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Which energy are we talking about?


There are many types of energy, but not all types are equal. Often they are sorted into: thermal, potential, kinetic, chemical, electrical, and nuclear. There are others, but these are the most common in our global energy system. We convert energy from one form to another until we get the kind we want.

To illustrate, let’s look at how we get electricity. Most of our energy comes from fossil fuels. The energy starts as stored “chemical” energy in hydrocarbons which is then released as heat through combustion. This “thermal” energy is then converted to “kinetic” energy, usually by forcing steam through a turbine. Finally, the energy is converted to “electrical” by using the spinning turbine shaft to move magnets past a wire coil. The table below shows how we get most of the world’s electricity.

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Each step can only convert a portion of the energy to the new form because in every process there are inefficiencies. But to truly be valuable, we have to look to what type of energy we want. For powering our computers we want “electric” energy, but for transportation we want “kinetic” energy and for heating our homes we want “thermal” energy.

Is it power or energy?

Often, journalists use the term “power” when they mean electrical energy. The proper definition is a rate of energy use (eg. energy used per second). Of course, energy and power are measured in many different units. Don’t worry about learning these, but for example (and for more see MIT_conversion):

energy unit conversion

Part of the reason for confusion is that the media often don’t distinguish between capacity and generation. To keep this discussion simple, for electricity, engineers usually use MW to describe capacity. A typical nuclear plant has roughly 1000 MW capacity while a wind turbine typically has 2 MW capacity. For generation, we simply multiply the capacity by the number of hours it operates (MW * hour = MWh) at that capacity. For the US nuclear plant running for an average hour, it produces around 870 MWh. For 500 wind turbines (1000 MW capacity), the US wind farm might produce 230 MWh during an average hour. To illustrate the overall difference on the US grid:

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Green sites tend to ignore this distinction suggesting that renewables are replacing fossil fuels, but over the last five years an average of 70% of new generation is still fossil fuels. We’re moving towards more renewables, but that movement is too slow.

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Three years ago, the IEA suggested that to limit impacts from climate disruption, all building of new fossil fuel infrastructure worldwide would need to come to a stop by 2017. The numbers so far this year (in the US) are the same as when the report came out. Cumulatively, the US has emitted the most greenhouse gases per person of almost any country. This suggests that Americans should stop all fossil fuel infrastructure immediately to allow other countries more time to increase their affluence and ability to pay for (currently) more expensive green energy.

Politically, this seems unlikely to happen. But maybe if green media were honest about the progress we’re making, we’d be able to incite more people to demand real change.