24v panel question

[ralphkaz]

Quick question - I'm looking to setup a very simple system to use to power a few LED lights for when the grid goes down (storms, etc.)

I have a 20watt 24 volt panel and I just picked up the following charge controller from ebay:



Since my panel is 24volt can I still use a regular 12v car battery? or are there special considerations given the 24v vs. 12v panel?

Here's the specs on the panel:
Short Circuit Current ( Isc ): 0.62 Amp
Open Circuit Voltage ( Voc ): 43 Volts
Maximum Power (Pm): 20 Watt
Maximum Power Current ( Im ): 0.54 Amp
Maximum Power Voltage ( Vm ): 36 Volts
Cell: Monocrystalline
Weight (Panel Only): 10 lbs
Dimension of module: 26 x 13 x 1.50 (in)
Solar Panel Grade: A
Operating temperature: - 40 to +85 C
Maximum system voltage: 750 V DC
Type of output terminal: Junction box
Cable Length: 9 ft.
Connection: Open End

Thank you!!

[Mike90250]

While a PWM controller can charge a 12V battery from a 24V (36V) panel, you will loose about 50% of your panel output.

When you drag your panel down to about 14V to charge the battery, the difference in voltage from the charge voltage (14) to the panel's Max Power Voltage (36) you are more than 50% below. A MPPT controller WOULD convert this extra voltage, to amps into the battery, but again, most of the import and fleabay stuff is so bad, you may as well wire the panel directly to the battery, and burn the controller safely in your BBQ.

There are really only 3 players in the small power MPPT market, and their stuff is easily 2-3x the PWM costs. Morningstar, Rogue and Blue Sky.

http://www.morningstarcorp.com/en/sunsavermppt

http://www.roguepowertech.com/

http://www.blueskyenergyinc.com/

MPPT is the only way to get the panel rated power to your battery.

Your other problem, is a 20W panel, can only generate 20W - regardless of the voltage, so you are not going to have a lot of power on hand no matter what.

[ralphkaz]

Thanks for the reply!

So if I switched to a 12v 20w panel I would be OK, correct?

This is my first venture into solar and its really just for playing around/getting my feet wet. The intent is to get a sealed battery for this setup and just have it as a backup for 1 room in the house in case of a power outage (hookup a couple of LED lights to it). It would not be used daily so hopefully the 20w panel would be sufficient to keep the battery 100% and recharge it when the lights are occasionally used.

[ralphkaz]

Also - speaking of LED lights - any recommendations for what to get? I understand the LED's could be hooked up directly to the charge controller. I assume I'd just need some kind of on/off switch between the two...

Thanks again!