Planning a Long Wire Run From a Solar Array to Your Cabin
The sunniest spot on a cabin property is often not next to the cabin. Putting the array in a clearing a good distance away can dramatically improve output, but only if the power actually arrives. Long wire runs are where small mistakes turn into wasted energy, hot cables and disappointing systems.
This guide covers the planning side: how voltage drop works, why string voltage matters so much, where the charge controller should live, and which parts need a licensed electrician.
Quick answer
- Power lost in a wire depends on current. Sending power at higher voltage means less current and less loss.
- Wire panels in series for a long run and use an MPPT controller near the battery.
- Many designers aim for a low single-digit percentage of voltage drop on the PV run; your installer or electrician will set the target.
- Never exceed the controller's maximum PV input voltage, including cold-morning voltage rise.
- Buried or exposed runs, conduit, disconnects and grounding are code issues. Plan them with a licensed electrician and the local permit office.
Voltage drop in plain terms
Every wire has resistance. Current flowing through it loses some voltage along the way, and that lost voltage becomes heat. The loss grows with three things:
- Current. Double the current, double the voltage drop, and roughly four times the power lost as heat.
- Distance. Remember the run is out and back: a 100-foot distance is 200 feet of conductor.
- Wire size. Thicker wire has lower resistance. In the AWG system, smaller numbers are thicker wire.
The practical conclusion: you can fight voltage drop with thick, expensive copper, or you can reduce current by raising voltage. The second approach is almost always cheaper at a distance.
Why series strings win on long runs
Panels wired in series add their voltages while current stays about the same as a single panel. Wired in parallel, currents add while voltage stays the same. For the same total power, a series string sends much less current down the wire.
| Example: four identical panels | String voltage | Current in the run | Effect on a long run |
|---|---|---|---|
| All in parallel | One panel's voltage | Four panels' current | Highest loss; needs very heavy wire |
| Two series pairs in parallel | Two panels' voltage | Two panels' current | Middle ground |
| All four in series | Four panels' voltage | One panel's current | Lowest loss; smallest wire |
This is the main reason long-run cabin systems use MPPT charge controllers. A PWM controller needs panel voltage close to battery voltage, which rules out high-voltage strings. An MPPT controller converts the high string voltage down to battery charging voltage efficiently. See MPPT vs PWM for a cabin if you are still deciding.
Respect the controller's voltage limit
Every MPPT controller has a maximum PV input voltage. Exceeding it can destroy the controller. The trap is temperature: solar panel voltage rises as panels get colder. On a clear, frigid morning, a string can put out noticeably more voltage than its standard rating.
Do the cold-weather math. Use the panel's open-circuit voltage (Voc) and its temperature coefficient from the datasheet, plus the coldest temperature your site sees, to check the worst-case string voltage. Many controller makers publish online string-sizing calculators. If in doubt, have a licensed electrician check it. Our cold-weather voltage check walks through the idea.
Where to put the charge controller
In most cabin designs, the controller sits near the battery bank, and the long run carries high-voltage, low-current PV power. That is the efficient arrangement, because the wire between controller and battery carries much higher current and should be as short as practical.
Putting the controller at the array and running battery-voltage DC to the cabin reverses this and usually means much heavier wire. It also exposes the controller to weather. There are setups where equipment lives at the array, but for most cabins, controller-by-the-battery is the default.
A worked example (illustrative only)
Here is how the reasoning goes, using round numbers. Your electrician will use exact conductor data and code tables.
- Array: four panels, each producing around 10 A at about 40 V at their working point.
- Option A, all parallel: about 40 A at about 40 V. Over a long run, that current produces a large voltage drop unless the wire is very heavy.
- Option B, all series: about 10 A at about 160 V, assuming that stays within the controller's cold-weather limit. Same power, a quarter of the current.
- Result: Option B's voltage drop as a percentage is a small fraction of Option A's on the same wire, so a much thinner wire can do the job.
That is the whole game: as much string voltage as the controller safely allows, then a wire size that keeps the drop within your target.
Choosing wire and protection
| Question | What to know |
|---|---|
| Copper or aluminum? | Copper is common for PV runs. Aluminum is sometimes used for long feeders but needs proper rated connectors and techniques. Let your electrician decide. |
| Wire type | PV wire or other sunlight- and moisture-rated conductors are used at the array; direct-burial and conduit runs have their own rated types. |
| Above or below ground? | Buried runs need specific depths and conduit types under code. Exposed runs need UV and physical protection. |
| Disconnects | Code generally requires a way to disconnect PV circuits; placement rules vary. |
| Grounding | Arrays and racking need proper equipment grounding; remote arrays have their own considerations, especially for lightning. |
Calculators are useful for planning. A voltage-drop calculator lets you try different wire sizes and string voltages before you buy anything. Use one to understand the trade-offs, then let the professional confirm the design.
Trenching and route planning
The physical route often costs more effort than the wire itself. Before digging:
- Call your local utility-locate service, even on rural land. There may be buried lines you do not know about.
- Pick a route that avoids driveways, septic fields and areas you will dig later.
- Plan conduit sweeps and pull points so wire can be pulled or replaced.
- Consider pulling extra conductors or a spare conduit if you might add a second array or a communication cable.
- Mark the route on a site map and keep it with the cabin's system documents.
Lightning and long runs
A long cable between a remote array and a cabin can pick up surges from nearby lightning. Surge protective devices at both ends and good grounding practices are commonly recommended. Our guide to grounding and lightning protection for remote cabin solar goes deeper; an electrician familiar with your area's lightning exposure is the right person to design it.
Common long-run mistakes
- Wiring everything in parallel "because it is simpler" and then needing very heavy wire.
- Forgetting that the run is out and back when calculating length.
- Sizing strings for warm weather and exceeding the controller limit in winter.
- Placing the controller at the array, then running high-current DC to the cabin.
- Burying wire without conduit or at the wrong depth, then needing to dig it up.
- Skipping permits on a run that crosses open ground and later causing insurance problems.
FAQ
How far can a solar array be from a cabin?
There is no fixed limit; it depends on voltage, current and wire size. With high-voltage series strings and an MPPT controller, arrays can sit a substantial distance away. Have the wire sizing confirmed by a licensed electrician.
What voltage drop is acceptable for a solar wire run?
Many designers target a low single-digit percentage for PV runs. The right target depends on your system, and your electrician will set it with local code in mind.
Should the charge controller be at the panels or at the battery?
In most cabin systems it belongs near the battery. That keeps the high-current battery cables short and lets the long run carry high-voltage, low-current power.
Can I use extension cords or regular house wire for a solar run?
No. Use conductors rated for the application, such as PV wire at the array and properly rated cable for burial or conduit. Ordinary cords are not designed for permanent outdoor DC use.
The bottom line
A remote array in full sun often beats a shaded roof array, and a long wire run is how you get there. Raise string voltage within the controller's cold-weather limit, keep the controller near the battery, and size the wire for a small, deliberate voltage drop. The trench, conduit, disconnects and grounding belong to a licensed electrician and the local permit process.