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teal95

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Posts: 2
Reply with quote  #1 
Wife is pushing (and I'm very curious anyways) for solar for my storage barn, a 40x40x10 that I'm using for storage. It's new construction this year and doesn't have any electric currently. It's about 300' from the house so running power would be a bit of a project. My loads would be minimal. I'm looking to power the following:

Garage door opener - The one I have doesn't have battery backup so to use it would probably require a hefty inverter that would have a lot of parasitic draw so I'm guessing it would be much easier to replace it with one with a battery backup.

Trickle chargers for 10 cars. I don't anticipate having to charge anything, mainly it's just to keep the parasitic draws from running batteries dead. From the research I've done I'm anticipating the float function would be sufficient.

Lighting - I have translucent panels on the east wall so it's all I need in the daytime but nights get long in the winter. I don't anticipate working, more along the lines of being able to have the lights on for 10 minutes to check things or grab parts off of the shelving I have.

Air compressor - Mainly to be able to pump up tires. With my minimal usage I'm probably going to be generating excess energy so I thought it would be nice to have a 50 gallon compressor with a 12v compressor to fill it. As I doubt I would use it very often if it took it a week in the summer or several weeks in the winter I would be fine with that. I would configure things to run this only when I have excess power.

I realize it would probably be cheaper to run electric out but I want to learn how to make it work. I'm guessing a couple of panels mounted on the roof, an MPPT controller and probably a battery for the lighting. I'm an electrical engineer but know enough to know that probably makes me more dangerous. I did most of the wiring in my shop by myself and have a local contractor who has been very helpful when I need it.

Any comments or suggestions?

stmbtwle

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Reply with quote  #2 
No-one seems to want to touch this so I'll bite...

I see no easy way to avoid the inverter.  You'll need it to run the battery chargers, the garage door opener, and a decent compressor.  Converting all this equipment to 12v will be complicated and probably expensive.  Also a 1500-2000w inverter will run most hand power tools, which can be handy.  The parasitic load of the inverter isn't that much and is a small price to pay for the convenience.  You could install a switch on the outside of the garage so that you can turn the inverter off after leaving if desired.

My GUESS is that a couple of deep-cycle golf batteries would be plenty for what you describe, along with 200-300w of PV panels. If you have extended periods of bad weather in the winter you might want a larger system.  PWM controllers are cheap, and for a small 12v system I'm not sure the MPPT is worth the extra cost. If you do decide to go with MPPT I'd get a larger one than you think you need.  The upfront difference in price isn't that much but replacing it later with a bigger one would be, if you decide to add to your system.

That's my take on it, others may have a different opinion.



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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
teal95

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Posts: 2
Reply with quote  #3 
Not opposed to an inverter, especially if the parasitic draws are reasonable.  I'm more concerned with load management.  I'm guessing ideally I would have it charge the storage batteries and trickle chargers when there is sufficient energy available, staggered if need be.  I don't expect the cars to need much charging, mostly it's keeping them up with the parasitic draws that newer cars have (EFI keep alive memory and whatever else it's drawing).  Then when the output gets high enough run the compressor.  My first attempt would be to use a 12v compressor, possibly one from a vehicle with air suspension (every Lincoln since 1983 and many, many more since then).  I would use a 50 gallon tank as I'm guessing they would be readily available and with a 12v compressor it's going to take a long time to fill but as I won't be using it much that's fine.  Even if it can only run for an hour a day (peak sun) and it takes a week or even 2 to fill that would be sufficient.

I think my main question is how to control the loads?  How would I prioritize it to run the compressor when it's making enough power and shut it back off when it isn't?

steve
stmbtwle

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Reply with quote  #4 
For starters simply prioritize the loads manually. You could also use timers. You can set up relays so that when one load comes on, it shuts something else off. You can get really fancy and use something like an arduino, but that's a project in itself.

Don't overthink it, or you'll never do it. Get the basic system up and running, and worry about the small stuff later. Good luck!

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #5 
I would take the compressor load off the solar by using a compressor on wheels. Wheel it up to the house to charge the tank and wheel it back to top off tires. That would reduce the energy and power requirements for the Solar PV system. A 50 gallon tank just for tires would be overkill.

The most cost effective strategy is Conservation of Energy not, the Tim Taylor syndrome (more power, more power).


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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
tacman7

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Posts: 39
Reply with quote  #6 
That compressor is the problem.

I ran a sub panel to a mobile that was 450' from the house with 2gauge aluminum wire (direct burial). Cost about $550 for the wire.

Got the wire from this place:

https://www.wireandcableyourway.com/

Without the compressor you could do a lot smaller system, led lighting etc.

What about running 3/4" PVC underground for air to the building? Makes a nice storage tank.


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