Sometimes, picture can we worth a thousand words. If you are getting started with an off grid solar system, this is the simplest complete diagram that available to learn how to connect your own off grid solar system.
In the following sections, I’ll cover what the parts of the system are, and important decisions that you need to make when wiring your system. While the diagram shows a very common way of connecting small scale solar system, this design may not work for everyone without some simple modifications.
Key Decisions You Need to Make While Wiring Your Off Grid Solar System
There are number of choices that you have to make when installing a DIY off grid solar system that affects how you wire the system together. In particular, you will need to decide:
- The number of panels and voltage of your solar panel array
- Your overall system voltage, based on battery bank size and your energy needs
How to Wire Solar Panels in a Solar System
When you are wiring solar panels, you have three choices on how you wire the system —
- Series solar panels — plus to minus, plus to minus
- Parallel solar panels — Plus to plus, minus to minus
- Mixed — strings of series panels connected in parallel
When deciding between the three, two important facts to consider are the maximum input voltage of your charge controller and the type of charge controller.
Every charge controller has limits on how much voltage it can accept (the maximum input voltage), anything from 20V on the low end to 160+ V on the high end. You must be sure that the power coming in from your solar panels never exceeds this number.
Series Solar Panel Connection
Since series connecting solar panels effectively adds the voltage of each panel, you should never series connect more panels than your charge controller can support. But, increasing the voltage allows you to use thinner and less expensive wire, which reduces the Total Cost Of Off Grid Solar Photovoltaic Systems. It also increases the potential energy production of your panels in low light situations like cloudy days, and during dusk / dawn.
When calculating how many panels your charge controller can support connected in series, be sure to use the solar panel’s open circuit voltage, rather than the nominal voltage. For example, most 12V rated panels will actually produce up to around 18V when your system isn’t drawing much of a load.
So, if you have a 80V max system, then you could only safely attached 4 each nominal 12V (18V max) panels in series without risking destroying your charge controller. Where as mistaken calculations using the normal voltage would say you could use 6 panels, a dangerous number.
Note that the type of charge controller you use also impacts of series connections make any sense. MPPT charge controllers are preferred, since they are able to down convert higher panel voltages to the 12–48V you typically use for your battery bank.
Charge controllers can be difficult to choose. With so many features, and fancy acronyms, it can be hard to know exactly which one is right for you. That’s why I took the time to sort through them all and can recommend this MPPT charge controller for your off grid system.
Otherwise, if you have a PWM charge controller, there is no reason to increase the array voltage, since this type of charge controller can’t make use of the extra voltage. So, you should wire your panels so that their typical voltage is the same as the battery bank voltage.
Parallel Solar Panel Connection
In parallel connection, we join all to the red plus wires together, and all the black minus wires together as well.
Using the parallel method of connecting solar panels, the voltage of the solar array stays the same as the voltage of each panel. (You should not mix panels different types of panels when connecting them in parallel.) But, the maximum current is increased.
All charge controllers have a maximum currents listed, but usually have internal protections that prevent damage from over-current conditions. This means that usually you can safely attach more panels in parallel than your charge controller can handle, but your system will not be maximally efficient on bright sunny days.
In some cases, it makes sense to over provision your solar array, especially if you live in a cloudy climate like I do. By doing this you can get more energy on cloudy days without necessarily buying a larger and more expensive charge controller.
Some charge controllers may not be designed to handle this method of wiring and solar system design safely, so be sure to check the manual of your specific charge controller, as only the manufacturer will know what your controller is designed for.
Be sure to choose appropriate wire for how much combined current your solar system can produce. This will either be the sum of all your panel’s max output current, or your charge controller’s maximum input current, which ever is smaller.
Mixed Parallel and Series Solar Panel Connection
For larger solar systems, you have the option of connecting multiple strings of panels in series, and then connecting those strings in parallel (see above diagram).
The primary reason for doing this is when you have too many panels to run all of them in series, given the voltage limits of your charge controller, but you want to keep the solar array voltage on the higher side to reduce wiring costs and maximum solar panel production on cloudy days.
Mixed systems must take in to account the voltage and current limitations mentioned in both parallel and series set ups, described above.
In addition, you need to make sure that each string of series connected panels produce the same voltage. In practice, this means you should not mix types, sizes, or brands of solar panels in the same solar array. And, that every string of series connected solar panels should have the same number of individual panels.
The only downside to this type of system is that you can’t add just one solar panel, if you need a little extra energy. You have to add whole strings of series panels at a time, which means you may end up adding 4 panels when you only really wanted one.
How to Wire Up a Battery Bank for Off Grid Solar
Battery banks should be wired to match your system voltage, which is the voltage allowed by your DC appliances or AC inverter. Typical DC appliances made for RVs run off 12V or 24V, although there are some 48V variants out there as well.
If you only plan on running AC appliances from your battery bank, you generally want to go match your battery bank voltage to the higher end of your inverter’s maximum input voltage.
In the above CAD rendering, I show one way of connecting low cost 3.2V lithium cells for a 12V solar system.
Batteries can easily be the most expensive part of your off grid solar system. That’s why I looked high and low for the most cost efficient yet reliable batteries I could find. Read this before you buy lead acid “deep cycle” batteries.
Using Bus Bars for Solar Battery Banks
The connections between each battery are made using copper bus bars sized to fit these particular battery packs (most manufacturers offer them, or they can be bought from third party manufacturers). This makes a clean, solid, and safe connection between each battery without a crazy tangle of wires.
In the example above, each pair of cells is connected in parallel, then the four sets of cells is connected in series to make a roughly 12V system. Using clusters of parallel connected cells is much cleaner than any other method, and makes it possible to install a single battery management system (BMS) to manage the whole bank if you desire.
If the above battery bank were installed in a 24V system, then all of the cells would be connected in series.
Adding more capacity to the above system would mean buying at least 4 more cells, wiring every set of three in parallel by using longer bus bars that connect six terminals (or three at the plus and minus connection).
Using Wires to Connect Up a Solar Battery Bank
Some people prefer to use short lengths of battery cables to connect their solar battery bank. Overall, I find this to be a big mess when compared to using bus bars. But it does have the benefit that you have more freedom when arranging your batteries.
In very cramped situations, using lengths of flexible wires might be preferable. Especially if your are using 12V or higher lead acid batteries with multiple cells built in to each one (similar to car starter batteries), since they are usually not well designed for use with bus bars.
How to Wire Fuses and Breakers in Off Grid Solar Systems
Another thing you need to consider when you wire your off grid solar system is the various safety systems.
How this is wired depends on the overall size.
Small systems wires up as shown, with about a few hundred watts of output capacity, can usually be wired up without necessarily having external fuses or breakers. This is because charge controllers wired as shown, with a dedicated pair of load terminals, will generally have short circuit or over-current protection built in.
Likewise, smaller inverters that have their own plugs will usually have similar safety features built in as well, eliminating the need for an external breaker or breaker box.
Wiring Charge Controllers Without Dedicated Load Connections
If your charge controller doesn’t have load outputs, then you will have to wire up the system a bit differently. Instead of connecting to the charge controller, the load wires will connect directly to the battery bank.
In this case it is absolutely essential that you have a DC fuse or DC circuit breaker installed in line with the load wires. Otherwise an accidental short circuit could easily destroy your battery bank and cause serious damage to your system including the potential overheating and fire.
DC Loads with More Than One Circuit
If you plan to run several larger DC appliances from you battery bank. It can be wise to include a fuse box, with several smaller fuses that each feed one line of the system.
Using a fuse box means one appliance drawing too much power won’t bring down the whole system. And allows you to safely use thinner, cheaper wire for smaller appliances. It is important that you know how much current your wire can support, which depends on it’s gauge and length, and pair that run of wire with a fuse that is rated less than the maximum current of the. This ensures that the wire will never overheat due to over current.
AC Loads With More than One Circuit
If you plan to run a whole house or cabin from your system using a large AC inverter, then it will need to be wired in several circuits.
This is accomplished exactly the same way as grid connected house. So, I won’t cover those connections here, since they are extremely well covered by DIY and home improvement people. But the just of it is that you will need to run the inverter in to a circuit breaker box, and then run wires for each circuit from the box out in to the home.
If a house is wired for grid power, it is possible to use that wiring for your off grid system, after grid power has been disconnected.
Do not connect your AC inverter, or any part of your off grid solar system, to grid power. While using solar to supplement your grid power, to sell back to the grid (in some states), or as an emergency fallback is possible, it is usually not legal for a homeowner to install such system themselves, and requires knowledge of electrical codes in your area. This guide only covers entirely off grid systems.
Ready to Go Off Grid?
For more info on building your own DIY off grid electrical system, check out my in depth guide —
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