# Point me to some reliable info



## Bosco (Aug 14, 2015)

Wanting to add some solar backup but don't want to buy stuff twice or regret what I bought.

Right now when powers down I can run the necessities, chest freezer, fridge, some lights, and gas furnace (plus a tv and dvd player) with the 30amp side of my generator. I want to run this same amount off of a solar system.

If I were faced with using the solar system long term I would swap the bulbs to CFL or LED for long term use. I would most likely quit running gas furnace saving my propane for the stove but would still want to run the fan to circulate heat from wood stove in basement.

From what I have gathered, I believe that a 3000 watt inverter would be sufficient, am I wrong? Where I really get lost is on storage capacity and panel size. I know if we hit a patch of that typical winter suicide weather when you don't see the sun for 5 weeks I'm not going to be charging full bore. Are there any *Practical* guides out there that provide a realistic estimate of what one would need?


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## Slippy (Nov 14, 2013)

Check out Backwoods Solar | Solar Panels | Micro-Hydro | Off-Grid Power

They know their stuff. Good luck.


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## budgetprepp-n (Apr 7, 2013)

I'm a long ways from being an expert on solar I have a small set up but that is a lot to run off solar.


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## Kauboy (May 12, 2014)

With rudimentary math, here's how I've broken down your needs.
First, you say you can run all of your devices off of a 30A generator.
Second, I am making the conservative assumption that all devices are 110V.
That yields a peak wattage required at 3,300W.
If any of the devices are 220V, that would need to be factored in, and would certainly raise the peak wattage.

Continuing on this assumptive line of thinking, you will need to provide, at most, 3,300 watts of power. Perhaps that number is actually less, but I'm allowing for error by using maximums.
For an inverter of sufficient size to provide 3,300 watts, it would need a battery bank that could sustain this 3kW+ draw, with conversion loss factored in, per hour.
Let's go with the cost effective "golf cart" battery for our purpose. A 12V 150AH battery, at a drain rate of a safe 20A/H will provide 240W/H(Trojan T-1275 12 Volt 150Ah Battery). For you to maintain a constant 3.3kW, you would require 14 of these batteries in your "bank". That's just for 1 hour of operation. With the 150AH batteries, you could sustain this for 7.5 hours at full charge. To make it a full day, at full charge, would require 44+ batteries. For batteries alone, you're looking at an investment of over $8.5K
Now, how much power would solar panels provide to you to charge these batteries daily?
Let's make another assumption, and say you find a deal on 310W panels at $315 a piece(Astronergy CHSM6612P-310 Silver Poly - Wholesale Solar).
At absolute peak performance in full sun and exact angle, you would get 310W/H minus efficiency loss of about 20%. So, each panel is pushing ~248 watts to the battery bank per hour. You need to completely fill up your battery bank in the time allotted by the sun in order to continue life as you now know it. Let's give a generous estimate of 8 hours of full, uninhibited sunlight. In those 8 hours, a single panel will push 1,984 watts to the battery bank. Quick figuring on the toes, and we realize that 2 of these panels will give us almost 4kW of power over the 8 hour period(3,968W). Woohoo! For 8 hours of sunlight charging time, we can sustain 1 hour of operation!
Ok, so not good enough... We need to go back and figure out how much wattage this system will use over the course of a full day. So, 3,300 watts every hour for 24 hours. That's 79,200 watts a day. Now, how many panels would we need to generate this much power in 8 hours, and account for the power used during the 8 hours of charging. If 2 panels gave us 3,968 watts over 8 hours, then we can figure out how many it would take to get to 79,200 over the same time. That's ~20 pairs of panels, or 40 solar panels operating for 8 hours a day to generate and store 79,200 watts of power for use. For panels, you're looking at an investment of ~$13K. Those 40 panels will take up a little over 10K sq ft. How big is your roof?
The 3,500 watt inverter will run you between $300 and $500.
Your total investment, with all necessary wiring, hookups, and mounting hardware will run you around $25,000.

Ok, so I'm having a bit of fun.
I could be way off on your hourly wattage, and that could drastically reduce the cost of this scenario. Also, finding better deals on equipment would help.
The point is, battery backup systems are NOT a good way to run a system that requires this much power.
You get far more efficiency, and a much better cost ratio, running that genny.
The freezer, fridge, and furnace will be your biggest amp draws, likely in that order. (I assume your furnace power is only for a fan)
Decide what you *truly* need in a grid down scenario.
Do your own experimentation with how much amperage or wattage each of those items draws. (this thing can help: Kill-a-watt)
Once you know your need, you can get a much better understanding of what equipment you'll require and what your investment will be.

(NOTE: I did this as a thought experiment to keep my mind fresh on the math. I didn't intend for it to be insulting. Take it with a smile)


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## alterego (Jan 27, 2013)

Bosco said:


> Wanting to add some solar backup but don't want to buy stuff twice or regret what I bought.
> 
> Right now when powers down I can run the necessities, chest freezer, fridge, some lights, and gas furnace (plus a tv and dvd player) with the 30amp side of my generator. I want to run this same amount off of a solar system.
> 
> ...


I have been looking at this for two years. You are looking at 21 thousand if you do the work your self. Do you have a well pump to run? 4200 watt at surge start watts.

Use your electric bills to find out how many kwh per month you are using average and worst month and let us know.

I have received several props also from professional installation companies and if you have the professional install you will be between 27 and 32 thousand.

I know you are going to blow this off and say I don't know what I am Talking about which is fine.
http://www.wholesalesolar.com/off-g...eydSA83GcgxC9hjc-gDIZI_KxsPNOEuSwMaAjZk8P8HAQ


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## paraquack (Mar 1, 2013)

Start off by reading the labels on the appliances you feel are an absolute must. During winter when you need to circulate heat from the fireplace do you really need the fridge and freezer. Could you store the cold foods outside in a vermin proof box? Anyway once you get the list written, figure out how many hours a day you need to run those appliances and can you create a time schedule where very few overlap. Take the highest overlap wattage total (amps times volts = watts), this is how big of a inverter you need, then double it for start up of fridge or freezer or for other motors. Take the total watts per day per appliance and that is the size of the battery system you need to handle the total load. IMHO go only with deep cycle batteries (gold cart type), they are designed for just this type of use. Batteries are usually rated in AH (amp hours). A battery rated 120 AH will give you 120 amps for 1 hour (1440 watts)or 12 amps for 10 hours (144 watts). This is not exact, just for the math. So let's say you actually need an average of 600 watts non stop (24 hours per day) for your house. So that is 14400 watts (600 watts times 24 hours). So you would need 10 batteries of the 120 AH type. You would need a solar array capable of putting that same wattage back into the batteries over the time period that you get sun. So if you get 10 hours of good sun doubtful, that would be 14400 watts divide by 10 hours = 1440 watts per hour from you solar panels going into your batteries. So if you had 100 watt solar panels, you would need 15 panels, 1440 divide by 100 watt (panels). If you had a cloudy day, or if it winter, obviously you wouldn't get enough power out of the panels, so you would need more panels. If it was cloudy for two days, you'd run the batteries down the first day and have nothing much for the second day, so you need a second set of batteries. I assume you're up north, so in the winter you have to worry about the snow, so the panels should be easy to get to for cleaning. If you get a lot of cloudy days, you might need 3 or even four sets of batteries and sets of panels to charge the batteries.
So this is a very, very basic idea of what you might need for solar, off grid.


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## Bosco (Aug 14, 2015)

Seems like my plans are a bit more ambitious than I realized. I do have a mini fridge and small upright freezer as well, might have to ditch the big ones and downsize. No well :-?, I was pretty unaware when I built the house 10 years ago. I hooked up to county water. I have a dug well on the other end of my place (400yds from the house) and there was a 4" drilled well under what is now my kids playground. I don't know that its salvageable. Do have a creek 50yds away but that's a whole different thread.
I'm at 37d North 91d West so the winters really vary. Past two have been pretty harsh for our area, prior to that we had had it easy for 5 or 6 years. 
Thanks guys, time to sharpen the pencil and decide whats most important.


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## Bosco (Aug 14, 2015)

alterego said:


> I have been looking at this for two years. You are looking at 21 thousand if you do the work your self. Do you have a well pump to run? 4200 watt at surge start watts.
> 
> Use your electric bills to find out how many kwh per month you are using average and worst month and let us know.
> 
> ...


Looked at my bills and we peaked in the extreme cold weather at 3200kw last February avg closer to 2600 in the non AC months. I feel I can do the work myself. Got an electrician I can rely on if I get over my head. I know my use would go down I just need to determine how much.


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## Kauboy (May 12, 2014)

Good to see that I was the way off on my estimates. If your peak was 3200kW for a month, then my number of 3.3kW per hour was way wrong.


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## PaulS (Mar 11, 2013)

Kauboy said:


> Good to see that I was the way off on my estimates. If your peak was 3200kW for a month, then my number of 3.3kW per hour was way wrong.


Kauboy,
Use 120 volts instead of 110. You weren't that far off considering he only wanted to run the same things he was using off the 30 amp side of his generator. 3600 watts would do it. at $2 per watt for panels that is $7200. Then the batteries, charge controller and a pure sine wave inverter the total cost of parts is only $11 or $12000.

If he wants to run his whole house then he can easily triple that amount and still be behind.


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