EME 810
Solar Resource Assessment and Economics

2.16 Sun Chart Shading Interpretation in SAM


System Advisor Model

Recall that you needed to install SAM in the last lesson. You will be using the tab on "Performance Adjustment" as demonstrated in the following video. You are now applying your interpretation of the shading diagram to input shading into SAM for energy simulations of system performance where shading interferes with the solar resource.

SAM is available from the National Renewable Energy Laboratory for free, and you should all have downloaded it by now. We have come a long way in interpreting sun path diagrams and plotting shaded areas as overlays onto the sun path charts.

Now, we would like to interpret the hours of shading and input those hours into SAM. The video below provides a demo of how shading patterns in SunChart can be applied in SAM simulations. 


This video is made for the older version of SAM, which applied shading factors differently (0 - for full shade, 1 - for no shade). Newer verions of SAM, which you may have, use a different scale for shading factors: 0 - for no shade, and 100% - for full shade, with partial shade in between. Beware of this difference when you work on your assignment! 

SAM Shading Intro
Click Here for Transcript of SAM Shading Intro Video

Now, you've done the initial shading analysis or shading plotting. We're going to use the example, the wing wall that we started with.

So, imagine that we had a photovoltaic array that, for some reason, the client wanted mounted vertically on their south-facing wall. And there was a wing wall off to the west. And this is off to the west here that they're seeing.

And we're trying to identify how many hours with that shade, when would that shading occur? And then, can we interpret those hours of shading and input that into something of our energy system modeler, SAM.

So, look at this. We see that we've got a plot here of different times when shading is going to occur during the June months, the summer months, and during the winter months. And we know that a lot of shading is going to occur in the afternoon.

So, now we go over. And I've actually collected these dates and times for each of these months together, January through December. And so, I'm roughly saying that in January, we're getting hours of shading from about four o'clock-- remember this four o'clock line travels all the way down here. So, from four o'clock on, we're going to get no sunlight; so, we give it a value of 0.

In the month of March, for example, I look on the March line. This is late March. So, if I go up to here to the middle of March, or the beginning of March-- excuse me-- I'm going to find that-- excuse me. This would be the end of March. I'm going to find that from about 2:30-- again, if I look up at the top of the line, I can see this is about 2:30 on through the rest of the day, I'm going to have shading.

So, maybe, in this one hour, I might assign it a half value. And I said the half hour is going to be shaded. And then the rest of the hours are going to be 0.

And I do this all the way through. So, I've kind of made notation where the hours, the shading starts for that first hour and whether or not it's a half hour for the course of modeling.

Now, if I bring up SAM, System Adviser Model, you're seeing the launching of that. And we've got-- I'm going to resize this so it will fit. This is going to be your first exposure to SAM.

So, SAM has an interesting launch page. It's got a lot of information. News in terms of what's happening in SAM. New webinars coming up, I guess in May.

And one thing I do not want you to do is to start the solar wizard. That is not for you. We are going to do it directly by choosing projects and the types of technologies that we're interested in and the financing project that we're interested in.

So, let's just call this one Shading 1. It's just going to name the file. And we're going to create that new file. And it's going to give us a choice.

You're going to see in one column: Select a Technology. Photovoltaics, concentrating solar power, solar water heating are going to be the solar ones that we would be interested in.

We're going to choose photovoltaics. There's a submenu. PVWatts is what you do not want. PVWatts is relatively simplistic modeling. We want component-based modeling that we get with either flat plate PV or concentrating PV.

So, once I've chosen flat plate PV modeling, I'm going to go over and I'm going to select a residential financing option. And we're doing this just as our first example. In the future, we can look at residential, commercial, power purchase agreement, and utility options.

So, let's just click OK. And it automatically creates a default case of photovoltaics. And you'll notice that all along here, I've got a list of tabs. Up at the top here, it's listed shading. My technology and market flat plate PV for residential is listed up here.

The location of the resource is here. So, I can go in here, and I can type in--let's see. State college isn't going to be listed; so, I'm going to list Pittsburgh. Yeah, sure.

So, I click Pittsburgh. And it inputs all the solar data for Pittsburgh. But we're interested in the shading part of this. So, we're just going to select out the tab on performance adjustment. In which case, I'm going to move this guy over and expand it.

You're going to see that we have a table here. It's a very convenient table that we can use alongside our litlittle-notedlues of shading in January, February, March, and so on.

So, I can go in here. And this is basically saying that when are you thinking that shading is going to stop your system from performing? And shading is a clear example of stopping your system from performing in photovoltaics.

So, I'm going to look at January and I'm going to say January from four to five on is going to be 0. So, I can actually go right here, select these cells, apply 0 to those cells, and they are redded out.

I can go to February three to four. Same type of process. I could either type 0 and then progress along, or I could just apply 0 to all of these selected cells.

So, similarly, I'm just going to progress along here. And finally, I'm at March. March, from the two to three hour, I had given it a value of 0.5. So, basically, just a half hour. And notice how it's about half the value of color. Otherwise, I'm just going to make everything red.

And so, I'm just going to progress through this. Three to four. 0's. May is 3:30 to four. So, here we've got another deviation, 0.5, that I'm going to apply.

And these guys are going to get 0's. Oops. Let me grab those cells one more time. There we go. Keep on going through here. And you see that I'm just methodically notating all of these guys down.

And, ultimately, I'm going to be converting a lot of these cells to 0's, in which case I can have all this information. Maybe some of these guys aren't as bad. Actually, those are four o'clock.

But all of these guys are going to be times when, if the sun is in the sky-- and SAM knows when the sun is in the sky-- if the sun is in the sky then there's not going to be output to your photovoltaic panels based on this input. Very useful.

Ultimately, what we would do-- I'm going to resize this. Oops. Ultimately, what we do is click the green button down here. It's going to compile your simulation. And it gives you a monthly output of power, cash flow, things like this.

What it's done is it's incorporated all of your performance adjustments into that system so that, in the case of our answers here where the annual energy was 4.169 kilowatt hours, I believe-- yep. For this case, if I were to take that performance adjustment out-- just take all these guys that I've selected.

And instead of that, apply them as 1's. Let's click that guy again. And instead of 4.61, I have 4.66 or 4,666 kilowatt hours.

So, I've increased things dramatically. And notice how that edge in the winter months is a lot higher now. And that's because that shading is occurring. So, this is way for your tool to be used in SAM to-- so, all this work that you've put together to do shading analysis, to understand angles that ultimately lead to shading analysis, is directly relevant to simulations inside of a tool like SAM where if I add shadows into a scenario, I'm going to decrease my annual energy output. Then I can calculate that.

So, I'm using this entire lesson to get to the point where I can use this inside of SAM. This connects us directly to our ultimate project goals at the end of the semester. All right. Great.

Credit: Jeffrey R. S. Brownson

So, the important take-home items are that we can use all of the earlier information to get us to a shade-based performance adjustment of our simulations, and that shading matters in solar energy. We use these SAM simulations in project design (or software very similar to SAM), as you will do at the end of the semester.

Notice how we can input partial values for hours of the months of interest. SAM conveniently grades the color scheme from white (full sun) to red (full shade) in the process. Also, note that the locale matters! The upper left tab in the tool column is for the resource location. We will explore that more in the future. The default for SAM is often in the Southwest USA, and you will need to choose the correct locale before running your simulations.