Page 3 of 7 FirstFirst 12345 ... LastLast
Results 21 to 30 of 65

Thread: Portable Emergency Power - Inverter

  1. #21
    Join Date
    May 2017
    Location
    SCV Ca, USA
    Posts
    69
    Quote Originally Posted by GoldDigger View Post
    Such PV systems work best with motor loads far enough below their nominal rating, or with a built in VFD or soft start capability.

    Sent from my XT1585 using Tapatalk
    Not all inverters put out "full sine wave". A lot of those on the market are synthesized square wave.
    Since VFDs are designed to harness the sinosoidal rise and dips of the AC cycle a square wave would be outside the design premise.

  2. #22
    Join Date
    May 2014
    Location
    AZ
    Posts
    2,118
    Quote Originally Posted by myspark View Post
    Not all inverters put out "full sine wave". A lot of those on the market are synthesized square wave.
    Since VFDs are designed to harness the sinosoidal rise and dips of the AC cycle a square wave would be outside the design premise.
    like Samlex pure sine wave inverters, and many others.
    if it were just for some basic tungsten bulbs the cheapy HF inverter would work. anything beyond that the pure sine wave inverters is the only way to go.

    a small Kohler propane gen is what i would be looking at.

    if pv/batts/inverter is the ask, i would seriously think about having a freezer full of ice jugs to keep fridge cold as needed when poco dies, and use inverter to power smaller items.

  3. #23
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
    Posts
    8,569
    Quote Originally Posted by FionaZuppa View Post
    what?
    i worked on US govt contract where we had pv's out in remote fields (off grid remote shelters), during the day the solar panels charged the batts AND ran the electric (+ hvac) during the day, a transfer switch went to batt when pv voltage dropped below a threshold. a propane backup gen was there if batts died down too low. batts and panels powered an array of inverters.

    what do you mean solar panels cannot power a load?
    Solar modules cannot directly power a load (there are exceptions, like agri pumps where one doesn't care when or how fast they run) because they produce a given amount of current relative to their insolation; they cannot deliver current on demand. The operative word in your above statement is "and". Your batteries have to be able to absorb the entire output of the PV or the array will shut down if the loads are calling for less current than the PV output plus what the battery can take. The way these systems are wired is the PV is routed through a charge controller into the batteries and the loads are powered from the batteries.

    The bottom line is that your batteries have to be big enough to absorb the entire output of the PV system and to power the loads on their own. You cannot build a system with a big PV section and a tiny battery and expect it to run sustainably.

    I obviously have not seen any electrical drawings for the systems you are speaking of, but I would be willing to wager that there was no transfer switch in them unless they were also grid tied, and PV output voltage doesn't vary with insolation, current does. PV modules are current sources (not voltage sources) over most of their IV curve; hence my first sentence above. To drive loads and keep voltage constant you need a voltage source, i.e., batteries.
    Last edited by ggunn; 10-05-17 at 12:11 PM.

  4. #24
    Join Date
    May 2014
    Location
    AZ
    Posts
    2,118
    i do not know of any batt bank that simply keeps charging because the pv's want to keep delivering, and if pv's cant deliver the pv's shut down.

    if i have one pv panel rated output 12v 12w, a 12ohm load will max out pv ability, a 24ohm load will just be 6w, the pv provides all the power and does not shut down. i do open ckt on output, pv just sits there @12v with 0A.

    how do large solar farms deliver pv power w/o batts when power demand varies?

    maybe i just not understanding what you mean.

  5. #25
    Join Date
    Mar 2016
    Location
    The Motor City, Michigan USA
    Posts
    520
    Quote Originally Posted by ggunn View Post
    Solar modules cannot directly power a load ...
    Um, no. Depends on the load. Domestic refrigeration might be quite suitable for being directly PV powered; the compressor could run when PV power is available and the refrigerator's thermal insulation could prevent the temperature inside the cabinet from rising too much, too fast.

    Quote Originally Posted by FionaZuppa View Post
    ... how do large solar farms deliver pv power w/o batts when power demand varies? ...
    Grid-connected PV farms deliver however much power they're capable of, and grid operators reduce the output of gas-fired and coal-fired powerplants so that generation & consumption remain in balance.

  6. #26
    Join Date
    May 2014
    Location
    AZ
    Posts
    2,118
    Quote Originally Posted by drcampbell View Post
    Grid-connected PV farms deliver however much power they're capable of, and grid operators reduce the output of gas-fired and coal-fired powerplants so that generation & consumption remain in balance.
    i posed to Q but already knew the answer, it was one of those Q's

  7. #27
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
    Posts
    8,569
    Quote Originally Posted by drcampbell View Post
    Um, no. Depends on the load.
    Um, you edited out where I said that there are exceptions, and the case you cited is not typical.

  8. #28
    Join Date
    May 2011
    Posts
    3,810
    Quote Originally Posted by Sahib View Post
    ggunn: Does the battery set up make it uneconomical?
    How do you put a price on harnessing power from nature after a disaster where the grid may be out for days (or weeks or months) and there may also be a liquid fuels shortage?

  9. #29
    Join Date
    May 2011
    Posts
    3,810
    Quote Originally Posted by FionaZuppa View Post
    what?
    i worked on US govt contract where we had pv's out in remote fields (off grid remote shelters), during the day the solar panels charged the batts AND ran the electric (+ hvac) during the day, a transfer switch went to batt when pv voltage dropped below a threshold. a propane backup gen was there if batts died down too low. batts and panels powered an array of inverters.
    Was this some very early experiment? I have to express some skepticism about the transfer switch. Simply connecting the PV to the batteries through a charge controller in parallel to the load makes a helluva lot more sense. (With such a setup it's also a little useless to discuss if the PV is 'directly' powering loads in any given moment when the sun is shining.)

  10. #30
    Join Date
    May 2014
    Location
    AZ
    Posts
    2,118
    Quote Originally Posted by jaggedben View Post
    Was this some very early experiment? I have to express some skepticism about the transfer switch. Simply connecting the PV to the batteries through a charge controller in parallel to the load makes a helluva lot more sense. (With such a setup it's also a little useless to discuss if the PV is 'directly' powering loads in any given moment when the sun is shining.)
    no, just a few years ago, i did mean to say transfer switch for Kholer gen. the pv's ran everything (hvac too) + charged batts during the day, if at night the batts went too low the Kholer gen kicked on to run things and to charge batts. its more like a backwards UPS system, on batts/pv all the time and if batts/pv went too low the gen kicked on and UPS xfer flipped over. batts/pv were the util side of the UPS, etc. most stuff was 48vdc, hvac was 240ac. if i recall correctly the inverters were on aft side of UPS doing 48vdc to 240ac.
    Last edited by FionaZuppa; 10-05-17 at 04:46 PM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •