Hi,
I have two master students that are going really deep into the solar algorithm and now have some questions that the official documentation is not being explicit about (and I am not a help either…). The questions are all related to “Solar Radiation Reflected from Ground”:
• What is the reason for having the number of receiving points equal to the number of sides on a receiving surface?
• Related to the first question, what is the reason for placing the receiving points on the surface, and not just at the vertexes of the surface? (could it be that by moving the receiving points inwards, it ensures that less surface area is considered shaded if rays from a receiving point does not reach the sky?).
• Why trace 90 rays from receiving points? (why not more, less, a Tregenza or a Klems distribution?)
• In the calculation of beam to diffuse solar radiation reflected from the ground, the reflection factor is a fraction of the hour of calculation and the previous hour. What is the reason for doing this weighing, and what is the distribution? 50/50?
Additionally, we believe there is a mistake in the Engineering Reference formula 6.6, where the formula should be divided by Pi (which would make physical sense and which is also done in the EnergyPlus source code).
Thanks!
Dear Steffen,
I am interested in your question. Would you please give a very short outline about the intended solar algorithm? You may give some figure or you may give a link for a paper describing the algorithm.
However i can give general concept for numerical solutions. They are an approximation of an exact solution. The error allowed depends on the numerical computation effort and the amount of uncertainty in the exact solution. The judgement on an algorithm is how far its results are deviated from the real solution, and how much computational effort it takes.
Best wishes
Hi Steffen,
I was about to make the same request as Prof. Zakry.
Could you please share the background document to your questions ? (The document entitled "“Solar Radiation Reflected from Ground”", I believe.)
Thanks.
-Sanjay
Abdelhalim Zekry & Sanjoy Roy: We are basically getting inspired by the solar algorithm source code in E+ which is also documented in https://energyplus.net/sites/default/files/pdfs_v8.3.0/EngineeringReference.pdf. The questions we have are related to the assumptions made by the developers of E+ - assumptions which we cannot find any documentation for anywhere.
Edwin Rodriguez-Ubinas: You address one of our questions, and yes, we also realise that it is probably due to a tradeoff. We were seeking the specific argument/analysis that the E+ developers used for choosing 90 and not something else. FYI, we are doing our own analysis of no of rays vs time vs. precision to make an informed decision. Your assumption about the typo is wrong: it is in "Beam Solar Radiation Diffusely Reflected from the Ground".
I am still looking for answers to our specific questions... It would be best if Fred Winkelmann or anyone with the same level of insight was around :-) Anyone other from the E+ team that can help?
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