Solar radiation components

[carstenhoyerklick]

Description of the issue

Solar radiation has different components, which need to be added to the ontology. We have started discussions about direct, diffuse and global radiation in the issues #1067, #1072 and #1073. To ensure consistency this is merge of the three issues.

Ideas of solution

Direct Radiation Definition: Direct radiation is the non-scattered radiant flux from the Sun within the extent of the solar disk only (half-angle 0.266 deg). Comment:

• ISO and WMO CIMO guide use the term “direct radiation” in the sense of direct normal radiation.
• The definition is also in line with (cfconvetions.org): direct_downwelling_shortwave_flux_in_air, with a slight adaption (moved "beam radiation" to alternative term). http://cfconventions.org/Data/cf-standard-names/current/build/cf-standard-name-table.html

Diffuse Radiation Definition: "Diffuse radiation is radiation that has been scattered by gas molecules in the atmosphere and by particles such as cloud droplets and aerosols."

This definition has been taken vom the cfconventions (cfconvetions.org): diffuse_downwelling_shortwave_flux_in_air. http://cfconventions.org/Data/cf-standard-names/current/build/cf-standard-name-table.html

Global Radiation This will be a subcasss of solar radiation (.... ocurrent -> process -> radaition -> solar radiation)

Suggested definition: Global Radiation is solar radiation received on a surface from a solid angle of 2pi steradians. It consists of direct radiation and diffuse radiation. Adapted from WMO G0560.

Direct Normal Radiation Definition: Direct radiation is the non-scattered radiant flux density collected by a surface normal to the direction of the Sun within the extent of the solar disk only (half-angle 0.266 deg).

• Comment to be added: WMO defines direct solar radiation by the means of the pyrheliometer as a measurement device: Direct solar radiation is measured by means of pyrheliometers, the receiving surfaces of which are arranged to be normal to the solar direction. By means of apertures, only the radiation from the sun and a narrow annulus of sky is measured (half-angle 2.5 deg), the latter radiation component is sometimes referred to as circumsolar radiation or aureole radiation”
• ISO und WMO CIMO Guide label direct normal radiation as it is defined here “direct radiation”

Workflow checklist

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

I am aware that

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

[l-emele]

In the protocol of the OEO Dev 33 I read:

These are differentiated by how you measure them and how you use them

If the difference is the way you measure it then these are not different processes but different quantity values or process attributes.

[mschroedter]

No, the difference in our setup is not the way how you measure it. The difference is a physical process (with/without scattering in the atmosphere or the sum ob both).

There are different measurement devices used, but this is a follow-on, and not the basis of the definition.

And yes, others base their definition on the different measurement systems, but this is not our approach for the OEO. We only mention it as alternative definition someone may find in literature. Therefore, this is inside a comment to make users of the ontology aware.

[carstenhoyerklick]

Can we agree on the above defintions and go to implementation?

[l-emele]

What is a non-scattered radiant flux density in the direct radiation? Reads a lot like a quantity value. We need here a different definition.

[carstenhoyerklick]

non-scattered means that it traveled the direct path from the sun without hitting something inbetween. This is opposite to scattered flux, which has hit some molecule or particle and changed its direction. The non-scattered photons are those that came directly from the sun and can e.g. be concentrateded through mirrors or lenses. Scattered and non-scattered is the usual term in radiation physics.

[stap-m]

non scattered radiant flux density sounds like a quantity value to me, too, and direct radiation sounds like a subclass of radiation. Luckily, for every quantity value we usually also need an "entity in reality". E.g.:

• direct radiation is the non-scattered solar radiation from the Sun within the extent of the solar disk only.
• non scattered radiant flux density is a quantity value / flux density (tbd) that measures the direct solar radiation within the extent of the solar disk only (half-angle 0.266 deg).
• axiom 'non scattered radiant flux density' 'is about' some 'direct radiation'

[carstenhoyerklick]

This sounds good, but where to place those now? As subclasses to solar radiation? Where should the 'non scattered radiant flux density' go? Where would the last point go to? In SubClass Of?

[l-emele]

What is the unit of non scattered radiant flux density? Watts per square metre? Then it would be a subclass of (or the same as?) areal solar power density.

[carstenhoyerklick]

Yep, w/m², it would fit well there.

[stap-m]

Where would the last point go to? In SubClass Of?

By "last point" you mean the axiom? Then yes.

[stap-m]

• direct radiation is the non-scattered solar radiation from the Sun within the extent of the solar disk only.

To continue with diffuse radiation Diffuse radiation is solar radiation that has been scattered by gas molecules in the atmosphere and by particles such as cloud droplets and aerosols.

[stap-m]

Global and Direct Normal Radiation both refer to the solar receiving surface #1074. The suggested def of direct normal radiation proposes a classification as non scattered radiant flux density which will be implemented as quantity value. Ok @carstenhoyerklick ? Can global radiation be defined/classified similarly to it?

[carstenhoyerklick]

To be discussed in OEO-DEV 46 https://etherpad.wikimedia.org/p/oeo-dev-46

[l-emele]

For documentation what was discussed in OEO dev meeting 46:

• Definitions:
  • direct solar radiation is radiation that is the non-scattered part of solar radiation from the Sun within the extent of the solar disk only.
  • diffuse solar radiation is radiation that is the part of solar radiation that has been scattered by gas molecules in the atmosphere and by particles such as cloud droplets and aerosols.
  • non scattered radiant flux density is a quantity value / flux density (tbd) that measures the direct solar radiation within the extent of the solar disk only (half-angle 0.266 deg).
  • (global radiation is the sum of direct radiation and diffuse radiation) --> alternative term of solar radiation?
  • Note: Solar radiation is the merological sum of direct solar radiation and diffuse solar radiation
• Axiom
  • Disjoint: direct solar radiation, diffuse solar radiation
  • 'non scattered radiant flux density' 'is about' some 'direct radiation'
• Where to place it in the ontology
  • As subclass of solar radiation
  • As quanity values?
  • "non scttered radiatiant flux density" as subclass of areal solar power density
• Next:
  • Direct / Diffuse / Global Horizontal radiation:
  • e.g. Direct/diffuse/global horizontal irradiation/irradiance is direct/diffuse/global irradiation/irradiance measured on a horizontal solar receiving surface
  • Axiome:
  • "An areal solar energy density (irridiation) is an areal energy density that gives the arriving energy of solar radiation per area. A synonym for areal solar energy density is irradiation."
  • "A horizontal areal solar energy density (horizontal irridiation) is an areal energy density that gives the arriving energy of solar radiation on a horizontal area."
  • same for power density, normal, inclined, vertical...
  • As a quantity value?
  • Direct / Diffuse / Global irradiation on an inclinced plane
  • eg. Direct / diffuse / global horizontal irradiation/irradiance is direct/diffuse/global irradiation/irradiance meased on an inclined plane which is defined by its azimuth and slope.
• Tracking surfaces https://github.com/OpenEnergyPlatform/ontology/issues/1088
  • Tracking sounds a lot like a process, so we should define it as such:
  • solar tracking: Solar tracking is a process of in which a radiation receiving surface is following the path of the sun on the sky.
  • single axis tracking: Single axis tracking is solar tracking in which a radiation receiving surface is following the path of the sun by roting along a fixed axis. Typical axis orientations are North-South or East-West.
  • two axis tracking: Two axis tracking is solar tracking in which a radiation receiving surface is following the sun by rotating around two axes. The plane is always oriented normal.
  • We could additionally add something like solar tracked receiving surface and subclasses as equivalent classes:
  • solar tracked receiving surface: A solar tracked receiving surface is a radiation receiving surface that participates in solar tracking.
  • single axis tracked receiving surface: A single axis tracked receiving surface is a radiation receiving surface that participates in single axis tracking.
  • two axis tracked receiving surface: A two axis tracked receiving surface is a radiation receiving surface th

[l-emele]

It is now almost three months since we had the discussion in the oeo dev meeting. However, no one has implemented what we agreed. So I will do this now.

[carstenhoyerklick]

Apologies, it is still on my todo list, and wanted to work on it the next days. I was to busy in autumn.

[l-emele]

Sorry, I did not know that. Anyway most of this is now in #1448. If you want, you can take over and finalise this.

The following part is not clear to me:

Next:

* Direct / Diffuse / Global Horizontal radiation:

  * e.g. Direct/diffuse/global horizontal irradiation/irradiance is  direct/diffuse/global irradiation/irradiance measured on a horizontal solar receiving surface
  * Axiome:
  * "An areal solar energy density (irridiation) is an areal energy density that gives the arriving energy of solar radiation per area. A synonym for areal solar energy density is irradiation."
  * "A horizontal areal solar energy density (horizontal irridiation) is an areal energy density that gives the arriving energy of solar radiation on a horizontal area."
  * same for power density, normal, inclined, vertical...
  * As a quantity value?
  * Direct / Diffuse / Global irradiation on an inclinced plane
  * eg. Direct / diffuse / global horizontal irradiation/irradiance is direct/diffuse/global irradiation/irradiance meased on an inclined plane which is defined by its azimuth and slope.

Is this ready for implementation or does this need further discussion?

[l-emele]

PR #1448 is now merged. The remaining parts of this issue will probably take a while so I move the milestone.