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louie728

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Posts: 2
Reply with quote  #1 
Hello all im a total solar newbie and would like to do the following solar application.  I live in South florida and would like a backup power source in case of hurricane ( or any power outage).  The source really needs to run a few led lights , fan or two and charge some phones tablets etc...  These are my questions and what I think I can get away with.

Equipment:

I am thinking of getting this 100 watt harbor freight kit
https://www.harborfreight.com/100-watt-solar-panel-kit-63585.html

maybe two of these 
https://www.harborfreight.com/12-Volt-35-Amp-Hour-Universal-Battery-68680.html

and this inverter
https://www.harborfreight.com/750-watt-continuous-1500-watt-peak-power-inverter-66817.html

Questions:

1. Can I just leave this always on excluding the inverter always charging and just use when I need it?

2. Is it safe?  I want to install in my garage and if power goes off turn on the inverter and run an extension cord inside.

3. can  get something that will just power off when batter is drained ( as to not ruin the battery)?

Thanks,
 




Rick H Parker

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Reply with quote  #2 
The source really needs to run a few led lights , fan or two and charge some phones tablets etc...

You need to determine the power rate of each and the time of day you would use power them.  If you can do that, make a list here.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
louie728

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Posts: 2
Reply with quote  #3 
Thanks for the reply.  


Nighttime use:

I would use 1 to 2 box fans I would assume they would be approx 70 watts each = 140
maybe 2 LED bulbs 10-15 watts each = 30

Night time total would be approx 170 watts usage

Daytime use:  
I would use 1 to 2 box fans I would assume they would be approx 70 watts each = 140

maybe charge cell phone tablet
phone 10-40 watts
Tablet?? 10-40 watts

Daytime usage would be around 220

I was looking on amazon and I see this setup 
https://www.amazon.com/Renogy-Watts-Volts-Monocrystalline-Starter/dp/B00BFCNFRM/ref=sr_1_sc_3?ie=UTF8&qid=1509639122&sr=8-3-spell&keywords=100+renogay


The goal is basically to have some air, little light and ability to charge the essentials..



stmbtwle

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Reply with quote  #4 
1: yes

2: Depends. If there is gasoline in the area, a definite NO! Probably safer in the house.

3: Most inverters will shut off before damaging the battery.

4: Hurricanes are not very friendly to solar power(been there). You might consider a generator.

5: you won't get much from 70ah of battery. "A few" LEDs for a few hours a day, ok. A small fan, maybe.


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

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Reply with quote  #5 
Night time total would be approx 170 watts usage

Watts is a rate not a quantity. Watts does not tell one how much energy is used, it tells how fast energy is being used.  You can use energy at the rate of 170W but there is no such thing as 170W of energy usage.  Driving 70 mph does not tell on how far one drove, but 70 mph for 2 hours does.

You need to determine the power rate of each and the time of day you would power them.

Power and time is what one need to calculate energy usage and peak power.

Example:
Fan 1: 70W 6:00 pm - 7:00 PM, 9:00pm - 5:00 AM.
Fan 2: 70W 9:00 PM - 7:00 AM



Two 12V 35ah batteries will give you 35ah of usable current capacity. You should not use more then 1/2 the total capacity of a lead acid battery. If you do, the batteries will have a short lifespan.  12V * 35Ah = 12 * 35 * VAH = 420 VAh420 Wh = 420 Watt-hours of energy... not 420 Watts of power.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
stmbtwle

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Reply with quote  #6 
Do the math. Your 2, 70w fans running for one hour will take a third of that (140wh). 3 hours, all of it (420wh). You can get a bit more from the batteries BUT it will shorten their life. Assuming this is an emergency, that may be acceptable.

IF the sun is shining the next day, you may be able to recharge them. If not, you're out of luck. If the solar panels have been damaged by the storm...

If you can live without the fans, you will get a lot of "run time" with just the lights. Consider cracking a window or two, and dressing accordingly.

It's all about the numbers.

__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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