Gigawatt to Kilocalories (th)/hour

1.21 GW is very real — it's about the output of a large nuclear reactor. Doc Brown needed it for the flux capacitor, but a single lightning bolt actually delivers far more instantaneous power (up to 1,000 GW) for a few microseconds. The movie got the pronunciation slightly off: Christopher Lloyd famously said "jigawatts," which is technically an acceptable older pronunciation but not the standard one.

It varies enormously. The UK peaks at about 50 GW; Germany around 80 GW; the US about 750 GW; China over 2,000 GW of installed capacity. But installed capacity and actual consumption differ: the US averages about 450 GW of actual demand. Developing nations can operate on strikingly little — some small African nations manage on under 0.5 GW for millions of people.

The Three Gorges Dam in China holds the record at 22.5 GW of installed hydroelectric capacity — enough to power a country the size of Switzerland. It has 32 main turbines each rated at 700 MW. Its annual output of ~100 TWh makes it the world's most productive power plant, though the Itaipu Dam on the Brazil-Paraguay border occasionally produces more in a given year due to higher capacity factor.

The world added roughly 420 GW of new solar capacity in 2023 alone — more than doubling the pace from just two years earlier. Total global solar capacity surpassed 1,600 GW by end of 2024. China installed over 200 GW in a single year, which is more than the entire US solar fleet accumulated over decades. At current trajectory, solar will exceed 5,000 GW globally by 2030.

A category 5 hurricane dissipates about 600,000 GW of heat energy through cloud formation alone — dwarfing human power infrastructure. A major volcanic eruption releases energy equivalent to thousands of GW sustained over hours. The Gulf Stream carries about 1.4 million GW of thermal power northward. Even a modest thunderstorm generates 10–100 GW. Nature operates on power scales that make our entire grid look like a nightlight.

In microgravity, muscles never work against their own weight — even walking requires zero effort. ISS astronauts exercise ~2.5 hours/day burning 400–600 kcal/h on resistive machines and treadmills with bungee harnesses, yet still lose 1–2% muscle mass per month. The problem is not total energy expenditure but the absence of constant low-level gravitational loading that Earth provides 24/7. Ground-based standing and walking burn only 80–120 kcal/h but provide continuous mechanical stimulus that exercise bursts cannot fully replace.

Most machines use crude formulas based only on speed/resistance and assume a 70–80 kg user. They often report gross calories (including resting metabolic rate you'd burn anyway) rather than net additional calories from exercise. Studies show treadmills overestimate by 15–20%, ellipticals by 25–40%, and stationary bikes by 10–15%. The machines have an incentive to flatter you — higher numbers keep you coming back. Always discount the displayed number by at least 20%.

Surprisingly little extra. The brain uses about 20% of resting metabolic energy (~15–20 kcal/h) regardless of what you are thinking. Intense mental work — chess tournaments, exams, complex coding — increases brain glucose consumption by only 5–10%, adding roughly 1–2 kcal/h. Chess grandmasters who lose weight during tournaments are not burning it with their brains — they lose it through stress hormones elevating heart rate, skipping meals, and disrupted sleep. The brain is always "on" at nearly full power; thinking harder barely moves the needle.

Almost linearly for weight-bearing exercise: a 100 kg person burns roughly 60–70% more kcal/h than a 60 kg person walking or running at the same speed. For cycling and swimming (where body weight is supported), the difference is smaller — maybe 20–30%. This is why heavier people find it "easier" to create a caloric deficit through exercise, and why lightweight people need to exercise longer for the same caloric burn. It's simple physics: moving more mass requires more energy.

Basal Metabolic Rate for adults is typically 55–85 kcal/h (1,300–2,000 kcal/day), depending on age, sex, weight, and muscle mass. It accounts for 60–75% of total daily energy expenditure — far more than exercise for most people. This is why crash diets backfire: severe calorie restriction can drop BMR by 10–20% (metabolic adaptation), reducing your burn by 200–400 kcal/day. Your body literally becomes more efficient, fighting your weight loss efforts.