Solar PV Storm and AC vs. DC Safety Considerations

On the Solar PV Installer Boot Camp Training + NABCEP Entry Level Exam Prep discussion board…

Student 1: Fred, what is the standard for lightning protection systems? The book touches this topic briefly. Is it the norm to have lightning protection? Do you install lightning protection on systems you install? There are many homes in my area in New Jersey that don’t have any lightning protection systems. Actually, I can’t see any lightning rods on any of them. Could it be just the area you live in? The system I will be installing will be on the roof of a two story building located on the Cumberland plateau in Eastern Tennessee. The elevation is about 2,000ft high. If lightning strikes the grounded PV modules I’m sure it will have some type of damage. So is a lightning protection system a system you install just to play it safe?

Fred: Hello, Student 1. Yes, we install both DC and AC surge protection on every project. Typically, such protection is at or near the inverter.

Student 1: Thanks for your reply Fred. I too have AC surge protection for all my circuits. But what about lightning rods on roof tops? I have very little experience with lightning rods. I see what lightning does to trees and houses that are struck. I don’t want that type of damage to PV modules. Will lightning rods on your structure attract lightning? Are you better off not having lightning rods?

Fred: Just happens that I know a bit about this issue since I once worked for a Surge Suppression manufacturer.

Beyond the typical surge protection under your desk, there are two additional categories including “whole-building” protection. We studied and applied these applications in the lightning capital of the U.S., Florida.

We would only deploy lightning rods if we have a good direct pathway to ground, along with MOV based surge suppression. Without a way to mitigate incoming surges and transients, you may not want to use rods.

When we speak of surge protection, there are three categories (ABC) A is the strip under your desk, B is for branch circuits within the building, and C is building protection at the main-panel.

Google this company: “MCG Surge Protection”, I am sure you will find world class technology and support.

For our solar installs we use both AC and DC Midnight Solar devices. Typically to save the inverter. We don’t get hit like Florida, so I am not as concerned about installing all 3 categories here in Massachusetts.

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Student 2: Quick question that may sound silly but, why does it matter if you use AC or DC to power your loads? I see the difference visually with the oscillations of AC and DC’s linear state but why is 110v AC the standard? And why does Europe and the rest of the world use the 220v standard which have physically different receptacles? They don’t even hold the plug safely so I’m curious who decides these things…

Fred: Student 2, thoughtful questions – here are a couple of points:

1. Alternating Current won the DC/AC wars because you can use an AC transformer to significantly increase the voltage while you simultaneously lower the amps. When you lower the amps you can lower the diameter of the cable and the cost of interstate utility lines drop significantly. Whew
2. Today, if AC is available that is the way to go. Yes, you can get a DC refrigerator – they do not look like a 2015 – 18 cubic feet Amana, but we see them in off-grid homes. The rational behind using DC appliances off-grid is that the efficiency is better without having the inverter loss.
3. The world is AC and all is good. AC is safer, in that – however small – there is an instant when the sine-wave crosses zero. Thus the staccato pulses you feel as you get a bad shock. Bad shocks with DC kill you faster – DC does not cross zero – it does not let go.
4. If the world did go DC, we would have local electric companies in every town. It would be too expensive to send power to another town.

As far as why the plugs are different around the world, I think is the same reason our trains will not fit on their tracks.

Enroll in Solar PV Installer Boot Camp Training + NABCEP Entry Level Exam Prep with expert instructor Fred Paris today!

About Fred Paris – NABCEP & PV Business Training, Wind Sun Institute

Fred has been teaching NABCEP students since 2008. At Massasoit College Fred introduced the PV course, wrote the curriculum, and taught the first PV classes. As a Solar practitioner, Fred’s PV projects include high school, residential, commercial, and church projects. Systems include: roof-mount, ground-mount and pole-mounted PV systems – with and without equinox adjustment. As invited faculty, Fred supports Northeastern University – teaching the final Strategic Planning module for graduating MBA students. Fred holds AAS, BS, and MBA degrees, and he is still paying off his student loans.

Fred is currently teaching:

• 58 Hours NABCEP Solar PV Training – Entry Level Exam Prep + 40 Hours Advanced / Online / Anytime
• Solar PV Installer Boot Camp Training + NABCEP Entry Level Exam Prep / Online / November 9 – December 18, 2015