The following are short notes describing the process to design a commercial PV installation using Helioscope.
Step 1: new project
Write name of project, select the location by address or coordinates. Select the type of installation (this case will be commercial; other options allow for different default settings); enter a brief description if needed.
Step 2: create new design
Create a new design by selecting the button highlighted in red and write a name in the dialog box that appears. If you want, you can copy an existing design and modify it, or otherwise start from scratch.
Step 3: select source for geospatial data
The source can be selected in the top right corner and the options are Google, Bing, Google Street and Nearmap; the former is only available by subscription. Ideally, when working with the roof of buildings, we would like a perfectly perpendicular image i.e. an image of the roof that does not show the walls. For example, the red area in the image from google are walls. While the Bing image is much more perpendicular. We are going forward with the image from Bing.
Step 3: draw the field
We now have to draw the plane(s) on which to design our array, so that we can have some boundaries. We do this by clicking in the left side on mechanical and then new; the pointer will become green and will allow us to draw the contours of the roof. One click places a vertex and clicking while holding shift allows for 90 degrees angles. Double click the last vertex to finish the plane.
Step 4: select layout rules
Subsequently, we have to select the layout rules. These are:
Racking:
In this case, we are going to select a fixed tilt racking.
- Fixed tilt racking: when the tilt of the panels does not vary with time but it is fixed during installation.
- Flush mount racking: ideal for pitched roofs, panels are mounted flush with the roofing, following its angle with the ground. Reduced lift force from wind
- East-west racking: solar panels are installed in couples, longitudinally, facing east-west directions, at a pitch angle. This is ideal for locations close to the equator and to reduce lift force from wind.
- Carport: to maximize shading underneath the panels, to be used, as suggested by the name, as parking covers.
Module height needs to take into account the height of the building where the panels are mounted on. In this case, given the lack of real measurements, we will assume a height of 165ft.
The azimuth angle is defined as the angle between the direction the panels are facing with the geographic south. The ideal angle can be selected via calculations, in order to maximize irradiance on a yearly basis. In this case, we simply align the panels with the south wall.
The tilt angle indicated the angle between the panels and the horizontal. As a rule of thumb, the tilt should be equal to the latitude of the location. In this case, we select 30 degrees.
The specific product selected will mostly depend on the energy demand of the application and the specific stock of the installer. In this case, we will select the standard TSM-PD14 320W.
The automatic layout rules allow the user to select different design characteristics which are very much project dependent. In this case, we will simply accept the standard values given that we do not have a real-life project constraint to work on. However, will will introduce a 6ft setback for safety. The setback is the distance between the rows of panels and the edges of the plane.
Step 5: select keepouts
Keepouts are areas where panels will not be installed, either due to physical obstructions or for maintenance purposes. In our case, LIDAR imagery shows the presence of 3 big heat pumping or air filtering units. Hence, we can assume a keep out area around them of about 10ft height.
Raised keepouts also generate shade. To analyzed which modules will be affected by the shade, we can click on Advanced, Shading and Calculate Shading. We can then set a threshold for the maximum shading accepted (in this case it will be 20%), so that we can remove the most affected panels.
Step 6: electrical
Next, the electrical tool allows you to select inverters, wiring and DC subsystems (i.e. recombiners that consolidate power from the modules into one main wire that is then fed to the inverter). In our case, we moved the inverters to the edges in order to facilitate maintenance and we left an AC/DC ratio of 1.20, to avoid clipping losses as explained in this page. Different wiring can be selected to reduce the losses.
We also added an AC home run to connect all the inverters. Further technical help on the electrical design can be found here.
Step 7: simulation
Conditions sets can be selected; they identify the assumptions like weather data and loss coefficients. In this case, we will leave the standard values. The simulation report looks like the figure below.
