Small solar project questions

Discussion in 'Off Grid Living' started by Prepper12, Aug 12, 2021.


  1. Prepper12

    Prepper12 Monkey+

    I've been looking at the idea of using solar power in case of long-term power outages caused by a cyberattack on the electrical grid, or maybe an EMP event. I just wanted to be able to do small tasks like charging up AA batteries, electric shaver, things like that. It wouldn't have to be big or fancy. But when I've done searches for solar panels on Amazon that I think would do the job, I hear that it wouldn't work.

    I was originally thinking of getting a small solar panel and connecting the positive and negative leads directly to a battery to charge it. Other than a diode being handy to keep the energy from flowing backwards, would it work? Also, how would I know if the panel I choose is big enough without being too big? The ones on Amazon looked good (costing around $10-$15), but I've been told elsewhere that they may not be big enough to even charge 1 battery. I also considered a 12volt vehicle battery maintainer. They have those at Harbor Freight Tools, but then I was told that it would be too much. Well, if it's too much energy going into one AA battery, then is there a way of spreading it out over 2 batteries or more?
     
    chelloveck, Dunerunner and duane like this.
  2. duane

    duane Monkey+++

    My bias is to use a solar panel, a battery, and a charge controller. I bought a 100 watt Harbor Freight one for about $150 on sale.

    100 Watt Solar Panel Kit

    Has 4 separate 25 watt panels, two 12 v lights, cables, cell supports, and a charge controller. I use a small marine battery for my float, several year old one used on electric trolling motor, put it on to keep it charged, got rid of boat and motor, kept battery. Bought 200 watt inverter and use it for fans, 12 v for lights, timers, and pumps in greenhouse.

    The unit controller is computer type with setup, battery monitoring and battery disconnect to protect battery. It has 12 volt outputs and usb outlets. Weighs about 40 pounds, no liquids etc, so have spare in Faraday cage, puts out somewhere in 7 to 8 amps range at about 13 v. Is it perfect, no, is it total junk, no, have I got my feet wet, kept batteries charged, had emergency lighting in greenhouse, backup if power goes off for watering etc, yes. With some of newer sealed car batteries it makes a nice backup that will charge cell phones, run a raspberry pi computer, can be picked up and moved, you know the rest. Ask around, I will bet someone in the area has 1 you can look at and decide yourself. I bought the first one years ago about half the quality, same price, and lower output, and have never been sorry as I like the ability to use all the 12 v car chargers and all the 12 v tractor and camper stuff, as well as the usb computer outlets for Lion chargers, cell phones, some 2 way radios, etc.

    The Harbor Freight pdf has a good description of setting it up, pointing it, and tilting it for maximum power output.

    That said, it is not a solar kit for a house or for survival power. I just find it handy for keeping batteries charged and short term limited power backup in greenhouse, lights at night and pumps if sun is shining, don't usually need to water if sun isn't shining anyhow.

    Don't know how handy it would be for those with radio uses etc, but for a few hundred watts a day, it is hard to beat. There well may be similar kits that are better, just that this one was about $150 with coupon, look at, pick up and walk out of door, and so far had good luck with Harbor Freight and returning things that are not up to standard or getting missing parts.
     
    arleigh, Dunerunner and TnAndy like this.
  3. TnAndy

    TnAndy Senior Member Founding Member

    Get a charge controller for anything over 30-40 panel watts or you risk overcharging a battery long term.
    I buy cheap ones (15-20 bucks) on Amazon for small things.

    For example, here is a setup with a 50w panel on the roof to keep a 12v battery up to run a small timer and door motor on one of my chicken houses.

    [​IMG] [​IMG]

    Then another small setup I have is a 40w panel with CC to keep the battery on my sawmill topped off.

    [​IMG] [​IMG]

    This is a 10w panel, no controller, leads clip directly on the battery of my garden tiller:

    [​IMG]

    This is a 100w panel wired directly (thru a thermostat and breaker) to a 16" DC fan in one of my greenhouses. Sun shines, fan runs (unless below the thermostat set point in winter)

    [​IMG] [​IMG]

    Four 175w panels that run directly to a DC element in a water heater in my shop. No charge controller or batteries involved.

    [​IMG] [​IMG]

    Then I've got a couple of larger setups as well....this is 16,000w. 10 feeds directly back to the grid to eliminate our bill, 6 is a backup for the house. They get a bit more involved. :D

    [​IMG]

    [​IMG]

    Another 6,000w system on my shop:
    [​IMG]
    [​IMG]
     
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  4. Prepper12

    Prepper12 Monkey+

    Wow, that is quite a setup you have there!
     
    chelloveck and duane like this.
  5. BTPost

    BTPost Stumpy Old Fart Snow Monkey Moderator

    Listen to TnAndy… he is our most experienced Solar Guru here on the Monkey since nadja went to the great Solar farm in the sky…
     
  6. arleigh

    arleigh Goophy monkey

    Start a system with the idea of growing, because as you go there are more things you will want to run on DC power and inverters rather than the grid.
    I bought used solar panels that were already 20 years old and some are still in service 20 years later.
    It is always best to have more panels that battery because cloudy days diminish the out put. I added a wind mill to my system seeing that if it's cloudy it is usually windy.
    A good controller will prevent your battery from being over charged, so that is not an issue. Not enough battery and you miss out on the surplus that occurs.
    If you were scavenging for water and only bring a coffee cup and find a spring running, all you can carry is the coffee cup.
     
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  7. duane

    duane Monkey+++

    Yep, the limit at the moment is batteries. Panels last a long time and a cheap used on at a slightly lower efficiency is still usable, but used batteries are a real crap shot and have a limited life. With my budget, I use the batteries as a large capacitor and use major power, pump water, etc, only when the sun shines. Never plan to install a roof full of panels, personal choice as electric bill runs about $80 a month and at 83, don't really see a long term payoff. Live at bottom of a valley next to a flood control pond. Good water table for shallow well, but tall trees etc make wind power very limited.
     
    chelloveck likes this.
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