Solar Heater help

System

Hi, I'm Jesse. I hope this is the right place to ask a few questions. If not, then I hope I can be pointed in the right direction. Thanks in advance and please bear with me.

I have a solar heater with aluminum cans painted black inside an insulated box, etc.

For moving the heated air I'm planning on using two 48-Volt fans like this.

I see this site has a store that has this. I hope that will help, but my knowledge of electronics is limited and rusty. So, I don't know if I'd need anything else, or if that would require wiring things up a certain way.


Another alternative for moving the heated air is to use a 12-Volt radiator fan I got from an old car. It's much larger than the 2 PC fans so I'd like to avoid using that if I can.

However, ^this (the 12v radiator fan) may be more convenient since I also plan to use a 12-Volt windshield wiper motor for tracking the sun. This way (I assume) I could power both the motor and the fan off of one source of power. Such as a 12 volt battery -that could also be recharged via photovoltaic/solar cells.

Suggestions, and/or help with what I could do are greatly appreciated.

Cariboocoot

Re: Solar Heater help

Most desktop computers use 12V "muffin" fans that are about the same as the one you spec'd; roughly 3" square. You should be able to find them surplus or at a second-hand shop or used comp store. That way you can keep all the electronics in the very easy-to-deal-with realm of 12 VDC.

From the sound of your project, you will soon be telling us how you did it - after a lot of experimentation!:D

System2

Re: Solar Heater help

I suppose I wasn't wanting the 48-Volt fans to go to waste. Someone else suggested (just a while ago in another forum) that 12-Volt fans would be easier to obtain than a 48 volt adapter. So that will definitely be the way to go!

...Perhaps I could trade the fans somewhere.





Looking ahead, the next thing I'll be looking into is how to recharge a battery to power the fans and motor AND power them from the house... Just so I have both options available.

BB.

Re: Solar Heater help

To run your circulation fans--you will probably want to do that directly from a solar panel. Simple and only blows air when the sun is out heating your thermal collector.

Run your fans from a battery bank will make your system more costly (more solar panels, batteries, losses from batteries, controls to turn fans on and off, need to watch that the fans don't over discharge the battery bank, etc.).

You will need to watch the solar panel output voltage vs the fans allowable input voltage.... Solar panel output voltage rises as the temperature drops (and falls with increasing load). Most "12 volt" solar panels have a Vmp (maximum power voltage) of ~17 volts... Which may be too high for a small 12 volt computer fan (large panel, small fan). And brushed DC motors which would work better with solar panels are not that reliable before needing servicing (typically brush replacement).

If you have 48 volt fans and a supply of appropriate 12 volt panels... You, for example, put three solar panel in series to power your 48 volt fans (3*17v=51volts).

There are many ways of addressing the problem.

-Bill

n3qik

Re: Solar Heater help

Tetrafish wrote: »

I also plan to use a 12-Volt windshield wiper motor for tracking the sun.

Your solar hot air panel does not need to track the sun. For electric panels, there will be a gain, but hot air, there will be little gain. Just mount it facing south.

If you had a trough style, then yes.

Remember the KISS rule, Keep it Simple Stupid.

icarus

Re: Solar Heater help

Used computer fans can be had from any repair/recycling facility for almost nothing. I buy 12vdc and 24vdc fans for ~50 cents each. You can run a 24vdc on 12 only it will run slower ( and quieter) A 48 vdc fan will probably run on 12 but pretty slowly. I would avoid the car fan as it is not very efficient.

I use 24 vdc on my fridge condensers to cool them faster. I like the 24s because they move just enough air to create a draft,, but make almost no sound.

Tony

System2

Re: Solar Heater help

I've changed my mind about the fans (for now). I'll go ahead and use the 2 - 48 volt fans. I'm getting a 48 volt / 500 mA adapter (from PowerStream) to power 'em. And for tracking the sun I've ordered a 12 Volt / 5 Amp adapter from Monster Guts that will power the Windshield Wiper motor.

I first made this last year but it had some design problems. I was inspired to make this from something I seen on a local (very local ;-) T.V. station.

http://stlcamp.org/solar_powered_heating

The cans in his unit have sand in them, this combined with the reflective mirrors increases the heat a LOT!... The idea is like when -back in the old days- when people would wrap heated bricks in newspapers and put them at the foot of their beds... Which would provide heat for quite a while -I guess. That's what the sand is for.

But this time around I'll not be using the sand. It's just too heavy.

Mr. Snyders heater is supposed to track the sun... But I've never seen any info on how he does that.

But I did find this...

http://www.greenwatts.info/index.php?page=sun-switch

The only problem is - I'm using ONE motor instead of two. And I'll have to look up info on a Bi-Directional Bridge Driver circuit. That has yet to be done. :-/

I'm also planning on having the fans controlled with a thermostat or hacking something up similar using an analog remote/wired thermometer.... If I can find one.

In the mean time (between now and winter) I'll look into getting some solar panels to either power the electrical equipment on it... or to store the energy. That was my original intent for it, but the 12 and 48 volt adapters will do for now - just to prove that I can do it.

Here's some pics of how I had it last winter. It wasn't really complete.

Front View

Side View

Yeah... It was a monster. :roll: And you can see what I mean by 'design problems'. There wasn't much air movement from it. In fact... I had a small solar powered window fan -that's used to remove heat. And the dryer vent coming out of the back -instead of the top.... If I was able to have it 'track the sun' the dryer vent would have to twist -and it couldn't very well and still have good air flow.

I've redesigned it and... well, I can't tell all just yet. Stay tuned.

Sorry for the huge post.

Cariboocoot

Re: Solar Heater help

Looks a bit ... complicated.

How about simplifying it a bit? Some thoughts:

Insulated back and sides (2" of the pink foam would be R10 - about the same as an ordinary house wall).
Line the back with ceramic tile for mass.
Use aluminium roof panel instead on cans - the corrugations provide air channels over the ceramic.
Be sure ducting both in and out is well-insulted to prevent heat loss.

Just tossing out some ideas for your consideration. It will be interesting to see if there is any actual gain from tracking vs. non-tracking in this sort of application.

System2

Re: Solar Heater help

The next thing I'm trying to figure out is how to have toggle switches to control the motor for sun tracking... But they need to be photo/light sensing. & I have no idea if such a thing exists.

Link to pic of what I'm talking about.

When sunlight is on both 'sensors/switches' the motor stops.
When sunlight is not on either of them - the motor stops (good for cloud cover).
When the East 'sensor/switch' is shadowed - the motor turns clockwise.
When the West side is shadowed - the motor turns counter clockwise.

I've considered using photo-diodes, photo-resistors... or those (ambient) light sensors that are used in the house. But those- I'm not sure they'd work with a 12 Volt DC power supply (as opposed to 110/220 AC Voltage).

It seems sooo close.


Edit: I was hoping it would be simpler than this...

http://www.sccs.swarthmore.edu/users/06/adem/engin/e72/lab7/

rplarry

Re: Solar Heater help

Tetrafish
Go here for the photosensitive trackers, inexpensive and work really well:
http://www.redrok.com/electron.htm#led3x
Looks like a fun project.
Larry

stephendv

Re: Solar Heater help

Tetrafish wrote: »

http://stlcamp.org/solar_powered_heating

The cans in his unit have sand in them, this combined with the reflective mirrors increases the heat a LOT!... The idea is like when -back in the old days- when people would wrap heated bricks in newspapers and put them at the foot of their beds... Which would provide heat for quite a while -I guess. That's what the sand is for.

But this time around I'll not be using the sand. It's just too heavy.

The heat capacity of sand is higher than air, so it can store more heat, the most efficient way to move this heat around would be to move the hot sand itself from the collector into the home... mmmm, so what you need is some sort of a liquid sand that can hold heat, mmmm, like, maybe, water?

Tracking the sun for solar hot water is already a waste of resources and too complicated for the gain - tracking the sun for something as inefficient at moving heat around as air is even more so. You'd do much better investing that time in doubling the size of the collector instead.