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-   -   I have a house off the grid.. How much power do I need? (https://www.askmehelpdesk.com/showthread.php?t=557021)

  • Feb 22, 2011, 09:25 PM
    dexforget
    I have a house off the grid.. how much power do I need?
    I have a 2k sqft house (NO AC/HEATING, no need)

    Washer and dryer (2 times a day ea.) 500w each.
    52" ceiling fan (high speed) 90watt
    Freezer (new star energy type) Energy Consumption (282 kWh/year)
    Large refrigerator, 440W
    42inch TV (200 watts) Power On
    PC.. 250w always on/mostly
    10 50-100w bulbs that light up my house during the night, in moderation.
    1 115V large water pumps for water flow in my outdoor pond/park (always on)
    100W Stinger Bug zapper which has a solar switch,
    100W microwave,
    1,178W electric stove, that I cook for about 30-1h each day 2-3 times a day
    12v Alarm Clock, that I just don't like.
    2 Cellphone Chargesr (always plugged in - newer phones)


    I know it's a big project and will take lots of electricity to power daily.. I just need to know what I need so I can start weighing in hydro electric pumps/solar arrays/wind power generation... etc. ANY help would be awesome... also any ideas
  • Feb 25, 2011, 11:26 PM
    dexforget
    930kwh / monthly
  • Feb 26, 2011, 04:23 AM
    tkrussell
    Listing all of the loads you have is a good start, at least to know what you have that will need to run.

    However, if one were to add all of it up, that would be to assume all of the loads were on at the same time, which is not what would be actual.

    Values such as KWH/year and per month are useless.

    If a home had a 100 amp standard electric service, that would be 24,000 watts available. Something this size would certainly be sufficient.

    What you need to do is start looking at the power plants that are available, determine what the costs are for the sizes available, and choose a size to meet your budget, and understand that is what you have for available power, and only run what you absolutely need at one time.

    Another thing to consider is that certain appliances such as refrigerators, washers, anything with a motor, while it may have a nameplate of 440 watts, using yours for example, that is running load. Motors draw much more current at starting than when running. Any power plant would need to be sized to handle this starting current.
  • Apr 1, 2011, 07:31 AM
    Newton1Law
    tkrussell is correct. You need to look at what you total demand might be at anyone time. That is what is the maximum amount of load you expect to have on at any one time. This will suggest a minimum starting point. For example, if you know you have 10 100 watt lights (1000 watts total), it is a reasonable assumption that they would be on in the evening. Also you have a water pump running 24/7 at lets say 1000 watts. If that were all that was runniing your evening total load is 2000 watts.

    During the day, no lights but you use your computer, 250 watts, use the electric stove, 1200 watts, the microwave, 100 watts, the washer and dryer, 1000 watts. Total day load is then 2550 watts. If your generation system is to supply this load it must be sized for the maximum expected load plus a reserve. So for day you would get 2550 watts / 240 volts = 10.6 amps. Your not done however, what about motor loads? These will take up to 10 times the amount of current to start them as it does to run them. The average starting load is about 6 times the normal running load. So, 1 horsepower motor (about a 4 amp load at 240 volts) will draw 6 times it running average to start so you have to look at 6 HP as the load during start up. Even though it is only there for a short time, say less than 5 seconds, it means your system has to supply 24 amps instead of only 4 amps. Do you have a well pump for drinking water? Motor on the freezer, the 440 watts for the refrigerator will be at 120 volts most likely, 440 watts/ 120 volts = 3.67 amps for normal running but 22 amps to start.

    I hope you have a better understanding of how to do a load calculation or at least see what is involved. Next, what energy source? PVs - only when the sun is shining, Windmills - only when the wind blows, hydro - as long as you have a steady source of water, the needed head pressure, etc. Perhaps all three are best and used to supply a battery bank which in turn supplys an inverter to supply your home.

    Let us know how you do. I for one would be very interested in what you decided and how you make out.

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