Off-Grid Garage System Question

I have a detached garage and I would like to power the Liftmaster opener with a solar power system. It uses 540 watts (120 volts), so I am guessing I need a 600-watt system.
But do I need that much power for something that is only used 2 or 3 times per day, for about 30 seconds total? Also, should I go with a 12 or 24 volt system?
Thanks.

More likely you will need 2000 watts or more to power it... motors pull a huge amount of surge to start.

Garage door openers in Klaifornia now have to come with battery backup , look for a CA model, and connect an approiate PV panel to keep the battery charged. The starting surge of the motor will need a large inverter, idling all the time.

The running wattage is not a problem but the starting wattage may very well be. The more load that motor has to lift the more that initial surge will be. Your main concern will be to determine that that Surge Wattage which will more than likely be nearer 1500-1700W but could be as high as 5X the running watts.

The Inverter chosen will have to support that surge rating. You "may" be able to use a Modified Sine Wave Inverter as it is just a motor and intermittently used for short periods only (the few minute to open/close).
12V systems can support up to 2000W comfortably without issues.
2000W @ 12V = 166.6A uncorrected. being pulled from the battery.
This should be fused at 175A.
Battery should be able to support a 175A Discharge rate. Can be Lead, AGM or other.
Battery Size at 12V would not have to be huge either... But 50AH would likely do it fine. (just for the door opener, not extras).
** Will just reviewed some Miadi ? or similar low cost but Really Good assembled batteries from Amazon. Check his videos.

Solar Panel - SCC
There are now AIO's "All in Ones" for 12V <2000W which are very affordable & simple to install and saving a lot of extra hassles & bits too.
A very respectable example here: https://usamppsolar.com/product/pcm60x/

Solar Panels (do NOT buy 12V panels !) can be had easily enough, used or new... Many buy used from companies like SantanSolar with great results. NOTE: DO NOT BUY Unlabelled / Unbranded panels NOR "House Branded" panels unless a warranty is explicitly specified.

Racking/Mounting will be required (if mounting on a roof, panels must be 12" below peak and 12" above the bottom edge and provide a MIN of 6" clearance between panel & roof surface) This is to prevent the panels becoming Sails in a windstorm, to stop them from "catching" stuff and the clearance to allow for heat dissipation and airflow (it gets really hot under panels).

Hope it helps, Good Luck.

Thanks everyone. Steve, I appreciate all the information. So I should buy 24-volt panels with a 12-volt battery? Also, I should have mentioned that the opener has a backup battery. If I don't buy a 2000-watt system, wouldn't the backup battery take over and supply any difference? It will lift the door, after all. Afterward, the system will recharge the battery.

The Solar Controller (whatever type it is) takes the Watts/Volts from the panels and sets the correct charge voltage & amperage the battery can take. Many people buy 12V panels for 12V batteries because they think it goes direct, it does not and they are tossing 50% of their cash in the trash. 12V panels are EXPENSIVE for what they are and what they produce... BUT they accommodate special cases because they can be quite small in comparison to 24/36+ V panels.

I do not know the product in question, so what/how it's own battery works and what it does I cannot say.

The system I showed as an example, could even be setup so that it can provide "emergency" power (minimal) that could be available in the garage with a 120V/15A Plug should it be required.

Your battery backup system is probably not a power assist backup. Instead, it only comes online when no AC power is detected.

Well, I thought it would be a good idea, but I don't see how a $1000 system would even come close. I thought it would be easier. I could see this turning into a $3000 job. Might not be worth it.

FWIW, I can't remember the last time the power went out in the Denver area long enough to prevent me from opening my garage door. Even if it did, I just pull the override lever and show my wife how tough I am.

The problem is that I share a garage with my neighbor. We recently found out that her side pays the electric bill. I really want to fix that, and I thought an off-grid solution would work and be kind of fun to set up.

Fun, yes. Expensive, yes. Could you get in trouble with building codes? Maybe. As long as there is no tie to the grid, I don't see how they could complain much unless you put in something obscenely objectionable.

One problem with codes is, you need to wire an outlet for it. Extension cords are not allowed for in use appliances over 90 days...

Update: I installed a Windy Nation system for less than $600. One 100W panel, 100ah battery, and a 1500Wpure sine wave inverter. Works like a charm!

DenverGuy said:

Update: I installed a Windy Nation system for less than $600. One 100W panel, 100ah battery, and a 1500Wpure sine wave inverter. Works like a charm!

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There is a solar charge controller in there somewhere?

Yes, a P30L. Works great!

DenverGuy said:

Update: I installed a Windy Nation system for less than $600. One 100W panel, 100ah battery, and a 1500Wpure sine wave inverter. Works like a charm!

Click to expand...

Im late to the party but I was going to recomend a 1500w UPS. Only needs to work when the grid is down and is likely half the cost.

This is off-grid. I don't care about cost. $600 is cheap, anyway.

DenverGuy said:

The problem is that I share a garage with my neighbor. We recently found out that her side pays the electric bill. I really want to fix that, and I thought an off-grid solution would work and be kind of fun to set up.

Click to expand...

Give her $20 a year and call it even. The project you're describing would simply be for the fun of it, and a good learning experience, but not really practical from a cost/benefit perspective.

I see you built one for $600 so nevermind.

gunningopher said:

Give her $20 a year and call it even. The project you're describing would simply be for the fun of it, and a good learning experience, but not really practical from a cost/benefit perspective.

I see you built one for $600 so nevermind.

Click to expand...

Whoever said it was practical? That's an odd statement.

DenverGuy said:

Whoever said it was practical? That's an odd statement.

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Nobody I guess. I'm just saying that the cost/benefit to adding an off grid power system to run a garage door opener where there is grid power doesn't financially pencil out. That thing can't cost more than $20 year to operate. You'll never recover the investment.