# Shadow in the PR calculation

## Recommended Posts

Hello,

Could you please inform me if my assumption about how different shading is taken into account within the expected energy balance and PR calculations?

Shadow from one row of solar panels on the next row(s) has its effect on the expected generated PV energy and so more shadow from panels on other panels leads to a lower expected PR?

Next, Shadow from obstacles (buildings, vegetation, other (roof) installations) has its effect on the Global radiation at the solar module and so more shadow from obstacles leads to a higher PR?

If my assumptions are correct, could you please explain me why the different kind of shadow has a different effect on the numbers?

Frederik

##### Share on other sites

Hi Fritz,

the performance ratio is calculated as the ratio of the total energy yield to the theoretically possible energy yield. That is, we take the energy output in kWh, E_total, and divide it by G * A * eta, where G is the irradiation on the module surface, A is the surface area of the plant and eta is the STC efficiency of the modules.

So, to answer your question, what exactly is G, the irradiation on the module surface? I will copy an energy balance here in order to illustrate the different shading and reflection items:

We calculate the reflection onto the module surface as the "Global Radiation at the Module" minus the "Reflection on the Module Interface", since this is influenced by the module properties. So the PR in this case would be

PR = 14194,57 kWh / ((1122,50 +27,61) kWh/m² * 83,83 m² * 0,181) = 0,8134, or 81,3%

We have two shading items in the energy balance: Module-independent shading in the meteo block, and module-specific partial shading in the PV field block. The first is not accounted in the calculation of the PR, the second is.

The module-independent shading is the diffuse shading that is affecting all modules equally. The diffuse shading is evoked by obstacles (near or far) that are blocking the view to the sky hemisphere and is applied to the diffuse fraction of the solar irradiation only. We calculate the diffuse shading factor for every module and determine the maximal value that applies to all modules. In real world situations this minimal factor will most likely only cover the horizon or shading by far objects.

When you have regular rows of modules then the diffuse shading factor for the inner modules will be higher due to the shading by the row in front, but the first row will have a lower value for the diffuse shading, so this value will be selected for all modules.

All the rest of the diffuse shading and the direct shading is considered in the module-specific partial shading.

Kind regards,

Martin

##### Share on other sites

Hi Martin,

Many thanks for your answer and the link to the help site, this helps in starting to understand the calculations and PR predictions from PV*SOL. Some additional questions for better understanding:

Could you explain how "Module-independent shading is not accounted in the calculation of the PR", as you use the "Global Radiation at the Module" for the PR calculation, and for determining the "Global Radiation at the Module" from "Global Radiation - horizontal" you use "Module-independent shading" as well?

When we use a 3D model as input with regular rows of modules where the diffuse shading factor for the inner modules is higher due to the shading by the row in front, will also then the value of the first row be selected for all modules? if yes, are 3D models than only for shadow calculations from buildings, vergitation, cooling installations, etc. relatively nearby?

Next, on the help site I found out that you are determining a heat loss rate UA. (where) is that included in the PR calculations?

##### Share on other sites

Hi Fritz,

the Module-independent shading is reducing the global radiation on the module, sure, but it is not part of the PR calculation. It just leads to a reduction of the radiation, like it would if you take climate data for another location with less solar radiation, for instance. In contrast, the losses due to the reflection on the module surface are both reducing the global radiation that is available for electrical conversion _and_ it is accounted for in the PR calculation.

Quote

When we use a 3D model as input with regular rows of modules where the diffuse shading factor for the inner modules is higher due to the shading by the row in front, will also then the value of the first row be selected for all modules?

Yes. Or more precisely, yes, given that the modules are connected to the same MPP tracker and are part of the same module area. The lowest diffuse shading value of the modules connected to one MPP tracker is taken as module-independent shading factor.

Quote

﻿if yes, are 3D models than only for shadow calculations from buildings, vergitation, cooling installations, etc. relatively nearby?

No, the shadow calculations work for all kinds of shading objects in the same manner.

Concerning the UA, you are referring to this help page, I guess:

The heat loss rate is part of the PV module temperature calculation and is therefore also part of the PR calculation.

To put it the other way round: All the losses you see in the energy balance, between (Global Radiation at the Module + Reflection on the Module Interface), and the PV energy (AC) minus standby use, is integrated in the PR calculation.

Hope that helps, kind regards,

Martin

##### Share on other sites

Hi Martin,

Many thanks for your support. fantastic!

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Unfortunately, your content contains terms that we do not allow. Please edit your content to remove the highlighted words below.

×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×