Electricity: Part 9 - Sustainable Energy
Gaining green credentials is becoming paramount for broadcasters but the solutions to achieving this are bound up with the wider societal issues surrounding electricity.
The broadcaster is totally dependent on electricity in every aspect of the capture, production and transmission of sound and images and these can only be received on electrically powered devices. Concern about where that electrical power is coming from and continuity of supply should naturally be quite high.
For many years the reliability of electricity supply grew and reached a level where it was essentially taken for granted. In a technological age, new scientific discoveries came along regularly and technologies were developed that turned them into useful products.
There were other types of scientific discovery too, including a growing realisation that some aspects of human activity were actually harmful and this led to concern for the environment. As the science was better understood, the performance of products improved. Some thought that process would go on for ever and that any time a problem emerged, someone would invent something to solve it, a kind of silver bullet.
At one time parts of the Earth were unknown and there were people called explorers who set out to look at these places and there were new and remarkable discoveries. But the Earth is finite and there is now no part of its surface that hasn’t been visited, photographed, mapped and whose resources are not known. There are no more explorers and Mount Everest is a rubbish dump.
At the other end of the scale, science found that the elements occupied a periodic table and as new elements were found, their characteristics were noted. When an interesting element emerged a technology would spring up to exploit it. Semiconductors, lasers, recording media, magnets, solar panels and so on all came from that. But, like the exploration of the Earth, eventually all of the stable elements were found and there are no more. There would be no further technologies based on newly discovered elements.
Metals are of course interesting as they conduct electricity and can be used to make batteries. For mobile applications, we want the lightest batteries possible, but we are already using Lithium, the lightest metal in the periodic table, and no lighter metal exists or could exist. This means that battery performance is not likely to increase dramatically and that progress will be incremental. In other words we are more or less stuck with batteries as they now are; a long way short of what we would like.
As science advanced it explained more and predicted performance bounds that were fundamental. As technology advanced, it came up against these bounds. One of the first was the laws of thermodynamics that set limits on the efficiency of heat engines. These would almost be reached, and then diminishing returns set in and there is no prospect of dramatic advances.
Information theory told us the bounds to coding theory that have essentially been reached with modern recording and communication equipment. Today’s modulation schemes are about as good as they are going to get. Error correcting codes now operate at the limit set by Shannon. Compression codecs have made all the great leaps and improvements are now incremental.
Hydrodynamics explained the wave-making of ships and why high speed is simply not viable. Aerodynamics did the same for airplanes and explains why airliners must remain subsonic in order to be viable.
All of the above explains that we are living in a new kind of era where we can no longer expect science and technology to dig us out of the holes we have made. The silver bullets have been fired and we must work with what we have.
It is vitally important to understand that electricity is not a source of energy. Electricity merely allows existing energy to be sent from one place to another. In that respect an electrical system is no different to the chain of a bicycle. It transmits power from the pedals to the wheel. If there is no power supplied to the pedals, no power arrives at the wheel. Electricity is not a fuel and is not used up.
At the point where the electrical energy is used, typically converted into heat after doing something useful, the emissions are negligible. But that means nothing, because the electrical energy must have been generated elsewhere, and that process would have resulted in emissions. It is those emissions we need to look at. And when we look, we need to look at the whole picture and not at some simplistic view.
The dominant sources of electricity generation are solar, wind, hydro/tidal, nuclear and thermal. Fig.1 shows that the criteria by which we judge energy sources include availability, sustainability, the embedded carbon of construction, the carbon emissions in use, the pollutants released in use (carbon dioxide is not a pollutant) and the difficulty of decommissioning. The sheer magnitude of energy use and the huge amounts of money that are involved mean that the subject is inseparable from politics, intense lobbying and corruption.
Fig.1 - A comparison of the major attributes of various sources of electricity shows that not one is ideal and that we may be stuck with sub-optimal solutions for some time.
Solar and wind power result in relatively small embedded carbon and practically zero carbon in use. The fact that installations are widely distributed puts generation nearer loads and reduces stress on grid distribution. However, solar and wind power have poor availability. They produce power when they can rather than when it is needed. Solar power is especially contrary in many countries, as it delivers the least power at night and in the winter, when demand for light and heat is greatest. Solar power is ideal to drive air conditioners as the available power matches the heat load perfectly. Wind power is as fickle as the weather, but in a large country with windmills widely distributed, they may not all end up becalmed at once. Locating solar farms in deserts is a viable strategy to maximise yield from prevailing weather conditions. Power-sharing between countries can also help.
Hydro-electric power uses the potential energy of rain water falling on high ground as it returns to sea level. The embedded carbon involved in dam-building is serious on account of the massive quantities of concrete needed, but the dams themselves last an extremely long time and the generating equipment can be replaced when it wears out, usually with units of greater efficiency. Availability of hydropower is purely a function of the presence of water at inlet level. That in turn is a function of rainfall patterns and water management.
Good water management brings the inlet level storage to full capacity at the onset of winter. Rainfall reduces the rate at which the storage goes down and snow melt, which comes later, adds more water to the storage. In the short term, hydropower can fill in when solar or wind power are not delivering. However, most of the world’s sites suitable for large hydropower installations have already been taken so future expansion is limited.
Tidal power is a relative of hydroelectricity as it works from the changes in sea level or currents induced by tides. Like solar power it is cyclic, not steadily available.
Wave power has not succeeded yet, possibly because the environment in which the equipment must work is extremely hostile.
Thermal power remains the biggest source of electricity. Some sort of fuel is burned to create a temperature difference that can drive a heat engine which then drives a generator. The heat engine can be a steam turbine, a gas turbine or a piston engine. The fuel will typically have a carbon content and burn to produce carbon dioxide as well as various pollutants. Coal and oil are worse in that respect, whereas gas has more hydrogen and less carbon and so burns with a lower level of carbon dioxide and pollutants. Needless to say, none of these fossil fuels are sustainable.
Coal and oil are easily stockpiled against harsh weather or supply difficulties. Gas storage is possible but harder.
Finally we can consider nuclear power. Although a fuel is used, it is not a combustible fuel and no carbon dioxide is created in operation. Instead the energy comes from the destruction of mass according to Einstein’s famous equation. Nuclear power is highly available and the amount of power generated is simply controlled by moderating the decay process of the fuel. In that respect nuclear power is like hydropower where the inlet lake is always full.
If the goal is to generate electricity with minimal carbon dioxide, then using nuclear power to top up what is available from solar and wind is probably currently the best option. Unfortunately, the construction of nuclear power stations is a long term process and the construction of appropriate numbers has not begun. This means that the goals for the de-carbonization of electricity will simply not be met and electricity will continue to come from fossil fuels, preferably gas.
It is quite easy to find how much fossil fuel is used by vehicles in any given country, and a back-of-napkin calculation shows how much electrical power would be needed to replace it. But if that electricity comes from burning fossil fuels in power stations to release carbon dioxide and pollutants instead of at the vehicles themselves, what would be the point?
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