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Alternative power source for garage.

  1. Mar 29, 2005 #1


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    I have recently moved house, the problem is the garage is situated about 100 feet from the house along with the garages of my neighbors. There are several houses between ours and the garage, and there is no mains electricity over there. The previous owners actually had mains power in the garage by trailing some wires around the back of the row of houses out to the garage, but that was removed before we moved in because our electrician said it was illegal.

    I was wondering if it would still be possible to install an electric garage door opener. Possibly using some photovoltaic cells charging a battery which could then be used to power it, or a similar alternative. It is a single garage and we are going to replace the door shortly. I could make a choice of door to best facilitate the electric opener.

    I need a system with parts that are commercially available in the UK. Solar cells are widely available as systems that can be used to charge 12V lead-acid batteries. Trouble is, most garage door openers are built for mains electricity, i.e. 240V a.c.

    After an opening/closing, is it such a simple matter as using the solar cell to fully recharge the battery even though it has not been fully discharged? I am not really sure of the energy requirements of each opening/closing. How many could I realistically hope to get out of a single charge of whatever battery could feasibly be used for this?
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  3. Mar 29, 2005 #2


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    I'd assume it's not just the motor that needs AC, it's the electronics as well. So even if you swapped out the AC motor for a DC one, you still need AC for the electronics, and changing them to DC isn't really an option.

    How about putting in an inverter, and keep everything in the door opener the way it comes? A 12 VDC to 240 VAC inverter shouldn't cost more than a hundred pounds I'd guess. Probably much less. Then you'd also have 240 VAC for other things such as electric power tools if you wanted.

    To charge the battery, it might even be easier to have an easily disconnected battery that you can walk into your home, and connect to a charger once a week or so.

    Also, look into marine batteries. They're much better made for what you want to use them for.
  4. Mar 30, 2005 #3


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    Is running an overhead line not an option?
  5. Mar 30, 2005 #4
    Solar-powered 373-watt garage door opener


    Everything you need to know to do this the solar way is here:

    You need to know the solar insolation values for your area. You also need to know how much peak power your garage door opener will draw (most of the ones in the US are only 1/2 horsepower, which is 373 watts). Perhaps one car battery with a modestly-sized inverter can handle this.

    After pricing out the above option, I would compare it to the option of using a remote-startup gas-powered generator. Honda is the only way to go in portable generators. (If you buy another brand, you will be very sorry.) Here are some 240v Hondas for sale on eBay in the UK:

    Regarding your questions at the end:

    You can charge any battery starting at any discharge state (with the possible exception of a full discharge; lead-acid batteries are largely destroyed by even single instances of full discharging, so you might not be able to charge one from a fully-discharged state). Lead-acid batteries like to be kept fully topped-off and discharged only very shallowly. The deeper you discharge a lead-acid battery the faster you destroy it. Shallow-discharged batteries can last for decades (e.g., never going below 90% discharge is good for the battery; telephone and power companies use lead-acid batteries that are literally decades old and function like brand-new).

    Off-grid people keep their lead-acid batteries topped-off by trickle charging them. Your solar panel will be continually topping off your lead-acid battery. You want to make sure you use a high-quality electronic charge controller (such as the ones made by Trace Engineering) to ensure that your batteries are not overcharged (something that will also destroy them). I believe Trace has some combo units that both control charge rate and handle power inversion.

    373 watts should be roughly the power. The energy use will be negligible since it doesn't take very long to open and close a garage door.

    As I said above, since you will be continuously recharging you won't need to worry about uses-per-charge (unless you are using it rapidly in succession, i.e., before the solar panel gets a chance to top the battery off).
    Last edited: Mar 30, 2005
  6. Mar 30, 2005 #5
    Running and overhead line ~100 feet would cost ~$5,000. Yes, it is an option.
  7. Mar 30, 2005 #6


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    Ouch. That's a big number. Solar is looking better and better.
  8. Mar 30, 2005 #7
    In general or specifically for this application?
  9. Mar 30, 2005 #8


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    For this application - in general, solar is nowhere near cost effective.

    A quick google turned up THIS: a 5 watt panel with voltage regulator for about $150. I don't know if you can connect that directly to a battery charger, but a nominal 5 watts of charging for 8 hours a day is enough to open or close a garage door 16 times a day (assuming 300 watts for 30 seconds each). Even if you typically only get 2 or 3 watts for a few hours a day, that should still be enough.

    The problems (financial) come when you try to turn that 5 watts into 5,000 and power your house...

    That site sells larger panels at about $4.25 / watt - to be viable as even a partial replacement of home power, it needs to be more like $1 / watt.
    Last edited: Mar 30, 2005
  10. Mar 30, 2005 #9
    The principle of conservative figuring in solar power planning

    It's a 1/2 horsepower motor, so I would figure ~600 watts input. That would be 5 watt-hours per 30-second use. That gives you two uses a day since a "5-watt" solar panel might put around 10 watt-hours per day into a battery. Two uses a day is not enough to even simply allow you to drive to work, unless you work 36-hour shifts. (It pays to figure conservatively with solar charging/drawing systems. There are power losses at many points in the system including the battery - the faster you draw from a battery, the more energy is proportionally wasted as heat. See Know Nukes. We discuss this there all the time.) I think a 75-watt panel with a Trace charge-controller/inverter might work just fine.

    Based on the number crunching I have observed at Know Nukes, a rule of thumb that seems to work well for highly-economical (meaning large insitutional) solar power systems is $10/watt. If infinite-lifespan 100%-efficient solar PV panels were available for free, that figure might reduce to $7/watt.

    Actually, the high cost of solar is tied up in things like construction/decommisioning, maintenance and land-lease. These costs are high for solar primarily because solar is diffuse, and also because solar is intermittent and solar is unpredictable.
    Last edited: Mar 30, 2005
  11. Mar 30, 2005 #10
    Do tell where you came up with this.
  12. Mar 30, 2005 #11


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    Garage door openers are a one-size-fits-all proposition and I wouldn't be at all surprised if they average a 50% loading or less. That's why I assumed 300w.
    No, I said for your house. Singular. If Joe Homeowner wants to install solar panels on the roof to get himself off the grid, it'll cost upwards of $20,000 (depending on the size house, of course), with most of that cost being the panels themselves.

    In addition to the panels, you need a battery backup (say, 10 car batteries at $50 apiece, or $500), a control system (I'm guessing $1,000), and a guidance system would be nice (I'd guess $1,000 or so also).
    Last edited: Mar 30, 2005
  13. Mar 30, 2005 #12


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    Thanks for the input. You've all given me a lot to think about here, so I'll try and compose a more detailed response later when I've digested this information.
  14. Mar 30, 2005 #13
    How much running your own solar-generation enterprise really costs

    When a house is wired for off-grid power, it becomes a generating station. All of the economic categories for institutional-size generating stations apply to homepower stations. The categories will take on a different profile of relative importance, and their economic efficiency per unit of power produced will be far lower than for an institution, but they will all be there. The management category is critical for successful operation of institutional-size generating stations; it encompasses hard work and is stress-inducing. Management compensation packages reflect this by being huge. That all applies for homepower as well. If the management costs for homepower seem in given instances to be zero, it will be because the management is donating its entire compensation package back into the enterprises. This doesn't make management costs zero. It means that some mysterious benefactor is covering them.

    This February 2000 estimate by Home Power Magazine figured 1.6kW of solar PV panels made up 37.43% (PV panels cost less now than in the year 2000, so I figure the panels would amount to ~30% these days) of the $22443.00 parts cost of a system for a house averaging 8.3kWh/day and utilizing a 4kW inverter. That doesn't include finance charges (again, if the homeowner pays cash he acts as a lender and constitutes a hidden benefactor mysteriously donating money - the interest he doesn't charge himself - to the enterprise), labor costs, land-lease costs, or insurance costs. Add in those things and the proportional cost of the PV panels shrinks even more.

    20 Trojan L-16 batteries: $3,000.

    The Trace 4kW inverter is $3,000. The Solar Boost Charge Controller is $660.00. Battery/Inverter Fused Disconnect is $329.00. The Battery Amp-hour Meter is $200.00. The list goes on for quite a ways, and this is just for a basic $22,000 system. Would you like wires and cables? $700.00. Would you like conduit and fittings? How about a rack for the panels? A lightning arrestor? If you don't use these things, you are mismanaging your power-generating enterprise - and mismanagement costs money.
  15. Mar 30, 2005 #14


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    Oops, forgot about the inverter - and I didn't realize they were that expensive.
  16. Mar 30, 2005 #15


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    I live at about 51.5 degrees North latitude. As it is England, it is usually cloudy too. I don't have proper data, nor do I know where to get it for my area.

    I would like to mount the panels flat on the roof so that they are not visible from the ground--it's a flat roof garage, about 8 feet tall. I suppose this means I'll need to buy larger panels.
    AC ones appear to be around 500 watts. There are ones with DC motors that are only 100 watts though.

    So I need

    •solar panels
    •charge controller
    •lead-acid battery
    •power inverter
    •DC disconnect
    •the opener itself

    Are there any vital components missing?

    Trace's products appear to be terribly expensive. I think I might have to look for a more modestly priced inverter. I just need to estimate a total for all of these parts and see if it is worth doing.
  17. Mar 30, 2005 #16

    Ivan Seeking

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    So the lesson is that it would be far cheaper to charge a battery powered system by installing a charge port on your car, and using it. Replace the door opener's AC motor with an DC motor and any additional AC inverter needs will be minimal an inexpensive. Also, the AC may be converted to DC [and stepped down] as soon as it enters the door opener's circuit board. Some AC devices can be plugged directly into a DC source of the same voltage. [not motors, but electronics]

    This would be a fraction of the costs discussed if it's practical for your needs.
    Last edited: Mar 30, 2005
  18. Mar 30, 2005 #17
    DC might be best for solar garage door opener

    Really? Maybe that would be ideal for this application.

    Regarding Trace, you don't want to use cheap equipment where expensive equipment is recommended. Everyone involved in homepower is trying to do it as cheaply as possible. If experienced homepower people are recommending Trace products or products of some other expensive company it is because experience has shown that it saves money in the long run. Cheap inverters burn out or deliver dirty sine waves, the latter burning out the equipment they are feeding power. Cheap charge controllers destroy batteries.

    Then again, Trace equipment may come with a lot of features you would never use in such a simple set-up. FWIW, here's the most minimal Trace charge-controller I could find. It's $89:

    I think I would try the DC door-opener with just a single solar panel, Trace charge controller, and either a single large car battery or a single deep-cycle (marine/RV) battery. I don't think you will need a separate DC disconnect, as I would guess that the Trace charge-controller will be able to handle everything you need for this app.

    If you just lay the PV panel on the flat roof, you won't desperately need any mounting hardware. There is some danger of high winds (PV panels are usually pretty heavy so it would have to be a strong wind if the panel is lying down flat) picking up the panel and throwing it off the roof, so eventually you might think about securing it down somehow.

    You'll need some wires and minimal tools to strip them, etc. You can pick that stuff up at Radio Shack as you find you need it and it won't be very expensive for the low power requirements/low wire-run distance of this app.

    There is a question of how big of a panel you will need, but you certainly won't need more than one for an application with an energy requirement as low as this one's. The panel Russ was talking about was only 5 watts. That's why I questioned if it would work. Typical single panels are rated at 60, 75, 80, 90 watts, etc. Even if it is usually quite overcast where you are, a 60-watt panel might do the job with power to spare.
    Last edited: Mar 30, 2005
  19. Mar 30, 2005 #18


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    It would be far cheaper to open the door manually each time I want to use the garage. That's not the point. Why does anyone want to install an electric garage door opener? Because they want the door to open easliy and conveniently. If I have to manually charge the battery periodically, that is not convenient. That's why I find the solar option so attractive, because once it is installed and working, it is essentially care-free.
    There are some openers operated by 24V DC motors. However, you do bring up a good point. If the control electronics have their own DC power supply, I could remove that and it would cut out the inverter entirely.
  20. Mar 30, 2005 #19

    Ivan Seeking

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    I guess you wouldn't like my idea of a handle and two springs, as a solution. :biggrin: I was thinking about your concern about cost.

    Depending on how this all works out, ie. if the solar option is too expensive, you still may want to consider the option of plugging in a trickle charge line, with diodes and a current regulator, and maybe even a timer, from your car to the door system, whenever you park. If you only need to top off the battery system daily, your auto battery should never miss the amp-hours. Just plug in when you park and unplug before you leave.

    You would need to be careful about the total amp-hours demanded from the car battery between drives, but you shouldn't need to leave the car running.
    Last edited: Mar 31, 2005
  21. Mar 31, 2005 #20


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    That's a lovely idea Ivan. Cigarette lighter socket and you're sorted.
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