01
Wind Power
Wind carries energy in proportion to the cube of its speed, which is the single most useful fact in the subject. Double the wind and you have eight times the power. It follows that a site with steady moderate wind beats a site with occasional strong wind, and that the difference between a good position and a poor one is far larger than the difference between a good machine and a poor one.
The usual mistake in small installations is mounting the machine on or near a building. Air coming over a roof, a treeline or a ridge is turbulent, and turbulence both robs the output and shakes the machine to pieces. Height and clear upwind distance are worth more than blade design.
The other thing that separates a working installation from a wrecked one is what happens in a storm. A machine with no way to shed load or turn out of an overspeed is a machine waiting for the wind that destroys it.
Worth remembering that electricity isn't the only output. Wind driving a pump directly, with no generator, no controller and no battery in the chain, was ordinary farm equipment for a century and remains one of the most reliable arrangements available.
02
Solar Power & Solar Heat
These are two different technologies that share a name, and the one that gets overlooked is usually the better buy.
Photovoltaic panels turn light into electricity. They're cheap now, they have no moving parts, and they need a controller, wiring and something to store the output before they're useful after dark.
Solar heat turns sunlight into hot water or warm air directly. It's far simpler, far cheaper to build from ordinary materials, and considerably more efficient at what it does, because it skips the conversion into electricity and back into heat. For a household whose largest energy demand is hot water and warmth, which is most households, this is where the biggest saving sits and it's routinely skipped in favour of panels.
Both are governed by latitude and season, so any figure quoted for one place is wrong somewhere else. What travels is the method: work out your own demand first, measure what your site receives across the worst month, and size to that.
03
Micro-Hydro Power
If you have falling water on your land, this is the best of the three, and it's not close. Hydro is the only one that runs at night, in the dark and through a still week, which means it needs a fraction of the storage the others do.
Output comes from head, the vertical drop, multiplied by flow, the volume passing per second. Head is usually the cheaper of the two to increase, because a longer pipe to a lower point costs less than damming for more volume, and a steep small stream can outperform a large slow one.
The practical work is mostly not the turbine. It's the intake: keeping leaves, silt and gravel out of the pipe, and keeping it working through the flood that arrives every few years, not just in ordinary conditions.
⚠ Water is the one energy source in this subject that's very often regulated. Rights to divert, dam or abstract from a watercourse differ by country, by state and sometimes by valley, and they can differ for the same stream depending on whether you return the water. Find out what governs your particular watercourse before building anything, because this is a subject where the engineering is easier to reverse than the legal position.
04
Capturing Waste Heat
The cheapest energy in any system is the energy you already paid for and are currently throwing away. Recovery beats generation on cost almost every time, and it attracts a fraction of the attention.
The candidates are the same everywhere: the flue of anything burning, the warm water leaving a bath or a kitchen, the back of a refrigerator or a freezer, the heat a compost heap makes as it works, and a glasshouse in the afternoon.
The engineering is undemanding. A coil of pipe in the right place, a mass that holds heat, and gravity or a small pump to move it. What makes the difference is thinking of the household as one system instead of a set of separate appliances, so that the output of one thing becomes the input of the next.
This is also the part of the subject that pays immediately, at low cost, with tools most people already own, which makes it the sensible place to start, and it's usually the afterthought instead.
05
Energy Storage
Storage is the real bottleneck, and it's where the budget goes. Generation is a solved problem. Having power at three in the morning in the fourth week of a still, grey spell isn't.
Batteries are the obvious answer and the most expensive one. What matters isn't the headline capacity but the cycle life and how deeply the store can be drawn down without harm, because those two decide what the stored unit actually costs across the life of the bank.
The less obvious answers are frequently better. Heat stored in water or in masonry. Water pumped uphill during a windy afternoon and let down through the same pipe at night. Cold stored as ice. A well-insulated building storing yesterday afternoon in its own fabric. Firewood, which is stored sunlight with a shelf life measured in years and no controller.
The discipline that makes all of it work is matching the demand to the supply instead of storing your way out of a mismatch. Doing the washing when the sun is out is free. Doing it at midnight from a battery is the most expensive way to use that energy.
06
Free Energy Claims Examined
This subject attracts two things at once, and a library that can't tell them apart is no use to anyone.
The first is a genuine and well-documented history of workable technology that was discontinued, bought out, left unsupported or simply forgotten because it didn't suit whoever was selling the alternative. That history is real, it's recoverable, and recovering it's what this library is for.
The second is the claim that a machine can return more energy than is put into it. That one has been sold, in various dress, for a very long time, and it's the claim this library will always ask to see measured.
Not measured by demonstration. A device that runs impressively for an audience proves nothing, because the interesting question is what it does over a period, with everything going in and everything coming out on a meter, including the charge that was already in the battery when the cover went on. That test isn't difficult and it's not expensive. What it's, reliably, is the test the strongest claims are never accompanied by.
The Ark has no institution to defend and no interest in telling a reader what they're allowed to wonder about. The position is narrower than that, and it applies to everything else in this library too: we will publish the measurement, we will say plainly when a thing works, and we will say just as plainly when it did not, including when that answer is the inconvenient one. A page that couldn't do the second would be worth nothing when it does the first.