Solar direct to fan for Greenhouse

[justgary]

Your panel should be able to run several pairs of 12v fans in series. These (shown below) are 0.2A each, so the panel may run up to six or seven pairs in full sun. You want series pairs so they work up to 24v, and you parallel those up to the current limit of the panel.

You probably want ball bearings and a two- or three-wire interface.

12v fans

 

[MisterSandals]

I then measured the short circuit current of the panel and made sure that it did not exceed the total current required by the fans.

This is misguided advice. The fans pull the current they need. The short circuit current (Isc) is irrelevant in regards to hurting the fans. Imagine connecting the fans to a car battery; the short circuit current is hundreds (thousands?) of amps but not an issue for fans that pull tiny amounts of current.
However, the panel needs to be able to provide the current the fans need to start and run, which is the tricky part to predict.

 

[justgary]

This is misguided advice. The fans pull the current they need. The short circuit current (Isc) is irrelevant in regards to hurting the fans. Imagine connecting the fans to a car battery; the short circuit current is hundreds (thousands?) of amps but not an issue for fans that pull tiny amounts of current.
However, the panel needs to be able to provide the current the fans need to start and run, which is the tricky part to predict.

Sorry, it was late when I typed that. I will edit it.
My next post offers a better solution for the specific case of her panel with ~22V open and ~1.4A max power. The fans I linked are 0.2A each at 12V nominal. Two in series will start and run slowly at low voltage, and 22V will not harm them. The 1.4A max power should be able to run several parallel pairs at 0.2A each.

 

[Hedges]

If Imp is more than what the fans draw, voltage will go above Vmp toward Voc.
With brush-type fans connected in series, they will simply run faster or slower with varying voltage, splitting it evenly between them. If one lags and the other gets momentarily higher voltage, it will speed up but not overheat in a brief time. If one stalls (e.g. seized bearing), the other might not be happy.
With electronic BLDC, if one draws current before the other decides to, the one not drawing current will see near full voltage. Series connection wouldn't be good, and Voc above max rated voltage wouldn't be good.

Some BLDC will start up as voltage gradually rises with the sun, but others will enter shutdown. I tested a few, selected some 24V Pabst fans rated 24V that worked fine with a 12V (nominal) fan having about 17Vmp, 21Voc. Also a 48V fan which originally had external controller (thermostat, variable speed, whatever) which works fine with two of those panels in series. I don't have fans in series.

 

[G20]

Any updates on your greenhouse fans ?

Thanks much.