Saturday, September 25, 2010

Lightning Strikes - What I've Learned

Right from the start, I want to make sure to explain that this post is about what Trish has learned. Science was never my subject, so much of what I've learned about lightning strikes is pretty elementary. I don't want you to think this is what Allen has learned. Allen is learning, too, but he started off knowing much more than I did!

First of all, I learned about lightning rods. Our system is grounded, but it didn't help us in either of our recent lightning strikes. Here's why:

A lightning rod draws lightning to itself, to keep the lightning from hitting something else that would be damaged by the strike. There is a limit, though, to the usefulness of the rod. It will, apparently, only draw lightning which was going to hit very close to the rod in the first place. So, if the lightning was headed for your roof, and you have a rod on your roof, the lightning will hit the rod and your roof should be spared damage. If the lightning was headed for a tree in your yard, the rod may not pull the lightning away from the tree, because the tree and the rod weren't close enough together.

When lightning hits a correctly installed lightning rod, the electricity hopefully travels down the rod to a metal cable, which runs from the rod to the ground. Then the electricity is disbursed through the ground, normally without causing harm to anything.

We haven't had a hit to our buildings, or even all that close to our buildings, so clearly a lightning rod isn't the solution to our current problem.

Most of that I already knew, to some extent, but here's what I'm learning that's new to me. After lightning hit a tree some 600' away from our buildings (two different times!), the electricity went down the tree to the ground, and then traveled through the ground to our buried electrical cables (which run between our two buildings and are encased in a "protective" plastic conduit). The electrical surge traveled along the cables and then into our equipment - traveling up to our equipment along the grounding lines which we had installed to take electrical surges away from the equipment in the event that we should experience a direct strike on the house!

Do you get this? The steps we took to protect our equipment actually facilitated the movement of these electrical surges into our equipment! Ouch!

Apparently if we were "on the grid" we might not have such a problem with this. When lightning hits the interconnected grid of electric lines servicing multiple buildings, the surge can spread out and cause less concentrated damage over a wider area. In our case, since we are the whole "grid" we are likely to take the entire force of the electrical surge, and therefore we can expect to experience a large amount of damage.

So, there's our problem. And we're not the only ones with this problem. Allen has been doing quite a bit of research on this (as we upgrade to better and more expensive equipment in the near future, we need to do all we can to protect our investment) and he has discovered that there is no generally accepted solution for the problem of ground surges damaging off-grid solar energy systems. Some people, in areas where they experience frequent lightning strikes and where the problem of electricity surging along the ground is common, take the risk of having no lightning rod or grounding of any sort on their electrical equipment. Their rational is that the probability of damage from a ground surge is higher than the probability of a direct strike to their equipment.

We're not yet sure what we'll be doing about this. But now you know about as much as I do about the situation.

1 comment:

Theresa in WV said...

Oh, what a hassle! So did you lose a lot of equipment?