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If you’re thinking of going solar, having a baseline knowledge of what your solar panel electrical requirements will look like can help you make more informed decisions along the way.

In this article, we’ll go over some key terminology, such as kilowatt-hours and voltage drops, considerations for grid-tie electrical panels, and information on wiring diagrams.

Terminology

Kilowatt-Hour

An important electrical term to understand for solar is kilowatt-hour. Simply put, a kilowatt-hour (kWh) is a unit of measurement that gauges how much energy you use over a set period of time. 

For example, if you had an appliance rated at 1000 watts (1 kilowatt = 1000 watts) operating for one hour, then it would use one kilowatt-hour (kWh) of energy over the duration of that time.

Utility companies bill for electricity on a cost-per-kWh basis and knowing how many kWh you use each month can be a great help in sizing your system properly. For more information, head over to our kilowatt-hour guide, which goes a bit more in-depth on these topics.

Voltage Drop

When current moves through an electrical circuit, a small amount of voltage is lost due to resistance in the wires. This concept is referred to as voltage drop.

Voltage drop can lead to a slight production loss from your solar system and can be more pronounced in systems with a longer wiring run. There are four main approaches to counteract this phenomenon:

  1. Minimize the length of the wiring run.
  2. Consider your inverter placement carefully.
  3. Use a bigger wire size. Larger wire = less resistance.
  4. Design your system with higher voltage to overcome resistance.

As you can see, solar panel wire sizing is an important factor to consider.If you have a solar designer assist in planning your system, they should take voltage drop into account as part of the process. For more specific information, you can refer to our voltage drop guide.

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Additional Considerations for Solar Electrical Panel Requirements

For grid-tie solar systems, the size of your electrical service panel places some inherent restrictions on the size of your solar system. 

Without these sizing restrictions, the combined energy from the utility grid and solar system could overload the electrical panel when you are backfeeding (in other words, sending power from your system through a circuit breaker in your panel).

The 120% Rule

When sizing your system in accordance with your electrical panel, remember the 120% rule.

The 120% rule holds that you can’t have more than 120% of your rated service (in amps) running through the busbars of your main breaker.

Here’s a hypothetical example to better understand what this means for the sizing of your solar project and electrical panel requirements for solar:

Let’s say that you have standard service rated at 200 amps, as well as a main electrical breaker rated at 200 amps. How do you figure out how large of a solar breaker you can get for this grid-tie system? 

In this case, we know that we can’t exceed 120% of the rated service (240 amps), so the largest solar breaker we could add would be rated at 40 amps. With a 40-amp solar breaker added, your system can handle up to 7600 watts of backfeed solar. 

Of course, as with any rule, there are exceptions. Larger solar systems can be feasible but require compromises like derating your main panel or incurring major costs to upgrade service panels. Alternatively, some companies manufacture PV-ready electrical panels that can increase the allowable solar wattage from 7,600 to about 10,000 watts.

Example: If you have a 200 amp electrical breaker, the largest solar breaker you can add would be 40 amps.
Example: If you have a 200 amp electrical breaker, the largest solar breaker you can add would be 40 amps.

Electrical Wiring Diagrams

Electrical wiring diagrams are an essential resource for the installation and permitting of your solar system to meet electrical panel requirements for solar. You’ll need one on hand before you can apply for a permit and pass final inspection.

How To Read An Electrical Wiring Diagram

Solar panel wiring diagrams can be intimidating if you’ve never worked on an electrical project before. Once you familiarize yourself with their basic building blocks, though, it’s not as difficult to comprehend:

  • Each symbol (such as a square, circle, etc.) represents a physical component in the system. Diagrams usually include a key for identifying which symbol corresponds to which physical part.

Here’s an example of some symbols, taken from one of our wiring diagrams:

In the graphic above, the rectangles labelled represent the system’s solar panels. The box labelled represents a Midnite MNPV-6 combiner box.

  • Each line represents a wire that connects components together. Wires are typically labelled by color, and diagrams include a key that lists abbreviations for each color used in the layout.
The two green wires are connected. The red and green wires are not connected.
The two green wires are connected. However, the red and green wires are not connected.

Lines will often overlap on wiring diagrams due to the number of connections that need to be represented.

If wires are meant to be connected, there will be a dot at their intersection to represent their junction. This is illustrated in the graphic above, where the two green wires intersect. The box overlapping their intersection indicates that they are connected.

However, overlapping lines does not necessarily mean that the two wires are connected. Let’s refer to the wire graphic again; though the red wires and green wire intersect, there is not box at their intersection, and therefore they are not connected.

Electrical Wiring Diagrams Illustrate Connections in the System

Note that wiring diagrams are not physical maps of how your system will look in real life. Rather, they illustrate the connection between all parts of the system so that they can be properly wired together.

Unbound Solar includes CAD (computer-aided design) electrical diagrams as a part of our packaged systems. In addition, our tech team reviews these diagrams to mitigate voltage drop. If you want to learn more about our wiring diagrams, click here.

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