Lightning protection of solar panels, batteries, inverters etc - Page 1
Forum section: electronics / general

author: Robert Smith Eco Warrior
author_rank: Regular Contributor
timestamp: April 12, 2021, 02:48:03 pm
content: Hi All,I started another thread and someone suggested I isolate my project from lightning. That prompted me to write this thread about lightning protection.I have wondered about the best way to do this.My solar panels are ground mounted on a wooden structure at a fixed 45 degrees pointing south, as we are in the UK. 45 Dgrees is fine as we get far more power than we can use in the summer and then in the winter they just need to point generally upwards at the grey sky.There are 16 panels in 8 pairs of two panels.It is all lashed up at the moment to just get things going and has been like that for a few years.I have planned a common 50sqmm negative heavy cable going to the shed and eight 6sqmm positive cables. I was given the 50sqmm cable and bought a huge roll of the 6sqmm cable really cheaply so this is my setup using what I can afford.Inside the battery shed the big negative and eight positives come into a household consumer unit (fuse box circuit breaker box if they are called other things in other countries) Each of the eight positives goes through a double pole 100A switch. They are designed for AC so I am going through one pole, across the back and then through the other pole to effectively double the arc gap. This allows me to switch panel pairs in and out and test that they are performing as they should and I can spot if a pair of panels is not upto scratch.My plan for lighning was to then have a loose pair of 35sqmm cables between this consumer unit and the charge controller with a big Anderson plug half part way along it. If we were expecting lightning or can hear thunder my plan was to unplug this big plug and coil up the cable to give about 4ft from the consumer unit to the batteries or charge controller.The Victron inverters are earthed with an earth rod and are internally connected to the negative battery feed so I could see that as a ground path I wanted to break.I have not found a decent answer to this problem so asking here. Any ideas?

author: David Hess
author_rank: Super Contributor
timestamp: April 14, 2021, 08:23:50 pm
content: I thought the same rules for lightning protection of an antenna installation would apply, with the metal frame and structure holding the solar panels separately grounded to Earth. Otherwise a strike is likely to cause a fire inside the structure.

author: jonpaul
author_rank: Super Contributor
timestamp: April 16, 2021, 05:05:27 pm
content: Hello check the isokeratonic maps for lightning frequency in your location.Use only approved lightning protection devices.Ground and earthing requirements vary with locality, in No Cal USA for instance two separate 18' deep copper ground rods bonded with #8 ga to the panel are reccomended.I highly suggest the protectors from Eaton, Transrector etc.https://www.transtector.com/search?Category=AC+Surge+Protection&view_type=gridFinally the best forum for electrical questions especially safety relater or regulatory is the Mike Holt forum:https://www.mikeholt.com/eghttps://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/SurgeArrestersTransientVoltageSurgeSuppressors~20020725.htmBon Chance,Jon

author: Robert Smith Eco Warrior
author_rank: Regular Contributor
timestamp: April 19, 2021, 08:05:49 am
content: Is that 18 inches or 18 feet?I guess 18 feet but I will hit solid rock after about 3 feet here

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2021, 08:38:37 am
content: 18 feet, or 6 meters, though if you are hitting rock after 1m you have high soil resistivity, and thus will need to have a good number of smaller rods, spread out into an array where each one is separated from it's neighbour by it's own length, and connected to each of it's neighbours by a cable of at least 10mm, so use the 6mm cable doubled up.Also depends if you are on top of a hill, a higher strike risk, or down appreciably into a valley, or if there is high ground near you. Going to guess you are in the northern parts of the UK, where the ground is a layer of soil over granite.Panels i would suggest having at least 4 short grounding rods per panel, hot dip galvanised steel rod hammered in till bedrock, one per corner, and used to space the panels off the ground a little. Bolt direct to panels, so at least you can drain charge off of the panels so it does not build up. Pile of rock salt applied to the area directly around the rod to improve soil resistance, though it will corrode the rod faster, and also nothing will grow around it, so dig down a depth, then fill the hole partly, and put the soil back on top.Still not going to protect from a direct hit, or even a hit within 200m, but at least will limit damage. To provide more protection will require the installation of a properly specified lighting system at a distance, using wide flat strip conductors to connect to a big ground mesh array, seeing as you have poor soil conductivity. Gets very expensive very fast, but again depends on location.

author: Robert Smith Eco Warrior
author_rank: Regular Contributor
timestamp: April 19, 2021, 08:51:29 am
content: Hi. Thanks for the replies.I wasn't sure whether to to go down the insulating route to avoid attracting lightning or go down the conductive route to track away lightning.I will have to look into my options more for grounding. We have about a foot of topsoil above burnt orangy stone but hard like granite. I think it is whatever the last glacier dumped here.David, I have my batteries and equipment away from the house in a separate shed. I guess a lightning strike would get the house too but I didn't want the fire risk of the batteries and noise of the equipment in the house so all that stuff lives in a separate shed that could more safely burn down

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2021, 10:00:16 am
content: Insulation will never work against a voltage high enough to create an arc discharge up to 40km long, so your best bet is to make sure that the strike does not go into the equipment, either by dissipating the static charge around you, and then having an alternate conductive path nearby for it to flow through, rather than through fragile silicon parts. At these currents, even steel strapping works well, as it has a large surface area, and steel reinforcing rods are the material used in high rise buildings, along with the steel girders and bolted or riveted together joints between them.

author: jonpaul
author_rank: Super Contributor
timestamp: April 19, 2021, 07:49:38 pm
content: Hello again: Please note that the lightning strikes involve currents of many 10s..100s kiloamps, and voltages in magavolt range, thus even a nearby strike induces ground currents and induced voltages in any conductor.There is substantial chance of equipment or person damage or even death.Thus the grounding system, protection and wiring are both critical and can involve liability.Broadcast towers, power distribution and transmission line and tall building antennas were fine examples of protection. STRONGL:Y suggest to find a LISCENCED ELECTRICIAN or other expert and not to DIY.Kind Regards,Jon