet clearly differentiate between electrical energy and power. In our current structure those classes should have the relation has output some electrical energy.

But your ideas of solution let me think that we can go a bit further. Every energy transformation has energy as physical input and energy as physical output. As every energy transformation is a process which which lasts for some time and power is the time-derivative of energy, every energy transformation has something like input power and output power. So we could introduce input power and output power as subclasses to power as general process attributes to energy transformation.

In #372 we already had a long discussion which touched also the aspect of connecting the objects to energy transformations. But as far as I can see we did only some top-level relations (i.e. relating energy converting device to energy transformation etc) but not for the subclasses. But I am to doing that now as we now have a much better structure in energy transformation as back then.

[sfluegel05]

I'm not sure about input power and output power. How is power related to the input or output of an energy transformation? As I read it, it describes the transformation itself and how much energy it transforms or transfers. Shouldn't the input power and the output power always be the same since the time is the same for input and output (the duration of the process) and the amount of energy should also be the same.

I like the idea of adding more relations between artificial objects and energy transformations. I will open an issue for this.

[l-emele]

You can have multiple inputs or outputs in an energy transformation. E.g. you can have as output electrical energy and thermal energy at the same time. Mathematically, the sum of all input powers is equal to the sum of all output powers.

[sfluegel05]

How would you relate the input / output power to the corresponding input / output? I seems to me that we have to distinguish between different input / output powers for the same process and I'm not sure how to do this.

[l-emele]

Every energy input has exactly one input power associated with and every energy output exactly one output power . One could interpret the input / output power as attributes of the energy inputs / outputs.

[sfluegel05]

How exactly would we relate the powers to the energies? Options I can imagine:

• create a new object property that can relate qualities and process attributes (or specifically power and energy)
• find a new place for power (which would have the disadvantage of breaking with #205, which included a long discussion about power)
• split the transformation process into input and output processes. The current process attribute power works, because it is related to a process and just describes the amount of transformed energy for the whole process. We could do the same with separate input / output processes which are parts of the original process.

[stap-m]

I'm not yet convinced by a distinction between input / output power. It disagrees at least with our current def of power: Power is the process attribute that is the amount of energy transformed or transferred per time unit. We have process attribute of as object property, but we haven't related the energy transformation processes and power yet. We should definitely develop a concept here.

I've the impression that this is a complex discussion that could result in some restructuring. I'd find it helpful to discuss this in a meeting, maybe supported by a whiteboard...

[l-emele]

I agree that power should be discussed separately.

[sfluegel05]

Conclusions dev meeting 22

In dev meeting 22, we came to the following conclusions:

• add axiom energy transformation has process attribute some power
• add object property has total power: A relation between an energy transformation and its total power.
• add object property has time derivative: A relation between an energy and a power where the power describes the flow of energy over a certain time.
• we can use has total power to connect an energy transformation to the sum of its input / output powers, and has time derivate to connect an energy transformation to each input / output flow individually (via has input / output some energy, where the energy is then connected to the power)

Open questions:

• should we change the definition of energy transformation?
  • new proposal: Energy transformation is a process in which input power results in output power.
  • current definition: Energy transformation is a process in which one or more certain types of energy as input result in certain types of energy as output.
  • in modelling, power is more relevant
• is there a better term for total power?
• how to connect power to a unit
  • suggestion: has unit some power unit, power unit: A unit which is a standard measure power or the rate of doing work.

To the last point I would add that process attributes are not typically related to units directly, but to quantity values. So the axiom should be has quantity value some (quantity value and has unit some power unit), or we should add a named quantity value subclass.

[l-emele]

should we change the definition of energy transformation?

* new proposal: _Energy transformation is a process in which input power results in output power._

* current definition: _Energy transformation is a process in which one or more certain types of energy as input result in certain types of energy as output._

We need to include somehow, that the output energies are of different types as the energy inputs to distinguish from an energy transfer which has the same types of energy as input and output.

[han-f]

should we change the definition of energy transformation?

From my perspective and what I gathered from our latest oeo-dev meeting it would make sense to change the definition. So a thumbs up from someone not "native" to physics.

I also think it makes sense to distinguish between output and input energy, without having a tangible suggestion up my sleeve on how to do this.

[l-emele]

We need to include somehow, that the output energies are of different types as the energy inputs to distinguish from an energy transfer which has the same types of energy as input and output.

Oh, I just saw, that don't have a general energy transfer, but only heat transfer which is a subclass of energy transformation.

[sfluegel05]

We need to include somehow, that the output energies are of different types as the energy inputs to distinguish from an energy transfer which has the same types of energy as input and output.

Oh, I just saw, that don't have a general energy transfer, but only heat transfer which is a subclass of energy transformation.

Do we need this distinction? If the common understanding of energy transformation excludes processes which have the same input and output type, i.e., energy transfer, we should separate them into two distinct concepts.

[areleu]

For reference this is an example of the current state of the ontology, power generating unit:

[areleu]

I think the input/output perspective is tangential. The power of a transformation unit is associated to its performance in a specific function. We have the has function axioms, it would be nice to be able to associate the maximum power of a device with its associated function. If it is not possible at least relating it to the definition of the power can be very helpful.

[areleu]

Could we have something like:

[areleu]

Example CHP

[areleu]

I think that this can be ugly because it would imply a relation between a specifically dependent continuant and a generically dependent continuant

[areleu]

Alternative without weird relation, make every subclass of power capacity have to be associated with an object with a function:

This is less "generic" but easier to implement as it is the status quo of power generating unit.

[areleu]

After letting this settle down a couple of nights I came to the conclusion that the latter solution is the most reasonable. It is rather clunky, and I do not see how can one enforce it but to me it is clear that transformation unit/component with a function can have one and only one function at the time (any kind of composition can emrge from the pattern we use with CHP).

On a tangential thread. I think it makes little sense that artificial objects have inputs and outputs. I these are properties of processes, this is expressed explicitely in the definition of has input [^1] I am searching the issue where the decision is explained but I can't find it. I think this can lead to incongruences down the road and that is cleaner to have I/O exclusively in processes.

[^1]: p has input c iff: p is a process, c is a material entity, c is a participant in p, c is present at the start of p, and the state of c is modified during p.

[l-emele]

What we need to depict is the following:

A energy transformation unit participates in a energy transformation process. There are a maximum input power and a maximum output power (= input and output "capacities"[^1]) and additional a momentarily input power and momentarily output power at a specific instance.

For example: An electromotive generator is involved in an process that converts kinetic energy into electrical energy. That generator might have an input capacity of 100 MW and and output capacity of 96 MW. In a specific instance that generator might work in partial load and have a input power of 50 MW (kinetic energy) and output power of 48 MW (electrical energy). Thus the efficiency is 50 MW / 48 MW = 96 %. Additionally in this process 2 MW of waste heat occur.

How do we depict all of that?

[^1]: I don't like the term capacity in this context, but sadly it is commonly used.

[stap-m]

On a tangential thread. I think it makes little sense that artificial objects have inputs and outputs. I these are properties of processes, this is expressed explicitely in the definition of has input 1 I am searching the issue where the decision is explained but I can't find it. I think this can lead to incongruences down the road and that is cleaner to have I/O exclusively in processes.

Agreed. ROs has participant and subrelations are reserved for processes. Yet, we opened OEOs has energy participant to artificial objects. This is confusing and proper documentation is missing. I'll open a separate issue.

[areleu]

What we need to depict is the following:

A energy transformation participates in a energy transformation process. There are a maximum input power and a maximum output power (= input and output "capacities"1) and additional a momentarily input power and momentarily output power at a specific instance.

For example: An electromotive generator is involved in an process that converts kinetic energy into electrical energy. That generator might have an input capacity of 100 MW and and output capacity of 96 MW. In a specific instance that generator might work in partial load and have a input power of 50 MW (kinetic energy) and output power of 48 MW (electrical energy). Thus the efficiency is 50 MW / 48 MW = 96 %. Additionally in this process 2 MW of waste heat occur.

How do we depict all of that?

Footnotes

1. I don't like the term _capacity_ in this context, but sadly it is commonly used. [↩](#user-content-fnref-1-53fa4caeceacf0eddc4a371aa411e06e)

Both the 100MW, 96MW, 2MW and the implicit efficiency are indicators of performance of that device. These values are usually obtained from operational tests, the producer conducts them based on certain specification and attaches them into the technical data of the device. Similarly, an operator could re-evaluate the values for a device that has been already been years in operation. In both cases there is a common denominator, the values are derived from a test. Said tests is a process in which the device was operated in a controlled environment. What I mean by this is that even for nameplate capacities there is a process behind.

I think that capacity, efficiency etc values still belong to the energy transformation units but everything related to inputs and outputs should be exclusively associated to processes. The performance values should be somehow associated to their functionality. I don't really see a case where material objects have inputs and outputs.

[l-emele]

It is true that nominal powers are measured at specific tests, but that is not what issue was intended about.

The idea was to describe the instantaneous values. A powerplant that is running just has these process attributes and the values of it may change at any time.