# Solar help



## rjd25 (Nov 27, 2014)

I want to build a solar generator that will be big enough to run a fridge and my house lighting. I don't know how big of a solar array I would need for that. Also I don't know how to calculate the power generation of solar panels. Can someone help with that?


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## Dubyagee (Nov 9, 2012)

Need the data from the fridge and how many lights youre gonna use.


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## paraquack (Mar 1, 2013)

Data = wattage for the appliance and lights you want to operate.


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## rjd25 (Nov 27, 2014)

my whole house runs on LED bulbs, I am not sure of the wattage that they run under. They are CREE 60's and I would say I have around 20 of them. The fridge is this one here but I can't find any info on power usage Sears.com


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## paraquack (Mar 1, 2013)

OK, here's some guessin' and by golly numbers for an example. My 2 door Whirlpool shows 6.5 amps at 120 volts AC which equals 780 watts *per hour* while it is running. Problem is that at start up, it could draw 1-1/2 to 1-3/4 or 1180 or up to 1365 watts for maybe 5-10 seconds until the motor settles down. 
My LED house lights are between 7.5 watt to 9 watt each, so i'm not really concerned with them.
So you're probably going to need an inverter capable of *2000 Watts* at 120 volts AC., that's kind of worse case given what you've said. BUT that doesn't mean you're going to need 2000 watts all the time. This Info stolen from: Refrigerator -Normal Run Time
*Refrigerator -Normal Run Time *
For a freezer to maintain a desired temperature of 0 degrees F or a combination refrigerator-freezer to maintain a 5 degrees F freezer and 35 - 40 degrees fresh food temperature, the compressor will usually run more than 50% of the time. Refrigerators have smaller, more powerful, high-speed compressors that generally cost less to operate than those in *older refrigerators*. These compressors are designed to run 80 % to 90% of the time. This makes them more energy efficient because the greatest amount of energy used when the compressor cycles on. 
Factors that contributes to run time:
In extremely hot, humid areas, run time may approach 100%. 
Loading the refrigerator or freezer with a large amount of food, especially warm or hot foods, will also add to the run time. Hot foods should be allowed to cool before being placed in the cabinet.

Based on the 50% which I'd say is minimum, that is 390 watts every hour/24/7 plus the LED lights, but I'm not going to worry about them since they are small in the grand scheme of things.

So 390 Watts = 3.25 AMPs at 120 VAC from the inverter. The inverter will need 10 times that + a tad to give you the 3.25 amps of 120 volts AC, so lets say 33 amps from the battery or lets say 425 watts of 12 volt DC times 24 hours in a day. So you'd need a solar array capable of putting 10200 watts back into a good sized battery array each day to break even. If the sun shines really strong like down here in AZ I could probably get away with 1000 to 1200 watts worth of solar panels. More if you're up north, *even more* during the winter. If the sun doesn't shine for a day, you're way behind the curve. So, if it were me, I'd be looking for a lot smaller fridge to be used. I've not seen them, but I've heard of a thermostat system you use with a freezer (preferably a chest type) because it has better insulation and cold air won't fall out of the chest freezer. 
Now all the numbers and calculations are based on everything being in good shape. Every time you open the door to fridge you are going to be using extra power. If you keep the freezer making ice cubes, it will use extra power. The light bulbs will use extra power when the door is open. If your fridge is going to run 80% of the time, well increase that solar panel array to maybe 3500 watts. To me, the idea of a regular fridge is too costly. I've got other ideas but I won't go into them here, too long and not enough info from you.


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## rjd25 (Nov 27, 2014)

hmm... we use around 700kw per month with the house running at full tilt. That averages out to 23Kw per day. Are you saying 50% of my daily power usage is from my fridge? I have 2 fridges and a chest freezer plugged in now factored into that 23kw a day. This is what isn't making sense to me. a 10kw solar array should power my whole house from what I have calculated but as I said it wasn't making sense so I put it to the geniuses on here.


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## Slippy (Nov 14, 2013)

rjd25 said:


> hmm... we use around 700kw per month with the house running at full tilt. That averages out to 23Kw per day. Are you saying 50% of my daily power usage is from my fridge? I have 2 fridges and a chest freezer plugged in now factored into that 23kw a day. This is what isn't making sense to me. a 10kw solar array should power my whole house from what I have calculated but as I said it wasn't making sense so I put it to the geniuses on here.


Get with your power company and the can give you average power useage amounts of the appliances. I guess that refrigerators, water heaters, HVAC are the biggest users of electricity.


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## James m (Mar 11, 2014)

There should be a silver sticker on just about everything. Would a clamp meter work for this. IDK.


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## HuntingHawk (Dec 16, 2012)

Here is what was mentioned to allow a chest freezer to be used as a frig.

Amazon.com: Johnson Controls A19AAT-2C Freezer Temperature Controller: Beer Keg Systems: Kitchen & Dining


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## HuntingHawk (Dec 16, 2012)

Where you live makes a difference. Also, are the panels going to be adjustable as you can loose up to 40% by them not being adjustable.

When you set up a solar system you set it up for the amount of sunlight you get in winter as that is the lest amount of daylight hours.


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## HuntingHawk (Dec 16, 2012)

Amount of people in the household makes a difference also. How many people in & out of the frig daily.


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## budgetprepp-n (Apr 7, 2013)

rjd25 said:


> my whole house runs on LED bulbs, I am not sure of the wattage that they run under. They are CREE 60's and I would say I have around 20 of them. The fridge is this one here but I can't find any info on power usage Sears.com


I did some testing on the 60 watt cree, They say they take 9.9 watts the ones I checked pulled 9 watts 
I have then in every room. My lights and some small stuff runs off solar


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## pheniox17 (Dec 12, 2013)

Average 23kw a day

That's 23000 watts a day 

That means 958.3 watts a hour needs to be generated to run your house

Already mentioned, biggest loads are fridge, freezer, hot water, air con/heaters 

So if your taking of running your entire home you need to generate at 120vac roughly 1kw per hour....

At 12v DC your looking at 10kw per hour....


So as already mentioned, more info is needed, and if I was you op... Start with your smallest fridge, or newest, but inverters don't like compressers, and fridges have a mean one....


Paraquack explains in detail of why so there is no point repeating that info... I hope the basic maths provided is enough for you to get what he is saying


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## Prepadoodle (May 28, 2013)

Since you know your average usage, I would next look at a good solar insolation map to find out how much usable sunlight you are likely to get in your particular area. It's not as simple as buying enough panels to meet your average usage, you will have to factor in seasonal changes in available light, panel orientation, and so on.

Here's a good starting point... U.S. Solar Radiation Resource Maps


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## sulfur (Mar 15, 2015)

those posting about kw need to understand the difference between kw and kwh. kw is a rate of power, kwh is a quantity of power. They are totally different terms and should not be interchanged. Posts above are using kw when they should be using kwh. Does the original poster want a grid tied or off grid solar system?


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## Slippy (Nov 14, 2013)

Does anyone have an idea of the cost of an off grid system to run a home that averages 1200-1300 KWH per month? We realize that we over consume and would obviously be willing to cut back, hell we have 3 refrigerator/freezers for heavens sake!...and realize that we would design our off grid system for emergency or SHTF.

Our home is located in the southeastern US and we have cleared the southern and western exposures to allow for solar panel expansion. Our home is also a Passive Solar design with deep porches on the northern and southern exposures and high ceilings. We also have small transom windows only on the eastern and western sides of the home to eliminate as much sun as possible. 

Just curious...


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## bigwheel (Sep 22, 2014)

Highly interesting thread here folks. Thanks for all the well informed info. AC and heating eats up our meager funds. Got a perfect location for solar array on the front roof but got a big piss elm tree casting shade and a Oak which trying to catch up. I would have to start with a a crew of Tongans to whack those. So I may wait a bit. I sorta try to follow the old advice that for every 10% that the roof can be shaded in the summer..it will knock 33% off the electric bill. Anybody ever hear that or similar?


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## Slippy (Nov 14, 2013)

Shade is good Bigwheel, but having excellent insulation is as important. One thing we did was take all of our HVAC ductwork and ran them through the basement and engineered truss style floorjoists instead of the thru the attic where heat accumulates. If you can create shade near your windows and eliminate sun getting into the house that way, you can reduce the HVAC burden. Double or Triple Pane windows and energy efficient doors and equally important. 2x6 wall studs give you the ability to better insulate the walls but making sure that you aren't losing heat/coolness up and out your attic is huge. 

I don't know shinola about solar but know that R Factor and wall construction is important in retaining temp inside the home. "Seal the envelope" is the term that the insulation companies are using today.


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## bigwheel (Sep 22, 2014)

Gotcha thanks. I used to work in the insulation field back in the good old days. Me and my Daddy ran the blowing machine. He carried the hose and I fed the beast..lol. Nasty job..and hot up in them attics whew. This little crib we live in got the attic filled up like a crack box. Cant even find the air ducts. Anyway the little bride been nagging we need new ducts. She things germs live in there. I think shes just hysterical or something. Vaulted roof on one half the house. Regular old crappy windows but not many of them. Ya know think the best energy savings we got was when the big electric company come out and did a great free job to mastic all the duct joints and get rid of the silver tape and a few other tricks which dont work well. Would venture to say it knocked 30% off subsequent bill. Thought that was mighty nice of them to do that. Course they prob pretty selfish and trying to save themselves from running out of electricity and such things.


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## sulfur (Mar 15, 2015)

Slippy said:


> Does anyone have an idea of the cost of an off grid system to run a home that averages 1200-1300 KWH per month? We realize that we over consume and would obviously be willing to cut back, hell we have 3 refrigerator/freezers for heavens sake!...and realize that we would design our off grid system for emergency or SHTF.
> 
> Our home is located in the southeastern US and we have cleared the southern and western exposures to allow for solar panel expansion. Our home is also a Passive Solar design with deep porches on the northern and southern exposures and high ceilings. We also have small transom windows only on the eastern and western sides of the home to eliminate as much sun as possible.
> 
> Just curious...


probably about $30,000 after tax credits, if you install it yourself


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## paraquack (Mar 1, 2013)

If you do the install on the roof, make sure you leave enough room for ventilation under the panels, 4 inch minimum, preferably 6 to 8 inches. Without proper ventilation, the heat build up can cause a 10 to 15% drop in power out.


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## 8301 (Nov 29, 2014)

paraquack said:


> If you do the install on the roof, make sure you leave enough room for ventilation under the panels, 4 inch minimum, preferably 6 to 8 inches. Without proper ventilation, the heat build up can cause a 10 to 15% drop in power out.


New NEC code for fire fighters also requires 3' of space along all roof edges and at the roof peak on each side for clear access for firefighters who may need to get on your roof while fighting a house fire..


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