Most energy arguments online run on headlines rather than numbers. The underlying physics is not complicated, and once you carry around five or six figures, a lot of those arguments resolve themselves. Here are the ones worth knowing.
Why Wind Speed Beats Turbine Size
The power available in wind scales with the cube of wind speed. Double the wind speed and you get eight times the power. That single relationship explains why siting and tower height get more engineering attention than the turbine itself, and why a location averaging 12 mph is worth far more than one at 9 mph.
There is a hard physical ceiling on the other side. No turbine can extract more than 59.3 percent of the energy in the wind, a limit derived by Albert Betz. Real machines land at capacity factors between 25 and 55 percent depending on site, with offshore beating onshore because ocean wind is steadier and less turbulent. Utility scale turbines run 2 to 8 MW today, with offshore models reaching 15 MW.
Deployment is not the bottleneck it once was. Wind added 158.7 GW of new capacity globally in 2025, with China installing 119.4 GW of that.
The Sources That Run All Day
Capacity factor, the share of nameplate capacity a plant actually delivers over a year, is the number that separates these technologies more than any other.
Geothermal clears 90 percent, because heat from the Earth's interior does not care about weather or time of day. Hydroelectric turbines hit 85 to 90 percent conversion efficiency, the highest of any generation technology, and hydro still supplies roughly 16 percent of global electricity. Solar sits at 15 to 25 percent and wind at 25 to 55.
Nuclear supplies about 10 percent of global electricity, and its energy density is hard to picture until you put it in units: a single uranium fuel pellet the size of a fingertip holds as much energy as a ton of coal. Whether it counts as renewable is a definitional argument, so it usually gets classified as low carbon instead.
Storage Is The Real Constraint
Lithium-ion dominates short duration grid storage, one to four hours, at 85 to 95 percent round trip efficiency. That covers the evening peak, which is most of what people picture when they hear grid battery.
The interesting gap is longer. Pumped hydro still accounts for about 95 percent of global grid storage capacity at 70 to 85 percent round trip, which surprises people who assume batteries own this space. Flow batteries scale duration by making the tanks bigger and fit the four to twelve hour range. For multi day storage the candidates are iron-air, projected below $20 per kWh by using the reversible rusting of iron, compressed air in underground caverns, gravity systems, and thermal storage in molten salt or heated sand.
Generation is largely a solved engineering problem. Multi day storage is not, and that is where the real work sits. The full renewable energy guide walks through each source and the grid integration side in more depth.
What It Actually Costs Now
Solar module costs have fallen more than 99 percent since 1976 and roughly 90 percent since 2010 alone. Onshore wind turbines are down about 70 percent over the same recent period. These follow learning curves: every doubling of cumulative installed capacity has historically cut costs 20 to 25 percent for solar PV.
The result, in levelized cost of energy per kilowatt hour:
- Utility scale solar: $0.03 to $0.05
- Onshore wind: $0.03 to $0.06
- Offshore wind: $0.05 to $0.10
- Gas combined cycle: $0.04 to $0.08
- New coal: $0.065 to $0.15
New utility solar and onshore wind are now the cheapest sources of new generation in most regions, subsidies aside. Green hydrogen sits at $4 to $6 per kilogram today with projections below $2 by 2035 as electrolyzer manufacturing scales.
The Takeaway
The science of renewable energy is settled. Wind scales with the cube of speed and caps at the Betz limit, geothermal and hydro give you the capacity factors that solar and wind cannot, and the costs already won the argument on new generation.
What is left is engineering, grid infrastructure and politics operating at planetary scale, with multi day storage as the technical problem that genuinely still needs solving.
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