PV Wires or Battery Cables Over Long Distance: Which Has Less Loss?

Off-grid installs rarely let you put the panels right next to the batteries. Choose the cable that travels the distance with care.

Short answer: When a solar array is more than a few meters from the battery bank, put the MPPT charge controller next to the batteries and run high-voltage PV wires from the panels to the controller. Wire the panels in series to push the string voltage as high as your controller allows. This uses far less copper, produces lower losses, and is cheaper and easier to install than running low-voltage battery cables the same distance.

Quick Facts

• Power loss in a cable scales with current squared, not with voltage. Higher voltage at the same wattage means lower current and much lower loss.
• Running panels in series raises the string voltage (typically 60 to 150 V on common MPPT controllers) and drops the current by the same factor.
• Doubling the string voltage cuts cable losses by a factor of four for the same wattage and cable size.
• A 600 W array over 30 m round trip needs roughly 35 mm2 (2 AWG) copper at 12 V, but only 4 mm2 (12 AWG) at 100 V string voltage, for the same 3 percent voltage drop.
• MPPT controllers are designed to accept high-voltage DC input and step it down to the battery voltage efficiently.
• The charge controller needs an accurate battery voltage reference, which is hard to guarantee at the end of a long low-voltage cable.

The Rule of Thumb

If the solar array is not in the same compartment as the batteries, keep the charge controller next to the batteries and run PV wire, not battery cable, the long distance.

This rule holds for nearly every off-grid, camper, boat, shed, and detached-garage solar install under a few kilowatts. The only exceptions are very large or very long runs where a grid-tie string inverter or a high-voltage DC bus becomes the better architecture.

Why High-Voltage PV Wire Wins

Voltage drop in a DC cable is governed by a simple formula:

voltage drop (V) = 2 x length (m) x current (A) x resistivity / cross-section (mm2)

Two facts fall out of this:

1. Current dominates. Voltage drop is proportional to current. Power loss, which is what actually costs money and melts insulation, is proportional to current squared.
2. Voltage at the source does not appear in the formula. But power equals voltage times current, so for a fixed wattage a higher source voltage means a proportionally lower current, and a quadratically lower loss.

Worked Example: 600 W Array, 15 m One-Way Run

Layout	Source voltage	Current	Cable needed for 3% drop	Relative copper
Controller at panels, battery cable to bank	12 V	50 A	~35 mm2 / 2 AWG	1.0x
Controller at panels, battery cable to bank	24 V	25 A	~16 mm2 / 6 AWG	0.46x
Controller at panels, battery cable to bank	48 V	12.5 A	~6 mm2 / 10 AWG	0.17x
Controller at batteries, PV wire from panels	100 V string	6 A	~4 mm2 / 12 AWG	0.11x

The high-voltage PV option uses less than one-eighth the copper of the 12 V battery-cable option for the same power, the same distance, and the same loss budget. It is also dramatically cheaper, lighter, and easier to pull through conduit or trench.

Why Not Put the Controller at the Panels?

Mounting the charge controller out at the array seems convenient, but it creates three problems:

1. Battery cables carry the worst-case current. At 12 V, every 600 W of charge is 50 A. At 24 V it is 25 A. These currents require thick, expensive copper and large fuses, lugs, and disconnects at both ends.
2. Voltage reference is unreliable. The MPPT algorithm relies on an accurate battery voltage reading to run absorption, float, and equalization stages. A long, loaded battery cable can drop several tenths of a volt, which confuses the charge stages and leads to chronic under- or overcharging.
3. Monitoring and control wiring still has to travel the distance. Temperature sensor, shunt data, and remote display all need their own run, which erases the "everything is at the panels" simplicity.

When the Rule Does Not Apply

Run battery cable instead of PV wire only in these specific cases:

• The distance is under about 2 m, where either layout is practically identical.
• The array is a single low-voltage panel wired directly to a small PWM controller in a compact package.
• You are using a grid-tie or hybrid string inverter that accepts 200 to 600 V DC and outputs AC. In that case the "PV wire" is already the long run by design.
• Local code forbids high-voltage DC in the cable path you must use, for example inside certain RV or marine bulkheads.

Safety and Code Details

Thin PV cable is only correct cable if it is the right thin cable:

• Use cable rated for outdoor UV exposure and DC solar service: H1Z2Z2-K in Europe, PV Wire or USE-2 in North America.
• Install a DC-rated disconnect and correctly sized PV fuses at both the array end and the controller end.
• Check the maximum input voltage of your MPPT controller at the coldest expected temperature, not at 25 degrees Celsius. Cold panels produce 15 to 25 percent more open-circuit voltage, and exceeding Vmax destroys controllers.
• In a trench, use conduit rated for direct burial, maintain the required burial depth for your jurisdiction, and separate DC and AC runs per local code.
• Ground the array frames and bond them back to the system ground at a single point.

How to Decide in Five Minutes

1. Measure the round-trip cable distance between the two candidate locations.
2. Look up the maximum input voltage of your MPPT charge controller, then derate it for the coldest local temperature to get a safe target string voltage.
3. Compute the current at that string voltage: current = array wattage / string voltage.
4. Compute the current at battery voltage for comparison: current = array wattage / battery voltage.
5. Size a cable for each case at 3 percent voltage drop, price both, and pick the cheaper one. It will almost always be the PV-wire layout.

Frequently Asked Questions

Is it better to run PV wires or power cables over a long distance? Run PV wires. Place the charge controller next to the batteries and run high-voltage PV cable from the panels to the controller. At the same wattage, higher source voltage means lower current, which cuts cable loss quadratically.

Does the rule change for 24 V or 48 V battery banks? It still favors PV wire, but by less. A 48 V bank needs only a quarter of the current of a 12 V bank, so battery cables become more reasonable. At distances above about 10 m, high-voltage PV wire still wins clearly.

What gauge PV wire do I need for a 25 to 50 foot run? For a typical 400 to 800 W residential-scale array running at 80 to 150 V string voltage, 10 to 12 AWG (4 to 6 mm2) PV cable is almost always enough to stay under 3 percent drop. Always verify with the actual current and length of your install.

Can I put the panels on a detached garage and the batteries in the house? Yes, and this is the textbook case for the rule. Mount the panels where they get the best sun, put the charge controller and batteries next to the loads, and trench PV cable between them inside rated conduit.

Does this apply to micro-inverter or grid-tie systems? Those systems already run high-voltage AC or DC over the long distance by design, so the rule is automatically satisfied. The question in this article is about DC-coupled off-grid and hybrid systems with a charge controller and battery bank.

Do I still need fuses and a disconnect if the PV current is small? Yes. Fuses and disconnects protect against fault currents and allow safe servicing. Size them for the short-circuit current of the array, not the normal operating current.

Summary

For any off-grid or hybrid solar install where the array is separated from the battery bank by more than a few meters, the optimal layout is: panels in series, PV cable the long distance, MPPT charge controller next to the batteries. It uses far less copper, produces lower losses, keeps the charge algorithm accurate, and is cheaper and easier to install. The only times to deviate are very short runs, pre-packaged low-voltage kits, or full grid-tie architectures.

If you want to skip the manual math, the VoltPlan wire sizing and voltage drop tools compare both layouts side by side for your exact distances, wattage, and battery voltage.