Clean energy systems such as solar connect and interact with the rest of the electrical equipment at your facility.  Inventorying that equipment will help your provider understand what might need to change to give you a more accurate proposal.

Electrical equipment varies in its type and size.  There can be small components like breakers or meters, or much larger equipment like switchgear and transformers.  They can also have different voltage ratings (low, medium, and high-voltage), outlining the maximum amount of power flow that they can take.  The variation of all the equipment can be a technically confusing task, especially if you've ever seen the National Electrical Code.  Let's break it all down below.

Single-line diagram

The single-line diagram (SLD), sometimes called a "one-line diagram," is a simplified graphical drawing of the electrical system throughout a building that's created by an electrical engineer.  Think of it as a symbolic map that ties together all of the components of your building's electrical equipment.  It displays all of the components, their respective ratings, and the path of power flow - in a single line - being distributed to all of the components.


Electrical equipment

A single-line diagram (SLD) for a solar project. Image credit: Heatspring

If your building has an SLD already, that's a great start in having a solar system proposed.  If no SLD is available, your solar provider or a certified electrical engineer may have to perform a site visit to inventory the equipment in order to create one.  The SLD that a solar provider drafts for your proposal will include the proposed solar system equipment in addition to the preexisting equipment.

If you don’t have an SLD, offering a site visit is important because it can inform everyone what equipment might need to be upgraded or replaced, and how that might affect the project’s cost.

Electrical room diagram

Unlike an SLD, an electrical room diagram shows the actual physical location and dimensions of the electrical components in a room (or throughout a building).  Think of it as a physical map that ties together all of the components of your building's electrical equipment.  While not a requirement to receive a quote from a solar provider, it can speed up the permitting and installation process.

Main service panels

Main service panels (MSP) are also referred to as panelboards, breaker boxes, or load centers.  The MSP is the central distribution point where your utility service line comes in from the power lines and connects to the breakers and wires that send power to all of your electrical loads.  Your building might also have smaller subpanels, which distribute power to a set of loads, or a particular region in your building.

The MSP contains busbars to facilitate electrical connections and overcurrent protection devices (OCPD) such as fuses and breakers, including the main circuit breaker, which can serve as a disconnect for the entire panel.  It's critical to understand the amps and volts ratings of the panel due to the additional power load that the solar panels will supply to it.  If the main circuit breaker in the MSP is under 200 amps, your provider might suggest upgrading the panel altogether.


A Main Service Panel (MSP) or panelboard.

Electrical meters

These devices measure the amount of electric energy consumed by your facility and are used by utilities to bill you for that consumption.  Since they measure consumption over time intervals, the readings are expressed in kilowatt-hours (kWh).  There are basic meters that either have a mechanical dial or LCD screen displaying the kWh, or digital "smart" meters that remotely send the data over the internet.

Electric meter

An electrical meter.

Identifying the quantity, location, and ID number of each meter on your property is important when the solar provider is designing your solar system as there might be one, or several meters, on the property.  They can be located either inside or outside the building.  If inside, it's usually co-located with the electrical panel, or main service panel (MSP).

Identifying the details of every meter allows solar installers to:

  • Design and size the system appropriately
  • Install solar energy metering systems
  • Ensure the system is properly connected to the grid and the electrical panel


Transformers are devices that are used to increase or decrease the alternating current (AC) voltage level to efficiently distribute power suited to a user.  You may have a transformer on site that steps down (decreases) the voltage from the electrical service lines to match your facility's distribution level needs.  Or you may need a transformer to step up (increase) the voltage in order to send the solar-generated power back to the grid.

There are a few types of transformers that you might encounter at a commercial building, depending on the size of your building and your site’s consumption.

  • Pole-mounted transformers. For buildings with less consumption, you will likely see a pole-mounted transformer outside of your property attached to distribution line poles. Your utility uses these to lower the voltage levels being delivered to your main service panel.
  • Pad-mounted transformers. These are usually big green or grey boxes located outside and sometimes have heat sinks (accordion-like fins) on the side or back. They're most common for buildings with larger consumption.
  • Station and sub-station transformers. These transformers are used in larger commercial and industrial applications with higher voltage and power levels.

Pole-mounted tranfsromer

A pole-mounted transformer.

Pad-mounted transformer

A pad-mounted transformer.


Switchboards & switchgear

Oftentimes, main service panels and switchboards are used interchangeably.  While similar, they are different.  An MSP is typically mounted to a wall or in a cabinet with a small door that opens, and lower busbar ratings (less than 1,200A).

A switchboard is effectively a larger service panel that can be accessed from two sides and handle higher bus ratings (greater than 1,200A).

Switchgear, on the other hand, is the largest of the three classes and is used for 2 primary purposes:

  1. Protection via fuses, breakers, or lightning arresters to identify faults or cut power to circuits before it can cause damage.
  2. Power control via relays, current transformers, and control panels to power generators, transformers, or motors.

The key difference between the two is that switchgear can disconnect from a power source during a fault, in addition to protecting and controlling power.  Switchboards are rarely rated above 600 volts, whereas switchgear can handle various voltage levels, including up to 350 kilovolts.  This makes it practical for industrial settings, such as factories, data centers, or even hospitals.


A switchboard.  Image credit: Bay Power


A switchgear.  Image credit: Bay Power

Whether it's a switchboard or switchgear, identifying and documenting the electrical equipment at your facility certainly helps get a more accurate proposal.  Switchgear is often what might require an upgrade.  This equipment can be expensive and there might be long lead times for a provider to procure one (in some cases, several months) so knowing if you need to upgrade switchgear is important.

Station A can help

If you're thinking about listing a project on the marketplace, provide high-level information to our clean energy advisors to start the process.