Jump to content

Small solar panel for roof top vent fans?


rbertalotto

Recommended Posts

Has anyone installed a small solar panel for a roof vent? My roof vent fan draws 1.2 amps, and I have two roof vents. Getting them off house batteries would save nearly 3 amps. I'm estimating I'd need a 50w 12v panel to run both..?.

 

Anything I need to do to protect the fan motors from too much current ???

 

Thanks

Link to comment
Share on other sites

I would NOT try to power the vent fans DIRECT using a solar panel ALONE........

 

First of all, a so called "12 volt" panels output voltage depends on the intensity and angle of the sunlight and could vary between near zero volts in low sun condition to maybe 17 or 18 volts (subject to their voltage rating and Vmp) in bright direct sun A MOTOR DOESNT LIKE LOW VOLTAGE, you could damage it trying to run it at low volage !!!!!!!!!!

 

If you coupled it with a Solar Charge Controller designed to take the panels raw energy output and varying voltage and control and regulate it to maybe 13 to 14 or so volts suitable for charging a 12 volt battery is at least better then the above, but NOT what I would try, since regardless, in low light it cant supply enough Voltage nor Power (Volts x Amps) to run the fans and they don like low voltage and could be damaged !!!!!

 

WHAT I WOULD DO is install the panel, but Id go ahead and use AT LEAST A 100 WATT since that's no harder to mount then a 50, couple it to a Solar Charge Controller, (20 amp will work for a 100 watt panel, PWM will work fine but I prefer MPPT) and connect that to your battery so it can allow you to harvest energy to replace what the fans may consume PLUS it will help keep your battery charged in addition.

 

I would NOT want to get them (fans) off the batteries as you state, THEY ARE A STEADY RELIABLE SOURCE OF 12 VOLTS AND CURRENT (subject to charge state) TO POWER THE FANS unlike a solar panel alone which has a variable voltage and is NOT intended to power a 12 volt motor but to charge a 12 volt battery and let IT run the fans .............

 

That's how Id do it, NOT use a solar panel alone (variable voltage source subject to sun, NOT a battery), but instead use a Solar Panel plus a Solar Charge Controller to supply energy to the battery so IT runs the fans with a good steady reliable voltage PLUS it charges the battery.

 

Others may have different opinions and can add to this, but FWIW that's how Id do it.

 

John T

Link to comment
Share on other sites

I had a great idea as what you are doing is similar to what a lot of folks do with solar water pumps and you are facing the same issues. However looking up the controllers they use for this type setup the cheapest I found was about $150 and most were near double that. Tra a search on: 12 volt solar pump controller

 

If you used something like DC brushless motors that can tolerate low voltages and being stalled without internal damage you could hook them direct to the panel. As folks mentioned panel voltage can be an issue so you might find you need to use a 24 volt fan to be safe from panel maximum voltage.

 

I also thought about a small solar controller like the Morningstar SG-4 hooked to a small super-cap instead of a battery to stabilize the output voltage. That might work to limit your maximum voltage but it would waste the additional power the panel makes past your needs. It should reduce the fan's stalled time in the morning and evening but how much and how your fan would deal with it would have to be an experiment.

 

I kind of lean to the charge your RV's batteries and use them option above, the loss in going through the battery would be offset by being able to continue to move cool air in the evenings in my opinion.

Link to comment
Share on other sites

Stanely, to your point:

 

"I also thought about a small solar controller like the Morningstar SG-4 hooked to a small super-cap instead of a battery to stabilize the output voltage"

 

Strictly theoretically speaking, in a sense, a capacitor is similar to a battery in that its an "electron bank" and can serve as a buffer or voltage stabilizer since capacitors oppose voltage change just as an inductor opposes current change. Now if he can get a capacitor charged to a voltage (and sufficient stored energy once sun settles) to run the fans and not drop voltage lower then necessary ????????????? Not something Id do but hey to each their own????

 

Of course as it appears we all agree, Id use the battery (steady reliable voltage source until its discharged) to power the fans and use a solar panel and charge controller to replenish battery energy the fans are depleting. I also have front and rear rooftop vent fans I might run all night if its warm, and the next morning when the sun pops out it don't take long to replace the energy consumed during the night.

 

As always I appreciate your help over the past year and enjoy your sparky chat

 

John T

Link to comment
Share on other sites

The reason I suggested the super-cap is because it has no problem being discharged to empty so you can avoid having to go with a more expensive solar controller with a low-voltage disconnect. You would have to do that with a battery setup unless you were sure you could do the load removal manually, without fail. I haven't read the detailed specs on that particular controller but many series regulating controllers need a storage device of some sort on the output to work properly.

 

Depending on the size of the super-cap you could get some run time from it but it looks grim.

 

3 Farad super cap for only $99.99

 

http://www.crutchfield.com/p_1203DDC/T-Spec-Capacitor.html?tp=739

 

I'm not doing the math for that one but that won't run a fan for very long. Capacity math here:

 

 

A 1.5 volt AA alkaline battery that stores 2 amp hours of charge (that’s 7200 coulombs) has the equivalent capacitance of 4800 Farads.

 

Link to comment
Share on other sites

I need to look more closely at the fan I just bought for the house to see how they are handling the solar with no battery issue.

 

This is the unit I bought.

 

https://www.amazon.com/gp/product/B00E382RQA/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

 

Works great! Wish they made one a wee bit smaller for RV use. Hard to believe Fantastic Fan or some other company doesn't offer one.

Link to comment
Share on other sites

No doubt it must "work", it must use a fairly low voltage tolerant motor and maybe they use some capacitor type of storage/buffer?? but only 20 watts of solar isn't enough power to charge up a "rubber chicken" and for the $247 they cost I just bought a 235 watt 24/30 volt solar panel for $212 and I run two max air type roof vent fans all night !!!

 

HOWEVER to each their own, their money their choice, but before Id spend $494 for two solar powered vent fans I would spend $212 for a 235 watt solar panel to charge my house batteries (or $424 for 470 watts) to run TWO fans PLUS other loads and charging purposes.

 

OF COURSE to compare apples to apples we need to know the CFM rating of vent fans and how much power it takes to run them etc etc before we can make a true comparison, heck those solar vent fans may be the best thing since sliced bread and more cost effective then buying panels BUT IM NOT BETTING THE FARM ON THAT LOL

 

Yall buy all them you want and they will "work" but I doubt I will spend $494 for a couple roof vent fans but instead $424 for 470 watts of solar panels.

 

Nuff said

 

John T Kind of a frugal tightwad fuddy duddy lol

Link to comment
Share on other sites

Agree with that! Folks put SOLAR on something and jack the price way over what is reasonable.

 

A small square panel mounted to your air conditioner cover (the least possible hassle location) and run to your fan is going to be far cheaper.

 

 

This would work too with a bit of fiddling with the fan mount. For $100 it is still high but not a complete ripoff.

 

http://www.solarblasterfans.com/products/rvoblaster/

Link to comment
Share on other sites

Gee Stanley, are you sure that whopping 3 watts (Solar RVOBlaster kit) wont overheat, overcharge batteries, or cause a roof fire now ??? lol You're right, when I see SOLAR anything at like Menards or Lowes the prices are highhhhhhhhhhhhhhhh. You see those so called "Solar Generators" or Solar back up power devices that may be 50 or even 100 watts max sell for hundreds of dollars. Maybe we ought to go in the business but I'm too old n retired n lazy lol

 

The Amish near us (where I buy my panels) are putting up stationary southern 47 degree tilt ground mounted 4000 watt solar systems with 3 or 4 K Inverters and L 16 battery banks, really getting with the program. If the REMC allowed grid tie I think my next home (planning to sell the farm and downsize) will have 4 KW of panels but if I cant grid tie I will probably pass.

 

John T

Link to comment
Share on other sites

Here's yet one other 12 volt RV ceiling fan, 3 speeds forward and 2 reverse but NOT direct solar powered like the $300 units above, you have to power them the old fashion battery way and if you have solar panels they can recharge your batteries as required. I've used and was satisfied with them, although NOT the CFM of the larger more expensive units.

 

http://www.ebay.com/itm/RV-Ceiling-Fan-12V-Volt-Roof-Vent-Multi-Speed-Vortex-II-Camper-Trailer-Motorhome-/252518317321?hash=item3acb43bd09:g:I50AAOSwMgdXxSBW&vxp=mtr

 

John T

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...