Connecting solar panels, known as "stringing," requires a sound understanding of how different wiring methods affect the performance of a solar array. Too high a voltage can overburden the inverter, shortening its lifespan, while insufficient voltage can prevent the system from starting. Even shading from nearby objects like trees or buildings can affect the voltage.
Types of Solar Panel Wires
Selecting the proper solar panel wires is crucial for creating an effective circuit to transfer current to the inverter, which will convert DC power to AC. Be sure to follow your local electrical codes and be aware that the National Electrical Code (NEC) prohibits regular cables in solar installations.
Specially designed solar panel cables are resilient to high temperatures, flames, UV rays, and moisture. These cables are built to last between 25 and 30 years. Two main types of wire are used in solar setups:
- Single Wire: A single solid conductor.
- Stranded Wire: Multiple strands, which enhance conductivity by increasing the wire’s surface area. Stranded wires are flexible and ideal for connecting multiple solar panels and components reliably.
To secure cables, use conduits, cable cleats, and weather-resistant or stainless-steel ties.
Reducing Voltage Drop
Voltage drop occurs naturally as current flows through an electrical circuit. To ensure your solar array maintains peak efficiency, minimize voltage drop through careful planning. Industry standards recommend aiming for a voltage drop of 3% or less, ideally under 2%.
Ways to minimize voltage drop include:
- Reducing wire length in your solar setup.
- Strategically positioning the inverter. For example, place the inverter closer to the utility panel if DC voltage is higher than the utility service panel voltage.
- Using larger wires, which have less resistance.
- Designing systems with higher voltage to further reduce resistance.
Solar Panel Wiring: Series vs. Parallel
Your wiring choice depends on the desired output. Series wiring increases the voltage of the array while keeping amperage steady, whereas parallel wiring increases amperage while keeping voltage the same.
How to Wire Panels in Series
When wiring solar panels in series, connect the positive terminal of one panel to the negative terminal of the next. This forms a PV source circuit, combining the voltage from each panel to produce a higher total output.
For example, five panels each producing 30 volts and 7.25 amps would yield 150 volts (30 x 5) at 7.25 amps when wired in series. One downside to series wiring is that shading or obstructions affecting one panel reduce the entire string’s performance.
How to Wire Panels in Parallel
Parallel wiring involves connecting all positive terminals to each other and all negative terminals to each other. This keeps the voltage constant while increasing the total amperage. An advantage of parallel wiring is that if one panel is shaded, it won’t impact the others. However, parallel wiring of panels with different voltages reduces efficiency.
Wiring 12V Solar Panels to 24V Batteries
To charge a 24V battery with two 12V panels, wire the panels in series by connecting the positive terminal of one panel to the negative terminal of the other. Connect the other terminals to the solar regulator, which will start charging the battery when sunlight is available.
Combining Series and Parallel Wiring
For larger installations, both series and parallel wiring can be combined to maximize power output. This setup is more complex and depends on the inverter or charge controller’s input limits. A series-parallel configuration can be set up by wiring two sets of panels in series and then connecting those sets in parallel.
Solar Panel Wiring Diagrams
Off-Grid Systems: Series wiring is typical, with a charge controller to monitor and prevent battery overcharging.
On-Grid Systems: These setups do not require batteries or charge controllers, as they feed directly into the utility grid and need DC and AC disconnects for emergency shutoff.
Combiner Boxes: Often used to merge multiple solar panels, combiner boxes simplify wiring and improve monitoring, particularly in large systems.