Design Help

toglotoglo Registered Users Posts: 9
Hello all,

New to the forum and love the info here. I have a small offbeat system I need help designing. I want to install some fans in the shed my horses use. The fans are 120v and rated at 255w. I would like to start with two of them and maybe add a third if needed. The fans only need to run for about 4-6 hours a day in the peak of the afternoon. This system is offbeat in that I do not care if it can't run on cloudy days. I was debating just installing 3 210w panels with an inverter and running the fans directly from the panels. I am worried that may provide too much stop/start on the fans whenever a cloud rolls by. Any thoughts would be greatly appreciated? Thanks.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Design Help

    Welcome to the forum.

    Before I even attempt the calculations I have to ask: why? Do you have no utility power available? because frankly 255 Watt AC induction fan motors running 6 hours a day is pretty far from "small". It is in fact 1530 Watt hours per fan. Two of them is more power for 6 hours per day than I run the whole cabin on in 24 hours. My system cost about $8,000.

    Second, inverters do not run directly from panels. No batteries = no system.

    Third, these fan motors will have quite a big start-up surge. That means they will require a hefty inverter to get them going. You're looking at $2,000 - $3,000 just for the inverter.

    Now, if you have got grid power available and want to reduce your operating costs, look in to what your utility has for a grid-tie policy. You may qualify for rebates and/or tax credits that would offset the capital investment somewhat and make it viable.

    If you still want/need to go off-grid we'll run you some equipment estimates, but be sure and have a paramedic on standby when you see the cost.
  • toglotoglo Registered Users Posts: 9
    Re: Design Help

    Thanks for the reply. As a laymen it seemed "small" to me. I did not realize what was involved. There is no utility service close or I would tap into it. As I said I was basically looking to come as close as possible to running the fans off the panels. As I said the application is noncritical and I do not need to have 5 days worth of backup battery power etc.
  • TheBackRoadsTheBackRoads Solar Expert Posts: 274 ✭✭✭✭✭✭
    Re: Design Help

    Welcome.

    Perhaps some new 12V fans and a panel setup would be more cost effective than a whole off grid setup. Like a gable fan or a through the roof attic fan with a thermal snap switch. How big of a building are we talking about?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Design Help

    Let's just look at the batteries needed for one fan @ 1530 Watt hours per day. Divide by 24 Volts (as that is likely a more favourable system Voltage than 12) and you get 63.75 Amp hours - call it 64.
    At 50% Depth Of Discharge maximum, that requires 128 Amp hours of battery at 24 Volts.

    To recharge that you'd need 12.8 Amps of peak potential current @ 28.4 Volts charging: 363.52 Watts.
    Since panels don't actually produce their rated Wattage you have to factor that in: 363.52 / 0.77 = approximately 472 Watts of panels.

    In terms of "harvest" you might expect those panels to produce up to 1452 Watt hours per day, based on 4 hours of "equivalent good sun" so you'd probably need even more panel to match the actual consumption. Using Icarus' famous fast formula: 1530 Watt hours needed * 2 = 3060 / 4 hrs sun = 765 Watts of array to account for all the losses inevitable in a system.

    Those fans; 24" with 1/2 HP motors by any chance? They'll probably hit about 10 Amps on start-up, possibly more. Motors do not have a fixed run current and the especially don't have a fixed start-up current. Fortunately fans are easier to start than pumps.

    So for three fans you'd probably want a 4 kW inverter at least. Plus a minimum of 384 Amp hours of battery and probably 2 kW of array to recharge them (with about a 45 Amp MPPT charge controller).

    You can look at some of the different types and prices of equipment at our host's store, to get an idea of costs: http://www.solar-electric.com/
  • icarusicarus Solar Expert Posts: 5,433 ✭✭✭✭
    Re: Design Help

    Once again, plese define your needs, as to the scope of th project. Perhaps the smart folks he can come up with reasonable alternatives. What are you venting and why?

    Tony
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Design Help

    dc fans are a good answer, but to move very much air they will draw similar wattages as the higher voltage ac fans do meaning more pvs to power them. i am assuming you wish to aim the fans to the horses to cool them, but additionally one to vent excessive heat from the shed in the roof would prove beneficial to them. can you also shade the shed with say a tree or ivy as keeping the shed out of the sun helps tremendously too?

    note: in using more than 1 fan be sure they can complement each others air movements and possibly allow the entire shed to have a small breeze flowing in 1 direction.
  • SlappySlappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Design Help

    my i ask, what type of fan, is it a direct drive or a belt driven type, like you can find in a chicken house, or a "whole house attic fan", etc. if it is a belt driven type it can be easily converted to a DC motor then you can run directly from the panels, but their is limits to this also, (with in reason of course. ) sorry but I had to ask.
  • toglotoglo Registered Users Posts: 9
    Re: Design Help

    Thanks for all the help. I have been mulling it over as time allows and finally found a DC powered fan that looks like it might be fairly powerful. Has anyone seen these:

    solarconduit.com/shop/heat-cool/ceiling-portable-fans/20-inch-freedom-fan-302-12-volt-battery-clips.html
    [NOTE: link broken by moderator as it showed as "untrusted". Proceed at your own risk.]

    What size panel(s) or setup do you think you would need to run 3 of these? Thanks for the help.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Design Help

    A little research on 20" Freedom Fan shows 40 Watts on high, moving 900 cfm.

    Is 900 cfm sufficient for your ventilation needs?
    40 Watts is certainly better than what a 1/2 HP AC induction motor will use!
    They don't look very rugged, though. That may be a consideration.

    Take a look at some of the other choices I found here:
    http://www.kansaswindpower.net/fans,_coolers.htm
    (DC intake/exhaust fans)
    NOTE: Not a site or product recommendation; just for reference.
  • toglotoglo Registered Users Posts: 9
    Re: Design Help

    That site, Kansas Wind Power also sells the DC Freedom Fan as well as a few others. They claim the 20" model puts out 3000 CFM on high. I am skeptical however even if it puts out around 1500 CFM that would put it on par with a standard box fan. An evaporative cooler would not work as there is no water supply close and in this area humidity is a problem so evaporation would not occur at any great rate. The humidity today is about 70% at 2:00 in the afternoon with a temp of 85 (miserable). Any idea on panel size setup?
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Design Help

    Sizing comes down to the usual questions:
    • How many watts
    • Volts? 12 VDC or 120 VAC, etc.
    • How many hours per day operation
    • During sunny day or at night (battery operation)
    • Summer and/or Winter operation (hours of sun per day)
    Note that DC fans, typically, use less power than AC fans because they move less air.

    Also, DC motor/fans tend to need repair/replacement more frequently than AC fans.

    If you only need air movement during sunny weather and can get away from needing a battery bank / inverter--Then DC fans can make a lot of sense (you will save a lot of money avoiding batteries + AC inverters, plus the 2x extra amount of solar panels need to run the extra equipment/loses).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • toglotoglo Registered Users Posts: 9
    Re: Design Help

    So if I wanted to run a 20" Freedom Fan, What size panel(s) do you recommend? The fan is 12V DC with a 4 amp rating on high. So 48 Watts right? Do you recommend an 80 watt panel to make up for some losses? The fan has a PWM speed control. I see many panels are 24v. How do I connect the fan to the panels. Thanks for all the help!
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Design Help

    I do not know anything about their fans--If you are planning on anything not listed on their website, you should contact them directly.
    [FONT=Trebuchet MS, Arial, Helvetica]A 3-wing polypropylene fiberglass blade with a square injection molded fiberglass venturi frame for easy installation and long life. The high efficiency DC motor has a 5000 hour life at 32 Volts DC and longer at lower voltage. This design moves more air with less power and noise. Use on battery systems or solar module direct with maximum open circuit voltage of 40 volts. 1 year warranty by factory. [/FONT]

    So, the limits are 40 VDC maximum and roughly 12-32 volts operational.

    Note that 5,000 hours is not that long of life... If you run it 8 hours a day:
    • 365 days * 8 hours per day = 2,920 hours per year
    So--You can only turn on the fan in hot weather, and/or run at a lower speed for longer life. And you will need to replace brushes every so often (no hours listed here--maybe every 1/2 to 2 years????).

    Say you choose ~17.5 volts... That is a "12 volt solar panel" and the fan is rated to use somewhere around 2.3 amps (if I am reading the correct chart).
    • 17.5 volts * 2.3 amps * 1/0.77 panel derating = 52 watts rough minimum sized panel for "full power"
    If you wanted to run the same fan at ~35 volts (two "12 volt solar panels" in series for Vmp=17.5):
    • 35 volts * 3.6 amps (or a bit more) * 1/0.77 derating = 164 watts minimum solar panel
    And--you can decide how much early morning/late evening sun (without batteries) cooling is too you...

    The above numbers will, roughly, drive the fans at rated speed from ~10am to 2pm, and taper down in speed at lower sun angles.

    If you want more air flow, you would use larger wattage arrays to collect a bit more sun in the early AM, late PM sun (maybe another hour or two at higher speeds).

    If you want battery power (longer runtime into darkness)--Plan on spending about 4x as much for solar panels + batteries + charge controllers vs the above solar panels alone.

    But you could also use AC powered fans (with inverter) for more reliable operation and probably less expensive fans (everything is trade-offs).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Design Help

    I don't think those fans are designed to be run directly from solar panels. You'll need batteries to supply consistent power and a charge controller to regulate the charging. If you want to use 24 Volt panels to charge a 12 Volt bank you'll need to use an MPPT type controller.

    Time is a big factor here. One 40 Watt fan running 24 hours is 960 Watt hours. That's about 80 Amp hours @ 12 Volts, so would require at least 160 Amp hour battery to run it.
    To make up for that 960 Watt hours you'd have to determine how much sun you can expect. You'll get a calculation like this: 960 Watt hours / 4 hours "equivalent good sun" per day = 240 Watts of panel after efficiency losses. Probably 300 Watt array. That also works out very close to providing the peak potential charge current for the 160 Amp hour battery (comes to 15.6 Amps by my estimation).

    However, if you can't actually get 160 Amp hours of battery you may need to increase everything.

    And that's per fan.
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Design Help

    There are several fans listed, and a couple say they are used with solar panels.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Design Help

    Hi everyone... this question leads into effective and useful "dump" or opportunity loads as well since he doesn't want to get into storing any power... Are there no good dc fans with variable motors that will run on variable/direct solar/wind/hydro power? I would imagine such a motor would possibly have a built in capacitor and such. I would certainly like one of these fans as well for my "opportunity" load.
  • toglotoglo Registered Users Posts: 9
    Re: Design Help

    I think I made a mistake by not providing enough information:

    I want to run a specific product. It is a 12v portable fan rated at 4 amps on high. It has a PWM speed control and a cigarette lighter plug. I only need it to run when the sun is out so I do not need batteries etc. The website claims the fan can be run directly from a panel. So what setup do you recommend? Thanks.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Design Help

    Sorry; the questions all start to run together after awhile and I get confused about which specific situation I'm looking at. :blush:

    If the fan manufacturer says it can run off a panel they should also say how much panel.
    Otherwise you'd be looking for something that could supply the roughly 48 Watts averaged over the daylight. That would likely be about 60 Watts of panel. It may be difficult to find one that meets that exact number, so you could go down a bit and possibly lose some fan performance or go up a bit and spend money on Watts you'll never use.

    Note also that small panels tend to be quite expensive on a per Watt basis. I think your original plan was to run two or three fans? In that case running multiple fans from the same panel becomes more feasible financially. For instance two of them could be powered by one 135 Watt Kyocera which is less $ per Watt than two small panels. You don't want to go higher than that or you'll find you get "24 Volt" panels which will probably exceed the V-max for the fans.
  • rplarryrplarry Solar Expert Posts: 203 ✭✭✭✭✭
    Re: Design Help

    Well that simplifies things considerably. Your fan consums apprximately 48 watts. Get a panel in the proper voltage range, 18v or so and somewhere in the 60 to 80 watt range and you should be good to go. Down here in Baja I have seen similar setups that the ranchers use, but they are pumping water. They use a small marine submirsible bilge pump and hook a solar panel right to it and when the sun is out it transferes some water for them. Seems to work well for them. Hope yours does to.
    Larry
  • toglotoglo Registered Users Posts: 9
    Re: Design Help

    Great thank you so much. That was my real question. If I wanted to run 1 fan I could get a roughly 60w panel. If I wanted to run 3 fans however That would be around 150w. Should I use the Kyocera and another small panel or two roughly 80w panels etc. Also the voltage at max power on the Kyocera is 17v. Is that too high for a 12v fan or do I need some kind of voltage regulator. Thanks.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Design Help

    If the fans are "12 Volt" and designed to run from a solar panel with their own PWM controller, then they should be compatible with standard "12 Volt" panel, the Vmp on which is around 17.5. It should function much the same as a 12 Volt charging system: 17.5 Vmp through a PWM controller to provide the approximate 14.2-14.8 Volts. Their particular controller may be designed to regulate the Voltage slightly lower. As Jimbie said, it probably does have a capacitor on the output side to "smooth out" the power.

    Yes you could run three from two 80 Watt panels paralleled. As I said, the manufacturer should provide data about what panel Wattage/Voltage the fans actually can run from. I'm just basing this on "standard electrical practice". :roll:
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Design Help

    Those 16" (20"?) fans can also run at higher voltages (~32 volt rated, 40 VDC maximum)--At higher voltage, they will move more air (and require around 165 watt Vmp~32-35 volt) panels.

    However, at the higher voltage/speed, they will not last as long.

    For the "12 volt" panels, you can use 3x 50-60 watt panels, one to each fan. Or one ~150-180+ watt Vmp=17.5 volt panel) and run all three fans from one panel.

    Note, as panels go over 100 watts, it gets more difficult to find Vmp=17.5 volt panels... The larger panels tend to have >>17.5 volt Vmp ratings.

    Make your choices based on best $$/watt delivered to your door (or local retailer). High wattage panels tend to be less expensive ($$$/watt), but more expensive to ship (large pieces of glass).

    ~135 watt panels (and smaller) tend to be small enough you will have many shipping options.

    ~175 watt panels are fairly large and about the largest one person can safely move by themselves. Larger panels will need two people to move safely.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • toglotoglo Registered Users Posts: 9
    Re: Design Help

    Let me take the time to thank everyone for the help. It is forums like these that can really help newbies learn the basics. As a newbie I have one last question. This may be best as a topic of its own however I was wondering about the diffenences in prices between brands of panels. NAWS sells a Kyocera 135w panel for $365. A 130W Sharp or Sunforce is $450 or higher. I know they might have different technologies i.e. poly vs. mono however why would anyone not just choose the Kyoceras? Can anyone explain to a newbie why there are such differences between brands and prices for roughly equivalent watts and voltages?
  • BB.BB. Super Moderators, Administrators Posts: 31,875 admin
    Re: Design Help

    Mono crystalline vs Poly crystalline--Mono is slightly more efficient and if you are packing limited roof space with panels, then the more expensive Mono Crystalline may be worth the extra money.

    Otherwise, always check the $$$/Watt packaged and shipped to your door.

    Normally, I would tend to avoid any Thin Film panels. They are the cheapest per watt by are around 2x the square foot for the same wattage. Many thin film panels are ~10 year panels vs 20+ year panels for crystalline.

    The other thing to look for is the operating voltage of the solar panels. Evergreen tends to be one of the few vendors that makes larger panels in Vmp=17.5 volt range...

    Certainly Kyocera has good panels and has backed their warranties well (when needed).

    So much is coming from China now, it is very difficult to know who is a good vendor or not (changing names, private labeling, etc.).

    Look for a UL rated (NRTL--CSA, TUV, etc.) panel--The vendor at least went through the time and money to have a third party test for safety.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SlappySlappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Design Help

    NAWS sells a Kyocera 135w panel for $365 that panel has the MC4 connector, but you will have to spend more for the MC4 cable to hook it up. the other Kyocera 135w panel has the junction box and it is $399. and you can use your own wiring. (Price is reflecting the time of this post!)
  • chevensteinchevenstein Solar Expert Posts: 100 ✭✭
    Re: Design Help

    Depending how handy you are, you might consider pulling some electric radiator fans from a junkyard if there's a "you pull it" yard near you, and fabbing up some mounts for them. You should get them for peanuts, they're 12V DC, and are designed for years of dependable service in extremely harsh conditions. The Lincoln Mark VII had one of the most powerful electric radiator fans you can find, a fan like that will move a couple of thousand CFM.
  • toglotoglo Registered Users Posts: 9
    Re: Design Help

    I am open to building my own fans. Can I run a fan like the fan in the Lincoln directly from a panel? As I said before I do not care if the fan does not run when no sun is present. Thanks.
  • SlappySlappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Design Help

    this will give you a basic idea, http://www.youtube.com/watch?v=caeEyhJZnTs Dan is using a HF 45 watt solar kit to run a RV fan straight from the system (with out a battery hook up). jump to 1:20 time frame when he runs the fan. and these are cheap panels. I just call them toys. I just linked this video just in case it could help ya in some way.
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