YOUR GUIDE TO WIRING AND CONNECTION OF SOLAR PANELS

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CONNECTION METHODS



A typical commercially available photovoltaic panel is rated between 50 and 300 watt. Given the fact a typical household needs several kilowatt, a single panel obviously is not enough for an entire house. To increase net power level multiple modules are connected into arrays. There are three main wiring configurations (see the diagrams below):


To wire the panels in series you connect the positive terminal of one device to the negative terminal of the next one. Solar panel wiring diaram
With this connection, voltage adds and current stays the same as with a single panel.

To wire the panels in parallel you connect together the terminals of the same polarity. With such connection the resulting output voltage stays the same as with a single module, and amperage adds.

With series/parallel connection, two or mores series strings are paralleled. In such a scheme both voltage and current increase. Assuming all modules are identical and receive exactly the same amount of sunlight:

Vout ≈ n×V
Iout ≈ m×I,
Series-parallel connection of PV panels
where V and I - voltage and current of each individual module respectively, n - number of modules in each series string; m - number of paralleled groups.
These diagrams of course are simplified. The strings are usually merged in a combiner box. Ideally, each circuit is fused separately. However, if you properly sized the conductors, you can protect several (probably up to three) circuits by a single fuse. Also, in practice, with series scheme the modules are often connected to diodes to protect shaded cells from a damage.

MAIN WIRING CODES AND STANDARDS



The main generic document in U.S. that governs most electrical installations is National Electric Code® (NEC®). It used to be updated every three years by National Fire Protection Association (NFPA®). The latest edition is NEC® 2014. Although technically this document is purely advisory, it is utilized nationwide as a de-facto standard. Nevertheless, the local authority that are enforcing the code, may always waive specific requirements, allow alternative installation methods, or conversely make the rules more severe. Therefore you should always check with the local codes.

Wiring of solar energy systems is covered by Article 690 of NEC® 2014. There are other applicable articles, such as 110, 250, 300, 310, 480, and 702. You should consult with these documents for all design decisions. Here is a quick checklist of some important facts, most of which are not trivial.



REFERENCES AND ADDITIONAL INFORMATION:
Suggested practices for photovoltaic systems installation.