System design for sheds where grid is secondary power source

stoneunhenged
stoneunhenged Solar Expert Posts: 39 ✭
in General Solar Power Topics #1
I have two farm sheds that get occasional light use and want to power them off grid. I currently have 24 175 watt panels that I am mounting on the roofs of the sheds. Grid power is available on site, but I want to primarily run the sheds on solar. I do not want to tie the solar power system to the grid, mostly because my local grid power company requires a $100,000 insurance policy to make the connection. My plan is to build an off grid system that begins with the 24 panels, later add enough panels to about double the output, have a battery bank, and have a Generac Ecogen to pump up the batteries as needed. The off grid system will be using an inverter to power loads at standard AC voltage. But, I would like to have the option of manually switching to grid energy to power the sheds in the event the off grid system fails.

My question is how to best configure this system? I'm open to buying whatever inverters, manual switches, etc., would most reliably operate the system.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #2
    Re: System design for sheds where grid is secondary power source

    The first place to start is get an idea of the loads you need to run. Do you need 240 VAC? Where are you located? DO you have a local battery supplier?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: System design for sheds where grid is secondary power source

    "Grid power is available on site". Where? At another building? How far away from these sheds?

    If it is at all possible, running a branch circuit from an existing grid service will be cheaper and more reliable than an off-grid system. All you need is a circuit breaker and enough wire to reach the other building(s). The power company has no say in what you do on your side of the electric meter.

    Otherwise what solar_dave said: you need to know how much power is required before you can plan an off-grid system. Otherwise you will be guessing at everything and likely either spend too much or not have enough power.

    Also, unless you already have that Generac don't buy it: read the posts around here and the reviews of them are not very favourable.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: System design for sheds where grid is secondary power source

    For my utility, they required insurance, and our standard homeowner's insurance was just fine. Other than the original application, they have never contacted us again (except for the normal bills).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Organic Farmer
    Organic Farmer Solar Expert Posts: 128 ✭✭
    #5
    Re: System design for sheds where grid is secondary power source
    Cariboocoot wrote: »
    "Grid power is available on site". Where? At another building? How far away from these sheds?

    If it is at all possible, running a branch circuit from an existing grid service will be cheaper and more reliable than an off-grid system. ... .

    I agree that grid-power is generally cheaper than off-grid power.

    To say 'more reliable' though requires stipulations. Is this urban? or rural? How often is the gird down?

    If the grid normally goes down more than twice a month, then I would suspect that off-grid power is far more reliable than grid power.

    We had lose of grid power yesterday for an hour. We were without power for the 23rd and the 24th. In November, we lost grid power once for a week, and two other times for half-days. Then we can look at October, etc.

    When anyone speaks of grid power being reliable, I must say that I can not imagine an off-grid system less reliable than the grid is.
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