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Old 02-22-14, 12:24 AM   #11
Ryland
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Put a Kill-a-watt meter on your fridge and freezer.
My fridge and freezer use about the same amount, just under 1kwh per day so if you have 4 sun hours per day you'll need about 300 watts of PV per fridge or freezer if you are running a battery based system because of all the losses that you have with battery based systems, then size your battery bank for at least 3 to 5 days of no sun, longer if possible, drained to 50% state of charge, unless you like lugging around dead lead acid batteries.

As far as splitting off the outlets, put a small sub panel in for those outlets that is designed for a generator with lock out switch for switching between grid and generator.

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Old 02-24-14, 10:22 PM   #12
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Originally Posted by dablack View Post
Ok guys. I believe there is a plug in device that I can use to get an actual reading. Then with that info I can figure out how many watts of panels I will need as well as battery capacity.

Austin
The device you are referring to is called a "Kill-a-watt" Got mine at Home Depot' The thing about refrigerators, and freezers are that they have different power requirements at different times of the year.

Dennis
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Old 02-24-14, 10:43 PM   #13
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[snip]1. To save on battery wear, can't I just flip the breaker off at night. If I do it before I go to bed and then turn the breaker back on when the sun is shining, as long as the doors aren't openned too many times, the stuff in the fridges and freezer should stay very cool/frozen. Basically, they wouldn't have power for maybe 12 hours. [/snip]
Don't do this! You can get away with losing power to your fridge for 12 hours once in awhile, such as when you come across a power outage but they aren't nearly as well insulated as they need to be for you to get away with this daily. Your refrigerated goods, especially milk last longer the colder they are. I managed to keep standard milk bought from the store and opened the day I bought it for almost 6 weeks when my refrigerator was on the edge of freezing it. With the temperature set to high 30's, I'm lucky to get even its standard shelf life 'sell by' date out of the milk.

Also if your refrigerator goes into a defrost cycle(they do this more often than you think!) and your 12 hour period starts before it has recovered back to temperature after, you'll have spoiled food well before the 12 hours is up.

With my defrost cycle disabled and the house kept at my winter temperature, my fridge uses about 1kwh per day if I never open the door during that day. I'd figure you want some wiggle room. Also don't forget you'll get a couple cloudy days in a row, you really need something automatic to switch back to the grid when your battery pack gets low or you'll be throwing away food if you make a mistake on sun estimates or how much battery you thought you had left. If you want to treat your batteries nicely(especially if going lead-acid) you need to size the system for very shallow cycles and plan for the cloudy days, also plan for the days you actually open and use the fridge, hot days of the year, and the ~300wh defrost cycles. I'd seriously consider oversizing to figure 2kwh per day unless you've got better than just energy star type stuff. You'll be spending more money on lead-acid and the solar PV modules than you'll probably ever save by running the fridge. You'd probably want to make the system big enough to power other things and then on days that aren't so sunny, scale it back down to the fridge.

I've considered going direct solar myself using a 1.2kw solar setup using 4 96 cell modules of the appropriate voltage for a ~48v LiFePO4 pack in parallel but decided to specifically exclude the fridge if I didn't have an automatic way of pushing it back onto the grid when my pack was low. I decided that life would be easier and I'd get more out of the system and the money spent going to solar by going the grid-tied route. 3.3kw grid-tied setup going on my roof this year.

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Old 02-24-14, 10:53 PM   #14
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The Kill-a-Watt is very good. I even tested one against a Fluke wattmeter and it agreed spot on with a 1000W heater. It's at low power where it starts losing accuracy.

Here's an interesting wattmeter circuit for building one into a device:
Wattmeter_from_Pease_after_Nelson
Probably not terribly useful on a refrigerator (very small changes in instantaneous power use, just differences in duty cycle) but might be quite useful on devices that vary greatly in power usage.
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Old 02-24-14, 11:03 PM   #15
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With my defrost cycle disabled and the house kept at my winter temperature, my fridge uses about 1kwh per day if I never open the door during that day. I'd figure you want some wiggle room. Also don't forget you'll get a couple cloudy days in a row, you really need something automatic to switch back to the grid when your battery pack gets low or you'll be throwing away food if you make a mistake on sun estimates or how much battery you thought you had left. If you want to treat your batteries nicely(especially if going lead-acid) you need to size the system for very shallow cycles and plan for the cloudy days, also plan for the days you actually open and use the fridge, hot days of the year, and the ~300wh defrost cycles. I'd seriously consider oversizing to figure 2kwh per day unless you've got better than just energy star type stuff. You'll be spending more money on lead-acid and the solar PV modules than you'll probably ever save by running the fridge. You'd probably want to make the system big enough to power other things and then on days that aren't so sunny, scale it back down to the fridge.
Modify the (standalone) freezer by adding a relay *after* the thermostat to run the compressor from solar power once the batteries reach full charge (or a little before), then switch back when the charge goes back down a little. Then it can only get colder than the thermostat setting. You'll also want to add a delay on break timer to avoid accidental short cycling.

That trick won't work for a refrigerator since it would freeze items you don't want frozen. But if you have a refrigerator dedicated to stuff that must be served cold but keeps fine at room temperature (water, beer, soda, etc.), you can indeed run it only during the day.
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Old 02-25-14, 03:50 AM   #16
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For a small system, grid-tie is much cheaper and more efficient. For every watt you feed to a battery bank, you will lose close to half a watt between charging on the way in and discharging and inverting on the way out.

Battery banks were made for people who have no grid power, like remote regions and marine/mobile applications. If you are a doomsday prepper, then of course none of these notions apply. But in the global system picture, batteries cost money and energy.

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Old 02-26-14, 08:49 PM   #17
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I think Jeff is correct.
With my http://ecorenovator.org/forum/solar-...-hookup-2.html, the first 1.2 kW recharges the 12 nearly new batteries. On a sunny day, I will use a total of 5.8 kW. That's out of 2,280 watts of solar panels.

Two hours after dark is about all the system will tolerate while running a small electric heater without going deeper than 50% battery discharge.

On the first solar setup I have is close to being identical to the temporary setup except it has 1,880 watts with 12 golf cart batteries. It runs a small electric heater 24/7 inside an old freezer. (That keeps items like glue and paint from freezing in the winter.) During the day, I use the chop saws, lights, drills and even a mortar mixer without any issues. When the batteries are fully charged on this system, the charge controller diverts the excess power to a chest type freezer. I wanted to see if the system would keep up and it does. The freezer has 5 five gallon buckets of water that stays frozen all the time. BTW, the panels are also propped up with 4x4 scraps of wood to allow the water to run off. It could be more efficient by orienting them to about 35 degrees at this time of the year for more power.

Maybe this will help you decide the best route to go. Also, a good quality charge controller is very important. I have a Midnite Solar Classic that takes 147 VDC from the solar panels, then steps the voltage down to 24 volts for battery charging. Higher voltage in the panels mean smaller copper wire = money saved.
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Old 03-04-14, 08:59 AM   #18
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Thanks for all the great info guys. With the recent ice storm, we lost power for a little bit. I'm surprised it wasn't longer.

Like someone said below, I need to get a kill-a-watt meter and see what I really need.

The reason I'm asking these questions now, is that I really want to be able to make the change over easy later on. There is no way i can afford to build the house and add solar at the same time. So, the "solar" subpanel will have to work. I can then power that subpanel with solar or a genny. If we lose power, I can just move those devices over to the "solar" plug that is already behind them. Then later, when I do get solar, I will already be set up for it. As the solar system grows, I can then just move more items from the main panel to the sub "solar" panel.

thanks
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Old 03-04-14, 04:25 PM   #19
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My stone age fridge uses 1.58 kw hours a day. Ive found that turning off things with heat pumps they actually use more elctricity. Did a test with an AC . Dont have the numbers any more . But power off vs leaving it on say 70 degrees during the day. Left it on and it was less electrical load.
Unless your just set on running everything completely off grid . Check into the grid tied first . Then later on add a small battery bank for backup.
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Old 03-04-14, 04:31 PM   #20
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The Kw meter will help the calculations a lot better and easier for figureing battery banks and panels. Found out last year. Before the insulation my place i pulled 15 kws a day for the whole house. Now have insulation in attic . And a efficient mini split. So im betting its around 10kw per day.

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