grid tie reccomendations are above 12 volts-why

I have consistantly noticed now that most diction/nonmeclature referencening grid tie systems is exclusive of 12 volts how come? All I hear about otherwise is power=voltsx amps so what difference does it make? accept maybee in battery charging ratios? which 24 volt is not reccomended for.
Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
2.3kW [10] Enecsys SMI-240-60 micro inverters

Comments

  • solar_davesolar_dave Solar Expert Posts: 2,392 ✭✭✭✭
    Re: grid tie reccomendations are above 12 volts-why

    It makes a,difference in the amount of amperage the devices need to handle. Higher voltage allows for lower amperage wiring and devices. Just think of how high the amps would be for 6000 watts at 12 volts vs 300 volts.
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: grid tie reccomendations are above 12 volts-why

    Grid tie systems are usually wired with panels in series to around 300 volts. The reason is that grid tie controllers are MPPT and down convert the panel voltage to supply 240 volts AC to the grid. To work efficiently the panels need to supply voltage somewhat above the 240 AC output.
  • ThomasThomas Solar Expert Posts: 291
    Re: grid tie reccomendations are above 12 volts-why

    I go ur stupid at the poer eq. so, volts kindof compliment amps as rise to a threshold of equivelant volts to the grid. Does it make sense that the inverter works less, converting amps- to watts at a highr voltage closer to the grid? I was essentially right though! It did have something to do with numerical voltage disparity.$$$ Is there any info on the pros/cons of 24,48 volt systems vs. 12v? What happened to 36v?
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

  • BB.BB. Super Moderators, Administrators Posts: 32,740 admin
    Re: grid tie reccomendations are above 12 volts-why

    Power = Voltage * Current

    So, power can be 120 volts * 1 amp or 12 volts * 10 amps -- They both equal 120 Watts.

    However, for wiring, transformers and such--they mostly are affected by current. When you cut the current by 1/2, you cut the area required by the wiring by 1/2 (~3 AWG smaller wire size) and you cut the size of the transformer iron, etc.

    On the other side, as you increase voltage, you need better insulation and the very small dimensions in transistors/electronics make for very high voltage/inch numbers. In fact, for high power/voltage transistors, the older semiconductor processes from 20+ years ago are actually better than the new processes that use smaller dimensions/insulation thickness, etc. (makes it easier for excessive/high voltages to "punch through" semiconductor insulation).

    36 volts was more used in marine industry (boats). Also, I think I have seen golf carts and possibly other electric vehicles use 36 volts even today.

    32 volts was actually (as far as I can tell) very popular for farms/pre-Rural Electrification programs (and old rail road passenger cars too). There was a whole bunch of 8 volt batteries, 32 volt tools and appliances (even toasters) that were powered by generators and wind turbines.

    But today... Notice that we use 6/12/24/48 volts as our basic building blocks. Each is 2x higher than the lower voltage before it. Frankly, 36 volts is only a 1/2 step change (but still somewhat popular in golf carts--I believe). Note that building higher voltage transistor switches is more expensive and less popular/volume than the lower voltage products.

    This thread has some historical information and pictures in it:

    Why are standard battery bank voltages so low?


    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ThomasThomas Solar Expert Posts: 291
    Re: grid tie reccomendations are above 12 volts-why

    Bill-thanks for the history link, it answered my question about what happened to 32 volt, I guess one could call 12 volt 19 volt.....;)

    Another question....
    what is about this 140VDC limitation? I have been tring to figure out why Xantrex makes the C-40 input voltage so highly flexible for the batteries it charges. The only difference is it accomodates for larger number of series 48v panels, right?
    also, what is this relationship of whole rated vdc in cold and 1/2 rated vdc in hot? does current remain constant or vary w the volts/weather also?
    I have been using paralell 12v as the medically accepted health limitation. whereas the medical health limitatin is tight[as I expected] it is not that limited to paralel12v,
    safety limits I have gatered are 32-48v paralel threshhold and a series threshold of 60-62 volts. right?;)
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

  • BB.BB. Super Moderators, Administrators Posts: 32,740 admin
    Re: grid tie reccomendations are above 12 volts-why

    The general 140-150 limitation on most MPPT charge controller is the voltage rating of input electronics.

    Why does the C40 PWM controller have such a high voltage rating when the maximum "nomimal"/"Useful" input voltage is around 80-90VDC... Probably because they had a choice of 80 volt or 140 volt components and just chose the next higher voltage rating (may have even been cheaper for higher volume/higher voltage components).

    In any case, a C40 type PWM charger should follow the normal PWM controller rules for best efficiency. roughly 17.5/12; 35/24; 70/48 Vmp/Vatt ratios.

    Yes, you could run a Vmp of ~100 volts on the C40 with a 12 to 48 volt battery bank, but you will still lose lots of power due to the mismatch of Vmp to Vbatt-charging.

    Nothing is "for free".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ThomasThomas Solar Expert Posts: 291
    Re: grid tie reccomendations are above 12 volts-why

    Yeah nothing is for free, but there has to be a way to CHARGE batteries , I am lost for the anogulous metaphores of putting your thumb over a water hose..or just let it fill the bucket at city pressure?huh...later
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

  • BB.BB. Super Moderators, Administrators Posts: 32,740 admin
    Re: grid tie reccomendations are above 12 volts-why

    Actually, that is not a bad analogy... Have a hose with the water valve cracked open--flows 2 gpm onto the ground with almost no force. (all flow, no pressure)

    Put your thumb over the hose, it still flows at 2 gallons per minute but will shoot 10' through the air--more "energy" drawn from the faucet/flow. (optimum flow * optimum pressure = maximum energy available from the faucet/hose system).

    Keep clamping down more on the end of the hose, the water flow decreases and the total amount of energy drops as the flow drops to zero (no flow, no energy).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ThomasThomas Solar Expert Posts: 291
    Re: grid tie reccomendations are above 12 volts-why

    OK so then the crack is the maximum that can be managed by the thumb.
    It must be a misperception that the bucket fills up faster... im confused.
    applications w bucket filling, ground saturation, or what?
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

  • BB.BB. Super Moderators, Administrators Posts: 32,740 admin
    Re: grid tie reccomendations are above 12 volts-why

    The bucket fill almost the same speed if your thumb is there or not (say you have 100 psi water, and your thumb can only block 20-40 PSI worth of pressure, without using a real valve/nozzle).

    Anyway--Look at the equation for power again:

    Power = Voltage (aka pressure) * Current (aka water flow)

    Depending on the energy/water source, V and C may change with back pressure--The MPPT controller just finds the "optimum" point where restricting water flow brings the pressure up. Past some point, you restrict so much water flow, the power curve falls again.

    If Volts/pressure goes to zero (open hose), there is no power developed.

    If the current/water flow goes to zero (blocked hose), there is no power developed either.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ThomasThomas Solar Expert Posts: 291
    Re: grid tie reccomendations are above 12 volts-why

    So a mppt inverter just does this from another end of it, and would need some high tech communication linking sikronization to function properly.$$$$$
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: grid tie reccomendations are above 12 volts-why

    Think of MPPT like a transmission/torque converter in a car with a finely tuned engine that produces peak power in a specific RPM range. Like a transmission MPPT allows you to have the engine (solar panels) revving at the peak point of power and efficiency while the wheels (electrical load) turn much slower but with multiplied torque (current).

    Pushing the analogy a bit would make PWM like a simple go-cart clutch and

    Voltage as RPM.

    What's the best way to generate the most power in the smallest package? Huge cylinders spinning slowly (12 volts) or smaller cylinders (48+ volts) spinning much faster.
    http://en.wikipedia.org/wiki/Formula_One_engines
  • ThomasThomas Solar Expert Posts: 291
    Re: grid tie reccomendations are above 12 volts-why

    My grid tie inverter has a mpptracking function, this does effect the whole line right? And I presume that it has one because it needs it, do I need another one to controll the volt/amp swings or is is controlled as much as it can be allready by the mpptracking ? I do not intend any other load than the inverter sofarsogood.
    I was told that 2 mppt functions were not a good thing.
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

  • solar_davesolar_dave Solar Expert Posts: 2,392 ✭✭✭✭
    Re: grid tie reccomendations are above 12 volts-why

    It is still amazing to me that those power jack inverters still advertise wall outlet plug in even with a 3500 watt inverter.
    http://www.ebay.com/itm/3500watts-grid-tie-power-inverter-14v-28vdc-240vac-50Hz-/120771280689?pt=AU_Solar&hash=item1c1e877f31#ht_2346wt_702
  • solarvicsolarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: grid tie reccomendations are above 12 volts-why

    Solar Dave. Did you also notice that inverter also is 50 cycle. This kind of junk these people are selling is illegal to use and we here at the forum keep having to tell new solar users they are illegal to use in USA. Just because they sell it on Ebay doesn,t make it ok to use. :Dsolarvic:D
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: grid tie reccomendations are above 12 volts-why

    solarvic is quite correct that they are illegal here in the u s a and that can't be said enough.

    on a sidenote, i do get a kick out of the translations sometimes.
    like this one says,
    [FONT=????]4. with big mos-fet inside, to make sure with long time use, keep the high effiency, make sure the mos-fet will not burned.[/FONT]
    one big mosfet instead of a bunch of little ones is something i was looking for, not.[FONT=????][/FONT]:p
  • ThomasThomas Solar Expert Posts: 291
    Re: grid tie reccomendations are above 12 volts-why

    I forgat about this wall of couneurmireism/capitalism..now I gotta go take a shower, darnnitall,and wash my readers out w/some clear-eyes, or something. My grid tie inverter Got all its shots, I checked it out. I think that the wall plug-in is that legality that Washingtron DC puts our new entrepreneurial neighbors thru enabling some people that may actually appreciate surfing with Norman Mailer. I changed the output of my unit to 8AWG terminal block... I gotta move it soon so..I am bringing it and my Batteries inside w/ the rest of the set up AGMs. I think that is why I am getting 21+ amps out of 240 watts at 12.5 batt volt. I comply with jingoists and their -isms:blush:
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

  • solar_davesolar_dave Solar Expert Posts: 2,392 ✭✭✭✭
    Re: grid tie reccomendations are above 12 volts-why

    Thomas we just wish to point out to DIY types that much of the hardware out there is inferior quality and not UL approved. Any grid tie needs to be sanctioned by the local utility and building codes. For home owners insurance coverage it is imperative that code and NEC is followed and utility is safe from midnight installs to their grid. This is not saying you should not DIY, it is your right to do so but all safety and code considerations apply. If yours is a guerilla install you may actually be paying for your excess generation if the wrong kind of meter is installed. If the utility finds out they may disconnect you and force the proper installation practices.

    This is only an FYI and not an attack upon you or any DIY types.

    Oh I forgot some of the codes in force are to protect fire fighters in the event of a fire, for proper disconnects, labeling and roof space considerations.
  • ThomasThomas Solar Expert Posts: 291
    Re: grid tie reccomendations are above 12 volts-why

    Interesting ordinance, roofspace for fire fighters, I was once good at milpers/milspec...anyway
    as far as guerilla midnight install, it has been slowly adjusted and corrected from such with all the breakers/fused extinguishers, sizing etc, it really has been interesting in -deed. also frustrating and expensive. I see my meter reader and know he knows I got something goin on with those panels....???!!!We exchange cordialities. My bill has been lower, maybee due to changing seasons. I did read somewhere abpout a 3 phase brittisdh meter double counting Grid tie attachment....
    OBVIOUSLY a safety issue, I really didn't really see why they are such an issue, I was unfamiliar to a disabled point when I bought it, I kept it outside....It doesn't really seem to run too hot by my observations, got warm a few times, and during the winter the fan doesn't come on at all sometimes.
    Always troubleshoot with adequate sunlight.  Hi Ho Hi Ho
    2.3kW [10] Enecsys SMI-240-60 micro inverters

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