Electricity, Solar, Sustainability

Chapter 10: Solar Powered 12 Volt DC System – Putting It All Together

We’re ready to put together a 12v Solar Powered Electrical System!

This chapter covers the basics of connecting the components of a solar system that we covered in the previous chapters. Not every installation will be the same and you may need to adapt some of the information provided to your situation or environment. While this chapter will only be focus on 12v systems or simplicity, if your system is 24v or 48v, you will find 90% of the information useful!

Whether you’re attempting to set up a single solar panel to maintain a battery, or you’re installing a 10k watt array on the roof of your home, the concepts covered on this page remain the same.

The Battery Bank

In my opinion, the battery bank is THE MOST IMPORTANT component of any off-grid electrical systems. The only other contender is obviously the solar panels, the power generators themselves. But we’ll get back to that in just a moment.

The first and most important consideration for designing your battery bank is its location. Where will you store the batteries? How much space do you have? Are there mounting points, if it’s a mobile application? Will it stay dry if it’s stationary in a flood zone?

Once you’ve figured out the space you’re working with and you’ve decided on the capacity and arrangement of your battery bank, it’s time to hook everything up and get it in place. If you’re not sure about your needs for a battery bank, go back to Chapter 5: Sizing the Battery Bank and then come back here.

Bus Bars.jpg

Once the battery bank is in place, we’re going to want to install at least (2) Bus Bars. As you can see in the image above, bus bars join the terminals of each 12v batteries in parallel to increase the capacity of the battery bank, and to distribute loads (charging and discharging) equally across each battery.

DC electrical systems are NOT complex; at the most basic level, you have two sides, a positive (red) and a negative (black), just like a car battery. You can think of wiring a solar panel the same as a car battery since solar panels output DC.

Bus Bars are SUPER simple! Take your 2 busbars and place them on either side of the battery bank; one side will be for all of the positive battery connections, and the other side is for all of the negative battery connections. This removes the need to have wires tied into each other, instead we have a clean installation that doesn’t have wires crisscrossing everywhere.

The picture does not show it, but it is always a good idea to place a fuse between the positive terminal of each battery and the positive bus bar. This will not only keep your system safer, but if one battery does malfunction, the others will continue powering your system. Always include overload protection!

Solar Charge Controller to Battery Bank

What solar charge controller you need will once again need to be determined by you, based on your needs. Regardless, the solar charge controller should be the first component you connect to the battery bank / bus bars. The idea is to have the closest connection between the charge controller and the battery bank terminals.

As you can see bellow, solar charge controllers typically have a set of:
Solar Panel (PV) inputs (+ / -) where you connect your solar panel combiner box wires
Battery (BAT) inputs (+ / -) where you connect your wires to the battery bank bus bars.

-Some charge controllers will have a temperature sensor port and/or an extra output for a small 12v DC load.The “LOAD+ and LOAD-“, is usually a supply of only a few amps at 12v DC. If your charge controller is mounted in a dimly lit area, this output would be sufficient for a few LED lights to brighten up the space while you work! The temperature sensors are used to compensate the voltage applied to the batteries depending on the batteries temperature.

We purchased the Outback Flexmax 80A MPPT solar charge controller for our 800-watt array. The Flexmax is a long-term purchase and is capable of regulating up to 3800 watts for a 48v battery bank. For a 12v battery bank, the Flexmax is capable of regulating a 960 watt solar array.
12 Volts x 80 Amps = 960 Watts

Another great option, at half the output, and less than half the cost, is the Renogy Rover 40A MPPT Solar Charge Controller. The Renogy charge controller is more suited to a Skoolie then an off-grid cabin. For a 12v battery bank, the Flexmax is capable of regulating a 480 watt array.
12 Volts x 40 Amps = 480 Watts

We will use 0 gauge welding wire from the MPPT solar charge controller to the bus bars, and we will keep the wires as short as possible on both sides of the bus bars, without placing the charge controller in the same “compartment” as the battery bank.

Now that we’ve got our battery bank and solar charge controller in place, lets talk about our solar panels and the solar array!

Individual Solar Panels, Strings, and Arrays

The, ahem, most important component of our system…the solar panels. If you’re unsure about Solar Panels, check out Chapter 6: Solar Panel Basics

We’ve elected to install an 800-watt array of (8) Renogy 100-watt Solar Panels. We chose the Renogy panels mostly for the price and convenience. I’ve had a lot of luck getting these panels in 2-packs for under $1 per watt, delivered to my door.

Once you have your panel, string, or array mounted and wired, it time to get them hooked up to the solar charge controller.

Solar Panels to the Solar Charge Controller

Let’s start our planning at the solar panel combiner box. The combiner box is simply an electrical box where all of the individual, or string(s) of, solar panels positive and negative lines combine. Usually, the combiner box will be placed as close as possible to your panels, or strings.

We combine the individual panels, or strings, in a combiner box so that we can run a larger gauge wire to the solar charge controller. This serves 2 main purposes: the first, 2 wires are much easier to route, then, say 3-10 pairs of positive and negative wires; and second, by using a larger gauge wire, we can reduce the amount of energy lost. Additionally, a combiner box allows us to fuse, or set up circuit breakers on, the individual panels or strings.

You can see in the example on the right, all of the smaller #8 gauge negative leads (from individual solar panels) are connected to a larger all black #4 gauge wire.

On the positive side, you can see each panel has a circuit breaker before connecting to the larger #4 gauge positive wire (with Red tape). The circuit breakers are important! If an individual solar panel malfunctions, it will trip the circuit breaker instead of potentially taking out the whole system or starting a fire! It’s better to plan for the worst and end up with reduced power, over no power.

The larger #4 gauge wires are used to transmit electricity as efficiently as possible, without the larger gauge wire, you essentially bottleneck the system and reduce its ability to transmit energy from the solar panels.The length of wire needed to join the combiner box to your solar charge controller will also effect the gauge of wire needed, therefore it is important to keep components as close to each other as safely, and reasonably, possible.

You will need to determine which gauge of wire you need based upon the amount of Amps (Amperage) you are planning to transmit. I will find a link asap to explain voltage and amperage by distance in wires.

Solar Powering Everything!

Don’t wrack your brain for too long trying to figure out how we charge the batteries while using them. Just know that, If the power coming in from the Solar Panels is greater than the power required, the excess is used to charge the batteries. Inversely, if the power coming from the solar panels is NOT enough for the required load, such as at night, ALL of your power needs will come from your battery bank.

  • If (Power In > Power Out) Than (Batteries Charge)
  • If (Power In < Power Out) Than (Batteries Drain)

From the Bus Bars, a positive and a negative wire will be connected to a 12v Fuse Box. 12v appliances such as water pumps, LED lighting, etc. will be powered through the 12v fuse box. All grouped components should have individual fuses; water pumps, fans, LEDs, etc. Fortunately this inexpensive 12V Fuse Panel provides space for 12 fuses, as well as common positive and negative poles to connect to the Bus Bar.

With 12 Spaces, we will have enough for necessities, with spares for expansion…

  • #1 Indoor LED Lighting (10 Amp Fuse)
  • #2 Outdoor LED Lighting (15 Amp Fuse)
  • #3 Fresh & Grey Water Pump (20 Amp Fuse)
  • #4 12v to 5v Converters, 3A each (15 Amp Fuse)

For our cell phones and tablets, I’ll install several female USB ports around the bus; powered by these 12v to 5v 3A Converters. For the laptop and tv, along with any other needs, we will be using an AC-DC inverter hardwired to a 120v Fuse Panel. The inverter will be connected directly to the battery bank bus bar due to the high power draw. A larger Fuse is required between the battery bank and the inverter, due to the increased power consumption of the inverter.

120v Power Inverter for Grid-like AC Electricity

Connecting  your inverter, for example, to the bus bar, instead of an individual battery, gives you the full capacity and power of the entire battery bank. When using something like a 2000w inverter, a full power draw can quickly deplete an individual battery, even a deep-cycle battery. By connecting our inverter to the bus bars, we are distributing the load required, equally across the battery bank.

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