About PV Systems

SolarNexus PV system design functionality is geared toward quickly and confidently sizing PV systems given the customer’s available roof or ground areas and energy needs. This level of design is suitable for the sales process. A solution may contain one and only one PV system.

New Systems

SolarNexus was created to design new PV systems and assess their economic value to the prospective customer.

Expansion of Existing Systems

The modular aspects of PV systems enables existing owners of PV systems to add more solar panels to a given system in the future. While this can help an existing system owner to improve the economic value of their overall system, conducting an economic analysis for an expansion project can be very complicated.

As such SolarNexus does NOT support economic analysis of PV system expansions. This does not mean that you cannot use SolarNexus to sell system expansion projects, just that its feature set will NOT provide an economic value analysis for the customer.

System Ratings

The size of a PV System is given as a rated instantaneous power output capacity. There are different ratings used in the industry:

• STC - This is the Standard Test Conditions (STC). It is given in kW-DC (direct current).
• PTC - This is PVUSA Test Conditions. PTC is also given in kW-DC. It is considered to reflect more real world conditions than STC and is always lower than STC. More about STC and PTC here.
• CEC - This is the California Energy Commission (CEC) rating. It is given in kW-AC (alternating current) rather than in DC because it accounts for the Inverter's efficiency, rather than just the DC output of the panels. To calculate CEC rating, multiply the PV module's PTC rating by the module quantity and inverter efficiency. See the CSI calculator docs for more.

Defining a PV System

The basic PV system definition steps include:

1. Create array areas using Google map imagery (only skip if necessary).
2. Specify a PV module from your Company Catalog
3. Configure array parameters
4. Get array layouts (if using), and modify results
5. (optional) Add inverter(s)
6. (optional) Configure inverter circuits
7. (optional) Define AC interconnections
8. Synchronize system configuration with line items list.

In SolarNexus, a PV system is primarily defined by its array(s). There are three variations for defining arrays:

1. You may define your arrays by defining "Array Areas" on top of aerial or uploaded imagery, and using the automated module layout features to layout modules in each array. This is the most expedient method, and works best in most cases.
2. You may choose to define your arrays using the defined array areas, but not using the new module layout features. In that case, the arrays will inherit the names of the defined areas, but instead of using automated layouts to determine the quantity of modules, you simply input the module quantity for each array manually. This is handy when you have determined array module quantity using another method.
3. You may choose to input arrays without defining array areas at all (for example, if no suitable imagery is available). In this case, all the array inputs are manual.

 

Administrative Default Values

As with most of SolarNexus, setting default values for fields that routinely have the same value is key to making the system fast to use, yet still offering a high degree of customization. There are several PV related parameter that can have default values. These are set on the Project Settings screen and include:

• Default PV System Parameters
• Default PV Output Parameters

Create Array Areas

When you add a PV system, SolarNexus checks to see if array areas are already defined. If not, it prompts you to see if want to create them.

In most cases, you will choose yes. This will open the Define Array Areas screen. You will see the property address shown in Google at its maximum zoom level.

Drag the image to center it in the viewing window.

Use the toggle view button to view 45 degree angle to get a good idea of the slope of the roof. Use the rotate view button to get a look from different angles. Click Next.

Now you define your area. At the top right, select the type of area – “sloped roof” is the default

Next verify your initial guess for the solar access. The default value is populated from the administered Project Settings.

Next provide a meaningful name for the area. Be descriptive enough so that when you see the name it will help you to remember which one it is, and it sufficiently distinguishes it from others. Note that if you put an array on that area, the array will share the same name.

Next draw the outline of the area. In most cases, the area is a sloped roof. Do your best to click the corners of each area as precisely as possible. Close the polygon by single clicking on the last point. After closing the polygon, you may adjust the placement of any corner by dragging it.

TIP: use the zoom feature of your browser to blow up the image and make it easier to click on the corners of the desired array area.

Now you need to select a baseline of the area that you will align the array with. For sloped roof faces, this will be an eave or ridge. The baseline selected will define the array's azimuth. When clicked you will see an azimuth arrow indicating which way the array will point.

Next select an estimated slope by clicking on the image of the roof that most closely matches what you see.

Click Finish. You can now add a new area or a Keep Out.

Create Keep-Outs

Use Keep-Outs to outline parts of the defined array areas where you do not want modules placed. These might be shaded areas, areas around chimneys, skylights, etc.  Do not try to use restricted areas around vents, they are too small.

Configuring the Arrays

The install type selected determines many of the other array attributes. Here is a description of the install types:

Array Mounting Structure Types	Description	Area Type
parallel roof	Common method of adding standoffs to an existing roof and attaching rails. Inherits its orientation from the roof face on which it is installed.	Sloped Roof
tilt-up roof	Method of using legs to tilt up a structural plane on which modules are placed. (Note, not for use on reverse tilt arrays, see Note below for modeling Reverse Tilt)	Flat Roof
ballasted tilt	The default for flat roof areas. Usually a pre-built product on which modules can be attached where ballast is typically added to hold down the structure.	Flat Roof
ground mount	For ground areas, like the tilt-up roof option above.	Ground
pole-mount	A structure mounted atop a pole.	Ground

 

The array's azimuth and tilt are set based on the install type. If "parallel to roof", then the array will inherit the roof face's orientation.

The standoff is the average standoff between the mounting surface and bottom of the PV module frame or mounting rack, whichever is closest to the mounting surface. Standoff affects the cell operating temperature.  0” average standoff is for flush mount or BIPV (building integrated PV) where the PV mounting rack is in direct contact with the mounting surface, or the PV modules lack outdoor air ventilation.  Use > 6” for ground or roof mounted systems.

Currently only fixed tilt arrays are supported (no 1 or 2 axis tracking).

Module orientation is an important field for module layouts. Modules mounted in landscape mode have the longer module edge parallel to the eve or gutter, while portrait mode has the shorter edge parallel to the eve. If not using layouts, then this field is for your own information.

NOTE: Modeling Reverse Tilt Arrays

A "Reverse Tilt" array is attached to a north roof and the lower edge of the array is tilted up so that it is pointed toward the south. For sloped roofs, SolarNexus ONLY allows "parallel to roof" as the install type. To make a reverse tilt array, simply define the north roof as if it were a south roof with the resulting tilt of the array. So draw your rectangle and then when defining the eave, pick the ridge line instead. For slope, pick the desired resulting array tilt instead of the actual roof tilt.

Setbacks

Below the array configurations, there is a link to Setbacks. SolarNexus can automatically apply setbacks to particular roof edge types so that your resulting array layout will conform to your local permitting regulations, ensuring that you sell a build-able design that won't require change orders to resize the system.

 

Module Layouts

See Module Orientation Layout Strategies for Array Layouts for details about specifying how you want the system to layout each of your arrays. Once you have configured the array's parameters, click the Auto-Layout button. SolarNexus will communicate with SolarDesignTool to get the resulting array layouts. This can take several seconds depending on size and complexity of the areas, as well as internet speed.

When initial layout is returned, each array has its own tab. You can click in the tab and the corresponding array area in the image will be highlighted. Or you can just click on the array area and its corresponding tab will become active. The specific yield (kWh / kW) is displayed for each array communicating its relative productivity. Each array's tab also displays the percent of the customer's annual energy that it will offset.

Use the Show/Hide button to toggle the shading of the modules, allowing you to see possible obstructions like vents underneath.

Click Edit for an array to enable you to click on any module space to remove the module. You can put a module back just by clicking on the outlined space. You can also change an array's layout orientation strategy and re-generate a new layout for each array individually.

Adjust the array layouts as desired and click Finish. Your arrays are now complete.

Deleting Arrays

You may delete an array from a system by clicking the "X" icon in the PV system's view. If you delete the system's only array, the entire system will be deleted. 

PV Production Modeling

See PV System Production Modeling for details about the parameters that go into modeling each PV array's kWh output. There is a button at the bottom of the PV System section that opens a window to view and edit parameters relevant to estimating the output of the defined system over the defined analysis period. Default values are populated for all required parameters from the defaults defined by your company administrator(s) on the Project Settings screen.

Add Inverters, DC Optimizers, and Other Items

Once array(s) are defined, you can specify inverter(s) for your system. Although SolarNexus does not require you to specify inverter(s), your account may be set up to require the specification of inverters.

If you used an AC module, the corresponding micro inverters will be automatically added. If you add stand-along micro-inverters, the default quantity will be based on the number of module inputs for the micro and the total PV modules in the arrays. You have to manually input the desired number of string inverters. 

You may change the make and model of any inverter by clicking the edit icon for that inverter in the Equipment list.

Inverter Circuit Configurations and AC Tie-Ins (optional)

Some things to note:

• You can associate multiple arrays with a single inverter.
• You may specify inverters without specifying their associated circuit configurations.

Circuit Configurations

Next, you configure the inverter circuits. SolarNexus automatically determines the type of source circuit you are creating based on the type of inverter selected (micro inverters get AC branch circuits, all other inverters get strings).  If you've selected a string inverter, you should consult your favorite string sizing tool (provided by either the inverter manufacturer or another third party, such as pvselect.com) to assist in specifying the number of strings and the modules per string.  If you've selected a micro inverter, you simply specify the quantity of modules per branch circuit.

AC Tie-In (Interconnection)

You may also specify the electrical interconnection information (where the system will be connected to the site's existing electrical system).  You can choose an existing electrical panel if one was specified in the site survey tab.

Synchronize with Cost Items

If your solution uses the cost item method for pricing, you can click on the Sync Line Items link to sync the module and inverter quantities to your line item pricing list and move to the Price screen.  You are now ready to develop your price estimate.