Renewable vs. Sustainable Energy

How many times have you heard people toss around the words “sustainable energy” and “renewable energy” as if they mean the same thing?

They don’t.

We’ll talk about this important difference. Not everything renewable is sustainable, and in turn not everything which is sustainable is necessarily renewable. The reason an energy source is sustainable often has nothing to do with running out. Contrary to conventional wisdom the world will not run out of fossil fuels. There is nothing scarier in the world to me than the amount of fossil fuels that humans have access to.

All of the energy that humans harness for our personal use comes from a small list of primary energy types. Some of these primary energy types get refilled at a predictable rate, and some of them will allow humans to get energy for such a long period of time that we won’t have to worry about them running out.

Renewable literally means ‘to make new again’. Any resource that naturally replenishes with time, like the creation of wind or the growth of new organisms, is renewable. Renewable energy means that the energy humans extract from nature will refill itself, more can be generated.

Generally renewable energy is taken to mean any of the following:

  • Solar power
  • Wind power
  • Hydropower
  • Tidal power
  • Geothermal energy

  • The downside is if the rate of use exceeds the rate of renewal – that is, the source is used more than it’s being recreated – its continued use will eventually become unsustainable.

    Resources are considered non-renewable if they take a very long time to be created (e.g. fossil fuels) or if their creation happened long ago and is not likely to happen again (e.g. uranium).

    Sustainable energy on the other hand is a source of energy which can be maintained for a definable period of time. If an energy source can be relied on for the next few decades, it’s reasonable to call it sustainable. Sustainable energy practices must rely on resources which can continue to supply our needs. This means that the primary energy source must last for those decades and that we can safely use them.

    Even a renewable resource becomes unsustainable whenever it’s used faster than it regenerates. Conversely, a non-renewable resource can be sustainable if it’s used in moderation, and the environmental impacts don’t cause huge problems. Really, any energy system that fails to take into account needs is not going to be sustained for long. (Here’s an interesting money metaphor to explain this idea further.)

    So what does this have to do with climate change? Everything. We are not running out of coal, oil or natural gas anytime soon. In fact, click play on the data visualization below to see what’s happened to the amount of recoverable natural gas as a function of time:

    Thanks to fracking (hydraulic fracturing) we have more natural gas in our reserves than ever before (the difference between reserve and resource is a bit tricky). Natural gas is not renewable but current technology allows us to access a staggering amount. The amount of natural gas that humans can pull out of the ground to burn will cause devastating changes to the world. Climate change however, even human induced global warming takes a while (decades); this makes it difficult for the human mind to wrap around why fossil fuels are not sustainable.

    The focus is shifting more and more from ‘renewable’ to ‘sustainable’. Determining if a source of energy is sustainable is tricky in a world where the consequences of having ‘enough’ fossil fuels will be disastrous for people.