National Energy System Analysis
Roy H W Johnston(Paper arising from the Feasta seminar at the Green Gathering, Woodbrook, Bunclody, August 18 2007.)
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AbstractThe following notes are a response to two papers, one by Folke Gunther(1) on the enhancement of agricultural productive systems using charcoal, and another by Patrick Devine-Wright(2) on issues tending to block project development.
BackgroundI do not propose to overview the papers in detail, but simply to highlight some key points which triggered the train of thought generating this background note.
The key point in the Gunther paper is the potential role of charcoal in soil fertility enhancement, possibly as a by-product of gas production using the Fischer-Tropsch process (fast pyrolysis of biomass, at high temperature). The porous structure of charcoal gives it a high surface area, which can be supportive of much microbiological activity, enhancing the uptake of nutrients from organic manure. It therefore makes sense to enrich farm-yard manure with charcoal, whether locally produced by traditional methods, or available on the market as an industrial by-product. The problem which arises however is, given the increasing price of fossil fuel, the alternative use of charcoal, or indeed wood, in the domestic stove is likely to be a preferred option. In what follows I suggest how this issue might be addressed.
The Devine-Wright paper outlines some of the 'NIMBY' issues arising when a specific local development proposal involving renewable energy becomes known. He analyses the imprecision and ambiguity of the term, and suggests various approaches which may lead to the promotion of community support. In what follows I outline some specific situations where effective community support would be necessary, and offer, by implication, some suggestions how it might be obtained. I also broaden the scope to suggest tentatively how an overall systems approach to transforming the national energy infrastructure might be developed.
Charcoal as fertility enhancerIf, as is suggested, there is a significant level of soil fertility enhancement to be obtained by the addition of charcoal to the fertiliser mix at tillage-time, then this needs to be quantified by serious agricultural experimentation under Irish conditions. If the fertility enhancement is long-term, then its growth needs to be monitored and quantified. This then will enable the comparative value to be determined in this application, as compared with the alternative of its use as fossil-fuel replacement. If the gain is positive, then there is a significant gain possible in the rate of reduction of atmospheric CO2. If the gain is negative, and it is decided, in the interests of atmospheric CO2 reduction, to encourage the use of charcoal in soil-enhancement rather than a fuel, then we need to consider how best to do this using a pricing or taxation mechanism.
A possible route which comes to mind is via the industrial processing of urban sewage to generate organic fertiliser. This is beginning to become attractive in situations where urban domestic waste exists uncontaminated by industrial waste which includes undesirable components such as heavy metals. If a supply of charcoal were to become available from a biomass pyrolysis plant, it would make sense to regulate the price of charcoal so that the priority market would be municipal organic fertiliser enrichment. Any charcoal surplus to this would be available for coal replacement, as solid fuel. How to regulate the price structure so as to make this happen needs to be explored. Whatever system emerges would need to discourage the wasteful production of charcoal on a small scale, so as to lose the valuable volatile biomass products.
Fast PyrolysisThis involves a relatively large-scale engineered process(3); current work would appear to be mostly at the pilot level and scale-up economics remains to be done. If it can be suitably scaled up and made reliable, it offers an opportunity to convert biomass on a large scale to charcoal (for use as solid fuel or soil conditioner), liquid fuel (for transport) and gas (for the gas grid). To attain this however would require serious planning of the biomass supply, and the logistics of the production, drying and processing of the feedstock would need to be taken into account in the overall techno-economic analysis.
Wave energyAnother factor is the possibility of availability of oxygen as a by-product of water electrolysis, the main product being hydrogen, either for transport or for enriching the content of the gas grid. A pyrolysis plant fed with O2 would produce gas which would not be diluted with nitrogen or polluted with nitrous oxides, thus being enriched. This raises the issue of the overall energy system: how can we plan for synergies between the system components? An obvious source of electrolysis power is wave energy(4), the application of which in the context of the requirements of the electricity grid is highly problematic. Wave-power generators along the Atlantic coast have been postulated. On-board DC generators feeding electrolytic cells seem to be an obvious way to harvest the energy. Presumably some of the hydrogen could drive compressors and the output would be cylinders of compressed gas. The cost of this would need to go into the economics of the overall system logistics. The economics of extending the gas grid in such a way as to enable the H2 from this source to be picked up would also need to be examined. If this takes place, would it perhaps make sense to lay an O2 pipe alongside?
Combined Heat and PowerCompact urban housing can benefit from having an electricity generator nearby, if the waste heat can be captured as a domestic hot water source. CHP(5) is a mature technology, in widespread use throughout Europe. However adapting it to a situation where we are depending on distributed small-scale power production from renewable sources requires some analysis. A typical small-town project could to run on gas from the grid, in which case it could match the thermal load to the thermal demand requirements, feeding the electricity grid when running. However there are conflicting demand patterns for thermal and electrical loads.
Some buffering would be needed for the thermal output, if the electrical output is to take advantage of the flexibility of the gas feed to work as a peak load supplier. On the other hand, if it is on a scale such as to be fed with wood chips, supplemented with clean municipal waste, then it could not easily work in start-stop mode; it would need managed continuity, and supply the base load.
Thus there are many complex systems issues to be addressed if the national energy requirements are to be supplied by a mix of small-scale sources. The design and management of the interconnecting grid systems, for gas and electricity, will need to be totally re-analysed, taking into account the environmental statistics of wind and wave-based sources, and allowing for a significant amount of pumped storage.
Biomass SupplyThe organisation of reliable biomass supply will require the development of an extended managed co-operative approach to the use of agricultural land, and serious policy decisions regarding how production is to be split between energy and food. There will be a demand for annual energy crops, such as oilseed rape, and these will need to be embodied in a planned rotation system. They provide animal feed as a by-product. Short-rotation forestry (SRF) can be developed by expanding the width of the hedges surrounding the fields into shelter-belts, easily accessible by culling machinery; there is thus a symbiosis between SRF and agriculture; they need not be incompatible.
Large-scale monoculture, with dependence on artificial fertiliser and pesticides, is to be avoided; dependence on locally produced organic fertiliser will need to become the norm; whence the importance of development of processing of urban domestic sewage, as mentioned earlier. There is need for a total systems re-assessment of Irish land use in this context; we need to get away from permanent pasture, and towards an integrated mixed farming and forestry system, with appropriate rotation. These processes need seriously to be quantified, as future sources of our national and global food and energy supplies.
Notes and References1. See http://www.holon.se/folke/.
3. See for example http://www.btgworld.com/technologies/pyrolysis.html for an outline of how this process generates gas, liquid fuel and char.
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Copyright Dr Roy Johnston 1999