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Ideas for fire protection?

Discussion in 'Photovoltaics' started by Jerry Ellinghuysen, May 6, 2004.

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  1. Group
    We are in the planning stages of building a house in mountainous Colorado.
    The site is at 7000 ft in an overgrown pine forest. Thinning has started but
    will be a life time project.
    House will be EXTREMELY fire resistant (metal roof, concrete walls, working
    on window protection).
    The weak point is that we have discovered that we will almost certainly want
    to go PV. Currently considering two tracking units.
    My question how do you protect this PV system from fire danger?
    A little more information. The building site is on an acre or so (total 40)
    of relatively flat area, surrounded by steep terrain. A couple of close
    natural chimneys involved that would generate a lot of heat as fire ran up
    through them. Site will require the PV trackers about 100 ft from one of
    these chimneys.
    Am getting well versed in "defensible space." That won't be the problem.
    Worried about the heat generated rolling up the hill and the possible damage
    that could be done to the PV trackers and panels.
    Would a soaker hose across the tops of the panels work? A sprinkler trained
    on the panels? Contemplating a 1300gal cistern, so will have water but will
    not be unlimited. At 10 gal/minute that only about 2 hours of protection.
    And somebody would have to be there to turn it on.
    Or are panels robust enough to not be a big issue?
    Any brainstorms greatly appreciated.
  2. SQLit

    SQLit Guest

    The PV will be expendable. 1300 gallons will not even be a drop in the
    bucket if your in a forest fire. You need to talk to your local fire
    marshal. He should have some training films that you could get educated
    with. I spent some time with one of the engines in Phoenix as a ride along.
    One home fire took 4 pumpers all with 1 4 inch incoming and 4 2 inch out
    going. A lady came out and said the pressure drop in her house was causing
    the toilet to fill slowly.
    You realize that the helicopters drop 2000 gallons at a drop and the slurry
    planes are more like 200000 gallons.
    Use the cistern to protect the house and get insurance for everything else.
  3. daestrom

    daestrom Guest

    Don't have any direct experience with forest fires, so take this with a
    grain of salt. But have defensible space around the home and PV so direct
    fire is *not* the big concern. If you're more worried about the heat, then
    find out just how long you have to hold out. True, forest fires burn for
    days/weeks, but not in one place. A fire could sweep up the hillside and be
    over the top and gone in just an hour or two. Mind, it could be hard
    breathing for a while :)

    If you're home, consider something like a soaker hose along the top and a
    fire-proof tarpaulin to roll up over them. The water would cool, and the
    tarp protect from embers/ash as well as insulate. You could probably get
    away with much less flow rate this way. The tarp would take the brunt of
    the radiant heating as well, and if cooled by the water underneath, may work
    quite well.

    But you might be better off taking steps to prevent the problem. More
    thinning might be better way to go.

    Interesting question though, let us know what you come up with.

  4. Thanks for the response.
    One idea I've found in the interim is the use of a spray on gel (like a
    polyacrimide) - can be wet down and will stay moist for 12 hours or so. The
    idea of a tarp could be a good one.

    Any idea one how rugged a typical PV panel is in terms of heat input? On a
    quick look, I didn't see anything on any spec sheet. Haven't tried any of
    the suppliers yet.
  5. Gary

    Gary Guest

    How about covering the panels with a rigid insulating material that has
    an aluminized coating on the outside? Some fire protection devices now
    in use have highly reflective outer coatings to reduce heat transfer to
    the item be protected.
  6. Gary

    Gary Guest

    Hi again,
    You might take a look at these two links:
  7. I think a better method would be to mount the tracking units in such a
    way that they can be folded down and lower the entire thing into a pit
    in the ground. When warned of an approaching firestorm the owner can
    lower the panels & tracker into that pit and cover the works with a
    few inches of gel. They would, of course, also have to bury the wires.

  8. Gary

    Gary Guest

    Hi again, again,

    Here is a thought on a simple protection system:

    1) Install a drip tube along the top of the PV panels that allows you to
    run water over the panel surface at a low rate (e.g. 2 or 3 gpm).

    2) Cover the panels with something like the "Fire Foil" mentioned in the
    link above -- i.e. a material that reflects most of the heat away.
    Space the foil off the panels by a half inch or so to provide a path for
    the water, and some insulating space.

    If you assume that the fire radiates like a 1500F(?) object, and the
    emisivity of the Fire Foil type material is about 0.05, and the panel
    area is about 100ft^2 (both sides) then the heat transfer to the through
    the Fire Foil is about:

    Q = 0.173 * 0.05 * 100ft^2( ((1500+460 degR)/100)^4 -
    ((100+460 degR)/100)^4)

    Q = 127000 BTU/hr

    If your supply water is 60F, and you want to keep the average
    temperature under the shield to 160F, you would need a flow rate of:

    Q = 127k BTU/hr = (GPM*60 * 8.3 lb/gal) (160F - 60F)(1 BTU/lb-F)

    GPM = 2.5gpm

    At this rate your 1300 gals would last 8.6 hrs. If the pump could be
    triggered by a sensor that would detect the onset of fire, it seems like
    this might be enough?

    The basic scheme is that the reflective barrier keeps 95% of the heat
    from reaching the panels, and the high specific heat of the water allows
    it to absorb the heat that does get through.

  9. Gary

    Gary Guest

    Gary wrote:

    On last thought is that the water exiting the cooling system could be
    sprayed around the PV panel area to lessen the chance of fire directly
    contacting the PV system??
  10. This is all great stuff!
    I'm trying to do my worrying ahead of time.
    The idea of a reflective shell with maybe a gel on some matrix may really be
    a nice concept. Turns out the material used in diapers is the major
    component of several of these products. It sucks up what and forms a
    water-retaining gel. I'm thinking now of making something along this line.
    Might even be able to use already made (but not used :( ) diapers. That
    way it would already be on a plastic matrix. With a fireproof shield on the
    exterior with the gel/plastic material of the diaper on some reinforcement
    (maybe a tarp). Then you could wet the system down from the top, the
    moisture would be retained for several hours, if not days. This could work!
    My future neighbor is the local fire warden, I'll have to see if I can't
    arrange for some beta-testing.
    Hey, great ideas. Again thanks.
  11. Thanks
    Good numbers to have.
  12. Chuck Yerkes

    Chuck Yerkes Guest

    You don't say where, but between global warming and natural cycles
    Colorado is in a deep drought and expected to burn.

    I live in an area of Berkeley that tends to catch fire every 20 years
    or so. We try to stop it.

    So yeah, talk to the fire people. They're usually delighted to
    talk to folks BEFORE the fires. Better: Organize for them to give
    a presentation to everyone interested in your area.

    The fire here was a firestorm. It generates it's own weather. High
    winds. no oxygen. temperatures exceeding 2000F. Roads melted. Steel
    light poles melted. PV panels will melt.

    Things that people note here: curtains behind (closed) windows would
    ignite from the heat coming through. The goal now for many is to run
    through and strip down windows if a fire is coming (and doing this
    wouldn't trap you there).

    First rule:
    1) get the hell out and don't worry about things like panels.
    Your insurance should cover it.

    - clear brush. be brutal. That's my weekend chore: Whack down a lot
    of what grew this last rainy season.
    - sprinkler systems. If you landscape the area and keep it moist.
    - If you're hardcore, a pool or pond is a benefit to firefighters.
    A friend who's VFD in penna scopes out the area before they arrive.
    A pool next to the house means a lot of water can be pumped onto the
    house. A pond: more water.

    In this area, new houses are required to have sprinklers. It makes a
    differences. Outside sprinklers can be flipped on a soak down fuel.

    But you won't have fuel near your stuff will you?

    50 feet or more of 'down to the ground' around your house mean that
    if/when firefighters get to your house, it's worth making an effort to
    defend. A house with fuel "ladders" - branches and brush under wooden
    porches and balconies, low brush under trees making it easy to jump from
    ground to trees, etc. make the house risky to life to defend.

    Panels? I dunno about the "lower it into a pit" notion, but perhaps
    being able to drop them into vertical would limit what's going to hit
    them. Of the poles are guy wired to concrete anchors or something,
    then you could cut cables and bring them down. but really, you'll
    spend that time loading the vehicle with "must haves" (uninsured stuff
    like pictures and your escape harddrive) and getting the hell out.
  13. Guest

    How about rooftop panels?
    You might cool them for more output power or useful hot water.
    I've practiced with "shake and bake" personal wildfire shelters :)
    That's about 127 pounds of steam per hour, ie 0.25 gpm at 212 F.
    You might mount the panels horizontally, with a reflective wall to the
    north to increase the sunpower and a greenhouse poly film air duct over
    the panels containing 1-2" of water for panel cooling and water and
    space heating. The wall might be metal roofing with reflective Mylar
    film greased to the south side and a Wood's metal link that allows it
    to fall over and cover the panels during a fire, at which time water
    could pond above the duct, with a float valve to keep the pond full and
    an air gap above the pond to allow evaporation...

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