Powering several small fans

To be proper you will need a Solar panel, charge controller, and battery. I have run fans directly from solar panels, but I was close enough to monitor the system. Fans convert electricity into physical motion and the motor dissipates heat as a side effect, with a direct connection if a cloud comes by (or dusk/dawn) and the power output from the panel drops too low to turn the fan(s) you will still have some power output going to them if it is not dark out, depending on the exact situation and components it is possible to have the motor windings in the fans overheat causing damage to the fan and/or fire. A battery acts as a buffer to smooth out fluctuations from the solar panel, and also prevents problems and shutdowns during clouds, etc. a used motorcycle/auto battery can be had for $5 to $15, so it doesnt make any sense to take any chances except for the purpose of demonstration or experiment. Most cheap solar controllers ($19) can be set to shut the system down at night so as to not drain the battery. As far as panel sizing all your fans appear to add up to about 15W total, you could double or triple that to make sure you have some headroom as panel ratings are Maximum output not average output.

It is also possible to use circuits of various design to monitor systems and shut things down when proper power is not available to run things correctly, but that would be more expensive and more complicated. Passive loads (no motion, no motor) like an old incandescent light bulb are no problem direct to a solar panel and when there is enough power it will light in varying degrees depending on available power, when the power fall below the threshold to produce light you will have no light. Things that move and involve motors can present other problems when some power is going to the device but it falls outside of the normal range that the designer created the device to work with. Solar panel output (voltage and current) vary more than most people first realize, not just with clouds and darkness, but even the difference between 9 in the morning full sun, and 2 in the afternoon full sun. The only shortcut is that it doesn't take much battery to keep things happy if you really don't need to store energy to use later, a charge controller will prevent an undersized battery from overcharging and the system just will not work much with no sun (which you don't want anyway). The charge controller will shut the system down when the voltage drops and ends up being a much safer system.

You can run many fans solar direct. If yours can I don't know.

First thing you need to find out is the working voltage range of the fans. 12V in the nominal voltage. You need to select a panel that has it's VMP within the working voltage range of the fans. It is nice to also have the VOC within that range but not required. Most 12v panels have a VMP of about 18V. Most 12v motors have a Voltage range of 10v to 15v. So you may have to find different fans or try finding a 24 to 28 cell panel. I would not try to build my own panel. The cost savings or dependability of the panel are not there. If needed one might be able to go with a grid tie panel that has a VMP of 24 to 28 volts and wire 2 fans in series.

On the amperage side you want a panel that puts out at least the total amperage but preferably at least 150% all your loads. The reason for that high is that panels only produce maximum power when aimed directly at the sun. They also put out about 70% of there power when the sun is shining at a 45d angle to the panel. That should give you about a 6 hour operating period for the loads on a sunny day.

WWW

You guys have been very helpful. Thank you. I'm inclined to try and run them without a battery. The fans are cheap enough that they could be replaced easily. I suppose I should be concerned about a fire, but it's going to be far away from any structures, and I need it to slow down and shut off when the sun disappears because of clouds, sundown, or whatever. Otherwise, the kiln will have trouble maintaining its temperature and I'll have to rig up some kind of high temperature thermostat.

If it helps, these are the fans:
Four of these: http://www.coolermaster.com/cooling/...t-fan-120-si2/
Two of these: http://www.coolermaster.com/cooling/...ed-silent-fan/

It sounds like I need at least 1 amp and about 30 watts. I understand the voltage part, I believe. I've dealt with that before. So I need something like this, right?

I'd recommend using either a shunt or series regulator. A shunt regulator is just a zener diode, sized so it can absorb the output of the panel. If the fans have a max voltage of 16V, then a big 15V zener would do it. You can get a 50 watt 15 volt zener for about $25. It needs a large heat sink to account for the case where the fans fail or get disconnected.

Or use a shunt regulator like an LM317T (or its various cousins.) This gives much more precise control over voltage, but dissipates power all the time. Again needs large heat sink.

Light bulbs are coming on. You guys are saving me from a mistake. Doing a little parts research. Thank you!

I would think, the simplest solution would be just take a car battery out there to run the
fans. Recharge it at night. Bruce Roe

Yeah, but it's going to start collecting heat as soon as the sun comes out. The fans need to come on too.

The more I think about this, the more I'm thinking maybe I do need a battery. I thought about a voltage regulator, but (and I have no idea) I wonder if it would just shut the fans down a lot because it's not getting a constant 15V or so. Unfortunately, a battery, a controller, and a solar panel puts me out of my budget. I might ought to just wait until I pull together a few more dollars (or risk disapproving glares from my wife).

Just power the fans with these:


They will limit the voltage to whatever you set. As a bonus, as the solar panel starts putting out more voltage, the step down converter will use even less power as its a power in= power out. You could ran more fans that way.

Not sure what your budget is, but I would focus on finding a deal on a capable solar panel, that is by far your biggest financial hurdle whichever way you go, and if you can save on that end the rest is pretty cheap. I got a good enough little controller off Fleabay new for $12, and you dont need a battery for storage so just to put something in the circuit to keep everything happy helps with the budget side of that, wmart has new 12v S.L.A. starting at around $15, or you might be able to get a motorcycle shop to give you or sell you a used one for $5, as long as it is not completely shot. How much have you been thinking you are going to have to spend on a Solar Panel?

I don't think so. This is a kiln for drying lumber. You want to remove moisture instead of heat from it. The fans don't need to come on until after the humidity has come up. Delaying the fans would help in drying by giving it time to evaporate out the moisture before you push a bunch of cold air in there. Angling the panels to the SW to delay there start by 2-3 hours and extending the run further into the evening would be beneficial.

WWW

Ok, wow. That's smart. And you're right.

I've got maybe $80 or so to work with, but if I can spend less, I will. I saw a battery on Amazon for about $15 too. So far I can't find a better deal than this:



It's also on Amazon for a little more right here:



If anyone knows of a better deal, I'm all ears.

In the long run it might be cheaper to run that extension cord.

Most people think that solar is low cost and provides free energy. It is neither.

Purchasing cheap equipment to keep your costs down ends up just wasting money and costing you more to get it right. (Trust me I know because I did it). You could end up purchasing all types of panels, charges, batteries, voltage regulators until you come up with the right combination to make your fans works the way you want but at what cost.

A solar grid tie system can lower your electric bills but will take years to break even. A solar / battery system will never break even.

A solar driven DC motor may work but on days you do not get the sun then you have no power to run that DC motor. That is when you start thinking about batteries and then the costs start to spiral out of control.