Solar safety

NovazNovaz Solar Expert Posts: 57 ✭✭✭✭
Still doing my research and thought I need to look at some of the safety requirements of a Solar PV system
as well as looking at all the "Goodies"

Question #1 I dont see much mentioned about lightning protection on RVs

Question #2 what would be the must have for a cabin based solar system regardless of cost

I understand about Ground/ Earth requirements but not sure about exactly how to match components used to the system i intend to have .
have watched a couple of Midnite Videos on the subject but see 3 models of surge protection devices .
Thanks
Roy

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar safety

    #1 Hard to protect and RV from lightning strike because there is no 'real' Earth grounding, being a mobile application. Various 'touch ground when parked' systems are of inconsistent reliability as they depend on local conditions for continuity and this is not assured. On the plus side the tires will insulate against conductivity to a certain extent, reducing the prospect of lightning 'seeing' the RV as a potential ground path. Doesn't always work, though.

    #2 Cabin applications do not require lightning protection at all, and it is only used where strikes are frequent. The nice thing about SPD's is that with proper grounding (a subject which has more debating than religion) they protect against line surges and stray Voltage (lightning induced).

    The details of how any type of system protection is designed and installed depends on the details of the system itself. Type and location of components, distances involved, wiring - all come into play. That is why you see so many different answers on how best to ground/protect something and why the code for such keeps changing. It is not as simple as "you do this and you are safe". Lightning has a mind of its own and will do what it wants, including blowing your safety measures to smithereens if it so happens. You can only reduce risks; you can't eliminate them.
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: Solar safety

    First question, are you going to have the rv in an area prone to lighting strikes?

    If yes, then you should make a Faraday cage of the living/work space. Basically a grid around the outside of 6awg wire. Bonded together at crossing/common points (not soldered). Any power /communications cables going inside should have surge protectors grounded to the cage.

    How close should the 6 awg wire be? Need to research... but probably 6 feet apart and at the 4 corners would be a good start.

    Grounding the cage to earth would be nice, but not a requirement except if going in/out during a storm.

    My starting guesses.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Iceni JohnIceni John Solar Expert Posts: 103 ✭✭
    Re: Solar safety
    BB. wrote: »
    First quotation, are you going to have the rv in an area prone to lighting strikes?

    If yes, then you should make a Faraday cage of the living/work space. Basically a grid around the outside of 6awg wire. Bonded together at crossing/common points (not soldered). Any power /communications cables going inside should have surge protectors grounded to the cage.

    How close should the 6 awg wire be? Need to research... but probably 6 feet apart and at the 4 corners would be a good start.

    Grounding the cage to earth would be nice, but not a requirement except if going in/out during a storm.

    My starting guesses.

    -Bill
    Bill, that's interesting. However, I have a bus with a steel frame and body ribs and with aluminum sides and roof - would that in itself work as a Faraday cage, or would additional protection be needed? (The aluminum body panels are electrically insulated from the steel ribs to prevent galvanic corrosion.) The reason I'm asking is that there's a high likelihood I could be parked in potential-lightning areas, plus I have eight big PV panels on the roof. How critical is it that Faraday cages are grounded? I would not relish needing to drive a copper grounding rod 8' into the ground every time I set up camp during lightning season!

    Thanks, John

    40' Crown bus with 2kW of tiltable panels on the roof:

    Eight Sharp 255W, two Morningstar TS-MPPT-60, Magnum MS2000, Champion C46540 generator converted to propane, eight golfcart batteries, and maybe a small Exeltech inverter for the fridger.

    Southern California

  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: Solar safety

    In general, a metal sided building has never been lightning safe--The metal is too think to carry the high currents and the lap joints do not make good connections:

    http://www.lpea.com/education/lightning_safety.html
    What is a Safe Shelter?
    A safe building is one that is fully enclosed with a roof, walls and floor, and has plumbing or wiring – a mechanism for conducting the electrical current from the point of contact to the ground. This can include a home, school, church, hotel, office building or shopping center. These mechanisms may be on the outside of the structure, may be contained within the walls of the structure, or may be a combination of the two.
    Avoid Unsafe Shelters
    Unless specifically designed to be lightning safe, small structures do little, if anything, to protect occupants from lightning. Many small open shelters on athletic fields, golf courses, parks, roadside picnic areas, schoolyards and elsewhere are designed to protect people from rain and sun, but not lightning. A shelter that does not contain plumbing or wiring throughout, or some other mechanism for grounding from the roof to ground is not safe. Small wooden, vinyl, or metal sheds offer little or no protection from lightning and should be avoided during thunderstorms.

    Safe and Unsafe Vehicles
    A safe vehicle is any fully-enclosed, metal-topped vehicle such as a hard-topped car, SUV, truck, etc. Unsafe vehicles include convertibles, golf carts, riding mowers, open cab construction equipment and boats without cabins.

    When driving into a thunderstorm, slow down and use extra caution. If possible, pull off the road into a safe area. Do not leave a safe vehicle during a thunderstorm, and do not use electronic devices such as radio communications as if lighting strikes the vehicle – especially the antenna – it could cause serious injury if one is talking on a radio or holding a microphone at the time.

    Lightning rods around the roof line, tided to copper cables, and down to the bottom of the vehicle. The "modern" aluminum sided vehicles I am familar with use "double stick tape" and/or adhesives to bond the aluminum together and to the frame of the vehicle. I would guess, that the frame of the vehicle is really what is providing lightning protection (Faraday Cage) type protection.

    Example of 707 wing damage from direct strike:

    http://www.atmos.albany.edu/deas/bvonn/707wingt.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar safety

    Might also want to point out that RV's aren't a solid metal can: they have windows with metal frames that could bring the strike inside.

    One way to look at the protecting idea: you're trying to turn the whole thing into a big piece of braided wire so that the high frequency, high Voltage energy travels around the outside of it rather than through it damaging things. This is usually what happens when panes are hit in the air, but not always.

    Any intruding conductors would be connected to the cage with SPD so that if they become energized that to will be directed to the outside 'wire shield'. There's no 100% guarantee on that working either.

    If the shield is connected to ground all the better, as the lighting and its effects is generated by the Earth and is trying to find a path to ground; if you help it along it may be grateful and not fry all your equipment. It's a bit impractical to do, though. Arguably so is the Faraday cage.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Solar safety
    Iceni John wrote: »
    Bill, that's interesting. However, I have a bus with a steel frame and body ribs and with aluminum sides and roof - would that in itself work as a Faraday cage, or would additional protection be needed? (The aluminum body panels are electrically insulated from the steel ribs to prevent galvanic corrosion.) The reason I'm asking is that there's a high likelihood I could be parked in potential-lightning areas, plus I have eight big PV panels on the roof. How critical is it that Faraday cages are grounded? I would not relish needing to drive a copper grounding rod 8' into the ground every time I set up camp during lightning season!

    Thanks, John
    It is not critical that a Faraday cage be grounded to do its principal job of avoiding electromagnetic waves, stray voltages and stray currents inside the cage.
    The principal problem with not grounding the cage is what happens to the occupants and the cage when the lightning currents do make the jump from the cage to earth. As long as the cage survives the current arc, the occupants will not be injured. If an occupant happens to be in the process of transitioning between the inside and the outside at the time of the incident, they will be in deep trouble whether the cage is metal grounded or not.
    SMA SB 3000, old BP panels.
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