It is now conventional wisdom that
- Combatting climate change calls for deep cuts in carbon dioxide (CO2) emissions from using fossil fuels coal, oil and natural gas.
- A shift to "clean energy", specifically to renewables, will solve the emissions problem.
- Solar and wind will become the main renewable energy sources.
Even though emissions keep rising, public policy takes for granted that the renewables remedy for CO2 emissions will eventually work. It's just a matter of persevering until "100% renewables" is reached. Problem solved. But is it? Here I try to quantify future clean energy requirements and check the progress being made. What emerges is a wake-up call.
1. What is "clean energy"?
Electricity was once seen as the shining example of clean energy. Yes, it was clean for users. Distant power stations did emit smoke and soot but only nearby populations suffered. The picture changed with realisation that CO2 emissions had a global impact. Location was not relevant, quantity was. Lots of CO2, anywhere, meant "dirty".
First, a quick look at measuring energy and emissions. Energy, the capacity to do work, is a quantity, an amount. Power is different from energy. Power is a rate. A simple analogy is that energy is to power as distance is to speed. (Colloquial usage of "power" for "energy" in terms like "power supply", "power station", "wind power" is a slight nuisance, safely ignored.)
The basic energy unit is the joule (J). The basic power unit is the watt (W). One watt = one joule per second. One sees joules and watts in everyday life, e.g. kilojoules measuring food energy, kilowatts rating the power of a toaster or car motor.
Measuring the energy a country uses calls for much bigger units. The most practical (in my view) are multiples of the joule. The petajoule PJ is 1015 joules, the exajoule EJ is 1018 joules. One strikes many different units in the energy field. Online tools like http://www.onlineconversion.com/energy.htm make comparisons easy.
The life-cycle CO2 emissions intensity, the quantity of CO2 emitted per unit of electrical energy, is themeasure of how clean the electricity from a given source is. It takes into account all production steps, like fuel and materials extraction; manufacture, transport and installation of energy conversion equipment; plant operation over its entire lifetime; and eventual end-of-life decommissioning and disposal. A solar panel, for example, emits no CO2. It still results in emissions because its life cycle uses fossil fuels. Methodology for calculating life-cycle emissions intensities is complex but well established.
This Table shows typical values for various energy sources and technologies (from Intergovernmental Panel on Climate Change).
Typical life-cycle emissions intensities for electricity from different energy sources (kg CO2/MWh)
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