Importing Google Earth files KMZ KML:

PVSketch Mega is designed to work with Google earth file formats (.KML, .KMZ). When a new project is created you can select “upload a .KML/.KMZ file in the welcome window. The project geographic location, land parcel boundaries and any obstructions such as wetlands, roads, power lines, etc. defined in Google earth will be automatically drawn and defined in the PVSketch Mega model.

Drawing/Modifying boundaries and obstructions

Boundaries and obstructions can be drawn or modified by the user using the tool pallet in the upper left corner of the screen. The total area, rackable area and % utilized values shown in the bottom left Summary Box will update in real time as changes are made. When an obstruction or ground mount area is selected, it can be named in the site tab on the right hand sidebar and a setback can be specified.

Loading Topography Data

To start topography analysis, select the blue “Get Topography” button in the top right corner. PVSketch Mega will download topographic elevation data from Google’s Elevation Service and create a 3D triangular surface mesh.

The Elevation service provides elevation data for locations on the surface of the earth, including depth locations on the ocean floor (which return negative values). In those cases where Google does not possess exact elevation measurements at the precise location you request, the service will interpolate and return an averaged value using the four nearest locations.

Google uses a range of digital elevation model data sources to derive the terrain layer. Throughout the US, it appears that the terrain layer comes from either 10 or 30 m (1/3 arc-second & 1 arc-second respectively) DEMs from the USGS National Elevation Dataset (NED). Globally the terrain data appear to be derived from either Shuttle Radar Topography Mission (SRTM) data or something like the NOAA Global Land One-km Base Elevation Project (GLOBE) dataset. Recently however, We’ve begun to notice bare earth LIDAR data patched into the terrain layer and expect that trend to continue.

Once completed, the screen will automatically split in two, with a 3D model of the terrain shown on the right hand side and an overhead map view on the left hand side. You can use your mouse to rotate and zoom in to the 3D model on the right hand side. It may take several minutes to retrieve the elevation data from Google’s server if the area is large or the internet is slow.

You can toggle between the split screen, map view or 3D view using the controls on the very bottom of the Analysis Tab on the right hand side bar.

Topography Analysis

Once topography data has been loaded, you can perform a slope analysis. There are five controls in the Analysis tab that are used for this purpose. The first control is the “Scale” input will adjust the scale of the 3D model in the Z direction, basically a larger scale value will make hills and valleys look taller and deeper and lower value less so; this is to make it easier for a user to visualize the topography. The second control is the “North Slope Threshold” that represents the maximum slope angle that you want to allow in the north direction, note that trackers installed on a northern slope will produce less energy than trackers mounted on flat or south facing slopes. Blue triangles indicate suitable slope tolerances and gray triangles indicate out of spec terrain slopes. Any triangle in the triangular surface mesh that exceeds the angle specified here in the north direction will turn grey to indicate that it is out of spec. Simultaneously, in the left hand map screen, orange obstruction areas will indicate these areas in the map as unsuitable for map. The Summary box will update. The third control is the “South Slope Threshold” it is identical to the “North Slope Threshold” except that it applies to the south direction. The third control is the “East/West Threshold” which applies to both the east and the west component of slope. The fifth and final control is “Minimum Contiguous Area” , this represents the smallest contiguous area that will be considered by software for placing modules in the layout. It can be used to eliminate small islands of rackable area that in practice are too small to use for a real world layout. The rackable area and %utilized values will update in real time as adjustments are made to the slope thresholds and minimum contiguous areas for the project.

Layout and Optimization

PVSketch Mega was designed to allow layouts of trackers and fixed tilt tables to be done in large batches using massively parallel cloud based computing. This will facilitate the process of choosing the optimal layout for a given solar project. To start creating layouts and optimizing your project go to the “Optimization” tab on the top level menu. PVSketch Mega will ask you for a target value, either a system KW size or a Kwh annual production target. If there is no particular target size in mind, choose an arbitrarily large number for this field.

The next step before generating layouts is to select one or more solar modules to use from our equipment database. Select the blue “Add Module” button to choose a module or specify your own “User Defined” module if you don’t have a particular module manufacturer preference. Select “Add Module” multiple times if you’d like to compare layouts using multiple different modules.

The final step before generating layouts is to add a Portfolio of mounting system values that you would like to include in the optimization analysis. Click on the “Add Portfolio” button and you will be prompted to enter a mounting system option, range of GCRs, module orientation, etc… Similar to “Add Module”, selecting “Add Portfolio” many times to compare layouts of different mounting configurations. For example, to compare fixed tilt to single axis tracker, or to compare two types of tracker configurations to each other.

Once you have all the mounting portfolios added, click on the “Calculate” button in the bottom right corner to generate layouts corresponding to every permutation of module, mounting system portfolio and GCR value. These results will be displayed in a table as well as a graph that is generated in the “Results” page on the top level menu. A layout for every permutation will be listed in the table with the one closest to the target value on top.

Viewing Layouts and Exporting Layouts to PVCAD

Each permutation will have three buttons associated with it in the table. To view any of the layouts in the table on a map view, click on the “Map” button. This will open that particular layout in the “Map” page where the layout can be viewed and modified. Clicking on the second button “PVCAD” will generate a web link that is uniquely associated with that particular layout and project. Share this web link with any PVCAD software user and they will be able to import the layout into PVCAD for more detailed design in the CAD environment. The third button “Report” is used to create a report for your project as detailed in the next section.

Creating Project Reports

Once the preferred layout has been determined, a .PDF report can be created for the project in the “Reports” page of the top level menu. Select the “Report” button in the results table or from the “Map” page. Select the “Reports” top level menu. You will be taken to a report preview, the first section of the report shows the 3D view of the topography if you hover your mouse over the view you can rotate and zoom in and out on the 3D view to get the viewpoint that you prefer to show in the final report. The other sections of the report populate automatically with a project layout, system summary that shows rackable area, KW, Kwh etc… as well as a bill of materials for the project on the final page. After previewing the report you can download a .PDF version by clicking on the “Download PDF” button in the top right corner.

Energy Model

PVSketch Mega gives you the choice of two energy models, Advanced and Simplified. This documentation will first address the simplified and then the advanced.

Simplified Model

The Simplified model is based on the PVWatts energy model from NREL. (https://pvwatts.nrel.gov/) PVWatts consists of a set of component models to represent the different parts of a photovoltaic system. PVWatts performs hourly simulations to calculate the electricity produced by the system over a single year. PVWatts assumes that there are 8,760 hours in one year.

The following is a high-level description of the algorithm PVWatts uses to calculate the photovoltaic system’s hourly electrical output:

  • Calculate the hourly plane-of-array (POA) solar irradiance from the horizontal irradiance, latitude, longitude, and time in the solar resource data, and from the array type, tilt and azimuth inputs.
  • Calculate the effective POA irradiance to account for reflective losses from the module cover depending on the solar incidence angle.
  • Calculate the cell temperature based on the array type, POA irradiance, wind speed, and ambient temperature. The cell temperature model assumes a module height of 5 meters above the ground and an installed nominal operating cell temperature (INOCT) of 49°C for the fixed roof mount option (appropriate for approximately 4 inch standoffs), and of 45°C for the other array type options.
  • Calculate the array’s DC output from DC system size at a reference POA irradiance of 1,000 W/m², and the calculated cell temperature, assuming a reference cell temperature of 25°C, and temperature coefficient of power of -0.47%/°C for the standard module type, -0.35%/°C for the premium type, or -0.20%/°C for the thin film type.
  • Calculate the system’s AC output from the calculated DC output and system losses and nominal inverter efficiency input (96% by default) with a part-load inverter efficiency adjustment derived from empirical measurements of inverter performance.
  • The Simplified Model allows for the following system loss inputs:

PVWatts does not factor in the specific I-V curve of the solar module or inverter efficiency curve. This simplification means that the results are not as accurate for specific equipment as our Advanced energy model.  However, the Simplified model has the advantage of not requiring .PAN or .OND files to run and therefore is a good solution for early stage project design where final equipment has not yet been specified.

Advanced Model

The Advanced model is based on Canadian Solar’s System Simulator (CASSYS), an open source energy model developed by the module manufacturer. The Advanced model considers a solar project details description such as arrays, inverters, and modules, site location, and weather conditions on a sub-hourly interval to calculate the state of the system at each step and provide a detailed estimate of energy flows and losses in the system.

The Advanced model is a more accurate model than is PVWATTS, allowing, for example, to consider the specific IV curve of the solar module and it’s interactions with the inverter input. Both energy simulations use the same transposition models Hays and Perez.

Comparison with PVSYST

The Advanced model is organized to function similar PVSYST using the same underlying equations, which all users to translate between these two models with relatively low effort and to obtain similar results, usually with 1% of each other.

The standard test condition (STC) parameters for the module are obtained from a .PAN file. Module behavior is calculated for several non-STC operating conditions such as open circuit, fixed voltage, and maximum point tracking. Values are then converted from module to array level and losses are applied in accordance with user input values.

Shading factors on the beam, diffuse, and ground-reflected components of incident irradiance, based on the sun position throughout the day resulting from a near shading model, are available for panels arranged in an unlimited rows or a fixed tilt configuration.  In the scenario of an unlimited row model, the Advanced energy model neglects edge effects because it assumes such rows are large enough that edge effects are not significant. This assumption reduces the calculation of the shading factor at different times of the day to a simple geometrical construct, as does PVSYST.

In a paper by Canadian Solar introducing CASSYS, they validated the model through cross-validation between CASSYS and PVSYST, as well as comparisons against measured data.

Real world comparisons between measured and simulated values (once all post-construction conditions and parameters are reflected in the system definition) show that CASSYS provides a reliable basis to estimate the energy production by a defined system on a sub-hourly basis. In the same paper it is referred that a more thorough study is required to further understand the sources of error, and the fine-tuning steps for the model inputs.  However, simulations that fall within a couple of percent of the actual values are usually considered excellent, as the accuracy of the various instruments used in the measurements themselves rarely falls below that threshold.

The agreement between the tools is found to be -0.35% for the energy predicted over an entire year (CASSYS being the more conservative tool) when the inputs to all models are closest to each other.

PVSketch Mega applies a hierarchy to available weather data sources to run the Advanced model. First the Advanced model will try to download data from NSRDB first (https://nsrdb.nrel.gov/), and if it fails for a given location, the model will default to download data from the PVGIS database (https://ec.europa.eu/jrc/en/pvgis).

Site Parameters

  • Latitude and longitude

System Design Parameters

  • Inverter model name and performance parameters
  • Module model name and performance parameters
  • Number of modules per series string
  • Number of series strings per array
  • Tilt () and azimuth of the array (or tracking angle algorithm for tracked arrays)
  • Albedo of the ground (or roof) surface)
  • Horizon map showing potential for shading from obstructions
  • Irradiance data is reported as three components: direct normal irradiance (DNI), global horizontal irradiance (GHI), and diffuse horizontal irradiance (DHI).

    [1] Pai, A., & Thevenard, D. (2017). Introducing CASSYS: An open-source software for simulation of grid-connected photovoltaic systems. 2017 IEEE 44th Photovoltaic Specialist Conference (PVSC). doi:10.1109/pvsc.2017.8366282

    [2] Pai, A., & Thevenard, D. CASSYS/PVSYST Comparison – A Model-to-Model Comparison of Two Grid-Connected PV System Modelling Tools. https://github.com/CanadianSolar/CASSYS/blob/master/Documents%20and%20Help/CASSYS%20PVsyst%20Comparison.pdf

    Pricing and Billing
    PVSketch Mega is billed monthly. Subscriptions start at $300 per month for up to 30MWs of projects. The billing period starts on the 1st of each month. Every additional MW is $10 and will be added to the monthly invoice. For high volume design in PVSketch Mega, contact info@pvcomplete for a price quote.

    How are MW calculated for billing purposes?
    Each calendar month, PVSketch Mega calculates the total number of new MWs that have been optimized. As actual MW project size can vary based on optimization (module swaps, row spacing, equipment, etc.), PVSketch Mega uses this simple area-based average calculation for determining MW: 20,000 m2 = 1 MW. This allows the designer to optimize MW and MWhs without incurring additional charges on an individual project site.

    Monthly Billing
    At the end of each calendar month, subscribers will get an invoice with monthly usage. A monthly minimum of $300 that includes the first 30 MWs of new projects designed within the month. Additionally, new MWs are billed at $10 per MW. Payment is due upon receipt of invoice. PVComplete accepts credit card and ACH for payment of monthly invoice. Please contact billing@pvcomplete to set up ACH payment or for invoicing questions.