The Generator Conundrum: Part 1 of Mike’s Guide to Hybrid Generators

If you're reading this, you're interested in hybrid generators. This topic is simple on the surface but has depth worth understanding. This article lays the foundation for projects we're excited to explore in 2026. I'll cover the key elements and explain the problems with traditional generators and how hybrid generators solve them while offering new advantages.

The Why's and How's of Generators

Generators exist for one reason: you need power but don't have a grid connection. This could be a remote job site that hasn't had power run to it yet, or a transient setup that isn't worth spending the time to connect. It could be a backup system providing power to critical loads in a building when the grid goes down. For those familiar with Victron equipment, it's often an off-grid home supplementing solar panels during winter, or an RV powering an AC unit while boon-docking in the desert.

This article focuses primarily on that first application, job site generators. By examining how these generators work and the challenges they face under common operating conditions, we'll build a solid foundation for discussing the value of hybridization in the next article.

Between a Rock and a Hard Place: Overload vs. Inefficiency

At its core, a generator is simply an engine—diesel, gasoline, propane, or LNG—spinning an alternator (a set of magnets inside of some copper windings) to create electrical potential. Many smaller generators have integrated inverters that rectify the output, allowing the engine to run at lower RPMs when demand is low. The larger generators used in job site and backup applications are known as synchronous generators. They must run at a constant 3,600 RPM to produce the 60Hz sine wave that all our AC-powered equipment is designed around. Since AC power also has a target voltage, depending on whether this is single, split, or three-phase, the alternator will be designed to also produce the required voltage at this speed. 

This fixed RPM, tied to output frequency and voltage, places hard restrictions on engine size. As power consumption increases, so does the load on the engine. A generator's peak output is determined by the maximum load the engine can handle while still turning the alternator at 3,600 RPM. When the engine can't maintain this speed, frequency and voltage drop, resulting in unstable power and potentially damaged equipment.

On the other end of the spectrum, the generator can't reduce RPMs when demand is low. This creates inefficient use of the torque curve, causing the engine to run colder than intended with increased fuel consumption relative to power produced.

For reliability and cost reasons, mid-sized job site and backup generators aren't built with variable gearboxes. They rely on a fixed design to meet peak demand while accepting the inefficiency of running at lower output.

To recap: a generator's engine must be sized to handle peak load. This creates a fixed efficiency curve for converting fuel to electricity. This curve varies by design but is typically most efficient at 70–100% of rated output. Running the generator at small loads significantly increases fuel consumption relative to power produced, as shown in the graph below.

Beyond inefficient fuel use at lower power levels, diesel engines suffer from "wet stacking." This occurs when a diesel engine runs below optimal temperature, causing unburnt fuel to accumulate as thick sludge in the fuel injection and exhaust system. The accumulated sludge increases engine wear and further reduces fuel efficiency, requiring more frequent maintenance to prevent damage.

From Theory to Application: How This Plays Out on the Job site

The logical conclusion: the best way to use a generator is to run it near full capacity in that optimal zone. Unfortunately, the typical job site load profile falls far short of optimal, often ridiculously so.

Most large inductive loads from heavy equipment run infrequently but consume significant power on startup. Take an industrial-scale compressor: it might run for 5 minutes every hour to recharge the pressure tank, demanding 2–3× power in the first seconds to get up and running. Since the generator has no means of handling a peak demand above its rated capacity, it must be sized for this startup surge at the expense of running inefficiently for the remaining 4 minutes and 58 seconds, and even more so during the other 55 minutes when the compressor sits idle. For this reason, it's common to see 40kW diesel generators running 24/7 to power a 1,200W load for 22 of those hours.

Certain job sites amplify this issue on an annual scale. A wind turbine site on the remote plains of North Dakota has drastically higher power demands during the summer construction and maintenance season. Onsite power generation must be sized to run multiple job and housing trailers with climate control, plus other job site loads during peak season. During the off-season, the site is left with a grossly oversized generator, even for its largest startup loads.

That's a quick overview of how large job site generators work and the challenges they face in real-world conditions. Join us in the next article, where we'll discuss how hybridization solves many of these inefficiencies—and the costs of doing so.