Solar energy is trending these days. It’s good for the environment, it’s renewable, and best of all, it saves money in the long run. But it’s still rather mysterious, isn’t it? How does the energy get from the solar panels to your appliances? What are all those wires for?
How Does Solar Power Work???
For off-grid systems, it’s really quite simple, and that’s what we’ll focus on today. Once you understand how an off-grid system works (does not interface with a utility company), it’s becomes much easier to understand how a grid-tie system works (does interface with a utility company), especially one that has battery backup. So, whether your plan to build a completely off-grid DIY solar energy system, or whether you plan to tie back into the grid, if you’re completely new to solar, this article should be a good place to start.
How Solar Energy Works
The goal for today is to help you understand the following diagram:
Don’t worry if this diagram looks intimidating. Let’s break this down.
In general, this is how off-grid solar power works:
Solar panels charge batteries, and batteries are used to power your appliances and devices.
But there’s a little bit more to it than that. Let’s look at the left side of the diagram. Between the solar panels and the battery, you need something called a charge controller. A charge controller will control the charge going into the battery, thereby protecting the battery from being overcharged, while maintaining a specific charge cycle that will prolong the life of the batteries.
This is where the charge controller goes:
Are you with me so far? Great.
This is the basis for all off grid solar power systems. Solar panels, charge controller, and batteries—all off grid solar power systems need these three components.
The right side of the diagram will vary, depending on what items you plan to power with your solar electric system. Let’s go through your options, starting with the most basic system.
Connecting 12 Volt Appliances to Your Solar Power System
Let’s say that we are running a 12 volt system, and we want to power one 12 volt fan with our 12 volt battery. We can simply connect the 12 volt fan directly to the battery. That overall diagram looks like this:
Easy enough, right?
(12 volt appliances, generally speaking, come with plugs that can plugged into a cigarette lighter outlet. We’ll get into the wiring specifics later. For now, let’s concentrate on basic connection points.)
However, most people want to power more than just one 12 volt appliance. They want a 12 volt outlet for charging their cell phone, a 12 volt water pump, a 12 volt fan, and they want to wire up 12 volt LED lights.
The simplest way to do this is to simply attach all of the wires at the battery posts.
Does this work? Yes, it sure does! Would I recommend it? Probably not.
It works fine for just one or two appliances, but beyond that it’ll be difficult to manage all of the wires attached to a single battery post.
Instead, for a small 12 volt system (for a tiny home or a small RV) I recommend connecting a 12 volt fuse block to the battery, and then attaching all of your 12 volt loads to the fuse block. (There are other options, but we’ll get into those at a later point.) A fuse block will have discrete terminals for each circuit, which will make attaching and organizing wires much easier. Each circuit will also have it’s own slot for a fuse, which will protect the entire circuit if its current exceeds safe levels. I use and recommend Blue Sea fuse blocks.
With a fuse block thrown into the mix, the diagram now looks like this:
Connecting 120 Volt Appliances
But what if you don’t have any 12 volt appliances? What if you just want to power a 120 volt appliance, like a toaster? (120 volt appliances have a standard American household plug that goes into a wall socket.)
In that case, you’ll need an inverter. An inverter will convert 12 volt DC to 120 volt AC. Let’s wipe our diagram free of the 12 volt fuse block and the 12 volt appliances. Let’s add an inverter and a toaster. The inverter attaches to the battery, and you can then plug your toaster in to the inverter.
Completing Your Solar Power System
And what if I want to attach several 12 volt appliances and an inverter?
Simply connect a 12 volt fuse block and the inverter to the battery, so the diagram now looks like the one at the very top of the page. 120 volt appliances are used with the inverter, and 12 volt appliances are wired to the 12 volt fuse block.
So, now you are more or less good to go. Hopefully, after having gone through the system piece by piece, this diagram looks a little less intimidating that it did earlier.
There is one thing that I should mention before you go running off to build your DIY solar electric system: Switches and fuses (or breakers)
Okay, three things.
Ideally, you would have a switch and a fuse (or a breaker) on every circuit in your system. Why? Switches will allow you to control where the electricity can go, and fuses (or breakers) will protect the wire and your equipment in case of a surge of electricity flowing through the system.
I have seen many DIYers install solar electric systems without switches, fuses, or breakers. It does work. However, it is much safer to have fuses and switches on every circuit. Here’s what the diagram would look like with fuses and switches added. The yellow squares are fuses, and the red dots are switches.
Okay, let’s tackle some questions that you might have.
Solar Q & A
Can I connect solar panels directly to a battery?
Theoretically, yes. However, if you are just starting out with solar, I would not recommend it. The charge controller’s job is to maintain proper charging voltage to the batteries, and to prevent the battery from being overcharged. Without a charge controller, you run the risk charging the battery at an improper voltage, and overcharging the battery—either of these would shorten the life of the battery.
Without a charge controller, it’s also possible for the battery to discharge through the solar panel. This drains the battery, and may ruin the solar panel in the process. There are ways around this, but it isn’t beginner-level stuff.
Can I connect solar panels directly to an appliance or device?
Theoretically, yes. However, I do not recommend it. Most appliances and devices are made to work with a specific input voltage. If you provide voltage that is too low, the device won’t work. If you provide voltage that is too high, you could damage the device. So, if you do your research about what voltage the solar panel is providing, and what voltage your device can take, and you know what you are doing, then sure, it’ll work. However, this kind of hacking is for solar and electrical experts only.
What about portable solar panels, such as the Anker 14 Watt Solar Charger, that are made to connect directly to cell phones?
These are usually okay to use. The manufacturer has designed the output voltage to work with cell phones. These units should come with a diode that will not let a cell phone battery (or any other battery) discharge through the solar panel. However, if you do a little digging, you’ll find that any portable solar panel of this style will have 1 or 2 bad reviews with customers stating that the solar panel actually discharged the battery that it was connected to. This is probably because of a faulty diode.
My charge controller has connectors for a DC Load. Can I connect appliances to this?
Yes, but there are limitations to what you can connect. You must read the manual that came with your charge controller to find out the maximum current (amperage) for your charge controller. Whatever DC load you connect should not exceed 80% of your charge controller’s amperage rating. 80% is a rule of thumb; your charge controller’s manual may list a slight slightly different percentage.
Hopefully, this was an easy-to-understand introductory overview on how solar power works. Along the way, you should have also learned:
- What a charge controller does
- What an inverter does
- What connects to what
- Where to put fuses and switches
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