5 Reasons Your Plans to Use a Solar Generator Will Fail


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Solar Generator InfographicIf you’re a prepper, you’ve probably seen all sorts of products that claim to be “solar powered generators”. There are tons of YouTube videos about how to make your own and there are plenty of companies that will gladly sell you one.

Heck, you may even have one that you put together yourself. In this article, I’ll be explaining 5 reasons that these products may not live up to your expectations when it comes to providing you with the amount of electricity that you might be expecting to have in a survival situation.

The main problem is that people have unrealistic expectations of how the solar powered generators will actually perform in a GDE (grid down event).

A well designed solar powered generator will consist of several basic components. I’ve listed them below for your convenience.

  • Solar Panel(s)
  • Charge Controller
  • Battery or Battery Bank
  • Voltage Meter
  • Power Inverter
  • 12 Volt Power Outlets
  • Heavy Gauge Wire

One might think that making homemade solar generators would be as simple as ordering up the parts and slapping them together but the key to a system like this working efficiently is in the proper selection of each component so that they will all work in harmony. If they aren’t sized properly, the components themselves could be very high quality but the sum of the components, being the “end product” won’t perform as you would have expected it to.

Without further ado, let’s get started and I’ll explain why all you preppers who have solar panels stashed away in your basements may find that they won’t be as useful as you had hoped they would be.

Why a Solar Generator Might Not Meet Your Expectations

  1. Many people don’t realize that not all solar panels are created equally. If you’ve never lived off the grid or you’ve never had to rely on solar panels, you might think that any old solar panel that you pick up from your local discount catalog will be sufficient, but that’s just not the case.

    Solar panels are rated by the amount of “watts” that they put out under ideal conditions. Many of the solar panels that I’ve seen on DIY solar powered generators are inexpensive 15 watt panels. The problem with these panels is that they won’t produce enough electricity to recharge the batteries that people plan on using. If you plan on connecting your homemade solar power charger to a 100 amp hour 12 volt deep cycle battery, you’re going to be quite surprised when you learn exactly how long it will take to charge it up.

    Let’s take a minute and do the math using the formula that is used to figure out how many amps a 15 watt solar panel should “theoretically” be able to produce. The formula that we’ll use is Amps = Watts/Volts. So, in this case 15 watts / 12 volts = 1.25 amps. If the 15 watt solar panel actually produced 1.25 amps, it would take Approximately 72 hours of direct sunlight to recharge your battery if it had been depleted down to 10% of its capacity (90 amp hours / 1.25 = 72 hours).

    Now, for the sake of keeping things simple, let’s assume that you have 10 hours of good sunlight per day. This would mean that it would take just over seven days to recharge your battery! Now let’s throw some real world variables into the mix. I just did a quick Internet search for 15 watt solar panels and in less than five minutes I looked at three different models that were being sold online. They all claimed to be “15 watt” panels but one claimed that it would output 1 amp, another claimed that it would output .85 amps, and the third claimed .83 amps.

    Keep in mind that these ratings are under ideal conditions when the solar panel is perfectly aligned with the sun and there are no clouds in the sky. If you don’t take the time to turn the panel throughout the day so that it continually gets direct exposure to the sun, the output will be lower and if clouds pass by, the output will also be lower.

    So, based on the three examples that I found in less than five minutes on the Internet, let’s do the math again using the one with the highest rating. Just like before, we’ll assume that the battery has been depleted to 10% of its capacity meaning that we will need to put 90 amp hours back into it for it to be fully recharged.

    In this case, 90 amp hours / 1 amp per hour = 90 hours to fully recharge the battery. If we again assume that we will have 10 hours of good sunlight per day and that we’ll be diligent enough to turn the solar panel so that it is always facing the sun as it moves across the sky, it will theoretically take 9 days to charge the battery! You read that right, NINE DAYS!

  2. The second reason that a solar powered charger might not meet your expectations is because of the way 12 volt deep cycle batteries actually take a charge. It’s not like filling up a bucket with water. If you have a 5 gallon bucket and you add 1 gallon of water per minute, it would take you 5 minutes to fill the bucket.

    That’s pretty simple math but unfortunately that’s just not the way batteries work when they are recharged. Think of charging a deep cycle battery like water going through a pipe that is slowly getting narrower in diameter. When a battery is deeply discharged, the diameter of the pipe will be very large and it will allow a lot of current to flow into it.

    As mentioned above, a charge controller is an essential component to this type of a system. This device regulates the amount of current that is delivered to the battery to prevent it from becoming overcharged and permanently damaged. Charge controllers often have three stages which are “bulk”, “absorption”, and “float”.

    During the bulk charging phase, the charge controller allows the maximum amount of current that your solar panel is capable of producing to flow into the battery. This phase lasts for about 80% of the charging cycle.

    During the absorption phase, the controller will decrease the amount of current that the solar panel will be able to put into the battery which will prolong the theoretical amount of time that it will take to fully recharge the battery. This is because less current will be flowing into it as it nears the point of being fully charged. This phase of the charging cycle lasts for the remaining 20% of the time.

    The third state is called the float stage and during this part of the charging cycle the voltage is reduced or completely cut off to the battery. The purpose of this stage of the cycle is to simply keep the battery fully charged once it has reached its full capacity.

  3. Now let’s throw another wrench into the mix. If you have a 100 amp hour battery when it’s fully charged, if you connect it to a load that draws 1 amp of electricity per hour, you should be able to use that device for 100 hours, right?

    Well, unfortunately that’s not the way it really works. The first reason is that even though you may be using a deep cycle battery, you should never completely deplete the battery before recharging it. Doing this will cause permanent damage. So, your 100 amp hour battery won’t really be capable of providing the full 100 amp hours that it’s rated at.

  4. The other little hiccup that you may have not thought about is that the temperature of the battery has a direct relationship to its charging rate, as well as to its storage capacity. I don’t want to make this article too complicated so for the sake of simplifying things, I’ll just put it this way.

    A cold battery is incapable of holding as many amp hours as a battery that is at its ideal storage temperature. This means that during the colder times of the year, you may think that your battery has the capacity of storing 100 amp hours but that’s just not the case. Just remember that the colder it gets, the less capacity your battery will actually have.

  5. If I haven’t already complicated things enough for you, there’s more to consider. Deep cycle batteries like to be fully recharged after each discharge cycle. This is where the matter of “balancing the components of the system” comes into play.

    If your solar panel isn’t large enough to produce enough current to completely charge your batteries after you use them, they will almost always be only partially charged. Essentially, this means that they will never fully be recharged because before they have a chance to become fully charged you’ll most likely put a load on them and use some of the electricity that they have stored.

    Why is this important, you might ask? If your charging system isn’t adequately sized to fully recharge the battery between each use, your 100 amp hour deep cycle battery will lose its ability to be charged to its advertised capacity. Over time, this will result in your 100 amp hour battery being reduced to 90 amp hour capacity, then to 80 amp hour capacity, then to 70 amp hour capacity, and so on.

Is There Really a Place for Solar Power in a Doomsday Scenario?

Solar power is a very complicated matter. The company’s that specialize in installing alternative energy systems in people’s homes are very skilled at putting together a well balanced system. They look at the home’s average daily electricity consumption and then they use that information to determine how large the battery bank needs to be as well as how many solar panels will be needed in order to fully recharge the bank on a daily basis.

I’m not saying that solar power doesn’t have a place in prepping. What I’m trying to get across is that it’s much more complicated than simply buying a few solar panels that you have stashed away in the corner of your garage or basement with the plans of hooking them up to a battery when doomsday arrives.

If you plan on using a so called “solar power generator”, look very closely at its specifications to see if the solar panel that it is equipped with will have the capability of charging its battery pack in a reasonable amount of time.

Now, taking into account all that I’ve written in this article, you CAN buy a small scale portable solar powered charging station that may not be as susceptible to these limitations. For example, if the battery pack in your solar power generator is lithium-ion based, my understanding is that these batteries do not develop a memory if they are not fully recharged after each use. If the battery pack is made up of NiCad batteries, it will be susceptible to the same problems that deep cycle flooded lead acid batteries are susceptible to.

Sources:

16 Responses to “5 Reasons Your Plans to Use a Solar Generator Will Fail”

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  1. Montana Rancher says:

    Very good article keeping it simple

    One thing I think should have been mentioned under #1:

    One 15 volt panel will most likely not charge a 12 volt battery most of the time. If you add any environmental factors like clouds, smoke, water vapor haze, or heat (which lowers panel output), the voltage output will likely not be above the 12.5 volts you will need to charge a battery unless it is almost dead.

    Fortunately most of these kits come with 2-3 panels so you can wire them in series and boost the watts up to 30 or 45 potential watts and after degradation from environmental factors is accounted for you will have plenty of juice. Now get a charge controller (usually rated in amps) that is the right size and it will take those 30 or 45 watts @1 amp and convert it to 12 volts with the benefit of a boost in your amperage.

    It varies by latitude and local weather patterns but as a rule of thumb you want your panels voltage output to be twice the battery voltage and then let the charge controller do the rest.

    A more cost effective setup would be a 240 watt single panel (about $220). Mine gives me 30 volts at 8 amps on a perfect day, using a 12 volt system your charge controller would be ramming around 20 amps per hour output, but the real world average would be 10-15 amps. Still that gets you to fully charging your battery in a day pretty easy.

    • Patty Hahne says:

      Hi Montana Rancher,

      Thanks for your kind words!

      Yes, bigger is better when it comes to solar panels (meaning the amount of current they output) but I think the mistake that a lot of people make is in trying to keep their solar powered charging station as portable as possible and that leads to the use of too small of a solar panel.

      As far as charge controllers go, I could be wrong but I wouldn’t think that a solar panel that puts out 30 volts would work with a 12 volt battery. If it did, the charge controller would probably lower the voltage to 14 or 15 charging volts.

      Also, wiring two panels in “series” will double the voltage while keeping the amp hours the same. Wiring two panels in “parallel” will keep the voltage the same but double the amp hours.

      I wouldn’t personally connect a 24 volt charging source to a 12 volt battery. If you us a solar panel that is rated at 24 volts or higher, you’ll need a charge controller that can handle that much voltage and a battery bank that is wired to make it 24 volts.

      My understanding and experience living off the grid is that you would want to wire two or more solar panels in “parallel” so the voltage stays the same but more amps flows into the battery.

      For example, modern “smart” battery chargers often have three settings. For example, they might be able to charge at something like 2 amps, 10, amps, or 20 amps. Regardless of what setting you choose, the charging voltage stays the same (roughly around 14 volts) but the current or “amps” going into the battery can be adjusted.

      Like, I said in my article, solar power is a bit of a complicated matter and balancing a system is tricky.

      Here’s a link to an article on series vs parallel wiring that might be helpful: zbattery.com/Connecting-Batteries-in-Series-or-Parallel.

      • Montana Rancher says:

        Hello again

        I tried to be brief so the description in the second paragraph of what a charge controller did was not spelled out again in the forth, and I’m still not sure I got me point across so I’ll try again.

        If you have one 15 watt panel and are trying to charge on an overcast day, the panel will only be producing (estimate) 7 volts and your 12 volt battery will not charge, period. If you have 2 of the panels wired in series that doubles the voltage to 14 volts and your battery would charge. If you used 3 panels as I suggested wire in series, now you have 21 volts which is too much but your charge controller would drop the voltage down to around 14 volts and you would have an increase in the amps produced through the process.

        If you use one of my 240 watt panels 30 volts at 8 amps, my 12 volt charge controller would adjust the volts down to 14 and the amps produced would go up.

        Not sure where you came up this the 24 volt charging source, I never mentioned one.

        And yes your premise is right, most people don’t have enough panels or the basic understanding on how to employ them.

        I run a 3,750 watt array at 48 volts for almost 2 years, so I series 3x 240 watt panels and then have 5 sets of those run in parallel. It’s a sunny day to day and I’m getting 101 volts at my charge controller at 9 amps, my charge controller is paring that down to 54 volts at around 19 amps, though by now I’m floating. It’s the winter that I need all this extra capacity when I at times don’t see the sun for a week.

        • Patty Hahne says:

          Thanks for the clarification Montana Rancher. I just misunderstood your first comment. I thought you were confusing series wiring for parallel wiring as I talk to a lot of people who do actually confuse the two. Clearly, you have a good understanding of why so many people might be confused when they think that building a solar powered generator would be quite simple.

          I simply used a “24 volt charging source” as an example to try and keep things simple for people who aren’t as familiar as you are with solar power. Most people don’t realize that a solar panel that is advertised as a “24 volt panel” is actually rated at 30+ volts under ideal conditions. That’s why I used “24 volts” in my reply to your comment.

          People tend to be most familiar with 12 volt systems because that’s what their cars, trucks, boats, and RV’s use. Since my intention was to clarify that wiring two 12 volt panels in “series” would result in a 24v charging source, that’s why I used that number.

          Our little misunderstanding is a good example of how people who just go out and buy a discount solar panel thinking that in a crisis, they’ll hook it up to their car battery and have all the power they’ll need will be disappointed when they realize that their plans won’t turn out very well.

  2. Davey says:

    Along with the solar panels, I would suggest putting up a couple of 12 volt windmills, permanent magnet / gm body type to help out (12 volt systems) I have 12 of those 15 watt and 1 /100 watt panel,1 6 deep cycle bat. 1200 watt inverter, plus dump controller and it works pretty good. The wind mills really help, and I’m not in a strong wind area. A little research and you’d find the windmills very effective and very reasonably priced. Good article and comments!

    • Patty Hahne says:

      Thanks Davey,

      We actually bought a permanent magnet motor to try building our own wind turbine. Just haven’t found a good source of rotors yet. The one we wanted to buy doesn’t seem to be available anymore.

  3. Paul says:

    Great to see articles that inform out there. Solar can be a tricky subject indeed.

    I agree with with the comments here. A big misunderstanding is the relationship between the components. In particular, the relationship between the module, charge controller, and battery. A good example is that a 12V battery really needs a 17 volt nominal module. This helps account for voltage loss through voltage drop and hotter temperatures. For the charge controller, I always look for multi-stage that at least have a bulk, absorb, and float feature. Also, it is good to have one with a night feature that reduces energy consumption at night time. Obviously, we could go on for hours on charge controllers alone.

    One point I want to make on batteries is that the depth of discharge really shouldn’t exceed 50%. Going to your 100Ah battery, you are absolutely right. You aren’t going to get 100Ah. In reality you have about 50Ah. While you can go down to a 70% depth of discharge, you are in turn shortening the life of a battery.

    Again, great article! I love seeing people reaching out and educating others.

  4. Mook says:

    Funny, I built my system, 4 100 watt panels, Xantrex inverter and charge controller, 4 deep cycle batteries, and I dont seem to have any of these problems. Granted its a bit bigger than the systems described online, but it works and has worked for days on end during outages as long as you know how much power you use and what power you really need to use

    • Patty Hahne says:

      Hi Mook,

      Your system is quite different than those that many people throw together using one little 15 watt panel. You’ve got 400 watts, a charge controller, and a battery bank that sounds big enough to handle the amount of power that you’re using. Your system sounds beefy enough to do a good job. Many don’t have enough wattage going in to keep up with the draw.

  5. will says:

    For more info read solar Bob. He says how it is with the solar industry. He is right that you have to be very carefull who you get for advice and equiptment. I have work in the electronics field for 40 years and I have seen a lot of misinformation. I have run into too many self appointed experts who knows nothing about electricity. Most people do not understand the difference between volts, amps and watts. Too many people thinks if you wire the panels in series to increase the voltage you will get more charging power. A charge controller will charge a battery at 14.8 volts and will burn the excess voltage, watts, up as heat. It is best to have panels that puts out around 17-20 volts and wire them in parrallel for a 12 battery. This way the charge controller will not be burning up the excess power because the voltage is too high and be able to put more power in the batteries. People do not realize if you feed too much voltage into a battery, it will quickly boil itself dry. When that happens the batteries are junk. The charge controller is to prevent this. Another common problem people make is to buy a cheap charge controller. Most of the cheap ones are made in china. They are nothing but pure junk which will destroy a battery. If you want more info look up solar Bob. He brags that he does not own a generator and lives off the grid in Montana.

  6. Vetmike says:

    Spend the money to get good panels. The ones made in China do not last very long and aren’t worth the price.

    • Patty Hahne says:

      Hi Vetmike. Thanks for your comment but it’s much more than just the quality of the panels. I agree, there are good ones and bad ones but the most important thing is your panels need to be able to produce enough electricity to replenish what you use. The best little 15 watt panel you can buy isn’t going to cut it if you use more power than your panel(s) can put back into your battery bank.

  7. Denise Moore says:

    Hi Patty. I am new to the solar power, but have been studying all the components, their specs. and characteristics for about a year. I am now ready to buy as much as is necessary to run home appliances, tools, electronics, etc. from a solar powered generator system during power outage or grid down situation. I’m looking at 2-100 w monocrystalline panels, a 30 watt PWM charge controller, a 125AH deep cycle SLA battery, and a 4000 watt pure sine wave inverter.

    Just curious….approximately how long do you think it would take to charge the battery after going down to the recommended % depth of discharge, using the solar panels on a sunny day in south Fla.?

    The above configuration and specs. are just about all my budget can afford right now. Is there any recommendations you have concerning my selections for my semi-portable solar generator system.

    Thanks for all the information you share with this community.

    • Patty Hahne says:

      Hi Denise,

      The best advice I can give you is to set them up and do a real world test to see how long it takes to charge them. Best of luck to you!

  8. Grampa Mullan says:

    As an electrical contractor I couldn’t agree more. using a combination solar and wind gives you a greater advantage. The large blade wind generators are ugley and noisy. plans exist that the average man can build one. If the grid goes down we can bet on seeing many abandoned cars. with each is a battery. harvesting these will extend your power capabilities. Remember you need to charge these as well. The wind will help and at night or during a storm. With clouds cones wind don’t make a large generator that takes too much wind to push several small ones is much better. Cut your power usage. The new led lights will give plenty of light and not suck the power. electric range forget it or air conditioning. anything with a motor will drain your resources. unplug every device in your home. Learn to sleep when it is dark and work when light Power isnt your big problem its water and food. lastly looters. If you can last for three months most will be gone.remember generators make noise and will attract the new zombies. and get used to discomfort for it will be with you for some time.
    Grampa

  9. Bill Klein says:

    Really good article. So many people think a solar generator will fulfill their needs, when it really won’t come close.

    I use solar all summer for my full time rv. I have 600 watts of panels feeding a 500 amp battery bank. This fulfills my needs unless I have three consecutive cloudy days. I then need my generator for a few hours.

    A 15 watt panel gives you nearly nothing.

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