Need HELP!! New system. I don't know how much power?? KW??



  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Need HELP!! New system. I don't know how much power?? KW??
    BB. wrote: »
    Even if you hire somebody--It still does not hurt to understand how everything works so you can make sure that consultant/installer is doing things right.

    Are you familiar with an automotive electrical system (battery, alternator, loads, regulator, etc.)...

    An off grid system is very similar. The battery is the "heart" of the power system. The alternator is the charging source and works fairly similar to solar panels. When the engine is running/sun is up, the current flows to the battery to recharge it. When you have loads, they draw energy from the battery and the alternator/charge controller as needed.

    The off grid inverter--Is just another load on the battery bank which "inverts" lower voltage DC power to higher voltage AC power (some inverters also have charging capabilities from attached gensets or even grid power--sort of like a UPS, uninterruptable power supply for a computer).

    A grid tied inverter + solar panels--For all the world is very much like an AC Battery system. In this case, the "Grid" (utility power) is the "AC Battery" and your loads are supplied from the grid... While the GT inverter "recharges" the AC Grid (there is a fundamental difference between a GT and and OG inverter if you want to get into that discussion. An OG inverter can never be connected directly to the AC grid without risk of fire or worse. And a GT inverter will not run appliances like an off grid inverter if the grid is down).

    Because you only have "useful" solar power for 6-8 hours per day, the solar array has to be larger than your average loads so that it can recharge your battery banks during the day, and the battery supplies power when the sun is down (same thing for Grid Power--panels "turn the meter backwards" when the sun is up, and your loads turn the meter forward otherwise).


    What he said.

    Another big difference between off grid and grid tied systems is the amount of design work that has to be done. A grid tied system is pretty simple; you choose an inverter and load it up appropriately with modules (most inverter manufacturers have string sizing calculators available to help you do that), coordinate with your utility for interconnection, and that's pretty much it. There are differences between utilities in the way that they handle excess production, and you use that to find the point of diminishing returns on system size, but the math is pretty simple.

    An off grid system is a different kettle of fish. If you want to be truly self-sufficient, there are many more factors you must take into account, there are many more components to the system, and it costs a LOT more. Designing a big off grid system is a daunting task for anyone, even those with a lot of solar experience.

    Many folks new to solar, when asked what they hope to accomplish by adding PV to their home, will answer, "I want to get off the grid," but when they start to comprehend what that actually means and what it takes to do it, virtually all of them change their mind. A system to run a large house completely off grid can easily cost a quarter of a million dollars or more.
  • mike95490mike95490 Solar Expert Posts: 8,967 ✭✭✭✭✭
    Re: Need HELP!! New system. I don't know how much power?? KW??
    LemonChips wrote: »
    .... last month I pulled about 3100KW! I figure if I'm going to pay a large bill I'd rather put it into this so I won't pay that for ever. .....

    You have not seen a large bill yet !

    put some prices to the components in my equipment list below. I'm about even with the $70K the electric company wanted for poles. (counting the 2 buildings battery shed, generator shed, replacement batteries.....)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

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