Help on selecting wattage output for Wind Turbine Generator to charge my Trolling Batteries

CC4MECC4ME Registered Users Posts: 1
edited January 6 in Wind Power Generation #1
I'm looking for help in rightsizing the wattage for a 24 volt VAWT Lantern style wind turbine to charge my two 12 volt deep cycle marine batteries (flooded lead acid), in a 24 volt configuration, to power my Minnkota trolling motor. Each marine battery is rated at 85 AH. The VAWT (with MPPT) I'm looking at has the following specs: Rated power:800W, Maximum power:1000W, Rated voltage:12V/24V, Start up wind speed:2m/s and Rated wind speed:11m/s. Wind speed at my target location just off Lake Erie typically ranges between 5-14 mph but can go above 20 mph. I've been told by my battery manufacturer (and from other sources) to keep the max charging amps less than 25% capacity or a max 21 amps to avoid damaging the battery. I normally take my boat out on the water on the weekends and looking to charge my trolling marine batteries in between outings. Currently, I have to either move my boat down the road to an electrical outlet to charge my trolling batteries or yank them and charge them at home  I have looked at solar panels but have ruled them out due to certain constraints.
Given the above information, can someone recommend a wattage (e.g. 500W, 1000W, 1500W, etc) to me that will meet my requirements? Any tips on reliable VAWT's I should be looking at that aren't too pricy? 
Any help would be appreciated. 


  • BB.BB. Super Moderators, Administrators Posts: 31,336 admin
    edited January 7 #2
    Welcome to the forum Lee,

    I will start by saying that I am NOT a fan of small wind power. My recommendation is to use solar panels to start--then if you wish, experiment with a wind turbine installation...

    To your specific questions... I have not seen any VAWT (vertical axis wind turbines) that generate any useful amount of energy--And are mechanically reliable. I will admit that I do not follow wind turbines, so there may be some out that are good...

    Next, notice the wind speeds... 2 m/s to 11 m/s (starting and max rated output). 2 m/s = 4.5 to 11 m/s = 24.6 mph. And in reality, most turbines (HAWT--Horizontal Axis Wind Turbines) start to generate "useful" amount of power around 10-12 mph.

    Wind turbines (of any time) need "clean" airflow to harvest power. That usually means >500 feet horizontally, and a minimum of 30 foot tall tower, to get into the good wind... If you have a house/trees/etc. nearby, then the turbine needs to be mounted above those obstructions.

    Turbines can be relatively inexpensive, but the cost of a tower (and concrete if free standing), having a tilt tower/crane/lift to service the turbine once a year, as well as wiring because you (generally) do not want the turbine near homes/yards with children because of noise and possible flying objects/falling nacelles.

    Looking at an MPPT type charge controller can be a very good idea--It allows better energy harvest from variable wind conditions (matches the alternator torque/RPM curve against voltage*current (think the equivalent of an automatic transmission between the alternator and the battery bank). Depending on the turbine selected, and the support equipment available--There needs to be a method to control the turbine speed (not usually a problem for VAWT, big issue with HAWT) and battery state of charge... Either need to shut down the turbine and/or have a "dump load" (resistor bank) and dump controller to get rid of excess charging current during windy conditions and full battery bank.

    If you are in a location that is "miserably windy" when you want to harvest energy (many hours a day)--A turbine may work for you. And you may wish to look at a home built wind turbine system. If you are near water--Conditions that give you good wind--Would also seem to cause rough water...

    Do you know of anyone that has built and operated a wind turbine system in your neighborhood for the last 1+ years (and it would be great if they can give you daily or monthly harvest numbers).

    Here are some links from our FAQ to (now ~10 year old) discussions and test results for small wind...

    Wind Power Links (good forum for DIY Wind Power)
    Hugh Piggott - Scoraig Wind Electric site for tons of info (from mike90045)
    Scoraig Wind "Recipe Book" for DYI Turbines (from Chris Olson... From his 4/11/2013 post) (added from "russ"--Like here but more wind/less solar)
    Small windpower a scam ? Survey says SO
    Truth About Skystream & SWWP
    Windmax HY-2000 2kW Wind Turbine (apparently, some vendors don't sell spare parts--just new turbines. However, the owner, Edward has been very happy with its performance from 2010-2012--BB. 5/31/2012)

    The "Small windpower a scam?" link has a test of 10 or so small wind turbines and their test results... And most of them barely produced any power...

    If you can tell us (roughly) where you are at and when you want ... We can look at available wind and solar energy and help begin sizing the system for you.

    Just to give you a minimum sized solar power system (I understand you have looked at solar, and probably cannot use it do to some constraints--But as an example)... 85 AH @ 12 volt batteries (2x) recharge at 5% rate of charge (5%, minimum, 10% to 13% rate of charge typical):
    • 2 * 85 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 160 Watt array minimum
    • 2 * 85 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 320 Watt array nominal
    • 2 * 85 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 416 Watt array "typical" cost effective maximum
    That is assuming you drain the FLA batteries to "dead"--Don't really suggest that--Typically to 50% and possibly down to 20% State of Charge for "true" deep cycle batteries.

    Of course, the amount of sun you can harvest (location, season, weather, shadows, etc.) will also affect the amount of harvest/sizing of the array.

    For example, say you get 3 hours of sun per day (spring/fall typical), and use 50% of your battery capacity per day (or per weekend):
    • 2 * 85 AH * 12 volts * 0.5 SoC = 1,020 Watt*Hours per day (same as 1 string * 85 AH * 24 volts * 0.5 SoC = 1,020 WH per day)
    • 1,020 WH per day *  1/0.61 DC system eff * 1/3 hours per day so-so sun = 557 Watt array (3 hour sun "break even")
    If you want to recharge over 3 days:
    • 1,020 WH per day * 1/0.61 DC system eff * 1/3 hours per day * 1/3 days to recharge = 186 Watt array "break even" @ 3 hours of sun per day
    I would suggest if you can install some sort of tower for a HAWT, you may be able to rack mount an 160-416 Watt solar array just about the same/or less money and hassles.

    One thing to watch out for... Most wind and solar systems do not like to have their Battery Banks disconnected while wind/solar charging... It can confuse/damage the charge controllers (or for VAWT allow to "overspeed"). If you are moving the batteries to the boat, then you need to first "shut down" the turbine/solar array first, then disconnect the batteries from the bus.

    Your thoughts?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,198 ✭✭✭✭✭
    What Bill said.   ditto
    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: ,

  • CC4MECC4ME Registered Users Posts: 1
    Hi Bill,

    Thanks for the great feedback and the supplementary websites. A lot to go through.
    I have looked into HAWT's and Solar but have ruled them out due to my specific requirements and certain constraints that I have.
    I also share your concerns about buying a VAWT that's a dud. Once I understand the wattage output I need, I plan on purchasing a 
    VAWT that has a 30 day return guarantee policy which will allow me time to verify it's output and performance.

    I plan on permanently mounting a VAWT on top of my 19 foot boat's T-Top frame. With the length of the support pole and the VAWT
    height, the VAWT will be about 15 feet off the ground. I park and launch so my boat and trailer is on land near the water and there are 
    no trees/obstructions blocking my T-Top. As I boat on weekends, I'm looking to have my trolling batteries nearly or fully charged in 
    between outings. In addition, I will be able to use my gas powered engine to exceed 12 mph and have the VAWT actively charging my 
    trolling batteries as I head for a given fishing destination or port. The VAWT may even be able to charge the trolling batteries (to a lesser 
    extent) while I'm trolling. As noted previously, wind speed at my target location just off Lake Erie typically ranges between 5-14 mph 
    according to NOAA but can go above 20 mph. When I am standing on the ground next to my boat, I feel a varying but steady wind most times.

    I'm not an electrician and have done only basic wiring. Thus the reason I'm reaching out for help in determining if a 1000 Watt VAWT is
    sufficient enough to charge my trolling batteries in between boat outings or do I need more wattage output (or less). Again, any suggestions on what wattage output I should shoot for in a VAWT? 

    You may be interested in these web links on VAWT's:

    Best Wishes,

  • BB.BB. Super Moderators, Administrators Posts: 31,336 admin
    This website has a lot of information and history about wind turbines and the mfg (including VAWT):

    Generally wind turbines should not be mounted to structures--But on their own tower/mounts away from inhabited space... The noise and stresses to structures/buildings/T-Top on boats/etc. can be significant.

    In general, attempting to harvest power from the boat's gas/desiel engine is a lost cause. The drag of the turbine (and inefficiencies of turbines/alternators) would just slow the boat down/cause more fuel use vs just bolting an alternator to the engine (if you are able).

    For sail boats, some folks have mounted wind turbines (typically HAWT types from what little I have seen)--And there are towed water turbines that attach to an alternator mounted on the stern of the boat (for sail boats). But I am not sure any of those would harvest enough energy to be useful (trolling motor power, vs power for LED lighting, GPS, radio)...

    I would be very interested to see what you find in the VAWT (or even HAWT) world, and how the install and operation is working out on your boat.

    Regarding sizing... More or less, the 'optimal' charge rate for a lead acid deep cycle battery is around 10-13%... And they can take upwards of 20-25% rate of charge into a discharged FLA battery.

    If you want to charge quickly (next day)--More or less, FLA batteries will accept full charging current up to around 80% state of charge--Over that, the battery is at the charging set point (say around 14.8 volts on a 12 volt battery bank) and starts to limit charging current as the SoC continues to rise. Reaching around 1-2% rate of charge near 100% SoC after 2-6 hours or so.

    If you need fast/high current charging... LeFePO4 type lithium batteries may be a better choice (not cheap, and need to be operated per the manual/specifications--Details matter here).

    But that leaves the question of charging... Lead Acid batteries on solar--Only charge when the sun is up--And not great for trolling during the day and docked/charging at night (unless you have a shore based battery bank+charger or genset).

    So, if I was sizing a "genset" (wind, solar, etc.)--I would probably choose between 10% to 20% rate of charge... If you need "fast", then 20%:
    • 85 AH * 29.5 volts charging * 0.20 rate of charge = 502 Watts into battery bank
    You would need to limit current. VAWT do not really need RPM control (they can free run in windy conditions)--But if you choose a higher wattage unit, you will have to regulate current from the turbine and/or have a dump load approximately equal to the turbine rating (battery will only take a fraction of the current when >80% state of charge--So you need to limit so that the battery does not over heat and/or "boil" (excessive gassing) of the electrolyte.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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