Horsepower (Electric) to Terawatt

It's a deliberate rounding for simplicity. The mechanical horsepower is 745.69987... watts — an ugly number for electrical calculations. The electric motor industry rounded to 746 W for clean nameplate ratings and straightforward calculations. The 0.04% difference is far below any motor's manufacturing tolerance. Some standards even use 750 W as an approximation. In practice, the distinction between 745.7 and 746 matters only to standards lawyers and unit conversion pedants.

Divide the hp rating by the motor efficiency and power factor. A 5 hp motor at 90% efficiency draws: 5 × 746 / 0.90 = 4,144 W of electrical power to deliver 3,730 W of shaft power. For three-phase motors, also divide by (√3 × voltage × power factor) to get amperage. Real-world efficiency ranges from 75% for small motors to 96% for large premium-efficiency ones. The nameplate always shows shaft output, not electrical input — a common source of confusion.

Because American homeowners and pool contractors have decades of experience sizing pumps in hp: "a 20,000-gallon pool needs a 1.5 hp pump" is ingrained knowledge. The Department of Energy actually mandated variable-speed pool pumps in 2021 and encouraged watt-based efficiency ratings, but manufacturers still prominently display hp because it drives purchasing decisions. A customer choosing between a 1 hp and 1.5 hp pump understands the difference intuitively; 746 W vs 1,119 W means nothing to them.

NEMA (National Electrical Manufacturers Association) defines standard motor sizes using electric hp: 1/4, 1/3, 1/2, 3/4, 1, 1.5, 2, 3, 5, 7.5, 10, 15, 20, 25, 30, 40, 50, 60, 75, 100 hp and up. These are standardized frame sizes — a 5 hp motor from any manufacturer fits the same mounting bolts. The hp(E) rating is the shaft output; NEMA also specifies efficiency classes (IE1 through IE4) that determine how much electrical power the motor actually consumes.

Not usually. EV manufacturers rate motors in kilowatts because the electrical connection is obvious and kW is internationally understood. A Tesla Model 3 motor is listed as 211 kW, not "283 hp(E)." However, marketing materials often convert to hp for American consumers: "283 horsepower" sounds sportier. Interestingly, EV motors are far more efficient (90–97%) than combustion engines (25–40%), so a 200 hp EV motor consumes far less total energy than a 200 hp gasoline engine.

The Sun delivers about 173,000 TW to Earth's surface. Human civilisation uses roughly 18 TW total. So we'd only need to capture 0.01% of incoming solar energy to power everything — an area of solar panels roughly 400 km × 400 km, about the size of Montana. The challenge isn't total energy availability; it's cost, storage, transmission, and the fact that sunlight is spread thin and intermittent.

Imagine 18 trillion light bulbs burning continuously, or 9 billion people each running a 2 kW heater non-stop. That 18 TW figure includes everything — electricity, transport fuel, industrial heat, cooking, heating. About 40% comes from oil, 27% from coal, 24% from gas, and the rest from nuclear and renewables. The US alone accounts for about 3 TW despite having only 4% of world population.

Replacing all 18 TW of human energy with clean sources would require roughly 60–75 TW of installed solar capacity (accounting for ~25% average capacity factor). That's about 40 times current installed solar. At 2023 installation rates of ~0.4 TW/year, it would take 150 years — but installation rates are doubling every 2–3 years. If that exponential trend holds, we could theoretically reach 60 TW of solar within 15–20 years.

Earth radiates about 47 TW of geothermal heat from its interior, driven by radioactive decay and residual primordial heat. That's 2.5× human energy consumption, but it's spread across the entire surface at extremely low density (~0.09 W/m²). Iceland, sitting atop a mantle plume, exploits geothermal for 90% of its heating. Globally, geothermal electricity capacity is only about 16 GW — a tiny fraction of what's theoretically available.

No — the terawatt scale is a very recent phenomenon. In 1800, global human power consumption was about 0.5 TW (mostly biomass burning). By 1900 it reached 1 TW with coal industrialisation. We crossed 10 TW around 1985. The jump from 1 to 18 TW in just 120 years tracks almost perfectly with global population growth times rising per-capita energy use. Pre-industrial humans used about 0.1 kW each; Americans now average 10 kW per person.