Hi. In this segment we're going to look at the impacts of orientation and tilt on electrical output. By the end of the segment you should be able to use the insolation data to predict electrical output based on tilt and using the online program PVWatts, as a resource to calculate output based on array orientation. As a reminder, we can use the NREL insulation tables to predict the solar insolation at several angles. We have zero degrees listed, latitude minus 15 degrees. Latitude, latitude plus 15 degrees and 90 degrees, In order to achieve maximum solar gain module tilt will vary based upon location. For example, at lower latitudes modules will have shallower tilts because the sun is higher in the sky. So, the module can be tilted at a shallow angle like latitude minus 15 degrees. In latitudes further from the equator, the module typically will have a steeper angle because the sun is lower in the sky even in the summer months. This is summarized in the insolation tables which provide the information on these key module angles. Note that these are always given at Azimuth angles facing towards the equator. For example, in the northern hemisphere, the azimuth angle is always due south or 180 degrees. What happens when this is not the case? Well, there are variations that could occur such as a rooftop not facing due south. In this case, we could approach due east which would be 90 degrees or we could approach due west which would be 270 degrees. Calculating for tilt is relatively easy using formulas or the given tables. Accounting for azimuth angle however is a bit more complex, but very important since insolation can decrease by as much as 40% or more for modules facing opposite the Equator. Trigonometric mathematical formulas and vector math can be used to calculate insolation but it's rather complex and beyond the scope of this course. Instead, computer models are the preferred source to predict the insolation levels because they can be used for free and they're reliable. PVWatts is one application developed by the National Renewable Energy Lab or NREL. And allows you to input a latitude or zip code, and it will calculate the insolation available at that location. After that, you can select the azimuth angle as well as the module tilt. So, both tilt and azimuth can be addressed in one calculation. We begin by going to PVWatts and entering a zip code or address. In this case, let's look at Syracuse, New York where SUNI ESF is located. From that point, you can accept the weather station data that's provided. You can then go to the system information tab and input a system size as well as a few other parameters including the module type, system losses, and what we are after, tilt and azimuth. At this point, I'm going to use a fixed system size of five kilowatts. I will also select the standard module type in a fixed roof mount array type. We'll use the default system losses of 14.08 percent. Optimal tilt will change based upon latitude and may be limited by the roof space or ground mounted space that you have available. In our location in Syracuse New York, the typical roof pitches around 28 to 31 degrees. Which also happens to map to the insolation levels of latitude minus 15 degrees. By inputting a tilt of 28 degrees and azimuth of 180 degrees, we get a projected system output of 5,847 kilowatt hours per year. If we go back and change the tilt to 45 degrees, which would be a very steep roof pitch, we see the output decreases only slightly to 5,805 kilowatt hours per year. Now, let's see what happens when the roof does not face due south. I'll switch the tilt back to 28 degrees and change the azimuth to be 90 degrees, which is due east. Under these conditions, the energy production decreases significantly to 4,842 kilowatt hours per year. A loss of over 1,000 kilowatt hours per year from the more optimal design. Likewise, if I change the azimuth to due north or zero degrees instead of towards the equator, it decreases even further to 3,607 kilowatt hours per year, or 62% of the annual production and optimal conditions. If we combine some of these non-optimal conditions it can make the situation even worse. For example, if I change the tilt again to 45 degrees with the azimuth still at zero degrees or due north, the projected energy production is only 2,718 kilowatt hours per year. Less than half the annual production of the same PV system set up at a more optimal position, So, while the system may be capable of producing 5,847 kilowatt hours of electricity per year at a given location, site related restrictions that don't allow for optimal tilt or azimuth angles will result in less energy being produced. These calculations show us how deviations from optimal configurations affect energy production. Specifically, variations in azimuth affect energy production more than changes in tilt. Combining changes in both tilt and azimuth can drastically affect solar energy production in real-world situations. PVWatts is an excellent tool for designing and predicting electrical output in the financial return for photovoltaic system. We'll return to use this tool later on as we learn more about designing solar arrays and accounting for system temperature in shading. In the next lesson, we'll learn why and how to use temperature as a factor for calculating voltage and solar modules in arrays.
