Solar Basics: Understanding Batteries

IMG_1916I recently announced that I am now selling a 90 watt Suitcase Solar Power system. Quite a few people wrote in asking just what that much solar could do for them, and that is a very important question. Before you put down your hard-earned money you want to know if it will meet your needs! Rather than try to give a detailed answer in a comment, I thought it deserved its own Post, so here we are.

Most people find learning about electricity very confusing, I know I did! The problem is it uses completely foreign words that we are unfamiliar with. When I started learning about it for the first time the idea of amps, watts, volts and amp-hours confused me for a long time! So in explaining it I am going to avoid the terminology and approach it in terms all of us can relate to: money. (While this is an analogy, if you changed the phrase “dollar per hour” to the technical term “amp-hour” it would still be completely accurate.)

I want you to think of your solar panel as a tiny factory full of elves that make money. How much money it makes depends on a lot of things like how much sun there is and how big the solar panel is. Solar panel elves only make money in daylight, and the sunnier it is the happier they are and the more money they make. Our little 90 watt solar panel makes about $5 an hour during the brightest part of the day. But if it’s cloudy out, the elves in the panel may only make 50 cents an hour, or even less depending how cloudy it is. So on an average sunny day it makes $35 total.

So our happy little solar panel is busy making us money, but, what are we going to do with that money? We can buy electricity and the pleasure and usefulness electricity provides. For example, at night it can buy me light so I can see, or it can power my portable DVD player so I can watch a movie. On a hot day it can power a fan so I can stay cool. It can charge my cell phone, laptop, iPad, Kindle, and all my other personal electronic devices.

thumb_piggy_bankSo you can see that our busy, hard-working little solar panel can greatly improve our life. But how do I use the money to buy those things? It’s simple, as your solar panel makes the money it very thoughtfully deposits the money into your piggy bank so you can buy things. Where is the piggy bank? It is your battery. The busy little elves in the solar panel make the electricity and then put it in a wheel barrow and carry it down to the battery which is the piggy bank. Piggy banks come in different sizes, but the one we have only holds $90. We can’t put more in it. And, we must always leave $45 in the bank. It gives the piggy an upset tummy if we take out more than $45 and we do not want to make our piggy bank sick so we always have to have a $45 balance in the bank.

The wonderful thing about our bank is that even during the night, I can keep buying electricity even though the elves are asleep and not making money. But, I must never let the bank balance fall below $45 and the closer it stays to $90 the happier and healthier our little piggy is. In fact if the balance were to always stay at $90, the piggy would probably live forever, and if it drops down to $45 every day he will get sick and die much earlier. If we let it drop below $45 every night, he will get sick and die very, very soon. Poor little piggy, we don’t want to do that to him do we?!!

This is my solar controller. It has a digital readout and I have it set here to show how much "money" (amps) is coming out of the panel. Right now it is 7.8 "dollars."

This is my solar controller(not the one on the Portable Suitcase System). It has a digital readout and I have it set here to show how much “money” (amps) is coming out of the panel. Right now it is 7.8 “dollars.”

During a sunny day the elves in our 90 watt Suitcase Solar Power System are making about $5 an hour. So if we buy $5 worth of electricity every hour, and they are making $5 an hour, the bank balance remains the same. If I spend more than $5 an hour, the bank balance will fall during the day, if I use less, it will rise during the day. We want to be careful to let the bank balance build until it is full at $90. That way we can spend up to $45 at night to buy electricity.

But we know that since our solar panel only makes $35 per day that is all we can practically spend. If we spend the whole $45 and the next day we only make $35, we will steadily run out of money until we are flat broke and in bankruptcy. The federal government can print money when they need it but we can’t. Our elves can only make $35 so that is all we can spend; we have to live in our budget.

What can we buy with $35? Everything we buy has a price per hour. So to know how much something will cost us we must know how much it costs per hour, and for how many hours we use it. For example, I have a fan that costs $2 an hour to use it. If I use it for one hour, it takes $2 out of the piggy bank. If I use it for two hours it takes $4 out of the piggy bank. So all we have to do is find out how much something costs per hour and multiply it by the number of hours I will use it. Here are some average prices per hour for some common devices:

  • Fan: $2 per hour
  • LED light: $1per 2 hours
  • Laptop: $4
  • Energy Star 19 inch LED TV: $2 per hour
  • Personal devices (cell phone, tablet, camera, Kindle, etc.) $1 for 2 hours
  • Roadpro 12 volt Oven: $10 per hour ( but it rarely is on for more than ½ an hour=$5 per 30 minutes of use)
  • Microwave: $100 per hour (But that is only $1.66 per minute or $8.50 for 5 minutes)

So what is the bottom line? A 90 watt solar panel should be able to let you run this realistic scenario:

  • LED light 4 hours a day ($2)
  • Laptop: 4 hours a day ($16)
  • Fan 2 hours a day ($4)
  • 12 volt Refrigerator ($11)
  • Various Personal devices ($2)

That is $35 total spent overnight, all that we are allowed to use overnight out of our piggy bank. There are so many variables, that you may or may not be able to do exactly all this, but you can do something close to it. In the winter you won’t use the fan at all and the Refrigerator will come on less, but there is less sun to generate power. You can also probably find much more efficient items than I have listed. I have a friend who switched from her laptop and mainly used a tablet and that saved her so much electricity that she was able to power a C-Pap machine overnight with just the 90 watt Suitcase Solar Power System.

Solar_Power_Basics_3_-505x399The important thing is you understand the idea of a $90 bank and you can NOT spend more than $35 overnight. You will just have to play with all your devices and see what combination will work for you. My friend had to have her C-Pap so she had to sacrifice the fan and get a more energy efficient computing device. After doing that she has been entirely satisfied with the 90 watts she has. I have another friend with the 45 watt Harbor Freight system and she was so frugal with electricity that it met all her needs quite well. Think how much happier she would have been with double the power of this system! Also, be aware that you can hook your piggy bank up to the starting battery of your van and the squirrels inside your engine will also make money/electricity for your piggy bank while you drive, increasing your power all the more.

I know this is a silly analogy, but you just learned the basics of solar power. If you change dollars to amp-hours, and piggy bank to battery bank, you will sound very wise and not at all silly!


I've been a full-time VanDweller for 12 years and I love it. I hope to never live in a house again!

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