Solar Systems the Right Way
“I’d like to charge my flux capacitor with a solar charger. Will your 3 watt panel do that?”
OK, maybe you are not charging your flux capacitor so you can travel back to 1985, but you may be a bit surprised at the questions we get regarding on and off grid solar charging.
As you might guess, there is quite a bit of info needed to correctly size your solar power backup system. There’s the wattage from the load you’re going to run, the approximate average run time per day, the average direct sunlight on the panel you would be comfortable relying on, and a few other bits required to get you started.
We try to help answer these solar power and solar charger related questions and more daily here at Batterystuff.com. Because these type of questions are so common, we have created an easy path that takes you from solar newbie to grand 
high poobah in a few easy steps. One of our goals is to educate our customers so that they understand not just what we recommend, but why. Many of our callers who wish to talk to us about solar panels don’t know the lingo and can feel a bit in the dark. Some have already done their homework, and finding a solution for them is easy. Others, deciding homework is for school kids, figure it’s not worth investing a few moments and ask us to simply guess. Sure, we can guess, and every once in a while we will get it right! We’d rather you go through a few steps first, as that can be more productive than us trying to pull bunnies out of our hats.
No matter where you are in this process, figuring out what panels, batteries and controllers you need is not difficult once you take the mystery out of it. A large part of the stumbling block with solar comes from not understanding the basic principles of electricity, or the basic principles of solar energy in particular. With our years of experience we have compiled a plethora of articles and tools that explain different facets of the process. Our goal is to outline the basics and to point you in the right direction to get what you need for your system. One of our most used, and useful, tools is our Solar Calculator. If you have a good grip on what pieces you need, this is a good place to start. If not, read on.
If you don’t have all of the information or experience necessary to make that calculator work immediately, we have created a few more comprehensive articles and tools to help fill in the gaps.
Here is a great starting point: Solar Info: The Down Low on Everything Up High
If you are looking for a solar powered system to run a fixed load, it can be very helpful to have an idea of the basic components necessary to get started; it also defines how one component is dependent on the others. A typical solar system will contain, in order:
- Solar Panel array
- Solar Controller
- Battery Bank
- Load or Inverter
The key here is that some of the components are dependent on others. For example, if you are looking to run a 60 watt light bulb (load), for 10 hours every night, you will need a battery bank capable of powering the 600 watts necessary to run the light AND have enough photovoltaic solar panels to bring it up to a full charge by sun down the next day. As an example you may live at a latitude and weather situation where you can only realistically count on about 5 hours of sunlight per day (direct on the panel). In this instance you would need a 120 watt panel (600 divided by 5) to bring the battery bank back up to fully charged. A 120 watt panel creates a maximum ‘flow’ of 10 amps, so you would need a minimum of a 10 amp solar controller to be able to control that power going into the batteries. Don’t get confused here- the battery bank is dependent on the load and the time the load is used, while the solar controller is dependent on the maximum output of the solar panel, and the solar panels are dependent on both the load, and the sunlight available.
Once you have an idea of the basic components you will need, the next step is to size the battery bank to your load. We have a variety of tools to help you do this depending on the information that you know, as well as exactly which component you are attempting to figure out.
For example, if you are starting your system from scratch, and do not already own the batteries for the system, we have a tool called: Sizing a 12 Volt Battery to a load. This does require that you actually know what the power consumption of your load is, which usually will be stamped on the device by wherever it connects to power. On a heater, it would be on the back or bottom where the cord enters the case. On a laptop, it will be on the converter box midway between the wall plug and the laptop itself. If you are using a 12 volt device, then all you would need to do is type the numbers into the calculator and go from there; however, if you have an AC powered device, (plugs into a wall outlet with a three pronged 115VAC) then you will need to convert your load into wattage using the calculator: DC to AC amperage conversion run through an inverter. This will give you the DC amperage necessary to plug into the calculator. If you are running a variety of different devices, you will need to average the load based upon each devices approximate usage over a 24 hour period.
Now, suppose you want to try to use those batteries your cousin gave you that he bought for his motor home three years ago, we have a calculator to show you how many hours it will run for under a known load… Determine Run Time for Specific Load. This will lead you through finding how many hours your load will run off of the batteries you already have. The calculator is also available in a slightly less accurate ‘modified’ version that does a lot more guessing(when all the info needed is just not available) than it does magic, but we encourage you to use the more accurate one and leave the fairies and unicorn wishes for another time.
Now once you have figured out exactly what batteries will run your load, or that Aunt Berthas’ batteries actually might work for you, you’ll need to figure out what panels to use to re-charge them. It’s back to the Solar Calculator. We already know how much power the load consumes, as well as the time it will run, so you can go through the first part of the calculator easily. The battery size portion of the calculator will allow you to account
for back up days using the AH rating of the batteries that you figured out using the previous calculators. Back up days are the numbers of days you want your load to be able to run if there is absolutely no Solar Input. The last step of this calculator will tell you how many panels you need to buy. This will be directly dependent on the amount of sun hours (hours the sun is shining directly on the panel) you have available, as well as the panel size you would like to use.
If you go through these steps, hopefully the mystery will be taken out and the reality of how these different systems interrelate will be just a little bit clearer. Our goal is to have you, our customer, satisfied with a system that works, and works very well. These tools and articles that we have put together aim to make that goal a reality.
For those who want to go beyond these basics into the realm of math to see how these calculators work, we have a couple tools you can browse through. The first will explain how the calculators figure out the correct AH rating of a battery that will run your load, but consider yourself warned, these articles have been known to make grown men cry and nerds laugh with joy… which brings me to: Peukert’s Law | A Nerds Attempts to Explain Battery Capacity. This article explains what Amp Hours really mean, and more importantly, what they don’t mean. And for the truly committed, or psychologically commit-able, there is the Math Behind the Magic. This is less of an article and more of a simple list of formulas.
That’s it. You made it to the end. Congratulate yourself, and order up some panels, and batteries, and chargers, and…and, well, have a great day!
BatteryStuff.com
