The good old days
This post is the second in the series ‘The Shape of Net Zero’. The series is based on an understanding that we cannot simply switch out one source of energy (fossil fuels) with another (wind, solar, nuclear and others) and carry on with Business as Usual. We need to consider the following parameters to do with a switch in the basics of our energy supply.
- Fossil fuels, particularly crude oil, possess features that are simply irreplaceable. This is the theme of the first post in this series — The Shape of Net Zero (1): No Substitute.
- A radical change in energy supply will require a huge energy investment just to make the transition. This energy will mostly come from fossil fuels, thus creating a “carbon pulse” of greenhouse gas emissions.
- Up to 15% of the production from a typical oil refinery becomes petrochemical feedstocks. These provide the material foundation of modern society — everything that we use, ranging from plastics to pharmaceuticals — comes from crude oil. If we do away with fossil fuels we will still need to find a way to manufacture this bewildering array of chemicals (or else do without).
- None of the proposed alternative energy sources (with the exception of nuclear) possess the energy density of fossil fuels, particularly crude oil.
It quickly becomes apparent that a switch from fossil fuels to alternative energy sources is not simple or straightforward; it calls for a fundamental rethink as to how energy is generated, transmitted and used.
The posts in this series are generally based on the following sketch. It provides an outline as to how the energy grid may look in a world where alternative energy sources have replaced fossil fuels. In this post we use the sketch to discuss the intermittent nature of many of the alternative sources of energy.
Intermittency is a major drawback when compared with the ability of fossil fuels to generate energy continuously. Fossil fuels are also dispatchable — their output can be quickly ramped up and down to meet fluctuations in demand. By and large, alternative sources of energy lack this feature.
Most discussions to do with future energy transitions are based on the assumption that we will transition smoothly from fossil fuels to a mix of solar and wind power. The difficulty with these two sources of energy is that they are both highly intermittent — solar only works when the sun is shining, wind only works when the wind is blowing.
Currently solar and wind constitute only a small fraction of the overall energy supply. (The post The Renewable Energy Paradox shows that (a) wind and solar currently constitute only a small fraction of the world’s energy supply, and (b) although they are growing faster than other types of energy source their percentage of the overall market is actually declining.)
Currently, therefore, conventional fossil-fuel facilities can ramp up and down to take care of the supply gaps that are an inevitable feature of wind and solar. When the sun is shining and/or the wind is blowing the conventional facilities slow down; they can then ramp up at night or when there is no wind. In other words, the fossil fuel plants provide dispatchable energy, i.e., they dispatch the energy as needed in response to customer demands. Solar and wind, on the other hand, are non-dispatchable; they cannot be easily ramped up or down in response to fluctuations in demand. In effect, the fossil fuel plants are providing a hidden subsidy to the renewables.
This way of running the grid will not work if and when solar and wind provide most of the energy that society needs, and when fossil fuel facilities have been phased out. Under those circumstances it will be necessary for the energy from the solar and wind facilities to be stored in some manner. Provision of energy storage capacity at such a scale is neither technically nor economically feasible. Therefore it will be necessary to provide backup power supplies that are dispatchable, which essentially defeats the purpose of the original project, which was to use just alternative energy sources. (A third choice that is rarely discussed is for society to drastically reduce its need for energy.)
Continuous — Not Dispatchable — Energy Supply
The sketch shows four sources of continuous energy supply. The fact that they are continuous does not make them dispatchable.
- Nuclear plants currently supply an important part of the base load and they are definitely continuous. However, they are not as dispatchable as fossil fuel sources. A nuclear power plant cannot be quickly ramped up and down in response to customer demands. (Another term that is sometimes used is that they do not provide load matching.)
- Hydro-electric power is similar to nuclear. It provides continuous power (although at reduced rates in drought conditions). However, it is not easily ramped up and down to take care of short-term fluctuations in demand.
- Geothermal is also continuous but, once more, is better at providing a steady base load.
- Ocean energy currently means tidal energy. Strictly speaking, this is not a continuous energy source, but it is predictable. Once more, this form of energy is not dispatchable. The tides do not come in and out at the times of our choosing.
The above analysis tells us that not all forms of energy are equal. Renewables are not going to directly replace fossil fuels. Their intermittent nature means that they are currently receiving an unacknowledged subsidy from fossil fuel facilities. But, if we are to achieve a Net Zero society, then these fossil fuel facilities will have been phased out. Hence some form of energy storage will be needed.
Energy storage issues will be discussed in a future post in this series. Suffice to say for now that storage poses many challenges, and it will be very costly.