Alternative Technology Assn Forums

1. 

   munter
   Member

   I'm looking for a little advice to help with a solar powered fan. The fan will be used to move air through an active solar air heater that I'm tinkering with at the moment. The fan only needs to operate when the sun is shining (and therefore the heater is heating) so I was thinking a direct connection of solar panel to fan would work acceptably well. I was thinking of a 12 Volt, 5 Watt panel in conjunction with a 100 mm 12 Volt, .2A brushless computer case fan. Is this likely to work? Am I going to have issues when the panel voltage drops below 12V? Can I use a brushless motor in this application.

   I'm totally new to photovoltaics so need all the help I can get on this. Are there any recommended resources on the web?

   Posted Monday 6 Jul 2009 @ 2:45:35 am from IP #
2. 

   Benny
   Member

   Hi again Munter - your project now has 2 threads eh ? (-;

   Before you consider using a solar powered fan, consider what sort of airflow you want to get. Will there be a lot of ducting between the heater and outlet ? I think you might be disappointed with just how little airflow you get from such a small fan (5W). For my system I just used 2 cheap AC extractor fans, $20 each. As my system is on the roof and I bring the outlet air down to ground level, I have about 1m inlet duct and 5m outlet - 30cm diameter aircon duct. Even with these 2 fans puling 60W I only get a slow airflow in to the room - I must measure it one day with the "garbage bag test". Still its enough airflow I think as it keeps the collector down to a reasonable temp.

   Posted Monday 6 Jul 2009 @ 4:06:33 am from IP #
3. 

   munter
   Member

   Thanks Benny,
   I agree that the 5W fan might be undersized. I'd like to keep it low voltage DC though so as not to require the services of an electrician. Perhaps a 10-20W DC fan would be better?
   The ducting on this project is very short. The heat exchange happens along the width of the panel (700mm) and then the duct turns 180 degrees and returns to the wall vent approximately in the middle of the panel (350mm), the duct then makes another 90 degree bend to go through the wall (double brick) and thats it. All up the duct will only be a bit over one meter long. I'm hoping that the short duct will result in low heat losses and low power requirements. The insulated ducting also has a slight upwards alignment so I won't be trying to push hot air downwards. If the power requirements get much over 10 Watts I'll be reluctant to fork out for a PV panel to power it (too many $$$ for an experiment) and will need to look at mains power again.
   Thanks also for the tip re heat transfer. I'll be using copper fins and because of the method of attachment they will be at an angle to the flow. Given my construction skills I'm sure the flow out the end of the heat exchange duct will be turbulent!

   I thought I'd start this second thread as it covers a specific question that I thought might get lost in the other one. I hope that isn't bad form. I'll get some photos up though I'll have to put them on my blog as this forum doesn't seem to allow posting of pictures.

   Posted Tuesday 7 Jul 2009 @ 12:29:24 am from IP #
4. 

   Solgen
   Member

   Air flow hates changing direction. Your proposed setup with 180 and 90 degree bends will drain a lot of energy out of the air flow and I suspect, like Benny, that the air flow will be inadequate for your purpose.

   Posted Tuesday 7 Jul 2009 @ 12:41:16 am from IP #

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