Running computer through solar system

cnewmancnewman Registered Users Posts: 1

I am looking to setup a computer at my remote farm that i will be installing solar. 

My question is, if i want to run a desktop computer that uses around 250-300watt @240v during the day (not required at night) what type of battery do i need? If i am satisfied with only using it while their is sun available to power the panels, do i just need to have enough amp hours to cover the times when the panels are not producing enough power, maybe fluctuation or something. Or will the PC pull power directly from the panels?

I am expecting to install around 600 watt of solar panels (2x300w) just for the PC. Which will then connect to an inverter that operates around 90% efficiency (600w). as mentioned, i dont need to operate on battery, just ensure the inverter can function and provide power to the PC while the sun is out. 

thanks for any feedback.


  • EstragonEstragon Registered Users Posts: 3,120 ✭✭✭✭✭
    Generally speaking, small solar charge controllers need a battery, as the panels isn't suitable for powering most loads directly. Among other issues, a passing cloud would cause the inverter to shutdown, taking the PC with it.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. Super Moderators, Administrators Posts: 28,305 admin
    Full off grid solar power system, power is fairly expensive... Something like $1-$2+ per kWH vs the $0.10 to $0.20+ per kWH for much of the US.

    In general, designing your loads to use as little energy as practical is a good place to start. For example, a laptop computer can run in the 8-60 Watt range... And give you a system that consumes much less power and an off grid system that is 1/10th the size.

    A laptop also gives you an integrated UPS (uninterruptable power supply) to boot (can sleep/shut down if batteries are going dead, etc.).

    Say you run the computer 10 hours per day... A quick system design may look like:
    • 300 Watts * 10 hours = 3,000 WH per day (this one load is enough to run a small, very efficient, off grid home)
    • 3,000 WH per day * 1/0;85 AC inverter eff * 2 days of storage * 1/0.50 max battery discharge (longer life) * 1/24 volt battery bank = 588 AH @ 24 volt battery bank
    • 4x 6 volt @ 200 AH * 3 parallel strings ~ 24 volts @ 600 AH using 12x "golf cart" batteries
    • 29.0 volts * 600 AH * 0.10 rate of charge (full time off grid) * 1/0.77 solar panel+controller deratings = 2,260 Watt "nominal" array

    And then there is based on how much sun you get in your location.  Sydney Australia, fixed array:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 56° angle from vertical:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    Based on your loads, and very sunny region of the world(?) 3.9 hours of sun June (use a genset during bad weather to help the solar):
    • 3,000 WH per day * 1/0.52 off grid system eff * 1/3.90 hours of sun (June) = 1,480 Watt array
    So, the suggested array would be around 1,480 Watts to 2,260 Watt array for the above "conservative" system.

    If you used a 30 Watt laptop, the above system would be 1/10th the size.

    I went through the numbers very quickly. We can do this in detail, but I wanted to suggest why a smaller computer (laptop) would possibly be a better solution here. It is almost always less expensive to conserve energy than to generate it.

    To better know your loads, getting a Kill-a-Watt type meter to measure your true energy usage can help better size your off grid solar power system to your needs (link below is just an example--I know nothing about this product):


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