[RE-wrenches] Lightning protection system

Tue Mar 10 18:14:31 PDT 2009

In 1983 Arco Solar and the Lightning & Transients Research Institute,
St. Paul, MN, presented a paper at the Greece PV conference titled
"Ability of Photovoltaic Modules to Withstand Lightning Strikes."

Summary: The ability of glass superstrate and metal/plastic substrate
modules to withstand lightning strikes was examined. Each of 3 different
types of modules were exposed to 4 nearby and 1 direct strike of high
voltage long arc simulated lightning (400,000 volts, 10,000 amps), and
to 1 direct strike of high current, long duration lightning (150,000 to
175,000 amps, 50,000 volts). Visual and electrical examination
demonstrated that the high voltage strikes produced no electrical damage
to the glass superstrate modules and little to the plastic substrate
module. The high current, long duration strike resulted in varying
degrees of physical damage to all modules but little or no loss in
electrical performance.

Conclusions: The experimental data indicate that a glass front module
with a rigid metal frame is able to withstand almost any lightning
strike if the frame is grounded to the earth. The metal frame acts as a
grounding rod attracting all the current to it. However, a strike which
breaches the integrity of the encapsulation might, under some
conditions, eventually destroy the module. Data from the field appear to
concur with the experimental data presented in this paper but also
indicate that while the modules survive a lightning storm, additional
protection may be required for the cabling, power conditioning
equipment, and control systems. A grounding rod will protect the array
from direct strikes but further protection is required for induced
voltages and side flashes they can create. Shielding (e.g. coaxial
cables) will protect the wiring. The terminals of the balance of system
components can be protected by the use of nonlinear circuit elements
known as terminal protection devices. These devices may be nonlinear
resistors or varistors, semiconductor junction devices and dielectric
breakdown devices or sparkgaps. The degree of protection needed for any
particular installation will be determined by factors such as site
location, size of the array, safety considerations and cost.

Joel Davidson

  ----- Original Message ----- 
  From: Matt Tritt 
  To: daryl_solar at yahoo.com ; RE-wrenches 
  Cc: trang donovan 
  Sent: Monday, March 09, 2009 11:04 AM
  Subject: Re: [RE-wrenches] Lightning protection system

  Hi Darryl,

  Just to see what your take would be, and other's - what would the case be should the modules have non-conducting frames (or even no frames)is the case with some systems on the market?

  Matt T

  Darryl Thayer wrote: 
Yes the electric power and atmospheric grounding systems should be connected together to serve as a larger better grounding system.  The Electrical code requires that at only one point does the neutral (grounded) conductor of the electrical power system get connected to the grounding system, this is to prevent the grounding electrode system from carrying electrical power system currents.  The electrical power system is to be grounded to prevent the electrical power system from differentiating its self via the injection of energy from other electric power sources including atmospheric electrical energy.    

The lightening protection system is to create a path from the atmospheric energy to the earth grounding system.  ((Wind rain, dust and friction cause the atmosphere to become charged relative to the earth, conducting objects can build a charge if not electrically connected to the earth, these current flow all the time, although they are small sometimes, and in the case of a lightening strike incredibly large.  Even small currents can build large voltages and fail electronic components.  

The frames of solar modules are electrical conduction components not normally charged that can present a personal, and physical damage potential (life-property) if they become charged by the electrical power system and therefor the underwriters require they be protected by grounding.  This accidental energy need to be safely returned to the electrical power system, and properly this is called bonding back to the neutral conductor.  This grounding is described by the NEC in 690 and 250 primarily.   The frames of the modules can become charged by atmospheric energy energy, this energy needs to be returned to the earth, via the lightening protection system, ie grounding electrode system.  The code says little about this, however, it is addressed in 690 and 250.  

Sorry I said so much.
Darryl        

--- On Fri, 3/6/09, Drake Chamberlin <drake.chamberlin at redwoodalliance.org> wrote:

  From: Drake Chamberlin <drake.chamberlin at redwoodalliance.org>
Subject: Re: [RE-wrenches] Lightning protection system
To: "RE-wrenches" <re-wrenches at lists.re-wrenches.org>
Date: Friday, March 6, 2009, 8:47 AM
I didn't get a reply to the question about connecting
the GEC to the 
lightning protection system on the 8 story building. 
Although this 
may seem like an intrinsically dangerous idea, a lightning
protection 
system is required to be bonded to the building grounding
electrode system.

"250.106 Lightning Protection Systems.
The lightning protection system ground terminals shall be
bonded to 
the building or structure grounding electrode system."

It would therefore seem that the suplemental ground could
connect to 
that system as well, and in fact use the existing
conductor.  Any 
input would be welcome.

Thanks,

Drake

At 09:19 PM 3/4/2009, you wrote:
    Hello Wrenches,

Can the supplemental grounding electrode conductor be
      connected to a 
    lightning protection system?

We have a case where it would be difficult to run a GEC
      down a multi 
    story building, but have a convenient copper wire, from
      a lightning 
    protection system, that runs to a rod.

Thank you,

Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
740-448-7328
740-856-9648

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      Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
740-448-7328
740-856-9648  

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