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On Grid and Off Grid Solar

  1. May 22, 2016 #1
    For an economical PV system, with zero-feed in tariff, for a family home, with no one at home during the day time, the best setup option would be:
    (some components might be in another)

    1) PV, batteries, charge controller, inverter
    2) PV, MPP tracker, batteries, charge controller, inverter
    3) PV, MPP tracker, batteries, charge controller, inverter, generator
    4) PV, MPP tracker, charge controller, inverter
    5) PV, MPP tracker, inverter, generator

    I think the components being in another would be the MPP tracker being in the inverter. The system has zero-feed in tariff, but it's tied to the grid.

    These were the 5 options I was given. I would use PV, MPP tracker, inverter and generator.
    If the system is tied to the grid anything with batteries seems like a waste. That leaves only option 4) and 5). Option 4) has a charge controller, which is used to limit the amount of current flowing into and out of a battery, and there is no battery in Option 4), so I wouldn't choose that one either.
     
  2. jcsd
  3. May 22, 2016 #2

    Merlin3189

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    I'm not sure what a zero-feed tariff is, but if it means you don't get paid for electricity fed into the grid, why would you do it?
    Surely it would be better to use it to drive permanent loads like fridges, air conditioners and heating, then save any balance until you come home. In which case, wouldn't you need the battery?
     
  4. May 22, 2016 #3
    I assumed zero-feed in tarrif means the energy company isn't buying back the electricity you generate.

    I guess that during the day all this electricity is going to waste. So I agree -- I think it would be better to have batteries. In that case you would need a charge controller as well, so option 1) 2) and 3) sound better.

    I guess what it comes down to now is if a generator is needed, and if the MPP tracker is in the inverter.
     
  5. May 22, 2016 #4

    Merlin3189

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    I assumed when they put MPP tracker and inverter, they mean to have both functions, whether they are in the same unit or separate, but if they say only inverter, they mean an inverter with no MPP tracker. Inverter seems to be assumed in all options, so it's just a question of whether you want the MPP tracker function or not.
    What is the purpose of the generator?
     
  6. May 22, 2016 #5
    The generator is used if there is power loss (PV stops working). But if you are tied to the grid then the grid acts as the generator I guess, so the generator isn't needed. So only Option 1) and 2) looked like the best ones.

    There was a supplementary note in the question that said "Some components might be inside one product"

    Solar inverters use MPP tracking to get maximum power of the PV system, so I would say Option 1) is the best answer.
     
  7. May 22, 2016 #6

    Merlin3189

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    You say MPP tracking gets the max power from the PV, but you choose an option without it? Is that to save cost?

    BTW are you sure that MPP tracking is part of the inverter?
     
  8. May 22, 2016 #7

    jim mcnamara

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    I think the reasons for some choices vary with climate, insolation, and your base system requirements.

    For example, if you live in the Southwest and turned off power all day long: with no cooling temperatures in the house could become close to unbearable, same problem with a heat pump in Maine or Northern Michigan and pipes or well heads freezing.

    Factor in appliances. Then there is really no complete "down time" for electric consumption in a modern house.

    In other words, you may believe your peak consumption is when everyone is home with lights on. Maybe. Consider: Generally there are winter peak consumption hours tied to ambient conditions, same is true for summer. They may not coincide.
     
  9. May 22, 2016 #8
    I choose an option without MPP tracking because the question said some components may be inside another.

    I find the question's answers rather obtuse. Both Option 1) and 2) are correct, but solar inverters use MPP tracking, so Option 1) is MORE correct.
     
  10. May 22, 2016 #9

    Merlin3189

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    Well, I doubted that (that the MPP tracker is normally included in the inverter rather than another component.) But if you are saying you are going to use MPP tracking which you think is part of the inverter, then I think you should choose an option where MPP tracking is included. For me, an option where it says inverter but does not say MPP, would mean it was not using MPP tracking at all. There are plenty of inverters that certainly do not include MPP. But it's your question.
    Perhaps it would help to think about the chain of processes and where each component fits in?

    I agree with Jim's point, which is why I listed AC and CH (though I'd not thought specifically about heat pumps.) But, either you generate excess power at some part of some days, or you don't. If you never generate excess power, fair enough you'll never want a battery, but the question becomes a bit limited on that assumption - 1 to 4 all have batteries. If you may sometimes have excess power, then you need to decide what to do with it and how.
     
  11. May 22, 2016 #10
    This source says solar inverters use MPP tracking: https://en.wikipedia.org/wiki/Solar_inverter#Maximum_power_point_tracking

    There is excess power in the day not being consumed, so using a battery would be a better option. A generator doesn't seem like a good option though because you are tied to the grid. The grid can work as the generator if the PV isn't working.
     
  12. May 22, 2016 #11

    anorlunda

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    I think it is really hard to answer the OP question without defining what you mean by economic.

    IMO, your list has a glaring omission -- energy conservation. Besides writing checks for more equipment, are you willing to cut your energy consumption via life style choices? Could you halve the number of square feet needed for housing? Could you relocate to a place with lower climate control demands, or could you simply live with broader extremes of temperature?

    Forgive me for being negative, but I see too many fellow Americans saying, "I want to be more green. Just tell me how big a check to write to whom." That approach is fundamentally flawed.
     
  13. May 22, 2016 #12
    Let's go with 'economic = being the most cost effective.'
     
  14. May 22, 2016 #13

    Merlin3189

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    As I say, it's your choice. If I wanted to use an MPP function, I'd choose an answer which included MPP. They all use inverters, so why specify MPP in 4 of them and not in the other? I think they are giving the list of functions, not a list of boxes. For a commercial system it is likely that all electronic processing is in one unit.
     
  15. May 22, 2016 #14

    anorlunda

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    In that case, the answer should be to cut your energy consumption. That's far more economic than those other options.
     
  16. May 22, 2016 #15
    Of these 5 options:

    1) PV, batteries, charge controller, inverter
    2) PV, MPP tracker, batteries, charge controller, inverter
    3) PV, MPP tracker, batteries, charge controller, inverter, generator
    4) PV, MPP tracker, charge controller, inverter
    5) PV, MPP tracker, inverter, generator

    1 or 2 is the most cost effective, no?
     
  17. May 22, 2016 #16

    mheslep

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    With no subsidy?

    6) on grid: grid only
    off grid: generator only
     
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