Set up for garage door opener

jeffwelc

Hello all...I'm new to this forum and new to solar power and was hoping for some help.

I just installed a genie garage door opener with 24v battery backup. The location of my garage doesn't allow me to run electric so I was planning to install a solar panel on the roof to charge the battery. I purchased a 20W 12v solar panel with a PWM 10A charge controller only to realize it's not enough to charge the battery. Next step is to purchase a second 20W 12v panel and connect them in series and into the controller. 

Will this work? Is there an easier or less expensive way of doing it? I don't use the garage door often (a couple times a week) so the battery doesn't need to charge quickly or even often because it can run 20+ cycles on a single charge.

Let me know your thoughts. Thank you!!

BB.

Welcome to the forum Jeff.

Where is the system installed (nearest major city like Red Bank or Trenton NJ)? For example, Trenton, fixed array:

http://www.solarelectricityhandbook.com/solar-irradiance.html

Trenton
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 35° angle from vertical:
(Optimal winter settings)

Jan	Feb	Mar	Apr	May	Jun
3.35	3.91	4.28	4.28	4.25	4.29
Jul	Aug	Sep	Oct	Nov	Dec
4.33	4.38	4.48	4.28	3.38	3.07

What voltage and AH battery(ies) are you using?

I.e., 2x 12 volt @ 20 AH in series? Flooded Cell Lead Acid, AGM/GEL/VRLA/Sealed batteries?

Will the panels be exposed to full sun (no shading by trees, pipes, overhead wires, etc.)?

-Bill

jeffwelc

Thanks for the reply Bill.

I'm in Red Bank - full sun without shade. It's a single 24v lead acid battery.

BB.

Flooded Cell or Sealed battery? Sealed (AGM/GEL/VRLA batteries need lower charging voltage and have lower self discharge.

Flooded Cell batteries (as long as you check the electrolyte levels once a month or so), are generally a bit more forgiving/rugged and can last a few years longer than sealed batteries (you cannot replace water after they vent from age/over charging).

Typically, we look for 5% to 13% rate of charge for solar... 5% is the minimum. 10%+ is better for batteries that cycle daily/fairly deeply (typically to 75% to 50% state of charge is "deep enough" cycling).

So, say you have a pair of 20 AH @ 12 volt batteries (2x 12 volt batteries give you 24 volts @ 20 AH battery bank), the recommended solar array would be:

• 29 volts charging * 20 AH battery bank * 1/0.77 panel+controller derating * 0.05 rate of charge = 38 Watts minimum
  
• 29 volts charging * 20 AH battery bank * 1/0.77 panel+controller derating * 0.10 rate of charge =75 Watts nominal
  
• 29 volts charging * 20 AH battery bank * 1/0.77 panel+controller derating * 0.13 rate of charge =98 Watts "typical cost effective" maximum

If you only use the door a few times a week (vs many times a day), then 5% to 10% rate of charge would probably be fine (for the mythical 20 AH @ 24 volt battery bank).

The array is tilted to give you best Winter performance (and shedding of snow if that is an issue in your area).

If you operate the door daily mulitple times, and/or have (for example) some LED lighting, then you really need to know how many Watt*Hours or Amp*Hours @ 24 volts you use in a day. Most garage door/gate openers do not use that much electricity... Say your do take 2 amps and 1 minute to open and close (one cycle):

• 2 amps * 1 minute * 1/60 minutes in a hour = 0.03 AH

Even if you open the door a 100x in one day (or over a week of poor weather):

• 0.03 AH * 100 operations = 3 AH of battery usage per 100 operations (no sun/charging)

Which is not much energy at all. Note that the larger the battery bank, the more charging current is suggested... Oversizing the battery bank AH capacity does push the array sizing up... Whereas the amount of solar power needed to recharge 100 openings (again using my very rough guess) is not much:

• 3 AH * 29 volts charging * 1/0.77 panel+controller derating * 1/3.07 hours of sun in December =37 Watt array (per 100 openings per average December day)
  

-Bill