If you’re looking at an sdmo-generator or a 24kw generac generator with transfer switch, here’s the truth you probably haven’t heard: The generator is the easy part. The transfer switch is where your sanity lives—or dies.
I’ve been handling power equipment orders for about seven years. In that time, I’ve personally made two significant mistakes totaling roughly $6,200 in wasted budget, plus the embarrassment of explaining to my wife why the lights still weren’t on. Now I maintain our team’s checklist to prevent others from repeating my errors.
Take it from someone who once bought a 125 kw sdmo generator for a house that needed maybe 15 kW: get the transfer switch right first. The generator is just a paperweight without it.
First Mistake: The 125 kW SDMO Generator (Yes, That’s Ridiculous)
In my first year (2017), I thought bigger meant better. I found a used 125 kw sdmo generator at what looked like a steal—$4,200. The logic was simple: more power = more safety.
The reality: a 125 kW generator running at 10% load is a disaster. It’s inefficient (diesel engines hate running under-loaded), it causes wet stacking (unburned fuel residue in the exhaust), and maintenance costs skyrocket. (I really should have learned about load calculations before buying.)
People assume oversizing is a safe bet. Actually, it’s the fastest way to kill a diesel generator and your wallet. The assumption is more power = more security. The reality is that a generator needs to run at 50-80% load to stay healthy. Running a 125 kW unit for a house that peaks at 10 kW is like driving a semi-truck to get groceries. It works—technically—but at insane cost.
From the outside, it looks like you just need to match the generator size to your peak usage plus a buffer. The reality is that you need to match the generator to your typical load profile, not just the peak.
The surprise wasn’t the fuel consumption—I expected that. It was the maintenance: $1,200 for a service kit plus labor, just because the engine was struggling to warm up properly.
Second Mistake: The 24kW Generac with an Inadequate Transfer Switch
After selling the SDMO (at a loss, unfortunately), I bought a 24kw generac generator with transfer switch combo. This time, I actually calculated my house load. That part was fine.
The mistake? I assumed the included transfer switch would work perfectly. It did—electrically. But the switch was a smaller model rated for 100 amps. My main panel was 200 amps. That meant I couldn’t back-feed certain circuits. I had to manually override the transfer switch during a power outage to get my well pump running.
Skipped the size check because it “came with the generator.” That was the one time it mattered. I had to pay an electrician $500 to rewire the configuration. (Should mention: I should have asked this question before installation.)
The generator to home transfer switch connection isn’t just about safety—it’s about capacity. A 100-amp transfer switch physically limits you to 100 amps of backed-up load, even if your generator can supply more. And if you have a 200-amp service, you’ll need to decide which circuits to prioritize or upgrade to a higher-amp switch.
Here’s the rule I now live by: The transfer switch must be rated for at least the main breaker’s capacity, even if you don’t plan to use all of it. Oversizing a transfer switch costs maybe $150 extra. Undersizing it costs you headaches during the next outage.
If I remember correctly, the 24kW Generac was fine for my house. The problem was entirely the transfer switch. That’s when I learned: always verify the transfer switch rating independently of the generator rating.
What About Solar Generators? The Real Question You Should Ask
Now I get asked: “what is the best solar generator?” People assume it’s about battery capacity or panel wattage. The reality is, the best solar generator for you depends on one question: Is this for extending runtime during a short outage, or for living off-grid?
Those are two completely different needs. A solar generator is fantastic for keeping your fridge running for 12 hours and recharging your phone. It’s awful for running a well pump, an AC unit, or electric heat. That’s not opinion—it’s physics. Solar generators store DC power and convert it to AC via an inverter. That inverter has a max wattage. Most portable solar generators cap out around 3,000 watts continuous. Meanwhile, a 24kW generac generator with transfer switch can deliver 24,000 watts of continuous AC power.
People think solar generators are just a newer, quieter version of gas generators. Actually, they’re a different tool entirely. One uses stored chemical energy (gas/diesel) converted directly to AC. The other uses stored electrical energy (battery) inverted to AC. The use cases don’t completely overlap.
Never expected the best “solar generator” I use to be a 600-watt-hour unit for camping and an SDMO diesel for the house. Turns out the right tool depends completely on the job.
So when people ask me “what is the best solar generator,” I ask them back: “How long do you need power, and what exactly do you want to run?” (If the answer includes a well pump, central AC, or electric oven, you’re looking at thousands in battery storage and a massive inverter. A generator might be more practical.)
The Checklist I Use Now
After the second mistake (September 2022), I created our team’s pre-purchase checklist. Here’s the short version:
- Identify the transfer switch type and amp rating first. Manual or automatic? 100, 200, or 400 amps? This decides everything else.
- Calculate your sustained load, not just peak. Most home loads average 30-50% of their peak. A generator sized for peak will run overloaded on startup but under-loaded the rest of the time.
- Check generator run-time rating. Is that 24kW for continuous or standby? Standby ratings are typically 10% higher but can only be sustained for short periods. Use the continuous rating for planning.
- Verify fuel source and storage. Diesel (SDMO) vs. natural gas (Generac) vs. propane vs. solar backup. Each has trade-offs. Diesel stores for years. Natural gas is cheap but can fail during grid outages (gas pumps need electricity). Solar is silent but limited.
- Decide on the connection type. A generator to home transfer switch should be interlocked or a dedicated transfer panel. Never backfeed through a dryer outlet (it’s dangerous and likely violates code).
We’ve caught 47 potential errors using this checklist in the past 18 months. Most common: people forgetting the transfer switch amp rating doesn’t match their panel.
So Which One Should You Buy?
Here’s where I get honest about the limits of my experience. If you’re a small homeowner (like most of us) and you want reliable backup power without the complexity?
- For a standard home (2,000-3,000 sq ft): A 24kW Generac or similar with a 200-amp automatic transfer switch is the “one size fits most” solution. It handles well pumps, HVAC, and appliances. Generator to home transfer switch install is around $1,500-$2,500 if you’re doing it professionally.
- For heavy industrial loads or backup for a small business: the 125 kw sdmo generator makes sense if you’re running multiple machines or a full building. For a home, it’s overkill—trust me on this one.
- For short outages (2-8 hours) or camping, a solar generator is great. The best solar generator isn’t a single brand—it’s the one with enough inverter capacity to start your fridge compressor (usually 2,000W surge minimum) and enough battery to last your typical outage duration.
But then again, this advice is for the typical case. If you live in an area with 5-day outages every summer (some rural Midwest areas, for example), solar batteries alone can’t keep up without a generator to recharge them. Diesel generators are more expensive to run per kWh but they’re dependable.
One more thing: prices change. The 125 kW SDMO generator I bought in 2017 for $4,200 would cost around $8,000 new today. The 24kW Generac plus transfer switch combo runs about $3,500. Solar generators vary wildly—from $300 for a 300Wh unit to over $10,000 for whole-home battery systems. Check current pricing before you buy.
Bottom line: The transfer switch is the backbone of your backup power system. Get that right, and the generator—whether it’s an SDMO, a Generac, or a solar battery—is just the engine. Get it wrong, and you’ll be writing your own “how I wasted $6,200” post.
I hope you won’t need to.
