Energy

Estas multe da konfuzo ĉirkaŭ Energio,
pri kio ĝi estas, kiel ĝi funkcias,
kiel uzi, generi ĝin, ktp ...

Estas ankaŭ multe da ekzaltiĝo pri
renovigeblaj energioj.

There is a lot of confusion around Energy, about what it is, how it works, how to use, generate it, etc… There’s also plenty of hype about renewables.

• Kio estas energio? What is energy?
• Kio estas utila energio? What is useful energy?
• Intuicia energio? Intuitive energy?
• Tipoj de Energio? Kineta kontraŭ Potencialo Types of Energy? Kinetic vs Potential
• Ĉu energio en ondoj? Energy in waves?
• Modernaj Butikoj de Energio Modern Stores of Energy
• Renovigebla Energio Renewable Energy
• Nula Punkto kaj aliaj spekuladoj Zero Point and other speculations

What is energy?

Here is the honest truth, and it surprises people: physicists don’t really say what energy is. They say what it does. Richard Feynman put it bluntly in his Lectures: “It is important to realize that in physics today, we have no knowledge of what energy is.” What we know is that there is a number you can calculate for any system, using a different formula for each form, and when you add all the forms up, the total never changes. That is the law of conservation of energy.

Feynman’s analogy: a child has 28 blocks. Each evening his mother counts them. Some are under the rug, some thrown out of the window, some in the toy box, and she learns rules for working out how many are hidden in each place (weigh the box, measure the bath water level). However the blocks are scattered, her calculation always gives 28. Energy is like that, except there are no actual blocks: only the calculation, which always balances.

Emmy Noether showed in 1918 why it balances: energy conservation follows from the fact that the laws of physics are the same today as yesterday (symmetry in time).

What is useful energy?

Energy is never used up, so why do we run out? Because what we use is not energy but its quality. A litre of petrol and the warm air left behind after burning it contain the same energy; only the petrol can drive a car. The second law of thermodynamics says that energy spontaneously spreads out and becomes less concentrated, and entropy measures that spreading. Useful energy (physicists call it free energy or exergy) is energy that is still concentrated enough to do work. Every engine, every living cell, and every economy is a machine for degrading concentrated energy into diffuse heat, and doing something interesting on the way.

Intuitive energy

Most of us feel energy as effort: climbing stairs, pushing a car. That intuition is decent. In physics, work is force times distance, $W = F d$, and energy is the capacity to do work. Climb a 3 m flight of stairs with a 70 kg body and you do about $70 \times 9.8 \times 3 \approx 2{,}060$ J of work, roughly half a food calorie (a kilocalorie is 4,184 J). Your muscles are only about 25% efficient, so you actually burn about two kilocalories. Which is why climbing stairs feels hard but is a terrible way to lose weight.

Types of energy: kinetic vs potential

• Kinetic energy is energy of motion: $E_k = \tfrac12 m v^2$. Doubling speed quadruples it, which is why a crash at 100 km/h is so much worse than one at 50.
• Potential energy is stored energy of position or arrangement: a raised weight ($E_p = mgh$), a stretched spring, chemical bonds, the nucleus of an atom.

A worked example: a hydroelectric dam

Water falls 100 m. Each kilogram loses $E_p = 1 \times 9.8 \times 100 = 980$ J of potential energy, which becomes kinetic energy, which the turbine turns into electricity. A flow of 1,000 kg (one cubic metre) per second gives $980{,}000$ J/s, nearly 1 MW, before losses of around 10%. Big dams pass hundreds or thousands of cubic metres a second, which is how they reach gigawatts.

Energy in waves

Waves carry energy without carrying matter. A sea wave moves water up and down in circles while the energy travels to the shore. Sound is a pressure wave in air; light is an electromagnetic wave (see Electromagnetic Theory). The energy of a wave grows with the square of its amplitude, and for light, quantum mechanics adds that it comes in packets: each photon carries $E = hf$, so blue light delivers more energy per photon than red.

Modern stores of energy

Storing energy is the central challenge of a renewable grid, because the sun and wind don’t follow demand.

• Pumped hydro – still the largest form of grid storage worldwide: pump water uphill when power is cheap, let it run down when needed.
• Lithium-ion batteries – costs fell around 90% from 2010 to the mid-2020s, and grid-scale battery installations have been growing extremely fast; cheaper lithium-iron-phosphate chemistry now dominates stationary storage.
• Others – sodium-ion batteries (entering mass production), compressed air, thermal storage, and hydrogen for long-duration and industrial uses.

Renewable energy: truth versus hype

The honest picture in the mid-2020s, according to the energy think tank Ember and the International Energy Agency: renewables supplied about a third of the world’s electricity in 2024, solar was the fastest-growing source by far, and in the first half of 2025 renewables generated more electricity globally than coal for the first time. But electricity is only about a fifth of total final energy use. Counting heating, transport and industry, fossil fuels still supply roughly 80% of the world’s primary energy. Both statements are true; hype quotes the first, cynics quote the second.

Zero point and other speculations

Quantum mechanics says even empty space has a minimum “zero-point” energy. It is real (it produces the measurable Casimir effect between metal plates), but it is the lowest energy state, so there is nothing below it to drain energy into. “Free energy” devices claiming to tap it violate the laws of thermodynamics. Rule of thumb: if a machine claims more output than input, check the wiring, then check the wallet.

Common misconceptions

• “We are using up energy.” We are using up concentrated energy and turning it into waste heat.
• “Energy and power are the same.” Energy is an amount (joules, kWh); power is a rate (watts). A kettle uses high power for a short time; a fridge low power all day.
• “Renewables can’t run a grid.” They increasingly do for long periods in several countries; the hard parts are storage, transmission and seasonal gaps.

How it connects

• Physics, Electromagnetic Theory, Climate
• Div, Grad, Curl for the mathematics of flows.

The truth revealed: energy is the one thing in the universe that is never lost, and the one thing we are always short of, because what we really need is order.

Solar Power

• [http://www.livemint.com/Opinion/GcJIuAqhXDRNRx1eddocAO/Solar-power-truth-versus-hype.html Solar-power-truth-versus-hype](http://www.livemint.com/Opinion/GcJIuAqhXDRNRx1eddocAO/Solar-power-truth-versus-hype.html Solar-power-truth-versus-hype)