What Is a Single Line Diagram (SLD) and Why Every Solar Proposal Needs One

If you've ever applied for net metering with Meralco or VECO, you've been asked for a Single Line Diagram (SLD). Most homeowners have no idea what it is. Many installers draw it by hand. There's now a better way.

What Is an SLD?

A Single Line Diagram is a simplified electrical diagram that shows how all major components of your solar system connect. It's called "single line" because it uses one line to represent all conductors between components — it's a schematic, not a wiring diagram.

An SLD for a residential solar system shows:

• Solar PV array (panels in string configuration)
• DC disconnect and surge protection
• Inverter (hybrid or grid-tied)
• Battery bank (if hybrid)
• AC disconnect
• Distribution board / load center
• Net metering enclosure and bidirectional meter
• Grid connection point

Why It's Required

The SLD is a mandatory document for:

• Meralco net metering application — they need to verify your system is properly protected and isolated
• Building permit — required by some LGUs for the electrical permit
• PEC compliance inspection — your REE/PEE inspector checks the SLD against the actual installation
• Insurance documentation — insurers want to see the electrical diagram for claims

The String Sizing on an SLD — What It Means

A proper SLD doesn't just show components — it shows string configuration: how many panels are connected in series per string, and how many strings per MPPT input.

This is calculated from the inverter's MPPT voltage range and the panel's Voc and Vmp. For example:

• Panel Voc: 41.3V — Panel Vmp: 34.5V
• Inverter max DC input: 550V — MPPT range: 80V–450V
• Max series panels per string: 550V ÷ 41.3V = 13 panels max (use 10 for safe margin)
• String Vmpp: 10 × 34.5V = 345V — within the 80-450V MPPT range ✓

Getting this wrong is a common installer mistake — overshooting the MPPT range means your inverter operates inefficiently or shuts down entirely.

Auto-Generated SLD on SolarEnergyPH

The SLD tab in the Installer Dashboard auto-generates a professional SLD the moment you configure a system. It includes:

• Visual diagram with all components labeled
• String configuration calculated automatically from your chosen panel and inverter specs
• Module spec table (Voc, Vmp, Isc, Imp, wattage)
• Inverter spec table (max DC input, MPPT range, output power)
• Wire schedule (DC string cable size, AC cable size)
• PNG export for proposals, permit applications, and net metering submissions

No more drawing SLDs by hand. Configure your system, click the SLD tab, export to PNG — done.

Try it free at solarenergyph.shop — Installer Dashboard → SLD tab.

Engr. Jason Morales — Founder, SolarEnergyPH