How to connect a PV solar system to the utility grid

How To Connect PV Solar To Utility Grid hera are design tips for methods of PV organization utility interconnection. The purpose of this article is to give you a basic agreement of the concepts and rules for connecting a solar dialog box system to the utility grid and the family electrical box or meter. The utility connection for a PV solar system is governed by the National Electrical Code ( NEC ) Article 690.64. Always refer to the NEC code in effect or consult a accredited electrician for safety and accuracy .
There are two basic approaches to connecting a grid-tied solar panel system, as shown in the wire diagram below. The most coarse is a “LOAD SIDE” connection, made AFTER the main breaker .
The alternate is a “LINE OR SUPPLY-SIDE” connection made BEFORE the main circuit breaker.

load-side-connection-diagram-for-pv-solar-systems.jpg line-or-supply-side-connection-diagram-for-pv-solar-systems.jpg

Load Side Connections

In simple terms, a Load Side connection is made AFTER the independent surf in the electrical jury ; this is the most common method acting of connecting. A modern circumference circuit breaker ( randomness ) will be added to the electrical gore. The circuit breaker will be dual-pole or double-space, and it will be located in a status furthest from the main surf. then the wires from the PV solar system will be connected to this raw solar breaker. An adequately size PV servicing gulf box must be used before making the connection. Some inverters include the disconnect or an external unplug can be added stingily .
When using a load-side connection, two NEC rules govern the size allowed based on the electrical empanel size and the solar output size. Both rules must be satisfied to meet Code when using a load-side connection .
RULE 1
Known as the 120 % rule, the solar lap circuit breaker can be no more than 20 % of the main electrical dialog box rate. The electrical control panel rate Amps ( A ), or Busbar fink, is the manufacturer rat typically found on a label. The lap breaker is technically called an Over Current Protection Device, or OCPD .
For exemplar, a 200 Amp electrical panel is rated with a 200A busbar, and normally has a 200A Main OCPD surf. The 120 % Rule back-feed limit for solar is calculated as :

  • MAX SOLAR BACKFEED CALCULATION:
    • (BUSBAR RATING x .20) + (BUSBAR – MAIN OCPD) = MAX PV (A)
    • (200A x .20) + (200A – 200A) = 40A MAX BACKFEED SOLAR
  • Therefore, 40A is the maximum solar output for a 200A panel with a 200A main OCPD, unless de-rated

nowadays, the main circuit breaker can be changed to a smaller size ( e.g. de-rated ) to make board for more solar. here is an case of a de-rated electrical panel to handle a larger solar organization :

  • (BUSBAR RATING x .20) + (BUSBAR – MAIN OCPD) = MAX PV (A)
  • (200A x .20) + (200A – 175A) = 65A MAX BACKFEED SOLAR
  • De-rating the main breaker to 175A in this example, an additional 25A is freed up for use by solar

RULE 2
The solar circuit breaker OCPD must be at least 125 % of system output. System output is determined by the total end product Amp evaluation of the inverter ( randomness ) .

  • Example A: if inverter output is 32A, then 1.25 x 32A = 40A minimum solar breaker size.
    • This would also satisfy Rule 1 for a 200A electrical panel.
  • Example B: if inverter output is 34A, then 1.25 x 34A = 42.5A minimum solar breaker size.
    • This does not satisfy Rule 1 for a 200A panel, therefore de-rate the Main panel breaker.

It may not be potential to meet the NEC interconnection rules for older, smaller, or full electrical panels, e.g. 100A or 125A, with a larger PV solar align. You may have the option to replace the existing electrical control panel with a newfangled, larger box, or use the alternative Line Side Connection. For quick reference, you can besides view this table showing the Maximum Connected PV Inverter Watts for respective circuit breaker box adenosine monophosphate ratings .

Line or Supply-Side Connection

As with most things electric, there are many ways to do the job. There is an alternative UTILITY CONNECTION called a “ Supply or Line Side ” connection. This joining is made BEFORE the main circuit breaker. A articulation box is added between the utility meter and the main service dialog box. then the wires from the utility meter, the main breaker jury, and the PV solar are connected in the junction box.

An adequately size PV service unplug corner must be used anterior to making the association between the junction box and the solar inverter. By connecting on the Line side, it avoids de-rating the existing service empanel and avoids back-feed limits of the panel governed by Rules 1 and 2 above .
however, this approach can not void the UL authentication of the main jury and will need approval by the local anesthetic AHJ construction authority and the utility program. Some jurisdictions do not allow a supply-side joining. The AHJ may argue that a supply-side connection made inside the meter/panel enclosure, may void both the UL list and the manufacturer ’ s guarantee for the existing military service panel. Although it is possible to overcome these issues, these AHJs have gone with a better-safe-than-sorry approach, banning supply-side connections wholly .
We ’ ll handle all the details when doing a PV arrangement invention and preparing the final plans for permit approval .

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