Air 40 wind generator

sheppisheppi Registered Users Posts: 6
Hi there, this is my first thread as I just joined the forum. I just got my off grid system up and running so I am in the learning stage. My question is, will the Air 40 wind generator from Southwest Windpower keep my batteries charged enough to survive when I head south for the winter? I am facing due south with fairly regular prevailing winds. The system I have is 24 volt , 6 -130 watt panels, c-40 controller, 4024 pure sine inverter with 8 L-16 Trojan batteries 740 amp hrs. There will be no load on the batteries when I am gone, is this good?


  • mike95490mike95490 Solar Expert Posts: 8,764 ✭✭✭✭✭
    Re: Air 40 wind generator

    If you have no or minimal loads, those panels should keep things topped off.

    be sure the auto equalize is DISABLED while you are away, and top the water up.

    I'd suggest giving up the idea of un-attended wind generators.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Air 40 wind generator

    It depends on,,,,the wind! That said, most people are not real happy with the net output of small scale wind systems. It is also important to realize, (unlike PV) you have a mechanical device that lives in a rough environment. What happens for example if it self destructs when you are not around to repair or salvage it? (You are likely to be left with a busted piece of junk!)

    Please also note, that your PV needs to be clean of snow to produce any power. Consider wall mounting your PV so that snow is not an issue,, then they will keep the battery on float just fine.

  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Air 40 wind generator

    For winter, you could install a smaller panel/array on your wall (or tilt your panels vertically as Tony says) and be quite happy with the results.

    Batteries when fully charged (when you button up the cabin) will not freeze even at -40C/F. And they have much lower self discharge.

    You could get away with a 1% rated panel and small controller (or use your existing controller):
    • 29 volts charging * 740 AH * 0.01 rate of charge = 215 watt panel/array
    Your existing array is on the "small side", but if you are using it weekends during the summer, it probably serves you well (not too much generator usage).

    Normally we recommend between 5% and 13% rate of charge for your solar array:
    • 740 AH * 29 Volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,394 watts (minimum 5% rate of charge)
    • 740 AH * 29 Volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,282 watts (large array at 10%)
    • 740 AH * 29 Volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,623 watts (maximum cost effective array)
    The above is just some starting point rules of thumb. Many people used to recommend that off grid power systems install a huge battery bank for best performance.

    Around here, we have pretty much convinced ourselves that you should design your battery bank to match your load requirements (typically 1-3 days of "no sun" and 50% maximum discharge) and install a good sized solar array to quickly and fully recharge the battery bank. Then size the solar array to your bank size (5-13% rate of charge) and your daily loads (I aim for generator usage only during the "dark" ~3 months of winter).

    If you have a "too large" battery bank, it forces you to install even a larger array (to meet minimum charging current requirements and to keep up with self discharge as the banks age)--And when the batteries eventually fail (every ~6-10 years or so), you have to pay a bunch of $$$ to replace the existing bank.

    A suggestion for the long term, take a look at a Battery Monitor (or Victron Energy)... It makes managing your (expensive) battery bank much easier--plus it is easy to teach spouse/kids/guests some basic usage... I.e., stop using power/start the genset if less than 50% state of charge; if approaching 20% state of charge, turn off all loads and ask for help (why genset is not charging, etc.). If you have flooded cell batteries, a hydrometer is still a good investment to check the health of the battery bank. And I suggest getting a DC Current Clamp Meter (like this inexpensive $60 one) so you can monitor current sharing between your two parallel battery strings.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sheppisheppi Registered Users Posts: 6
    Re: Air 40 wind generator

    I was suprised to hear that my solar aray is on the small size. I plan on living at the cabin every day spring through fall. If I understand you I will need to double my array to run things day to day. Lights, tv, stereo, ect.
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Air 40 wind generator

    I really don't know what the size of your solar array and battery bank should be... But, using some basic rules of thumb as a starting point, a large battery bank should have a larger array for proper battery charging (which usually increases battery life).

    But, back to your current battery bank... More or less we use 1-3 days of "no sun" and 50% maximum discharge in "normal use". Lets take 2 days and 50% max discharge, or basically the battery is 4x your daily average load (or you discharge the battery by 25% per day):
    • 740 AH * 24 volts * 25% = 4,440 Watt*Hours per day average load
    • 740 AH * 25% = 185 AH @ 24 volts per day (if you prefer working in Amp*hours)
    Using PV Watts for Toronto Canada (guess), more or less your hours of sun per day are:

    Month Solar Radiation (kWh/m2/day)
    1 2.69
    2 3.51
    3 3.98
    4 4.68
    5 5.29
    6 5.48
    7 5.51
    8 5.23
    9 4.96
    10 3.61
    11 1.95
    12 1.97
    Year 4.07
    Using February as your worst of 9 months of the year, you have 3.51 hours of sun (fixed array mounted at latitude), and you would need a solar array of:
    • 4,440 WH per day * 1/0.52 PV system derating * 1/3.51 hours of sun = 2,433 Watts of solar array
    So, a 2,433 watt solar array would just about break even based on using 1/4 of your battery bank capacity per day (4,440 WH or 185 AH @ 24 volts per day).

    Your current panels are 6x 130 watts or:
    • 6 * 130 watts = 780 Watt array
    • 2,433 Watt array recommended for your battery bank / 780 watt existing array = 3.1
    Your battery bank, from our normal rules of thumb is about 3x larger that we would have recommended for a "balanced system"...

    But, again I do not know your needs... Are you using 4,400 WH per day or much less? Is this a weekend cabin with summer only use? (yes, I understand you are planning on Spring through fall usage--just giving some rough guidelines I like to start with) Do you use the genset to keep the battery bank well charged when needed? Is generator fuel easy to obtain and cost efficient for your needs? Is there seasonal power variations (irrigation, fans, visitors, etc.).

    I am not trying to say that everything was done wrong--But I do not understand yet your power needs (WH/AH per day, Seasonal usage, trade-off between generator usage vs more solar panels, etc.).

    So, I have now calculated the the "optimum array", both based on battery charge capacity (1,400 to 3,600 watts) and on estimated power usage assuming you use 1/4 of the battery capacity per day (no sun) (~2,400 watts based on worst of 9 months--February).

    In the end, power usage is very personal. And I (we) are just trying to give you the tools to design/build a system that will, cost effectively, meet your needs.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Air 40 wind generator

    Here is the general off grid rule of thumb.

    First you have to figure your loads,, as all other calcs derive from the loads. Then to power those loads, you have to have enough PV. My rule of PV is this: take the name plate rating of the PV, divide that number by two to account for all cumulative system loses, then multiply that number by 4 to account for the averge number of hours or good sun one might reasonably expect, per day, on average, over th e course of the year. One can adjust that number up or down to account for seasonal and regional differences, but 4 is a number that works out pretty well. Most people at once and the same time will over estimate their solar potential, and underestimate thier loads. Loads also, always,,always grow with time.

    So for example, 1000 wats of PV might look like this: 1000/2=500*4=2000 watt hours/day. As an FYI, we live off grid in Northwestern Ontario. We live very sparsely, we propane for the fridge, hot water and cooking. We use a genny for most shop tools. We have 400 watts of PV, and on an average day, we consume 5-800 WH of power.

    Our system is just about balanced. On an averge day, we put in ~800 WH on a great day, we can push 1.5 kwh. We have three days reserve of battery (450 ah 12 vdc) and can get that three days back in one if we have a perfect day. On a daily basis we seldom discharge more than ~20%.

    Good luck, and keep in touch.

  • sheppisheppi Registered Users Posts: 6
    Re: Air 40 wind generator

    Obviously I was misdirected when I bought my package. Basically I will be running my lights a couple 60 watt , Entertainment centre, 46 inch hdtv, reciever, sound system. Occasionally a microwave 1000 watt and a 24 volt demand water pump for dishes and showers. Every thing else is propane, heat, cooking and refrigeration. If I downsized my bank of batteries to one set of 6 volt L16 batteries , would that be enough to run day to day and would my array of 780 watts charge the batteries. Sorry for all the questions but I am at a loss for what to do.
    Thanks Mike
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Air 40 wind generator

    I really do not know... A 780 Watt array is fairly small and, for most people, requires the owner to be pretty thrifty when using power around the home/cabin.

    Using my 3.51 hours of sun for February as the "break even" month:
    • 780 Watts * 0.52 system losses/derating * 3.51 hours of sun = 1,424 WH per day
    A 24 volts battery bank sized for a 1,424 WH per day load (1-3 days of no sun, 50% maximum discharge) assuming 2 days/50%:
    • 1,424 WH * 1/24 volts * 2 days of no sun * 50% maximum discharge = ~237 AH @ 24 volts battery bank
    Note: I am being conservative here--If your spring through fall are April through October, then you could use April's 4.68 hours of sun minimum and have "more power".

    So, a 46" TV (no metric TV's in Canada? ;)) + digital receiver + sound system + 2x60 watt lamps may run you 500 watts (or more) of average load (just guessing--ignoring the water pump and microwave for the moment).

    Using the (conservative) number of 1,424 WH per day:
    • 1,424 WH / 500 Watt load = 2.8 hours a day of use
    It turns out, that for most people, the Microwave is NOT the the PV system killer... Most people only run them 10-20 minutes per day.

    The killers are the appliances that run 5-10 hours per day. Like TVs, DVRs, Desktop Computers, etc...

    Your choices usually end up being A) get new, more efficient appliances; B) more solar panels+battery bank; C) more generator runtime; D) turn stuff off... Or some combination of A-D.

    You really need to measure your existing loads (Battery Monitor, DC current clamp--as in my previous post--And/or a Kill-a-Watt type Watt*Hour meter for your AC loads).

    It would be unfair of me to "tell you" what your loads are from 3-4,000 miles away. Electrical loads and usage are highly personal choices and what is "acceptable" use for me and my family may not be for you.

    Also, solar PV power is most cost effective when you use most of the power produced... I.e., 9+ months of the year with a PV System that is "matched" to your power needs.

    A PV system that is only used 3 months of the year is less cost effective, as is one that is many times larger than your power needs.

    Again, I am not trying to beat you up on your first system choices--I am not there and have no idea of your actual power needs and the trade offs made (solar array, backup genset run time, etc.). I hope I did not look like I was. We all start from someplace and move forward.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sheppisheppi Registered Users Posts: 6
    Re: Air 40 wind generator

    Thank you for your time and patience
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Air 40 wind generator

    You are very welcome Mike,

    By the way, forgot a "NOT" in my previous post (microwaves are NOT usually the PV off grid system killer).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Air 40 wind generator

    Couple of questions,, just looking, even without calcs you don't have enough PV for the loads. Most off gridders think their loads are small,,until they realize that a 42" TV, sound system, sat box alone probably draw close to 500 watts. Run that load for 2 hours, and you use twice what I use. (I am not trying to brag, merely pointing out what are truly small loads). That 500*2=1kwh. That 1 kwh would take, by my rule of thumb would take 500 watts of panel for those loads alone.

    The next question would be,, why are you burning 60 watt bulbs? Simple CFLs burn ~1/4 as much power per lumen, LEDs are even less. Conservation is your best friend.

    As for the battery suggestion,,,as I tried to suggest in an earlier post, all calcs, and ergo all hardware choices evolve from the net size of the load. Battery bank size should be sized to provide enough load, plus some reserve drawing the batteries down to an acceptable level of discharge on a regular basis. Inverters and charge controllers are sized to the battery bank. PV is then sized to properly charge that battery bank, with the charge controller also sized for the PV and the battery bank.

    I suggest that you figure out how to keep your batteries on float for the winter, then spend the winter redesigning your system so that it is as balanced to your loads a possible. Battery to loads, inverters to loads, PV to battery bank etc. With out knowing what your daily average loads are, no one can properly assess what your PV/battery sizes ought to be. I can tell your, that your current PV of ~700 watts, will likely deliver ~ 1.4 kwh/day on average out the inverter. That same 700 watts might under an ideal situation put out ~ 46 amps,, enough to charge a battery bank in the 450-900 AH range (12 vdc). If you have more battery than that, you most likely will be chronically undercharging it.

    Good luck and keep in touch.

  • sheppisheppi Registered Users Posts: 6
    Re: Air 40 wind generator

    Just to clear a few things up, the loads in question are just proposed loads. I am stil finishing off the inside of the cabin. Also all my lights are CFLs I have a 4500 watt yamaha inverter generator that I have been charging my batteries with and I do get them to the float stage. Obviosly I have to rethink the loads that I will be running. Since I have already purchased the 8- L16 Trojan batteries and my system is set up as a 24 volt system I dont have much choice except to increase my pv array. I do have a question though. If I add say 6 more 130 watt panels wired in series to get 24 volts x3, will I have to change my c-40 charge controller? There are only two of us and we can definitly live without the big screen and sound system. This is going to be basically a summer cottage and all our big loads are propane. Cooking, heating, refrigeration. Mike
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Air 40 wind generator

    Are you asking about a 12x 130 Watt array? Typically they are Vmp~17.5 volts (need exact Voc/Vmp/Imp ratings):
    • 12 x 130 watts * 1/17.5 volts = 89 amps
    So, you would need 3x C40 controllers to stay within their ratings.

    Otherwise, there are 60 amp / 80 amp / 80+ amp MPPT controllers which would allow you to use only two, or even possibly one controller (one ~$700 mppt).

    Take a look at this one and read the specs and the manual: Midnite Solar Classic

    May, or may not meet your needs (I am certainly not the expert in this controllers). But a good start to learn about the higher end solar charge controllers.

    Something else to think about too... If you have not purchased your panels yet, you may wish to look at larger/higher voltage panels... They tend to be less expensive per watt and have fewer electrical connections (i.e., fewer 200 watt panels vs a bunch of 130 watt panels). Also, with MPPT charge controllers, you can run a higher voltage Vmp-array (~100 VDC max for typical 150 VDC limit controller and weather conditions). You can use smaller gauge wire and/or a longer run from the solar array to the battery shed/installation.

    You may have to do several designs with different controller/panel combinations to see which is the best fit for your place.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sheppisheppi Registered Users Posts: 6
    Re: Air 40 wind generator

    I like the idea of larger higher voltage panels. As I am running a 24 volt system anyway it would make sense. The Midnight Solar controller looks good. I would need a new combiner box as well because the one I have now only has 3 breakers for my 3 sets of 12 volt panels wired in series to give me 24 volts x 3. I really appreciate the suggestions and help. I'll get there, Thank You
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