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Standard Nomenclature for PV Systems
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Irradiance data abbreviations #10

Open Nicolas-Chouleur opened 4 years ago

Nicolas-Chouleur commented 4 years ago

A few comments 1) you use lowercase, often abrevations of dni, ghi etc... are upper case

2) DHI sometimes stands for diffuse horizontal irradiance. Maybe you could add DIF (or dif) then in the list to cover both direct and diffuse?

3) In addition to poa, I'd suggest to add gti: global tilted irradiance. This is more frequently used in Europe than poa.

toddkarin commented 4 years ago

  1. Yes, I'd agree those abbreviations are better in upper case, but we have compromised because we are attempting to make a consistent style throughout using lower case variables.

  2. This is a good point, while dni typically stands for direct normal irradiance, dhi could be either direct or diffuse normal irradiance. We'll have to think about how to resolve this.

  3. Is gti just the European version of poa? E.g. for a tracking system, is gti always in the plane of array?

Nicolas-Chouleur commented 4 years ago
  1. yes, we also talk about GTI for tracking systems. I used to work for Sunpower Europe and we used to apply poa to be aligned with our Amercan colleagues. Since I joined Everoze, all contracts I've reviewed, performance tests, etc... always refer to GTI, either for FT or trackers. And I think it's not only in Europe. Many large developers are active world wide, so GTI is very often seen in other regions. I'd suggest that you just add the reference to gti = poa so you just have to define it once
cwhanse commented 4 years ago

  1. We used lower case to be consistent with python style rules. Do you anticipate that upper/lower case is a barrier to adoption?

  2. 'dhi: direct horizontal irradiance' this is a cut and paste error, it should read 'dhi: diffuse horizontal irradiance'. Thanks for catching that!

  3. What is the commonly-understood meaning of 'gti'? Is it both direct and diffuse in the plane of array? If that's so, what are the terms used for the direct and diffuse component in the plane of array?

Nicolas-Chouleur commented 4 years ago

  1. I suppose lower case could work though it is not the current usage. Not using python, but in general software should be a tool and not impose a way of work.

  2. GTI mean Global Tilted Irradiance, so it's like GHI means Global Horizontal Irradiance, but in the plane of array: direct component + diffuse component. To my understanding POA is also refering to direct + diffuse, at least for PV. GTI is generally mentioned in PR or other performance assessment, and it is not requried to distinguish direct and diffuse components for standard PV. For CPV, you'd use DNI I guess, but this is a marginal technology on the market

toddkarin commented 4 years ago

Currently, we have poa_diffuse, poa_direct, poa_global. I added gti as an alternate for poa_global. Should we change the suggested name for poa_global to gti? It's a little more compact, but I'm not used to using it in the US.

cwhanse commented 4 years ago

I'm -1 on changing poa_global to gti because it breaks the naming pattern for plane-of-array irradiance components.

Although some common PV models use only gti (or poa_global, e.g. PVWatts, the Huld model) others (e.g. Pvsyst, the CEC model) account for reflected irradiance which as a function of poa_direct. So there's reason to keep poa_diffuse and poa_direct.

I have mixed feeling about including both gti and poa_global. It depends on the purpose of pv-terms: is it a glossary, or a (hoped-for) standard? If we are regarding pv-terms as a glossary, then it makes sense to include synonyms such as gti and poa_global. If pv-terms is meant to become an informal standard that encourages compatibility among software, then having duplicate names for the same quantity is not good.