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  #1  
Old 10-13-2016, 10:13 AM
cramptor Male cramptor is offline
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Default Running an upright freezer

Is it possible to run a 15 cubic foot upright freezer on a dedicated solar system? I have the freezer in an out-building and would like to set up a stand-alone solar system just for that freezer. Thank you
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Old 10-14-2016, 10:23 AM
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Hi, Cramptor. Welcome to the forum!

Your question reminds me of Carrol Shelby, the designer of Ford's famous Shelby Cobra. The sign over his shop read "Speed Costs Money. How Fast Do You Want To Go?"

I'm not an expert on this technology. Others here are and will no doubt answer you in detail.

My take on wind & PV energy is that using it won't save the environment, nor will it save you money unless you're so far off grid that running new lines is cost prohibitive.

OTOH, it is the way to go to provide energy security. I use solar for my deep well pump and will use it for my boiler & circulating pump when I install a hydronic heating system. Our grid in rural Wi is not all that reliable ordinarily and I don't want to be left dry & cold when TSHTF.

I'm also considering it for the same reasons for a freezer and look forward to the others' answers to your question. The system may cost in the range of $2000 but would be worth it if it saves $1500 worth of freezer meat once or twice in 20 yrs.

Ron Castle at Sunshine Works is very friendly & helpful and will tell you exactly what you need for your location & application. http://www.sunshineworks.com/index.html
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Old 10-16-2016, 10:10 AM
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Howdy and Welcome! It's possible but location is a factor. The battery should be in a temperature controlled environment so consider that also..
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Old 10-17-2016, 02:04 PM
MichaelK Male MichaelK is offline
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Hello Cramptor

Its doable, but let's work through the numbers to design a functional system that isn't likely to fail and ruin all you're trying to preserve. In designing a system that will work for you, I'll outline some parameters that you may change as you see fit. Almost always, people try to get by with a system much smaller than what it should be and it crashes and components get ruined.

First off, let's decide on a system voltage. Gone is the day when everything needed to be 12V, which is just for automotive. Today's off-grid systems are designed for higher voltages, because 12V just doesn't convey enough power for lots of electricity-hungry appliances.

Today, everybody is moving to either 24 or 48 volt systems. I think 24V will work fine for you. The first thing you need to decide is how much power all the appliances are going to consume. I recently looked a chest freezers at Home Depot and a big one was consuming about 0.6kwh per day (600 watt-hours per day). Let's assume you'll need something larger, say 1000 watt-hours. A typical 18 cu.ft. .refrigerator/freezer is about 1100-1200 watt-hours per day.

You'll need battery storage. Assume you don't want to deplete your batteries more than ~15% of their capacity per day. At that rate, your batteries will last a decade. A popular battery for off-grid systems is Trojan's 6-volt L-16RE-B, which has 370 amp-hours of storage. With 4 of those wired in series for 24V, you'll have 370AH X 24V= 8880 watthours of storage.

Fifteen percent of 8880 watthours is 1320 watthours, or a bit more than what you need for the freezer. So, that size battery fits your application. Now we need to move on to charging those batteries.

A good rule of thumb is to have enough back-up storage to cover at least 3 days of cloudy, sunless weather before they get recharged. What's your weather like? Assuming you have 3 days of rain, you want your batteries fully charged at the end of the first sunny day, so you'd need 1000 watthours X 4 days = at total charge of about 4000 watt hours. Another rule of thumb is that you don't want to drain your batteries lower than about 50%, so 15% per day, and three rainy days fit into those criteria.

You get might get about 5 USABLE hours of sun during summer, and maybe 3 in winter. Looking at worst case in winter, you need 4000watthours/3 hours= 1333 watts worth of solar panels. Because there are losses at every step, assume you only get 90% of the panel's rated output, your charge controller only feeds 95% of what comes out of the panels to the battery, and the inverter only feeds 95% of AC converted from what comes from the batteries, you'll loss ~25% of the total power.

So, take that 1333 watt value and divide by .75.
1333watts/.75=1777 watts. So, you'll need 1777 watts of panels.

Renogy has some very nice 300 watt panels now that are less than 1$ per watt.
https://www.renogy.com/renogy-300-wa...e-solar-panel/
I bought these panels myself for my new system. They run at 37.5VDC each, and you could wire sets of 3 in series to get 112VDC. Couple that to a MPPT charge controller to drop the 112VDC to the 28.8VDC your batteries need to charge at.

You can instead buy their cabin kit, which includes the panels, charge controller, combiner, and wiring for 3000$.
https://www.renogy.com/renogy-1800-w...lar-cabin-kit/

In addition, you'll need the batteries, and Trojan L-16s run about 330$ each. Assume you'll be paying ~ 1320$ for those.

Finally, you'll need a good inverter. Schneider makes a very nice 24V inverter, which runs at ~1250$. What's nice about it is it puts out either 120 or 240VAC, and has an automatic hookup to a backup generator.
http://ressupply.com/inverters/schne...nvertercharger
I myself purchased Schneiders bigger 48V inverter for my system.

All together these amount to 5570$ Round that to 6k once you add some racking and extra wiring.

Good luck!
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Last edited by MichaelK; 10-17-2016 at 02:53 PM.
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Old 10-18-2016, 11:11 AM
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Quote:
Originally Posted by MichaelK View Post

All together these amount to 5570$ Round that to 6k once you add some racking and extra wiring.

Good luck!
Excellent analysis. Very helpful.

If your grid bill runs you $0.25/kW-hr and you need 1.2kW/d for the freezer, you'd have to run that system for more than 54 yrs for your "free solar power" to recoup your investment (not to mention lost investment potential) on the $6 Grand shelled out up front.

A $400 generator and a couple bucks worth of gasoline will keep your cache from spoiling and your lights & TV running at the same time when the grid goes down-- rarely more than a day or two at a time.

In a real TEOTWAWKI scenario, we'll be drying, salting or smoking our meat to keep it & hide or carry it, not worrying about a stationary freezer.
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Old 11-01-2016, 02:23 PM
cramptor Male cramptor is offline
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Thank you all for the responses. I've got some research to do.
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Old 11-02-2016, 12:46 PM
ScrubbieLady ScrubbieLady is offline
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Don't know enough about solar, but an upright freezer will use more electricity that a chest freezer. When the lid is raised on a chest freezer there is minimal amount of loss of the cool, when an upright freezer door is opened, cool spills out.
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