Only when a live hot wire shorts into a metal component will electricity "conduct" through the EGC and into the earth. Thus, an equiipment grounds plays a critical role in every circuit without ever being part of its regular operation. Sizing Conductors and Identifying Wire Types. To determine the wire you need -- including types, colors green for ground, white for neutral, etc.
Then they address the electrical characteristics and other variables of each section in turn. A simple grid-tied solar electric system includes three sections:.
However, since home grid-tied systems normally possess the same electrical characteristics on either side of the disconnect, this tutorial will mesh the two sections into one. PV Source Circuit.
Your solar modules come with four or five-foot long cables already attached, including a positive and a negative lead. In most cases, the wire type on module leads is PV Wire.
The two leads should include snap-in connectors, male or female, which makes connecting the modules together a straightforward process. Be sure to note the type of connector on the module you select for your array -- for example MC4 -- since you may need to buy a few more of these connectors to wire the circuit. Our sample array consists of two parallel strings of 10 modules. So the wiring diagram and all subsequent calculations will take this into account.
For now, the diagram above shows one string of 12 modules. The negative polarity conductor is indicated on the nearest end of the module row to the combiner box. Meanwhile, the positive conductor runs from the opposite end of the string, across the top, and then into the box. In the parlance of installers, whichever conductor is at the far end i. It can be either the negative or positive wire, depending how you choose to interconnect your modules. Here, the home run is positive.
As you can see, some extra PV wire must be added to the array in order to complete the source circuit. You'll also have to decide on how you want to ground all the modules and racks together. There are two options:. Run an equipment grounding conductor EGC from module to module, rack to rack, and onward to the junction box. Traditionally, a sturdy bare copper wire of AWG 6 solid not stranded is run from lug to lug. AWG 6 is pretty sturdy, so it can stand up to the elements or a rodent gnawing on it without breaking.
But bare copper is the usual choice. Bond the racks and modules with grounding clips and jumpers. Instead of connecting a ground to every module and rail section, you can accomplish the same result by slipping in little grounding clips they look like washers when you clamp your modules onto the rails.
You'll also insert electrical jumper cables on either side of spliced rails in your racking to keep the equipment grounding path uninterrupted. See photos below.
Once that's done, you'll only need to connect your bare copper ECG at one lug attached to each row, then run the same wire to the junction box or combiner. The clip is the flat plate with the two little dimples. At right, a WEEB jumper cable is connected across a rail splice. Equipment bonded together in this manner insures that a stray current will move efficiently in the desired direction - to ground. For more on how the clips and jumpers work, watch this video.
When used with WEEBS and jumpers see above , you need only to ground each row at one location, then run the bare copper wire to the junction box. This securely grounds a roof array in accordance with NEC rules. Both types have the same electrical characteristics as far as their ratings and the NEC. Both types are UV and moisture resistant, and rated for 90 degrees Celsius.
It's also now required for systems that include a transformerless inverter. As far as picking a gauge, since the module manufacturer has already sized the leads either AWG 10 or 12 , sizing for other wire in the PV source circuit can be considered pretty much done for you.
One very important exception to the rules for wiring the PV Source Circuit is an array that uses microinverters or newer AC modules.
Wiring in these scenarios is a totally different animal. In particular, you'll have volts of AC by the time the electricity leaves each microinverter or module. If you decide to go either route, you must follow the wiring instructions in the product installation guides, and in some cases install special mult-wire cables sold by the manufacturer.
For more on this subject, see the Enphase installation manual. You can use black for both the positive and negative lead by simply adding a colored piece of tape on either end to identify the grounded and nongrounded conductors or positive and negative.
Wire jacket colors other than black contain less carbon and deteriorate faster in the sunlight, so you should avoid them on the roof. Solar equipment suppliers usually offer a single product for roof array wiring -- AWG 10 PV Wire, sold in foot rolls.
If you measure the distance of the home run from the end of each string to the junction or combiner box, then you'll know how many feet you'll need. Most of the time, you can connect the module lead nearest the box directly to it. However, if the distance is too far, you'll to add an extension, which might be referred to as the "near end run". When buying PV wire, you also have the option of having one or both ends equipped with the snap-in connectors.
To reiterate, different brands of connectors don't interconnect, so you'll need to select the same type that's used on your module leads. Usually, but not always, it's an MC4. Get in Touch. Read More. January 13, The lines between living space and moving space are being blurred. Activities that people wish Solar Surge will teach you all about being energy independent and how to set up On the lookout for a thin, lightweight panel?
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Day 4 of the our Tesla Solar Roof installation where the crew is preparing to Because the current remains the same through the entire string, the current is reduced to that of the panel with the lowest current. Stringing solar panels in parallel shown in the right side of the diagram above is a bit more complicated.
Rather than connecting the positive terminal of one panel to the negative terminal of the next, when stringing in parallel, the positive terminals of all the panels on the string are connected to one wire and the negative terminals are all connected to another wire. When stringing panels in parallel, each additional panel increases the current amperage of the circuit, however, the voltage of the circuit remains the same equivalent to the voltage of each panel.
Because of this, a benefit of stringing in parallel is that if one panel is heavily shaded, the rest of the panels can operate normally and the current of the entire string will not be reduced. There are several important pieces of information about your inverter and solar panels that you need before you can determine how to string your solar array. As noted above, a function of inverters is to maximize power output as the environmental conditions on the panels vary.
However, for a given MPPT, the conditions on the panels must be relatively consistent or efficiency will be reduced for instance, differences in shade levels or the orientation of the panels. It is also important to note that, if the inverter has multiple MPPTs then strings of panels with different conditions can be connected to a separate MPPT. These specific lab conditions provide consistency in testing but the real-world conditions a PV system experiences may be very different.
As a result, the actual current and voltage of the panels may vary significantly from these values. Ensure that the maximum voltage complies with code requirements in the area where you are designing. In the U. In Europe, higher voltages are allowed. We know that voltage is additive in series strings while current is additive in parallel strings. As such, you might intuitively assume that you can determine the voltage of our proposed PV system design and whether it falls within the recommended range for the inverter by multiplying the voltage of the panels by the number in a series string.
You might also assume that you could determine the current of the system by adding the current of each parallel string which would be equal to the current of the panels multiplied by the number in the parallel string. Thus the simplified calculations taken from STC values only give you an initial rough estimate; you must account for how the voltage of the system will change depending on the temperatures it may experience in the area where it is installed.
At colder temperatures, the voltage of the system may be much higher; at higher temperatures, it may be much lower. To ensure that the temperature-adjusted string voltage is within the input voltage window of the inverter it will require a more complicated formula, like the ones below :.
For more information on stringing in Aurora, see this help center article. Aurora also performs a variety of other validations to ensure that the system will operate as expected and not violate codes or equipment specifications — this can prevent costly performance issues.
For a detailed overview of these validations see this page in our help center. For a real-world example of why it is so important to accurately account for how environmental conditions will impact the voltage of your PV system, read our analysis of an underperforming system in Cathedral City, California.
Mismatches in the conditions on the strings will reduce the efficiency and power output of your solar design. This will allow the inverter to ensure each string operates at the point where it produces the maximum power. However, there are additional factors that a solar designer can consider to arrive at the optimal design that is, the design that maximizes energy production while minimizing cost.
These factors include inverter clipping, the use of module-level power electronics MLPE — devices which include microinverters and DC optimizers, and design efficiency provided by software tools.
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