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We have touched on this in several previous threads but it is something that deserves a thread of its own. Basically we are talking about the direct use of the heat that is given off when plant matter like wood, non food quality corn, saw mill residue, etcetera are burnt in one way or another.
One of the big problems with generating electricity is the inefficiency involved in generating and distributing it and overall the process is between 30% and 40% efficient. While any form of resistance heating is 100% efficient there is no way to get round the overall inefficiency of the system so whatever energy you use this way around twice as much is wasted. This means that you are also creating three times as much pollution and are consuming fossil fuels three times faster than necessary.
In 2004 the global consumption of energy was around 471 EJ (471 x 1018 Joules), however, many countries and energy producers do not track the amount of energy being consumed accurately and there is at least 10% uncertainty in the figure above. By far the majority of this total comes from fossil fuels and other non renewable resources, however, the amount of energy available from renewable sources, mainly the Sun, is around 3.8 YJ (3.9 x 1024 Joules). This totally dwarfs our energy consumption by a factor of around 8,000 fold, so theoretically, drawing all of our energy needs from renewable sources should be simple to archive. After all we are only talking about diverting around 0.0125% of the renewable energy available for out use and ultimately it all ends up in the atmosphere so it would likely have no detectable effect on the Earths climates and ecosystems.
If we break the total energy consumption up according to usage roughly 16% or 74 EJ is used for heating purposes. If we were to utilize plant matter to supply this energy the problem now becomes how much land would be needed to grow plant matter that is dedicated to use as heating. It is difficult to calculate the yield a given area can produce because it varies dramatically according to the crop, location, climate and a whole host of other factors. However, a good starting point is the amount of bio-diesel that can be produced from a given crop.
Bio-diesel production varies from around 172 l ha-1 for maze and 5,950 l ha-1 for palm oil. If we take the energy content of bio-diesel which is 35.1 MJ l-1 that gives a yield of:
6,073 MJ ha-1 for maze and 208,845 MJ ha-1
If we take the earlier estimate for the energy consumed in heating we end up with
12.185 x 109 ha for maze and 354 x 106 ha for palm oil.
That means world wide there would need to be an additional area dedicated to cultivating plant material of between 3,450,000 km2 and 121,850,000 km2.
Clearly the use of low yield crops would make the area needed for cultivation unworkable but for high yield crops the area is not unrealistically large although it is larger than some countries. Something that is vital is that this area must be in addition to any existing crop area otherwise the impact on food production would be catastrophic and the effect of clearing and cultivating that amount of land is not going to have a substantial effect. The land, however, does not have to be contagious nor does it need to be confined to a single country but it does need to be land capable of supporting the crop and this eliminates large tracts of land throughout the world.
The figures and background information used in the calculations were obtained from the following articles.
Before anybody jumps in and says the yields are for the energy in bio-diesel and a crop that is used directly for combustion would have a greater yield. Yes, this is true, however, to be able to utilize a crop directly you need to install specialized furnaces and it is not as easy to transport and use as a liquid fuel. At least initially there would be a need to turn the crop into some sort of liquid fuel and bio-diesel is not greatly dissimilar to heating oil in energy content and so would be ideal as an initial source of energy for heating. It also means that the fuel can be used for purposes other than heating making the final product more viable.
What are your thoughts on using a crop to heat, can the world afford to clear and cultivate the required area, or would the results of doing so be unacceptable? Given the current level of damage being done can we afford not to go down the energy crop path? Certainly the amount of energy that is being released naturally could easily supply all our energy needs, so why do we continue utilizing the ever depleting fossil fuel reserves?
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