12v dc vs 220v ac usage from PV

TaslimTaslim Registered Users Posts: 9 ✭✭

What would be the better to load to consume from dc 12v directly and 220v ac using inveter from PV power.Which thing will be economical if we dont have dc supporting appliances??


  • BB.BB. Super Moderators, Administrators Posts: 28,768 admin

    In the old days, AC appliances where pretty wasteful of energy. I have a (very nice for me) 30 year old stereo radio/tape player that takes 20 Watts off and 40 Watts just turned on (no music playing). It was a modern transistor based system--Just hugely wasteful.

    Today, My 50 inch TV takes less than 1 watt of energy while on standby (the Kill-a-Watt meter actually reads 0 Watts). And, it seems, that many AC appliances use almost the same amount of energy as their DC counterparts these days (assuming you can find a DC appliance).

    The best thing to do... Research how much energy your solar powered appliances will take... For example, there are lots of "kill-a-Watt" type energy meters these days--Get one that will work in Pakistan:


    And there are DC Amp*Hour/Watt*Hour meters too:


    In general, it is almost always cheaper to conserve energy (very energy efficient loads, turn off devices when not in use, pick a laptop computer vs a desktop computer, etc.) that to generate electricity.

    The "losses" of using 230 VAC power of ~1/0.85 inverter eff = 1.18 ... You just need to add 1.18x more battery and solar panels to your system to make up for the AC inverter losses... Not that much extra.

    And, you also need to look at your DC loads... It is generally quite difficult to take 12 VDC and send more than a few amperes more than a few meters away (need heavy/expensive copper cable to send low voltage DC power any large distance). (10a * 12v = 120 watts a few meters)

    Whereas, with 230 VAC power, you can send 10 amps (10a * 230 VAC = 2,300 Watts) 30+ meters very easily and cheaply with standard house wiring/AC extension cord.

    You really need to define and measure/estimate your energy needs, and design a system to support them. If your loads are charging a cell phone and tablet computer, then a small 12 VDC only system may be the answer.

    If you are running a home with refrigerator, lighting, computer, TV, water pump, etc.... Then a 230 VAC power system+inverter is probably the better solution.

    And regarding battery bank voltage... Typically, smaller systems are probably 12 VDC--But if you want to run a refrigerator+stuff, you are now in the 24 volt battery range (and 24 VDC appliances are less common, and tend to be more expensive marine or long haul truck appliances). And if you have a large system, you are looking at a 48 VDC battery bus (not many native 48 VDC appliances out there).

    It makes more sense to start with your loads and design a system to support them--Vs just trying to design a system with no idea of what your loads are (back pack and bicycle vs small car, vs light truck, vs an 80 ton lorry--They all carry things economically, for their designed use).


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TaslimTaslim Registered Users Posts: 9 ✭✭

    Thanks for your opinion. So helpful

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