Solar Need calcuations

Discussion in 'Homesteading Questions' started by angus, Dec 13, 2005.

  1. angus

    angus Somewhere in Oklahoma

    Apr 30, 2005
    I'm still pretty new to the Solar/Wind idea so please bear with me ...

    Assuming you used candles/Solar Lamps/Kerosene for Lighting, and were pretty much using only :

    1) Washing Machine
    2) Refrigerator
    3) Microwave
    4) HotPlate
    5) Small Computer

    No TV, No Dryer, No Dishwasher, No HairDryer, No Oven ...

    and assuming you lived in an area that gets reasonably good solar resources ( west central Oklahoma ), could you conceivably get by with $10,000-$20,000 for an "off-grid" setup???
  2. JAK

    JAK Well-Known Member

    Oct 15, 2005
    New Brunswick
    1) Washing Machine - it would be fun to make one
    2) Refrigerator - save energy by adding insulation but keeping the coils cool
    3) Microwave - yeah I can see that
    4) HotPlate - you can also use a 3 wick candle or an alcohol stove
    5) Small Computer - a notebook and lcd screen will save on power and often come with a feature that they come right back where you left off without having to reboot.
    6) Small electric lights should also be available also for convenience.
    7) A battery charger for small batteries is good also.
    8) You should also have a small heater that only switches on to dump load to when there it too much power being generated and/or the batteries are charged. You should have an alarm also, so you can do some laundry or something that will use power.

    Of you 5 major appliances you could never have more than one on at a time. You can have an alarm on the fridge to remind you to turn it back on after a time or if it gets too warm. Once you have reduced your demand you need to work out what the peak load is and what the average load is and how it varies over time. Next you provide a combination of wind, solar, and generator power to provide the average load, and batteries to charge when the power is not being used directly. The amount of batteries is often determined by the maximum charging rate rather than reserve capacity, since you can go without some of those loads when wind and solar are scarce.

    Solar: $5000 Runs at least $5/watt but provides a good base source. $5000 will give you 1000watts which will average perhaps only 200-250watts but more in summer than in winter. The cost is expected to drop steadily over the next 20 years so leave some room for the future. If you have lots of wind you can make this an even smaller part of your system but it will provide a fairly reliable daily charge to you batteries, and direct power for what you might use mid day.

    Wind: $3000 Even a half decent wind resouce is a good compliment to a solar system especially if you get more wind in winter. Many avialbale systems are too expensive but wind projects can be done yourself. Usually requires a tall mast and distance from neighbours. 1000watts might also average 200-250 watts and you can make the rotor a bit bigger if you need to. Cost of wind systems vary more than the Solar but should be cheaper if the wind is available. On a $3000 homebuilt system you might even average 500w on that but you will need to dump excess power to a heater if it is too much for your batteries at once. If you use more wind power than solar power you will need more batteries so the cost will work out cheaper but not all that much cheaper.

    Batteries, Inverters, Backup Generator, Default Load: $2000
    There are times you might generate 2000watts without load, so you will want to be able to charge batteries no faster than a 24 hour rate even though the sun will only generate full power 6 hours at most. That is 48kwhr which is about 400 ah which cost about $400. Since your capacity factor is about 20%, perhaps 25% in peak season, you can get used to using power at 10-12 kwh/day on average. You don't want to get down below 50% but this will give you 2 days of backup. You can add more batteries or use your backup generator more often. You will need an inverter but it shouldn't have to supply much more than 1000w/2000w peak and cost under $1000. A small generator need not be that expensive or efficient either if it is only for backup power and to top up your batteries.

    If you average 500w and 12kwh/day that would be $17,500 over 10 years at a cost of $0.40/kwh. If you get you cost of 12kwh/day down to $10,000 over 10 years by shopping around and building the wind power yourself your cost of power will be down to abiut $0.25/kwh which is about as low as you can go. Still that is only $85 to $145 per month if you can make it work for you. As the cost of solar modules and other components come down you can add capacity and live large, but it is best to start small. You could start with $7000 1kw solar based system for 6kwh/day and then build your own wind power systems increase it to 12kwh/day.

  3. sisterpine

    sisterpine Goshen Farm Supporter

    May 9, 2004
    Zone 8a, AZ
    Personally I think it is nuts to go off grid and then plan on having any appliance with any kind of heating coil. I would lose the hot plate unless they make gas ones and would use a gas fridge as well. then you would need very limited solar, tv, computer, lights (compact flor) and you can get a good low energy use wash machine like a staber or fischer paykel or such.
  4. WisJim

    WisJim Well-Known Member Supporter

    Jan 13, 2004
    It depends on the particular appliances you plan to use, as there is a tremendous difference in energy use and size of things like refrigerators and washing machines.

    I am in western Wisconsin, not at a good wind site, and have about 1800 watts of PVs that produce 6 to 8 kw-hrs per day on a yearly average--varies from nothing to over 10 kw-hrs a day. I have invested about $20,000 in our system since 1977 or so, including a top of the line set of $4,000 batteries, a Trace/Xantrex sine wave inverter, Ourback MX60 charge controller, etc., etc. Our windgenerator is a 1940s vintage Jacobs unit that would cost you $6 to $8 thousand dollars for a professionally rebuilt one now, plus the cost of the tower and installation. We got ours for MUCH less than that at least 25 years ago, and I would be very careful to do a wind survey at the proposed site of a wind generator installation. (Having said that, I hope to put up another generator on my marginal wind site, just because I have the unit and a tower that would work.)

    My latest array of PVs, rated at 1500 watts, cost about $8000 includeing the mounting rack, wiring, charge controller, etc., but then I got a couple of thousand back in rebates from Focus on Energy here in Wisconsin. That dollar figure didn't include batteries or inverter, which I already had.

    So, I think you could put in a usable PV system capable of producing 150 kw-hrs a month, on the average in my area, including a set of batteries and decent inverter, for $10,000 to $15,000, plus installation labor costs. Maybe Jim-MI will chime in here with figures based on recent installations. Depending on the wind resource, a wind generator may make sense too.

    Appliances: A chest freezer might use 400kw-hrs/year or less depending on size, a refrigerator, chosen for low energy use, maybe 250 to 350 kw-hr/years, so a decent manual defrost refrigerator freezer of 12 to 14 cu ft size could easily be run by a PV system in your price range. I would use electric lights, too, for convenience. Back in the 1980s we replaced our Servel propane refrigerator with a Sunfrost 12 volt 12 cu ft unit because of concerns with cost of LP gas and the fumes from the burner in the refrigerator. We discovered that about 120 to 160 watts of PVs was all it took to run the refrigerator. Some of the modern "regular" brand refrigerators don't use an awful lot more power than the Sunfrost, which was designed for solar powered households.
  5. Gary in ohio

    Gary in ohio Well-Known Member Supporter

    May 11, 2002
    The items you listed are generic items and hard to tell becuase they will vary by age and type of item. WHat you might want to do is invest in a "KILL-A-WATT" metter. You can get them on ebay for under $20 and buy them otherplaces under $40. They will tell you how much power amps/kwh something is using. Very nice to help with you calculations and give you a REAL values.
  6. Jim-mi

    Jim-mi Well-Known Member

    May 14, 2002
    Your item number 4 - hot plate, might be. better off if it were run over by a tractor tire so as to lighten your load.
    Items 1 & 2 - Do you have newer more efficient units or older heavey users ?? Your better off $$$$ wise, updateing older appliances than getting more PV's to power the older guzzlers.
    And items 1 & 2 really should have a larger inverter to handle the starting inrush (surge). Yes theres a lot of mod square wave inverters out there (read lower $$$) runing households, but today there's some very fine sinewave inverters available that in my book are well worth the money ...

    One item not on your list was ----water. ... well pump ?

    I would be wary of any homemade wind stuff being able to survive your okie winds. Buy wind systems that are engineered to withstand big winds..........period.
    A damnable fact of life is the big increase in the cost of steel ... and along with that the cost of towers for your wind turbine.
    PV and batterys: theres a huge price spread available there.
    20 k is a realistic figure.
    If that figure is cut in half will you regret later for buying too small ... ?
  7. WindowOrMirror

    WindowOrMirror ..where do YOU look? Supporter

    Jan 10, 2005

    Washing machine - 920 watts / hour
    Refrigerator - 540 watts/ hour
    Microwave - 1200 watts / hour
    Hotplate - 1200 watts / hour
    Small Computer - 150 watts / hour

    Now, how many hours for each?

    Be CONSERVATIVE (overestimate)

    Washing machine 10 hrs/wk
    Refrigerator 112 hrs/wk
    Microwave 2.2 hrs/wk
    Hotplate 7 hrs/wk
    Computer 2 hours each day

    1133 amp/hr normal usage. The fridge is the killer.

    So, you're gonna need 14 or so 20 amp panels.

    WisJim's system at $8000 would cover your projected needs easily, though I would say that you are underestimating your needs (no lights, etc).

    Easy answer, $8-$15k if you a fair bit of the work yourself.

  8. Hip_Shot_Hanna

    Hip_Shot_Hanna Well-Known Member

    Apr 2, 2005
    Staber make a Very energy efficient washing machine and it dont use that much water either , now looking at fridge freezers they are FAR more efficient than they used to be , they use about 1/3 rd more energy than the "specailist" off the grid units ,and are around $1000 cheaper , spend the money on solar panels instead of the specailits units , lighting go for low energy bulbs, the compact flourescent types , ANY system should cope with half a dozen bulbs using 15 watts each (15 watt compact = 100 watt incandesant ). there are even very expensive LED bulbs about that use next to no energy , Electric stoves are a NO NO as is electric water heating and air con . Fridge / freezers do not run constantly , perhaps 6 hours a day max , microwave perhaps only 1 hour a day , but adding up a fridge , freezer, microwave, lights , TFT TV , you should come in around 5000 watts a day ,(Phantom loads are the killer , TV left on standby clock radios VCR DVD player left on standby are eating energy) keep them Switched off and the energy needs are well within the capacity of a decent solar system , especialy if you use a wind generator as a top up ,
  9. mightybooboo

    mightybooboo Well-Known Member

    Feb 10, 2004
    So Cal Mtns