Choosing the Right Generator for Your Solar System

What You Need to Know

Introduction
The First Question: 120 Volts or Split-Phase 120/240 Volts?
Next: How Many Amps (or Watts) Did the Old Generator Deliver?
Do You Have AGS (Auto Generator Start)?
Conclusion

Introduction

Every once in a while, I get a call from a customer whose old generator has finally quit for good. The question is always the same: “What generator should I buy next?” And my answer is always the same: “Well… that depends.”

A generator isn’t a one-size-fits-all purchase, especially when it’s tied into an off-grid solar system or being used as backup power for your home or cabin. Before choosing a new one, you need to know exactly what your old generator was doing electrically, and more importantly, what your inverter or electrical system actually needs.

The First Question: 120 Volts or Split-Phase 120/240 Volts?

Not all generators are created the same. Some only produce 120 volts, while others produce split-phase 120/240 volts. This matters more than most people realize.

If your system only needs 120V

A standard 120V generator may be all you need. These work well for:

Small cabins
Systems with small inverters
Battery chargers designed only for 120V input
Lights, small appliances, or basic tools

If your system requires 120/240V split-phase

You must get a generator that outputs both phases. This is required if:

You have a 240V well pump
Your inverter/charger needs 240V for proper charging
You’re powering a full home panel
Your transfer switch uses both L1 and L2

If your system expects split-phase and you buy a 120V generator, devices like your 240 pump won’t work.

Next: How Many Amps (or Watts) Did the Old Generator Deliver?

This is where the details start to matter.

Generators are rated in watts or amps. You need to know what your old generator was actually supplying. Ask yourself:

Was it 23 amps?
30 amps?
50 amps?
70 amps?

A generator’s amperage rating determines:

How quickly your batteries can recharge
Whether large loads can run without tripping the breaker
How well your inverter/charger performs under load

If your inverter can accept 50 amps of AC input but you replace your old generator with one that only produces 21 amps, you’re going to notice the difference, especially in winter.

Do You Have AGS (Auto Generator Start)?

This is one that many people overlook.

If your system has AGS, or if you’re planning to add it in the future, your generator must be compatible with automatic start functions.

There are two important questions to ask:

1. Does the new generator support remote start?

Not all generators do. Some require a physical key or manual choke, which means:

AGS won’t work
You’d need modifications later
Or you might have to buy a different generator altogether

2. Does the generator use 2-wire or 3-wire start?

Solar inverters typically use a 2-wire start system for AGS. Some generators use:

2-wire start (ideal)
3-wire start
Proprietary start systems (problematic)

If your generator doesn’t match your inverter’s AGS requirements, your auto-start system simply won’t work.

This is especially important if:

You leave your cabin for long stretches
You rely on the generator during cloudy periods
You want your batteries protected from deep discharge

Choosing a generator today that supports AGS can save you serious money and headaches down the road.

Conclusion

Before buying a new generator, take the time to understand what your system actually needs. Was your old generator 120 or 120/240 volts? How many amps did it provide? Does your inverter expect a split-phase feed or a single phase? And perhaps most importantly, do you use, or plan to use, Auto Generator Start?

These details matter more than the brand name or the size of the fuel tank. A little attention upfront can save a lot of frustration later and make sure your generator, inverter, and solar system all work together the way they should.

If you’re unsure, reach out anytime. Helping people choose the right generator, and making sure it actually works with their system, is something I do every day.

IOTG SOLAR LTD 5 Critical Mistakes To Avoid Before Buying Solar.pdf

For individuals seeking consultation, education, or assistance in system designs related to grid-tie or off-grid solar applications, IOTG Solar stands ready to help. Our team is available to address questions, provide valuable insights, and offer support at every stage of the solar energy journey. Feel free to reach out to IOTG Solar anytime for expert assistance and comprehensive solutions tailored to your specific needs.

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