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Discussion Starter #1
Greetings,

New to this board, old to survival skills. Canadian immigrant to USA. I guess it will be one of the numerous questions I'll ask, and I am quite sure I'll be abble to answer a few too :D:

First of all, let me tell you I wired entirelly my house. I know the basics of AC electricity, but I am in no way an expert. I am just good at reading DIY books and apply them.

I have been reading since a little while about an emergency Solar array system that I would like to build, but I can't get the sizing and parts right in my head. Maybe it is because there are too many choices or because the different systems are not explained in a way I can understand and choose the right parts. I need someone who did it or knows his stuff.

My goal is very simple: I want to have a battery bank that I'll be able to use to power my chest freezer and normal refrigirator. At the same time or not, I do not care. It is really for emergency purpose. For the night, it would be nice to be able to plug a few CFCs to have light if needed and if it is secure. If not, we can deal with our night vision equipment.

So, How many deep cycle batteries would I need? I calculated I would need about 3500w DC/AC converter to handle the surge, which one would you recommend? How many pannels would I need to MAKE sure the batteries do not run out (under 40% charge of course) and which ones would you recommend, and which charger would you recommend?

Thank you
 

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Let's use 1 fridge/freezer for now. Roughly 8 amps at 120v which is 960 watts. Let's say it's used 25% of the time, roughy 5750 watt hours.

LEt's say the cells are in a good spot and get 8 hours of charging time in. Something like a 725 watt solar cell array for 100% efficient recharging. Each of my 1 foot square cells put out about 1/4 amp for a 12v battery, but they plant reject models. That's 4 watts per cell. You'd need about 175 square feet of battery charging. 10 foot x 18 foot or so for one fridge. Likely you chances of good sun aiming at your fixed panel aray are like 5-6. I'd get 20x25 to power one fridge.

Most deep cycle batteries have a 175 minute reserve capactity at 20 amps. That roughly 3500 watt hours of energy. To save up for one days fridge use, you need 2 batteries. What about a cloudy 2 or 3 day spell. Your looking at 6 batteries for one firdge. Regular RV or bass fishing boat battery sizes.

All of these assumptions are 100% charge efficiency and 100% inverter efficiency. If my memory serves me correctly, inverters are 85% efficient and battery charging is like 60-70% efficient. Combine these inefficiencies, you pretty much close to double the solar array size. 20x50 solar panel array, six batteries, a 2000w inverter, 120v powered chargers, and a charger controller. That's one nasty bill. And this system may not recover well from a cloudy week.

Propane fired fridges can last a long time on a big tank of propane for much less.

I have a 6 square foot solar array designed to provide minimal 12v lighting around the house, recharge small batteries, provide temporary power to a small 120v aplliance or two, and to recharge the diesel generator battery. One Deep cycle battery for the accesories/lights, one deep cycle battery for the diesel. I got the cells for about 75 bucks, the batteries were about 200, maybe another 100 for wiring a couple of 12v lights around the house. I use a department store variety inverter. I made my own charger controller. Diodes prevent reserve power and a simple circuit slows down charging of the cells when they're full.
 

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Discussion Starter #3
Greetings,

You confirm what I found....:xeye:

I am beginning to think to buy a 12v chest freezer.

I was planning to buy about 8-12 batteries. I know those would have lasted a little while. But the charging part (pannels) is the one that always was oversized and costed a bundle...

Thank you
 

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Forever Vigilant
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Once you know your 24 hour wattage requirements and your latitude, you can figure out everything else based on knowns.

Example: if your 24 wattage load is 750 watts and your latitude is 35 in SE Arkansas, you can create the following:

Using a Solar Insolation map: http://www.solarcraft.net/sun-hours-map.htm you can determine the average worst-case available sun hours for your location. 3.3 in this case. This is the amount of full sun power you can expect to hit your non-articulating solar panels in a full day - worst case.

You need 4x the battery bank and 3x the charging than your 24 hour discharge rate. The reason for this is so you do not ruin your battery bank. The deeper you discharge a battery bank, the more you shorten it's life. You must also account for shorter sun days due to weather, as well as discharge and charging inefficiencies.

So, at 12 VDC, you will need a 250 amp hour battery bank minimum.
750 (watt load per day) divided by 12 (VDC) times 4 (reserve power)

For solar you will need 680 watts of panels minimum.
750 (watts charging) times 3 (reserve charging) divided by 3.3 (available sun hours)

For the above scenario, you will remove 62.5 amp hours per day from the battery bank. There will be a 15% loss for an inverter which brings the total up to 72 amp hours per day. Your charging capability in normal sun conditions will be 131 amp hours per day. You will lose 20% in charging inefficiencies for a net of 104 amp hours per day.
 

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Live Secret, Live Happy
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Step 1 is to actually measure your loads. Freezers and fridges do not take 4 amps each at 120 volts.

Step 2 is to look up the average sun hours as mentioned by SMM123.

Step 3 is not to buy crappy panels or car batteries, buy good panels of at least 80 watt size, Kyrocera make nice panels. Buy good batteries built for extended use at deep cycles. I suggest (4) 6v 220 AmpHr golf cart batteries in series. They make much better high capacity batteries, but they cost more per AmpHrs.

Step 4 is to decide how many cloudy days you wish to store in the batteries, I suggest at least 3 days at 80% depth of discharge.

I would expect that you would need 5-600 watts of collection and 200 AmpHrs storage at 24 volts. I would use a low frequency inverter that uses copper wound transformers. Xantrex TR series is good. Don't forget to use heavy gauge wire to carry the currents.
 

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Step 1 is to actually measure your loads. Freezers and fridges do not take 4 amps each at 120 volts.

Step 2 is to look up the average sun hours as mentioned by SMM123.

Step 3 is not to buy crappy panels or car batteries, buy good panels of at least 80 watt size, Kyrocera make nice panels. Buy good batteries built for extended use at deep cycles. I suggest (4) 6v 220 AmpHr golf cart batteries in series. They make much better high capacity batteries, but they cost more per AmpHrs.

Step 4 is to decide how many cloudy days you wish to store in the batteries, I suggest at least 3 days at 80% depth of discharge.

I would expect that you would need 5-600 watts of collection and 200 AmpHrs storage at 24 volts. I would use a low frequency inverter that uses copper wound transformers. Xantrex TR series is good. Don't forget to use heavy gauge wire to carry the currents.

Hick is completely correct. I've done tons of research for our RV system and started implementing a system recently.

Figure out your loads. That is #1 and most important. We have a large dorm fridge in the RV that draws .9Ah at 110v. I've never figured out the run time, but I assumed 100% for our load usage. I then converted this to 12v usage which comes out to aprox. 10Ah @ 12v. Then multiplied by 24 to figure out daily usage. So 240 amps per day.

Golf cart batteries like mentioned are much better than most, but we couldn't fit them so we used 115ah group 27 marine batteries. You don't want to drain a battery below 50 or 60% (75-80 is optimal) so we figured just for the fridge we needed 4 batteries to stay within limits.

After figuring out your loads, follow everything else Hick said with the exception of the 4 golf cart batteries. You may need more or less. You need to research series and parallel wiring if you go the golf cart battery route since you'll probably need both.

You may also want to check out the Sundanzer products which are designed for efficiency. http://www.sundanzer.com/Home.html

If you need any help feel free to PM me. I've got a degree in EE as well as years of experience (professionally) in the car audio industry and am always happy to share.
 

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Wanderer
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Look at the Backwoods Home Magazine's web site, backwoodshome.com, and refer to articles by Jeff Yago. He writes clear articles about alternative power with all the detail you need to calculate your specific requirements, and covers solar, wind and microhydro installations.
No affiliation with the magazine, just a subscriber. Great magazine, though.
 

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remember when you run a series your voltage doubles but your amps remain the same. so if you have say 30 volt modules at 8 amps each and are running 10 of them. your array would be [email protected] if you run 10 modules at 30 volts each pumping 8 amps a piece in a parallel then your out put would be [email protected] Your freezer is not going to require 80amps. 10 modules at those numbers will not make [email protected]

when doing a stand alone system your battery bank is one calculation and your array is another. both need each other but both need their own calculations that go with your inverter and charge controllers specifications on top of your load requirements boosted by 25%
 
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