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Inverter Q

Discussion in 'Photovoltaics' started by Chuck Yerkes, Apr 23, 2004.

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  1. Chuck Yerkes

    Chuck Yerkes Guest

    I'm looking at putting in 3kW or so panels up on a grid tied roof.
    calif (rebates and all that).

    Quick background:
    PG&E being who they are, they assure us that the problem transformer
    will be fixed this time for sure; but in the meantime, we've had
    multihour blackouts every 6-7 weeks.

    Now, on the other hand, as a new englander, a blackout in California
    means being trapped with no heat and temps plunging into the 50s.
    Just don't open the freezer much.

    ok, the dilemma:
    If I lose grid, I have no power. 16 panels over my head being
    REALLY efficient, but no power.

    Were I to not use the debated SMA2500 or Sharp 3500 (room to add
    5 more panels), I'd have to go with a xantrex or another Inverter
    that speaks battery.

    Unfortunately, from my perusing:
    grid tie only -> run panels in series at ~300VDC
    = small wires = ~93% efficiency

    grid + batteries -> 48VDC run is > 50A is FAT wires.
    And a claimed 80% efficiency (by reputable solar contractor).

    Now, I'd HOPED that it was not unfeasable to run a couple strings at
    high voltage to the inverter and perhaps have a tap off that that can
    charges batteries at 12/24/48VDC and running from batteries during
    an outage.

    Has this not been figured out?

    Odds are high that I'll end up with a backup-less grid system, but I
    know I'll feel like an idiot sitting with bright sun, 3kW over my head
    and a freezer full of spoiling food.

    Battery PLACEMENT isn't an issue (I can easily put a forklift battery
    in a well ventilated place near the power input. I can also easily do
    the same with a generator.

    (eh, maybe I just fine a 20 ton mill stone and make a fly wheel :)
    - it'll keep the house stable in a quake (or make all my downhill
    neighbors hate me a WHOLE LOT )
  2. Steve Spence

    Steve Spence Guest

    Use the grid to keep a large UPS charged. Big enough to get you through the
    multi-hour blackouts. Only power critical systems.

    Steve Spence
    Renewable energy and sustainable living
    Discuss vegetable oil and biodiesel
    powered diesels at
  3. SpiderG

    SpiderG Guest

    You might look at Beacon Power's unit.
    Smart Power M5 is a 5kW grid tied unit, that does battery backup also. I
    just got a flyer in the mail about it - says its UL listed & CA state
    approved too.


  4. Chuck Yerkes

    Chuck Yerkes Guest

    Well, not sure how this really varies from the Xantrex 4048...
    It wants 48-100VDC inputs. Which means dropping 62AMPs @ 48V
    from 16 panels. Which means "fat wires" (where 3000Kw run in
    strings of 6 (48VDC) would be 288VDC @ 4Amps (a halogen light will draw
    4 amps). 3 of these strings would be 12Amps which is less than the
    wire going to your electric sockets (14gauge, usually).

    Otoh, beacon has flywheels!

    CA listing *is* important....
  5. Chuck Yerkes

    Chuck Yerkes Guest

    well, the house is microsoft free (macs and unix), but the actual losses
    would be over 10%.
    Right, but then you have to RUN said wires. And mount the conduit
    holding said wire to the house. Which has a lower aesthetic value and
    then *that* must be dealt with. And costs mount.

    Low voltage will require 6 awg at the least, high voltage would require
    (very common) 14 awg min.

    Power losses, plus running very large wires and hence large
    conduit plus things to mitigate the large conduit. Then lower
    efficiency for the system as a whole which gets us to "add 3-4
    more panels to deal with a LowV battery system to get to the same
    place. Which buys a generator.

  6. Get a new freezer with good insulation. Much simpler. Will also help to
    reduce your energy consumption when there aren't any blackouts.

    excerpt from the webpage:
    USDA also states that ordinarily, a half-full freezer can maintain
    freezing power for roughly 1 day after losing power. A fully stocked
    freezer will keep food frozen for 2 days. Meat or poultry that still
    contains ice crystals may safely be refrozen. For meat and poultry
    products that have been kept in a refrigerator section, though, or have
    only managed to stay "cool-feeling," cooking is a better option. After
    you cook these items, you can refreeze them. Throw out any product that
    has even a slightly unusual color or odor.


    Chuck Yerkes a écrit :
  7. Chuck Yerkes

    Chuck Yerkes Guest

    Well, on the plus side, I'm mainly vegetarian (I eat some fish just
    cause I hate thems fishes and know they are plotting to evolve and take
    over. Unless we keep eating ;).

    And I *have* tossed a down comforter over a fridge before for this
    reason. But the icecream... and no power for a blender.

    Good to remember those stats though. I used to keep milk bottles of
    water in the fridge and freezer when it was largely empty just to keep
    it cool (air cools quicker on an open/close than water, once cooled).

    if it turns out that I really want this, I'd believe that putting up an
    additional couple panels to feed into a small xantrex or outback and
    feed some batteries... Or I'll get a gennie. It would be about 2M from
    where the power enters, so trivial to put 240VAC plug there for it to
    come in.
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