690.1 scope (section 690.1)
Word-for-word NEC:
â690.1 Scope. This article applies to solar PV systems, other than those covered by Article 691, including the array circuit(s), inverter(s), and controller(s) for such systems. [See Figure 690.1(a) and Figure 690.1(b).] The systems covered by this article may be interactive with other electrical power production sources or stand-alone or both, and may or may not be connected to energy storage systems such as batteries. These PV systems may have ac or dc output for utilization.
Informational Note: Article 691 covers the installation of large-scale PV electric supply stations.â
Discussion: For the most part 690.1 is self-explanatory, however, if we read the 2014 and the 2017 NEC carefully, we will notice that energy storage systems (batteries) are no longer part of the PV system.
2017 NEC language:
âmay or may not be connected to energy storage systems.â
2014 NEC language:
âmay be interactive with other electrical power production sources or stand-alone, with or without electrical energy storage such as batteries.â
It takes some careful analysis of the language, but we see that being connected to batteries in the 2017 NEC is different than with batteries in the 2014 NEC.
So what does this mean for us? Batteries are no longer part of the PV system as of the 2017 NEC and are part of a separate energy storage system that is covered in the new Article 706. Consequently, rapid shutdown and other requirements that are specific to PV systems no longer apply to the batteries.
Figure 1.2 2014 NEC Figure 690.1(a) PV power source
Next, we see diagrams that will show us the dividing line between the PV system and not the PV system.
Section 690.1 also has some figures that we can look at in order to get a picture of what we are talking about.
Figure 1.2 is an image from the 2014 NEC.
Figure 1.3 is an image from the 2017 NEC.
Figure 1.3 is from the 2017 NEC with the added dc-to-dc converter.
From comparing these images, the main difference here is the insertion of the dc-to-dc converters. The writers of the NEC left the dc-todc converter definition open-ended for your billion-dollar invention. 2017 dc-to-dc converters are usually one per module, rather than three modules per converter in this image. Take note that, as we will learn coming up in Section 690.12 Rapid Shutdown, in 2019 the 2017 NEC will increase requirements for rapid shutdown on buildings and module level shutdown may be one of the only methods to comply. However, new inventions in the meantime could introduce other methods not currently foreseen.
Figure 1.3 2017 NEC PV Figure 690.1(a) PV power source
It is interesting to note that the solar cells in the diagram have gone from round in the 2014 NEC (really old style) to square in the 2017 NEC (polycrystalline). For someone first learning about solar, it could be confusing to see a solar module with 12 cells and then to see panels made of three modules. It would be even more confusing to have one dc-to-dc converter per three modules that is being connected with fuses to a dc-to-dc converter combining busbar and then off to a dc-to-dc converter output circuit. Dc-to-dc converters being installed in 2017 have a single PV module with a dc-to-dc converter under the module and then a number of dc-to-dc converters connected in series, and then the dc-to-dc converter source circuit is connected directly to the inverter.
Figure 1.4 Interactive system [2017 NEC Fig 690.1(b)]
Figure 1.5 Ac module system [2017 NEC Fig 690.1(b)]
Images are good to learn from. Next, we will go over the different images in Figures 690.1(B), paying close attention to the various PV system disconnecting means, which separate the PV system covered here in Article 690 from systems covered in other areas of the 2017 Code. Remember, much of this has changed in the 2017 NEC.
Interactive (grid-tied) inverter circuits are very simple. The inverter is used only for PV power; it has no other purpose and therefore is part of the PV system.
A big question installers have is: âWhat is the difference between an ac module and a microinverter bolted to a PV module?â The answer is that if the PV module was listed to UL1703 while the inverter was bolted to it and the inverter was tested and listed to UL 1741 while bolted to the PV module, then it is an ac module and we do not consider dc part of the product when installing this module.
If the module and microinverter were not listed together, then we are responsible for applying the NEC to the dc circuit going from the module to the inverter. It is also interesting to note that the word microinverter does not appear in the NEC. The NEC looks at a microinverter as nothing more than a small (micro) inverter.
There is a lot of information in Figure 1.6. First of all, dc coupled and multimode are different things, which can go together. A dc coupled system is a PV system that is typically charging batteries with a charge controller connected to a PV array. The inverter in a dc coupled system will be coupled with the inverter and the charge controller working with dc voltage. In fact, it is possible to have a dc coupled system that does not have an inverter, but most people would like to utilize ac electricity with their dc coupled systems.
Figure 1.6 Dc coupled multimode system [2017 NEC Fig 690.1(b)]
As we can see in the 690.2 Definitions that we are about to dive into, a multimode inverter is an inverter that can work in different modes, such as stand-alone (off-grid) and interactive (grid-tied). This type of inverter was also known as a bimodal inverter for a time and will have different outputs. One output will go to the stand-alone (backed up) loads and the other output will go to the loads that are not backed up and to the grid. When the power goes down, the interactive output of the inverter will act exactly as an interactive inverter and anti-island (stop sending voltage or current to the grid). No interactive inverter circuit is allowed to be an âisland of powerâ and must disconnect from the grid.
Multimodal vs. hybrid
There is often confusion about multimodal inverters and hybr...