I've been reviewing generator specifications and managing power equipment orders for seven years. In that time, I've personally made and documented more than a dozen significant mistakes, totaling roughly $60,000 in wasted budget. Now I maintain our team's pre-purchase checklist, and I write this because I'd rather you learn from my errors than repeat them.
If you're here because you typed “sdmo-generator” into a search bar, I'm guessing you're in the middle of a decision. Maybe you're comparing a 20 kW SDMO diesel generator to a 120 kW SDMO generator. Maybe you're wondering whether a mobile diesel generator would suit you better, or whether you should be looking at a Patriot portable solar generator. I've watched buyers struggle with all of these. The most frustrating part is that they usually argue about the wrong things.
Let me be clear: when I say the problem is not the generator, I do not mean the unit is irrelevant. The question I hear most often is: “Will a 20 kW SDMO diesel generator run my building?” In my opinion, that's the wrong question. The right question is: “What are you trying to run, and for how long?” That distinction changes everything.
The surface problem: you think you need a generator
The surface problem is obvious, right? Power goes out, you want it back on. But when I dig into an order, I find that most people are trying to solve different problems with the same tool. Some need to keep a few lights and a fridge going during a storm. Some need to power an entire workshop. Some need temporary power at a construction site. Those aren't the same job.
In my first year (2017), I made the classic mistake of selling based on price per kilowatt. A buyer asked for a 20 kW SDMO diesel generator, and I assumed the spec was correct. It looked fine on the load list. Then we installed it, and the compressor started, and the generator died. That incident taught me to never approve a generator without understanding the starting loads. “Fine on paper” is not the same as “fine under start.”
That's a hard lesson, and it's not uncommon. For a long time, I didn't understand why the same mistake kept happening. Then I realized: the real problem was not kW. It was the total absence of a load-analysis process.
Deeper cause #1: kW is not the whole story
If you look at any industrial generator, the headline numbers are kW and kVA. For an SDMO generator, you'll see ranges from around 20 kW to well into the hundreds of kW. For context, according to Kohler's published product range (kohlerpower.com, accessed January 2025), SDMO industrial generators cover approximately 20 kVA to 1250 kVA. That's a wide range, and it's exactly why “just pick a generator” doesn't work.
The natural reaction is to think “bigger is better.” To be fair, bigger is safer for steady loads. But starting loads are a different animal. Motors draw a surge of current when they start. A 7.5 HP compressor might only consume 2–3 kW while running, but it can demand 15–20 kW for a fraction of a second during startup. If your 20 kW SDMO diesel generator is already carrying other loads, that surge can cause the voltage to dip below the equipment's tolerance. The motor stalls. The generator trips. The breaker opens. Everything stops.
This is why I use kVA and starting watts instead of just average watts. A 20 kW unit can handle a lot of continuous load, but it cannot handle every start. Conversely, a 120 kW SDMO generator might feel like overkill, but if your facility has several large motors that start at different times, the higher capacity is what makes it work.
If you ask me, the spec sheet should come after the load inventory, not before.
Deeper cause #2: you're comparing the wrong categories
Another mistake I see constantly is category confusion. People compare a Patriot portable solar generator with a 20 kW SDMO diesel generator as if they were two versions of the same product. They're not. A battery-based solar generator is designed for lower power, shorter runtime, and quiet operation. A diesel-fueled industrial generator is designed for higher power, longer runtime, and continuous duty when the grid fails.
To be clear, I have mixed feelings about the phrase “solar generator.” On one hand, it makes the product approachable. On the other, it creates an expectation that a battery inverter can do what a fuel generator does. The power strip vs surge protector analogy fits here. A power strip and a surge protector look almost identical. They both give you extra outlets. But only one is designed to protect equipment from voltage spikes. Once you see the difference, you stop asking which one is “better” and start asking which one you need. That's kinda the point.
That mental model translates directly to generator selection. A 120 kW SDMO generator isn't automatically better than a 20 kW unit. A mobile diesel generator isn't automatically better than a stationary one. It depends on the job. The mobile vs stationary decision kept me up at night on a 2023 project. On paper, a trailer-mounted mobile diesel generator was more flexible. But my gut said the client would rely on it as permanent backup, not temporary power. Ultimately I recommended the stationary unit because the site had an existing transfer switch and a fixed weatherproof pad. Flexibility is useful. Dependability is better.
The same logic applies to solar. A Patriot portable solar generator is great for camping, tailgating, or keeping a few devices charged during a short outage. I would not specify it to run a workshop with motor loads. That is not a criticism of the product—it's just not the right tool for that job.
What these mistakes actually cost
In September 2022, I approved an order for a 20 kW SDMO diesel generator with a slightly weak load list. The buyer was happy, the price was fine, and the delivery date worked. Then the first startup load exposed the problem. We had to redo the electrical connections, upgrade the generator, and re-test everything. The redo cost around $3,200 plus a one-week delay. We didn't have a formal approval chain for rush orders back then, and that's exactly how an unauthorized risk got through.
The most frustrating part of my job is that these failures are predictable. You'd think a written load list would prevent a wrong spec, but it doesn't if nobody verifies the starting numbers. After the third repeat, I created a 12-point pre-purchase checklist. It has saved us an estimated $8,000 in potential rework in the past 18 months. That's not a headline-grabbing number, but it's real.
Last year, a buyer insisted on a 120 kW SDMO generator. The site had maybe 45 kW of steady load. We did a proper analysis, and the largest motor's starting surge was around 70 kW, so a smaller unit with a soft starter would have been enough. The 120 kW would have cost about $18,000 more upfront and consumed more fuel for its entire lifespan. We caught it before ordering. That's the difference between prevention and cure.
For what it's worth, I'm not 100% sure every market has the same price gap, but based on distributor quotes I received in Q3 2024, an industrial 20 kW SDMO diesel generator generally landed between $12,000 and $16,000, while a 120 kW SDMO generator ranged around $45,000 to $60,000 in my region. Take those numbers with a grain of salt—prices vary, and you should verify current quotes. The point is that a sizing mistake on a 20 kW unit costs thousands; a mistake on a 120 kW unit costs tens of thousands.
What I'd do instead: a short checklist
If you're serious about avoiding this, you don't need a long explanation. You need a process. My current checklist is short:
- List everything that will run at the same time. Include lights, computers, motors, compressors, pumps, and anything with a heating element.
- Find the starting watts. Look at the motor lock-rotor amps or the equipment's startup data. If you can't find it, use a conservative estimate of 3–6 times running watts.
- Choose kW and kVA based on the worst case. Not the average, not the sum of running watts, but the worst-case start plus the load that's already running.
- Pick the right fuel and mobility. Diesel for long runtime, stationary for permanent installation, mobile only if you actually need to move it.
- Get quotes from distributors and compare the package. Include transfer switch, delivery, installation, fuel tank, and commissioning in the comparison.
- Test under 100% load before you need it. A generator that hasn't been load-tested is just an expensive paperweight.
This is not a complete engineering manual. It's a way to avoid the most expensive mistake I see: buying a generator before you understand the load. 5 minutes of verification beats 5 days of correction.
Personally, I've stopped selling generators without a completed load analysis. I'll walk through a site, review equipment data sheets, and calculate starting demands. If a client isn't willing to supply that, I politely decline the rush order. That sounds stubborn, but it's cheaper than rework.
Granted, this requires more work upfront. But it saves time, money, and embarrassment later. If you're comparing the power strip vs surge protector question in your head, you're already on the right track. A surge protector doesn't make you safe if you're using it as a power strip for a space heater. Likewise, a 120 kW SDMO generator doesn't help if you only need 15 kW and a backup light. Choose the tool that matches the job.
And if someone tells you “just buy the bigger one,” ask them to show you the starting load numbers. If they can't, you're about to make a very expensive mistake.
