Guide to the Right Distance between Solar Panels and Battery

This is a question that often comes up in solar power forums. The point of the question is, “what should their proximity be to each other to minimize energy loss?” We all want to get the most out of our solar systems, and that includes the set up of batteries and panels.

The maximum distance between solar panels and batteries should be 20 to 30 ft. The shorter the distance between them the better. Long, thin cables increase the amount of energy lost as the conductor resists current flow. With a shorter, thicker cable, energy loss is minimized during transmission.

How Distance Leads to Cable Transmission Energy Loss

As any seasoned solar power user will tell you, short cables makes solar phone charging faster. That applies to solar panels and batteries too. Because of the Joule Effect it causes energy loss in the form of heat. In electric power plants the loss can go up to 15%. The amount lost in solar power systems depends on the cable used, solar panel and battery design and how far apart they are. While energy loss is inevitable, that does not mean we cannot do anything about it.

If you are going to use solar power, you want to minimize these energy losses as much as possible. Fortunately, there are ways you can do this without calling a technician.

How to Minimize Solar Energy Loss in Cable Transmission

There are two methods to reduce / prevent energy loss. The first is to shorten the distance between the battery and the panels. A large, short cable designed for solar systems is recommended. Solar optimized cable wires like the WindyNation 8 AWG will definitely help in case the panels and batteries have to be far apart.

In RVs the solar panels are usually on the roof and the battery is inside the vehicle. There is only a few feet between them so energy loss is minimal. The 20-30 ft. distance is more important in homes, as the distance between the two can go beyond 30 feet. if the distance is greater than this, make sure you use high quality cable.

The second way is to use a high voltage battery. A high voltage transmission produces minimal current flows. It reduces heat in the conductor and helps preserve energy. 12V batteries need a lot of power to move current. A 120W 12V system has a 10A current. If the cable resistance is at 0.1 ohm, the energy loss could reach 10 watts.

If you use a 24V battery the watt loss can be reduced in half. If you have to use 12V batteries, position them as close to the panel as possible. Otherwise, use large cables to reduce energy wastage. it should be pointed out that these losses are most apparent in small to medium sized solar systems. With a 600W system, these losses can be discounted.

How to Connect Solar Panels, the Charge Controller and Battery

So now you have the right cable for the battery and solar panels. Is it time to set up the system? Not yet, because you also need a charge controller to ensure hte battery operates smoothly and safely. As we have explained before, you should not connect solar panels directly to battery. Doing so puts devices at risk of overloading, overcharging, sudden power fluctuations and more.

Here are the steps. Your solar panels, batteries and charge controller have labels where the connectors go. Refer to your installation guide. But the process is similar to these.

Important: the charge controller must be close to the battery, 3 feet apart at most. It does not have to be near the panels. If you set up your system before getting a controller, compare the energy loss difference. It is smaller when you use a controller, especially an MPPT. Whether you use an MPPT or PWM, they will both provide protection for your devices against changes in voltage.

Step 1. Connect the input terminals of the solar panel to the charge controller. You can use the same cable wire specs to connect the batteries and charge controller.
Step 2. Connect the inverter to the system. Skip to the next step if you will not use devices that run on AC.
Step 3. Hook up the battery to the controller. A positive and negative cable is required here.

Important: the charge controller must be close to the battery, 3 feet apart at most. It does not have to be near the panels. If you set up your system before getting a controller, compare the energy loss difference. It is smaller when you use a controller, especially an MPPT. Whether you use an MPPT or PWM, they will both provide protection for your devices against changes in voltage.

Why You Need a Charge Controller

A charge controller provides safeguards for your devices and the solar panel. It regulates voltage current flows and ensures the battery receives maximum energy without overcharging. With an MPPT controller such as the Victron SmartSolar, you can configure the solar panels in a series to minimize energy cable loss. With a PWM controller it’s not as efficient but will still reduce cable transmission energy waste.

A solar panel series configuration also increases voltage output. This allows you use to use longer wires without losing too much power. However the battery and panel voltage have to match otherwise it won’t be as effective. If they don’t match you have to use an MPPT controller. The controller converts the excess volts to amps for faster charging.

If you have a small scale solar power system, a PWM charge controller will work. But for large scale systems and sensitive electronics, it is better to invest in a quality MPPT charge controller. It is no different from investing in an expensive but quality inverter to ensure appliances run at optimum levels.

What is the Right Charge Controller to Battery Wire Size?

The charge controller amp capacity decides what cable wire size (iAWG) you must use. If you cannot find a specific wire size, go with the next biggest available. Going bigger will not hurt, but opting for a smaller size could cause problems. These are general guidelines only, so refer to your operating instructions for specific wire sizes.

Charge Controller Size (in Amps)	Cable Wire Size
10A	16 AWG
30A	12 AWG
40A	10 AWG
60A	8 AWG
80A-100A	8 AWG

The cable size is only one aspect to consider. You should only use high quality, flexible cables. The best cables are UL listed, have shrink tubing, high end lugs, durable and designed for solar power systems.

Most solar panels 50W and above use 10 AWG wires. With a 10 AWG wire, 30A current can move from the panel without any problems. If you set up a solar array in parallel, a 3-8 AWG combination is needed to run the controller.

You can use the same wire size in the chart for the wires that connect the battery and solar panel. The exception are controllers that run 12/24V power banks even if the solar panel is at 48 VDC or more. These controllers add to the battery current input. Check the charge controller user guide on what wire size to use.

Solar Panel Wiring Size Chart for RVs, Vans and Campers

RV setups differ widely from one to the next, so it’s impossible to give a one size fits all guide. The best way to find out is to check the manual for your solar panel, battery or whatever solar component you want to set up. The manual will tell you what cable size to use. That being said, here is a general size guide you can use.

Connection	Cable Wire Size
From busbar to battery	2/0
From inverter to busbar	2/0
Charge controller to solar panel	10ga
Battery to charge controller	Varies, but no more than 3.2 ft. apart
Cables for USB devices and others	12ga

If your RV is solar ready, it may have particular measurements for connecting wires and cables. The figures above work for most vans and campers, but yours may be different.. it also depends on how many batteries and components you are going to set up. The larger the total watt load, the larger the wire sizes you have to install.

Solar Cable Size and Distance Chart

This chart is for a 2% to 3% percentage loss (which is acceptable) and 12V systems. To use the chart, find the amp that matches your solar power system. Next, choose the cable size and match it with the corresponding AWG size at the top. If you have a 20A solar power system and want to use an 11 foot cable, you need an 8 AWG cable.

The acceptable energy loss level is still at 2%, but systems are getting better and better all the time. If your system can avail of lower systems loss that is great. However there may be some cases where energy inefficiency goes up to 5% or more. as the cost will add up eventually. If you are still unsure what cable size to use, contact a professional solar installer.

Wires between Battery Bank Size

Battery bank wires are larger than those used by the solar panel or charge controller. Because they are often used with the inverter, power demand is high. The most common battery bank wire size is 1/0. The wire and gauge have to be the same in a battery bank. if not this could cause malfunctions later on.

This also brings up the question of whether a fuse should be installed between the battery ad charge controller. Usually it isn’t necessary as the wire has to produce the maximum current it can. A breaker is recommended however. Just to be sure you should check the manual that came with your system.

Conclusion

it’s hard to overemphasize the importance of proper distance and wiring for solar panels and the battery. Some still believe that a longer wire is better whereas the opposite is true. If you are planning to go solar, hopefully this guide was able to help you find the specs for your system. it can literally mean the difference between an efficient and ineffective solar system.