AC PV Panels:

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Anyone have good info on AC PV panels? For a big system, does it make sense to use these over an inverter?

The water purification system we are looking at now comes in:

1 phase 220 - 240V
3 phase 220 - 240V
3 phase 380 - 400V

Which power supply is recommendable when dealing with RE?


Simon

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: AC PV Panels:

    Simon,

    Do you have a link for an AC Solar PV panel?

    I believe I read about one "AC Solar" system that was a combination of panels with, effectively, each having a form of Grid Tied inverter that could be wired together in a grid (say a small village). However, I believe that there was also the requirement for a battery/inverter module to absorb deliver power as needed (IIRC, there was also communications among all of the modules to control the "Grid").

    But, basically, a Solar PV panel is a DC device. Of course, a DC to AC inverter can be designed to take the power from one panel or a hundred panels and create something that looks like AC Grid power.

    However, without a storage or alternative energy source, the power available from an AC Solar Grid (without batteries or generator), is going to be subject to the amount of sun available. Most standard electric appliances don't like brownout and short interruptions (think refrigeration compressor--as voltage drops, current rises, motor eventually overheats... Drop power for 1 second, motor stops, power comes back, motor is stalled because of back pressure in condenser--thermal switch opens for five minutes, motor cools, pressures equalize, motor restarts).

    Unless you have a load that can deal with variable input power (whether AC or DC), I cannot think of a usable system that would work well with a "AC Solar Panel".

    However, if you have a system that can take variable input power (either AC input with a communications channel that gives the amount of instantaneous power available--or tracks the panel power via MPPT and current available like some MPPT chargers and inverters) and change the speed of the pumps/etc. (and therefore the load), you could design a battery-less system (maybe that is how that RO water cube system is designed--but I kind of doubt it--adding batteries makes things so much easier).

    There are large Wind Power and Solar Powered systems that can give you 3 phase power--but those are probably just a larger version of Grid-Tied Inverters.

    And, I am sure that you could find the 3 phase UPS around to produce power--but that gets you back into the whole Battery/Generator/Inverter thing again.

    Choosing 12 VDC, 48 VDC, 240 VAC, 3 phase 377 VAC, etc., is all just a matter of how much power you need and the most cost effective method to design the equipment consuming the power. Generally, 240 VAC and higher, and 3 phase systems assume a lot of power (and/or long distance power transmission)... So, typically, the higher the voltage and the more phases, the more power that you are assuming to be using--And to generate that power is going to take Capital (money), fuel (if using a generator), and maintenance (parts, consumables, wear, etc.)--the bigger it is, the more money needed.

    RO is a brute force type of application. The saltier the water you want to process, the more pressure to purify (more power). The more volume you want, the bigger the pumps/longer it needs to run (more power). Want lots of salty water purified (more power^2).

    From my two cents... The type of power you need is a combination of the source and the load. In your case, the load has defined inputs and you will need to match those with whatever power source(s) you have available. There maybe some conversions required--and those conversions will produce additional losses and costs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
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    Re: AC PV Panels:
    szimmer wrote:
    Anyone have good info on AC PV panels? For a big system, does it make sense to use these over an inverter?

    The water purification system we are looking at now comes in:

    1 phase 220 - 240V
    3 phase 220 - 240V
    3 phase 380 - 400V

    Which power supply is recommendable when dealing with RE?
    Simon


    :-o :-o I can only hope you have a lot of money available.

  • System2
    System2 Posts: 6,290 admin
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    Re: AC PV Panels:

    Hi Bill!

    I just remember hearing about AC panels like the ones here:

    http://www.exeltech.com/ex_root/ex_products/ex_inverters/ex_pvac/ex_pvac_modules.htm

    I was just curious to see if these are commonly used and if it could possibly work for our situation. Basically I am checking all our options and learning at the same time. :-)

    Thanks for the info.

    Simon
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: AC PV Panels:

    technically there isn't any such thing as an ac panel, but they are coining ac module as the terminology for a dc pv to feed a builtin inverter on the pv that can feed the grid!!!!! :-o this may be ok for a small 1 or 2 module system, but i doubt it is very cost effective for more.
    update: i could be wrong on the cost effectiveness and i am inquiring with exeltech on these modules as a search on the net yielded a place listing them preliminarily for $200-$250 per module u.s..
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: AC PV Panels:

    Simon,

    Overall, this is the same as any ordinary Grid Tied Inverter system... Instead of on large 3kW Grid Tied inverter with 20 panels... You have 20 panels and twenty 150 Grit Tied Inverters--each inverter attached to its own panel. Instead of DC wiring between panels, you now have AC wiring between panels.

    Sounds like a neat idea--to scale a Grid Tied solar PV system, just add a panel.

    However, there are a lot of down sides too... Basically, costs are higher (20 small power supplies vs 1 large supply). Installing complex electronics out in the sun, heat and weather (thermal cycling and operating at high temps are two items that kill electronics--water seepage is another). If a solar panel goes bad--have to replace panel and inverter? If inverter goes bad, have to replace the panel and inverter? If can be serviced separately--heavier panels, more work to replace failed inverter (now get on roof and pop a panel to get at inverter/wiring). Also, I would be concerned about bringing my AC mains right into the optimum zone for lighting strikes.

    In the end, the assembly is a Grid Tied power system with all of the normal limitations. Only advantage to this would be if you can save costs (short and long term). There is no functional difference (that I can see), in terms of your project's requirements, with this panel/inverter system.

    I tried to find an article that I read a few years ago which used sort of used a modified version of these type of solar panels + inverter + battery/inverter/charger to supply distributed power--however I could find it. That is what I thought you may have been talking about.

    But, in any case, I don't think these will do anything special for your project. You don't need distributed power (village)--you need a single power plant (multi-fuel/sun/wind/etc.) for your single purpose (RO water plant).

    There are lots of interesting project out there (say tracking arrays with Sterling Heat Engines) to generate lots of, hopefully, cost effective power (you probably will still need a battery bank with replacement every 5-7 years). You might even find a company/university partnership to get you the hardware to install--but I would be concerned about a high-tec/high-maintenance installation thousands of miles away from support staff.

    Assuming you are sizing the power plant to operate a specific piece of equipment (RO Water)--sizing the power source to a relatively stable continuous load is relatively straight forward. Get a diesel generator and you can generate 10kW*hours per gallon of fuel. If, however, as an example from other organizations, you are running variable loads (lighting, refrigeration, radios, TV, i.e., average village life)--they have found that efficiencies can drop down to ~1.5kWHrs per gallon of fuel.

    Using battery banks/inverter/charger plus a diesel generator (this one organization was calling it a hybrid system)--got the efficiencies back up to near 10KW*Hour (their loads were 10-20% daytime loads vs Evening/night time loads).

    But, if you have a fixed load/fixed need--adding batteries/inverters/etc. only adds costs and complexities. I would only add those complexities if they solve some other problem (examples: reducing costs, reducing noise).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset