How to Install an Off-Grid Solar System
DISCLAIMER: This is only an installation overview and is not meant to be a comprehensive guide. All systems are different, and therefore no single set of instructions can be used to cover all options and configurations. Do not attempt to install your own solar system if you are not comfortable working with electricity and tools. Northern Arizona Wind and Sun is not responsible for anything that happens during the installation process. Before you start installing your new off-grid solar system, let's first discuss safety.
An off-grid solar electric system involves working with both alternating current (AC) and direct current (DC) voltages. These voltages can be lethal if all safety precautions are not followed. If you are ever uncomfortable with any aspect of your installation, please consider hiring a qualified electrician or get help from a knowledgeable friend. If working with electricity doesn't bother you, then just remember to handle all wires as if they are live. The safety element cannot be stressed enough. If you don't know how to work with electricity, you could potentially be putting your life in danger. If you need help or advice on how to install your system, we highly recommend taking advantage of our free online solar discussion forum. You will find lots of valuable information and be able to ask questions to very knowledgeable individuals. You can find the link to the discussion forums on our main home page or you can follow this link.
Off Grid Installation Overview
Let's first go over some of the basic tools and materials that you may need for an installation. Some tools are specific to certain material types. For example, you would only need PVC glue if you plan to use PVC pipe for electrical conduit.
Here is a list of the basic hand tools you will most likely need at some point:
- Phillips-head and flat-head screwdrivers (large and small)
- channel lock pliers (also called tongue and groove pliers)
- lineman's pliers
- needle nose pliers
- wrench set
- socket set
Other things you may also need could include:
- electrical tape
- steel fish tape
- wire nuts
- wire lubricant
- electrical conduit
- conduit couplings
- conduit 90-degree elbows
- conduit connectors.
- An electrical multimeter (you won't need an expensive one; as long as it can read AC and DC volts, amps, and resistance (ohms), it should work fine.)
- A portable battery-powered drill
- A generator (if your installation is off the grid)
Most off-grid solar systems will have their panels mounted on a roof or on a pole. Both configurations have their advantages and disadvantages but work equally well when installed properly. Regardless of which method you choose, your solar panels must be mounted securely. Follow the assembly instructions for whichever type of mount you have selected. From an electrical standpoint, there's really not much difference between a roof-mounted system and a pole-mounted system. But if you use a pole mount, you will need to get the power from the solar panels to your house. This is normally accomplished by digging a trench between the pole location and the part of your house where you want the electrical wires to enter the building. The National Electrical Code (NEC) requires the trench to be no less than 18 inches deep to the top of the conduit.
NOTICE: Many cities and counties have their own electrical regulations in addition to the National Electrical Code. A lot of those jurisdictions actually require a 24-inch depth and some require up to 36 inches. So if you plan to get your system inspected, you should contact your local Authority Having Jurisdiction (AHJ) and inquire about the minimum depth requirement in your area. Be sure to look up the PVC schedule rating requirements too.
If you are using a pole mount, you will also need to install an eight-foot copper ground rod at the pole location. If you live in a very dry or desert-like environment or have very sandy and rocky soil, you may need to install two or three ground rods and connect them together for a better Earth connection. Ground rods must be driven vertically into the ground whenever possible. If rocks or other obstructions are preventing the rod from penetrating the ground vertically, the NEC does allow for the ground rod to be driven in at a 45-degree angle or even laying flat in a trench. A vertically-driven ground rod is always best whenever possible. A sledgehammer is often required for driving the rods into the ground. If you own a jackhammer, you can find a bit attachment for driving ground rods that makes the job much easier. The ground rod(s) at the pole mount needs to be connected to both the combiner box ground bar (more on that later) and to the copper ground rod for your house. The house ground rod and the pole's ground rods must be connected so that you do not have two isolated grounding systems connected to the same electrical system. There are lots of technical and scientific reasons as to why the ground rods need to be connected together, but that's not the focus of this article. Just take our word for it and you'll save yourself a lot of frustration. The easiest way to do this is to lay a bare copper ground wire in the same trench as your conduit. Do not run the bare wire inside of the conduit. You will get a better Earth ground connection if you run the bare copper wire directly in the trench, next to your conduit. The pole mount array will normally consist of the mounting hardware, solar modules, wiring, and a combiner box with circuit breakers or fuses. A basic combiner box has more than one function. It combines the output power of multiple solar panel strings and it's also a transition point where the smaller gauge wire from the solar panels can be increased in size, if necessary. The distance from the pole mount to your solar charge controller, along with the array amperage, will determine what size wire you will need. If you purchased your system from us, we probably already informed you of which size wire to use. If you purchase your equipment from us, our system designers will be happy to calculate the wire size that you need. Otherwise, you can always use the wire ampacity chart NEC 2014 Table 310.15 (B) (16) or find help from an electrician. Some websites offer free wire sizing calculators too. In previous versions of the NEC, this same table can be found at 310.16.
TECHNICAL NOTE: If you need more information about wire conductor size, please see the Wiring & Cabling section in our Learning Center, specifically, the article on voltage loss tables and ampacity for AWG wire sizes.
A roof-mounted system will also use a combiner box. It serves the same function as it does on a pole-mounted system. However, it can sometimes be a little more tricky or difficult to run wires from the roof's combiner box to the charge controller, especially if it's being installed on an existing house. The best time to run electrical conduit and wires is when the house is being built. This is one reason why a pole mount system can sometimes be easier to install for existing homes; the electricity can usually be piped into the house directly into the equipment room. Installing a roof-mounted system in an existing home is certainly possible if you have the proper tools. Most large solar panels now come with the negative (-) and positive (+) wire leads already connected to the junction box. The leads usually come with some type of male and female interlocking connectors. The modules that we sell come with either the MC4 connectors or the H4 connectors, but there are also other types of connectors on the market. They all pretty much work in the same way. If you need help with solar panel connectors, we have an article that explains MC4 connectors and how to use them.
TECHNICAL NOTE: If you need more information about Multi-Contact MC4 interlocking connectors and how to use them, please take a look at our article about MC4 connectors and extension cables. The H4 type connectors function the same as the MC4.
Modern charge controllers allow for a wide range of voltage inputs, which will directly affect how your solar modules must be connected and wired. Always pay attention to the voltage ratings of your equipment so that you do not inadvertently use too much or too little voltage. The proper solar panel voltage should be determined during the design phase, based on the equipment you will be using. As an example, let's say we are using a MidNite Solar Classic 150 charge controller with 260 Watt solar modules.
TECHNICAL NOTE: The MidNite Solar Classic is an MPPT type of charge controller. These types of controllers can convert voltage into amperage. So if your battery bank is set up for 12 volts and your solar panel puts out 31 volts, the MPPT controller can convert the “extra” voltage into usable amperage to charge your batteries. This is much more efficient than a standard PWM type of controller. With a PWM controller, any voltage above the usable voltage for your batteries ends up not getting used. If you would like to read more about the different types of solar charge controllers, see Solar Charge Controller Basics.
The Classic can handle up to 150 volts DC input from the panels and has a maximum output of 96 amps DC to the batteries. The open circuit voltage (Voc) rating of the 260 watt module is 38.3 volts DC. The Classic 150 can safely handle up to three of those modules connected in series.
TECHNICAL NOTE: When you connect solar modules in series (negative to positive from one module to the next), the voltage is added together but the current remains the same. When you connect modules or strings of modules in parallel (positive to positive and negative to negative, from one module or string of modules to the next), the current is added together and the voltage remains the same.
That would be 38.3 volts multiplied by three modules in series. That equals a total of 114.9 volts DC. That is within the operational range of the charge controller. If you tried to use four modules in a series, that would equal 153.2 volts DC. Because that voltage is higher than the allowable input voltage, the charge controller will turn itself off until the voltage drops down to 150 volts DC or below. However, some brands of charge controllers do not have a shut-off feature. If you go over the allowable input voltage, it could potentially burn up your controller or even cause a fire. Never exceed the voltage and current ratings of your equipment; it's not only dangerous, but it will almost certainly void the manufacturer's warranty. Once the three modules are connected in series, you will need an MC4 or H4 extension cable, depending on which types of connectors you have on your modules. If your modules only have a junction box, you won't need extension cables. You can use outdoor rated PV cable or USE-2 rated cable. Follow the instructions in the MC4 article for using the extension cables. The extension cables will terminate in your combiner box. The positive leads will usually connect to circuit breakers or fuses and the negative leads are usually terminated to the negative bus bar. This is a good time to go over the basics of the combiner box and how to make the proper connections. A combiner box is needed for combining multiple modules, or strings of modules, into a single circuit. It also incorporates overcurrent protection for each module or string. A basic combiner box is going to consist of a PV negative bus bar, a ground bus bar, a PV positive bus bar, circuit breakers or fuses, and lightning or surge protection (optional). See the picture below for a simple combiner box wiring diagram using the MidNite Solar MNPV3 combiner box. It's using three circuit breakers for the three PV source circuits. The solar panel strings' positive (+) wires all connect to the circuit breakers and all the solar panel strings' negative (-) wires terminate to the PV negative bus bar. The ground bus bar must be connected to Earth ground. If this is at a pole mount location, you will use a ground bar as the Earth ground connection. If this is for a rooftop installation, the Earth ground can be connected using a ground bar at the house or connected to the ground bus bar in a properly installed electrical load panel.
The output PV positive (+) and PV negative (-) circuit leaving the combiner box will generally be routed into an enclosure with circuit breakers. The PV negative circuit will ultimately go to the solar charge controller PV negative input, and the PV positive circuit will pass through a circuit breaker before connecting to the charge controller PV positive input. This circuit breaker allows you to disconnect the PV solar array from your charge controller input. For instructions on connecting your specific charge controller, please check your owner's manual. If you're not sure which size breaker you need for this, we can help you with that. The charge controller output to battery positive (+) will pass through another circuit breaker. This breaker allows you to connect and disconnect the charge controller from your battery bank. Some charge controllers will also have a temperature sensor and/or voltage sense wires. If your controller has those features, the instruction manual will tell you exactly how to connect them to your system. Generally, the voltage sense wires will connect to the main negative and positive battery bank terminals. There are a couple of different types of battery temperature sensors. Some sensors use a ring terminal and connect directly to the battery's electrical terminal. For that type, you simply slip the ring around the terminal stud and tighten it. Other temperature sensors will usually come with a small adhesive probe that sticks to the top or side of a battery. Your manual will tell you exactly where to place it on the battery. Now you need to get the energy from your battery bank to your inverter. Once you have your battery bank wired, be sure to check it with your volt meter to ensure it's at the proper voltage and polarity. Most inverters require 12, 24, or 48 volts. If the voltage is correct, you can begin connecting the battery bank to the inverter. If you need help wiring your battery bank for the proper voltage, check the instruction manual for your charge controller and your inverter.
NOTE: If you can't find any instructions, you can usually find good wiring diagrams with a Google search. If you purchased your system from us, you can always call or email us and we will be happy to help you.
The battery bank negative (-) terminal will connect to the battery negative (-) terminal of the inverter. The battery bank positive (+) terminal will connect to the “line” or (+) side of a DC circuit breaker. The opposite end of the circuit breaker will connect to the battery positive (+) terminal of the inverter.
TECHNICAL NOTE: You may also use a DC rated fuse instead of a circuit breaker. Circuit breakers are preferable because they can also act as a disconnect switch. However, fuses work really well when space or cost is a factor. Just be sure you have an extra fuse or two in case something short circuits and blows your fuse. Many off-grid installations are not anywhere near a store that sells fuses. A blown fuse can set you back for a few days while you wait for a replacement. During that time you will be burning gasoline for your generator. So be sure you have an extra fuse.
Many low wattage inverters can only supply power from an electrical outlet located on the inverter. These types of inverters are not meant to supply power to an electrical load panel and will usually cause problems if you try to power an electrical panel. That's because the neutral and ground are bonded inside those types of inverters. However, once inverters get to 2,000 watts and higher output, they are normally designed to provide power directly to a load panel. Instead of having only electrical outlets, the inverter will also have AC output terminals. In order to provide power to an electrical load panel, you must use a circuit breaker rated for back feeding. This allows you to connect the inverter's AC output into a circuit breaker, which provides power to the load panel. The neutral terminal from the inverter AC output should connect directly to the neutral bus bar in the panel and the ground terminal of the inverter should connect to the ground bus bar in the load panel.
IMPORTANT: Under no circumstances should you use circuit breakers on the AC neutral wire (usually white) or the ground wire (usually green or bare copper). It's dangerous and it's also a code violation.
Consult your inverter and charge controller manuals for details on powering up your system. This article is meant to be a general overview of how to install an off-grid solar system. It is not meant to be a complete set of instructions for every person, every system, or every situation. If you understand these instructions and you feel comfortable working with tools and electricity, you can probably install your own system without any trouble. However, if these instructions sounded complicated, you may want to consider recruiting a friend to help or hire a qualified electrician.