Solar panel connection

[creightons]

I'm trying to use a 200W solar panel to power a 36W load. However, I don't understand solar panel behavior very well. If I attach the 36W load to the panel directly, will the load forcibly reduce the output of the solar panel? Or will the full power of the panel be directed into the load?

If it turns out to be the latter, is there a way that I could redirect the excess power from the panel? One way I was thinking of doing this was by attaching another device in parallel. I was thinking I would just size a resistor bank to dissipate the specific amount of energy I was thinking of as heat.

Please let me know if either of these ideas is feasible. Thanks for the help.

 

[Skogsgurra]

Forget about power for a while. It is more about what voltage and what current your solar panel can deliver and what rated voltage your load is.

For low loads (high resistance) the solar panel outputs a voltage that increases when temperature gets lower (yes, that's right) but stays quite constant for normal temperature variations. If your load's rated voltage is about the same as the panel's voltage, then you will be OK. With 200 W panel and 36 W load, the panel will deliver 36 W to the load. There is no "forcing it all down the throat" behaviour in the panel.

Well, that's about it. Just make sure that the panel's voltage and the load's voltage are the same. It is just like connecting a load to a battery. The load takes what it needs and the battery doesn't force the load to swallow more than that. Simple, no mysteries.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[creightons]

The panel characteristics are the following:

V(Open Circuit) = 22.3V;
I(Short Circuit) = 12.3 A;

The load I'm using is a thermoelectric refrigerator rated for a 12V, 3A DC input. I'm planning on using a DC-DC converter in the link below to get a constant output of 12V. I

http://www.dfrobot.com/index.php?route=product/product&product_id=504#.UUuc9RekqYg

The converter is rated at 72W and puts out a 12V, 6A signal. However, if I attached it between my refrigerator and the panel, could I expect the converter to put out a 3A current?

Also, thanks for the information about the solar panel output. I've always figured that the power output of a panel would be tied down to the requirements of the load by Ohm's law, but I've never been able to find a source to confirm it.

 

[itsmoked]

Yes you could expect your converter to put out 3A in that case.

There are lots and lots of gotchas so we can't say 100% that it will all work. But in principal it should.

I'm not sure why you aren't using a solar charge controller to keep a battery properly charged while running the refer from the batter via the DC-DC.

Or way better yet, using a charge controller that will take WHATever the panel provides and using Power Point Tracking charge a 12V battery directly and correctly. Then you simply run your refer off the most common battery voltage on the planet. This would allow the refer some non-sun-up running time.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[creightons]

Thanks for the advice. The reason I'm not using a charge controller is because I'm just trying to build an example system of a thermoelectric refrigerator running off a renewable energy source. This is only for a one-time project, and since I'll be done with it afterwards I don't want to spend too much money on it.

 

[OperaHouse]

You have made suprisingly good choices. The panel is teh minimum needed. The converter should operate the panel most of the day at the power point. The boost cspsbility will hurt a little but that is a good price and will operate better than a controller.. The thermoelectric refrigerator is the weak spot being inefficient and limited cooling range,

I have a solar only chest freezer at camp. Microprocessor controls temp and regulator. Battery used only for 90A inverter surge. At night temp maintained by solar mass. Post your project on fieldlines.com for other RE people to see results.