Wrenchbender is back with usage data-

Discussion in 'Off Grid Living' started by Wrenchbender, Oct 26, 2012.


  1. Wrenchbender

    Wrenchbender Monkey

    I posted a month or two back about putting together a PV system to run my 5 cu ft chest freezer and my 17 cu foot refrigerator/freezer at my house. I purchased a Kill a Watt Ez meter and montiored the usage.

    I ran the freezer for 1113 hours, using 42.58 total KWH. The unit draws 95 watts or .84 amp while cycling.

    Next, I hooked it in line to the inside the kitchen 17 cubic foot refrigerator/freezer. Over 1920 hours I used 130kwh. It draws 2.2 amps on inrush (1 second max) and then settles down to 1.07 amp, or 129 watts.

    IN the night they are not opened and in the day when nobody is home they tend to stay shut. I was wondering if a single, 350 watt panel would be sufficient? I have a really good south and west exposure.

    What batteries and charge controllers and inverter would you use?
     
  2. Wrenchbender

    Wrenchbender Monkey

    Well maybe I did not collect my data right? Could someone at least point me in the direction I need to go in order to make proper sizing calculations? Can't believe I had all these views and no comments.
     
  3. melbo

    melbo Hunter Gatherer Administrator Founding Member

    Our resident solar experts seem to be on vacation... @Nadja @TnAndy @BTPost may be able to help.

    With regrets, ETA that Nadja has passed. - ghrit
     
  4. techsar

    techsar Monkey+++

    1625wh + 918wh = 2543wh / 24 hours = 106 watts per hour usage for both on the average. But you'll end up needing close to 3kw per day to recharge your batteries - soooo

    3000 / 7 (charging hours per day) = 429 watts of panels.

    No, a single 350 watt panel will fall short even before losses are figured in.

    If my math is off, please feel free to correct me!

    I still use Xantrex C60 for charge controller, Sunforce for PSW inverter and 40 AGM batteries...but Outback is an excellent brand, too.
     
    BTPost likes this.
  5. TnAndy

    TnAndy Senior Member Founding Member

    I agree, about 2543w/hr per day for both.....or 2.5kw/hrs a day.

    With inverter, battery and charging losses, I'd figure closer to 3.5 - 4kw/hrs/day of generation needed.

    Assume 5 good hours of sun ( you may get more, you may get less ), you'd need 800watts per hour.....and that's 800 TRUE watts.....not panel rated watts. So I'd figure 1,000 panel rated watts at a bare minimum......or 3 times what you came up with.

    AND that is ONE DAY. 5 cloudy days ? Many more times the panels AND we haven't even gotten to battery storage yet.
     
    kellory and ghrit like this.
  6. Wrenchbender

    Wrenchbender Monkey

    WOW was I way off. I looked at the freezer and saw around 100 watts, the fridge 200 watts, figured that's about 300 watts, and that a 350 watt panel would do it. Now I understand why I never made it past general math in 8th grade. Looks like I have more figuring to do for sure. One thing I see as a constant in this, buy a larger inverter than you think you need of a high quality, and an equal charge controller, and you can add panels/batteries and upgrade it later.

    Thanks for the replies to my newbie questions. If you guys ever have questions about 1950's Case tractors, 60's Ski Doo snowmobiles, or making very bad puns and bad smells I can help you in those areas of my expertise. :)
     
  7. BTPost

    BTPost Old Fart Snow Monkey Moderator

    For quality Inverters and Charge Controllers, look at the Outback Power Systems stuff..... These are the same guys that designed most of the Trace Stuff, Back in the Day... There equipment is a bit more expensive, that the rest but It is "Bullet Proof" rugged, and will out last your Grandchildren.....
     
  8. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    Your math is fine, the problem lies elsewhere.

    Carrying TnAndy's comments a bit further, there are a number of open questions still needing answers before sizing the panels and storage batteries.
    -How many days of cloud cover do you need to provide storage to get thru? (It is not adequate to take the average available from meteorological data, you will need more. The same conservative approach should be taken with the average insolation, worst seasonal exposure.)
    -What other "nice to have" loads might be added? (Even a weather radio is a load, however minor.)
    -Is there a plan and hardware in place to shift the load from battery to commercial power? (Two is one, one is none.)
    -Do you want to have a backup for battery charging, say off a gennie or commercial power? (Or either.)

    Solar and wind are easy IF you think like a tree hugger. Reality can bite and leave marks on your wallet. The way I look at it is as an investment that will either break you or pay off big time. As with dealing on the stock market, you need to assess your ability to take the risk of investment with questionable return.
     
    mysterymet, DKR and BTPost like this.
  9. bob0usa

    bob0usa Monkey+

    having installed my own system, think alot to what ghrit posted!
    there's also panel angles to think about also, down to 47deg in summer and up to 70deg in winter for me!
    and in my area, i some times need to use com power for up to 5 days because of overcast weather!

    but bottom line, i'm happy with it and you learn to manage your power usage better!
     
  10. Wrenchbender

    Wrenchbender Monkey

    I am fully aware that at this point, grid power is cheap. As far as converting back, all I will have to do is unplug the appliance from the inverter and plug it back in to the wall. This will be a doing it because I want to deal. As far as cost, well I have thrown more money away on things like hotrods and an ex wife and have little or nothing to show for it, so at least I will have some hardware here. :)

    BT, I will look at the OUtback stuff.
     
  11. ghrit

    ghrit Ambulatory anachronism Administrator Founding Member

    VERY cool. Please keep us in the loop on the learning curve. I've a sneaking suspicion we'll learn a lot looking over your shoulder.
     
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