I was wondering, in laymen terms, what is the exact definition of renewable energy and what are its various forms, which ones are better and in what situations can they / can they not be used.

How do you weigh the cost of setting up this technology with its payoff, and how do you set these benefits apart from those derived by investing in other areas such add healthcare, research, and development in other areas such add food and disease fighting?

Sends like there are manpower-based investments and research based investments.

I realize this is a very broad question, but tried Wikipedia and could not find a laymen answer to my broad question.

NOTE: If my question is to broad, then please just pinpoint this very basic question: how do you define renewable energy?

  • 2
    $\begingroup$ What's wrong with Wikipedia's definition? $\endgroup$
    – Algo
    Oct 13, 2016 at 5:24
  • $\begingroup$ This cannot by definition be too broad. SE has a specific "renewable-energy" tag. The question is simply asking to elucidate the tag you yourselves have devised... $\endgroup$
    – Paul Uszak
    Apr 30, 2017 at 21:42

1 Answer 1



Renewable energy is one for which the input energy is renewed on human timescales.

Remember, energy is always conserved. It doesn't come from nowhere. Pretty much all the energy we use on Earth comes from the stars - and almost all of it comes from one star in particular, the Sun.

not renewables:

Uranium (for nuclear power) is in the earth after being manufactured in generations of stars. This takes billions of years, and is thus not renewable. Coal, gas and oil are in the earth after having been living organisms (plants, animals, etc) millions of year ago, and are thus not renewable.


Wind, solar, hydro, biomass and waves are all powered by incoming solar energy every second of the day, and so are constantly replenished at human timescales. The tides are renewed every day by the relative motion of the Earth and the Moon (and to a much lesser extent, the sun too). Geothermal energy is renewed every second of the day by slow nuclear reactions deep in the ground, and in some cases by being replenished constantly by the heat emitted from magma.


You've asked a very broad range of questions. Many of them, when refined, would be best handled on our Sustainability Stack, where we already have quite a few questions on renewable energy - the economics, the engineering, and so on. You'll also find questions on the physics concepts behind renewable energy, on our Physics site.

  • $\begingroup$ Thank you. So the difference is one of timescale, that is what renewable refers to. How can you exploit h hydro, biomass, waves, tides, and geothermal? I don't understand these terms. $\endgroup$ Oct 14, 2016 at 8:31
  • $\begingroup$ Very nice of us to have a Sustainable Living stack exchange. I was not aware of it. $\endgroup$ Oct 14, 2016 at 8:32

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