Dear Ron
I agree with Jock that the metric you want depends on the question asked. The promotion of stoves at a national level is almost always attached to cleaner air and lower fuel consumption but not always. It depends where it is. I have seen an opportunity is present for consideration of the amount of charcoal produced. To present a convincing argument, it has to be in a context where raw fuel consumption is not the primary consideration. Where there is sufficient biomass, i.e. the available supply is considered sustainable, one can present an argument that in view of the available supply being sufficient, it can be considered an advantage to create char (for any purpose) provided it does not increase the offtake. In short, if ‘no harm is done’ to the sustainability equation, then credit can be given for anything one prefers provided the explanation is accepted. I wonder what you think of this proposition: Suppose the baseline stove in an environment has a system efficiency of 20%. That is measured using the energy available in the fuel consumed and the energy that is gained by the cooking pots. Then you propose an ‘improved stove’. This will deliver some benefit that might be lower CO, lower PM emissions, great fuel efficiency plus any other ‘non-standard’ consideration like char production efficiency, faster lighting, greater controllability and so on – something that is not directly affecting the fuel or emissions. All of these are considered plusses by various stakeholders. The market is free to promote any solution so the only question arising is whether the benefit is viewed as being one by a project that wants to spend money on it. If the project is ‘conventional’ (not aimed at creating char) one could make a case that if the stove in question delivers two or three benefits the project is interested in, then if it also produces char with some additional value (such as for example is the case in Vietnam with rice hull charcoal) some consideration might be made and a lower demand be required for saving fuel. To be more specific, suppose the desire of the project is reduce emissions and reduce fuel consumption, and it is taking place in a region where the biomass is sustainable, then the provision of an economic benefit (from the char) could be argued to offset the fact that although it may not save fuel, there is ‘no harm’ caused. The offer then is a stove that does not use less total fuel, but it reduces emissions and produces at least one clear benefit. My suggestion is that this could fly as a fundable argument. It is a matter of demonstrating that a) primary goals of the project are being met, b) that the sustainable supply is not undermined, c) that the production of char has value in the target region. Putting hard number on this means showing that the thermal performance increase is such that the char is created from fuel that has been saved by the stove while not using more. In this way all criteria are met save the fuel reduction aspect which is arguably unnecessary. Then one could either show that the remaining char is a) a biofuel for another stove that is within the same region (showing an increase in total cooking using the available resource) or that is will produce income by being sold for some purpose. The nuts and bolts of this are that there is a difference between the way a stove uses Joules of available energy and the way a programme interprets the stove in context. When asking an engineering question you can expect an engineering answer. That answer does not stop policy makers from taking a holistic view of how the energy supply (or carbon chain) fits into the whole environment. The stress I see in the discussion is the desire to integrate the two – policy and engineering metrics. I don’t see how this can be done. If I ask how much heat gets into a pot, I can wish it was more, but it only gets what it gets. I can set a policy that is should be more, but it only gets what it gets. The measurement is not susceptible to policy. Reducing this to an example, here is a stove, a project target and an improved stove: Stove A has a system efficiency of 20%, CO and PM emissions of 12 g and 500 mg respectively per MJ delivered into the pot. The target for an improved stove in the programme is a system efficiency of 30%, CO of 9 g and 250 mg of PM per MJNET. Stove B has a system efficiency of 20%, CO of 4 g and 100 mg PM per MJ and produces 20% char (based on the dry mass of the fuel consumed). If you were able to develop your argument that the char has practical value (there are several ways to show that) then you can make the case that you are meeting the air quality/health goals while not increasing the drawdown from the fuel supply, which is already agreed to be sustainable at present. Within the sphere of influence of the project, it could be an acceptable proposition. Keep in mind that projects are not universal in focus. At an international level one might present other arguments. The argument could be convincing in at least some cases where there is enough biomass to provide either fuel switching or where a determination of sustainability has been rendered. (There are clear rules for that.) Where it will not work easily is where the biomass supply is not sustainable, or it would be harder to be convincing because you would have to show some fuel saving (higher system efficiency) while simultaneously having a heat transfer and combustion efficiency that accomplished the same amount of cooking while saving enough fuel to create char. I think that is technically possible, it is just a harder case to argue. The reason it is harder is that in such fuel stressed areas, there is a lot of pressure to maximise fuel efficiency with emissions being secondary. But I still hold out hope. While this is not an over-the-top enthusiastic message, I am trying to demonstrate how to approach programmes that might consider promoting, at programme expense, stoves that produce char as a concurrent performance goal while not necessarily reducing fuel consumption. It is possible that a programme initially intent on saving fuel (in a sustainable region) might discount the efficiency requirement if the char was a fuel for other stoves. I have recently seen and crunched in my hand some charcoal that was made from a nut shell that is plentiful in some regions. It is hard enough to be transported long distances in sacks. Being sustainably produced it is very attractive to turn this into a commercial urban fuel – something the area does not export at present. I do not think production of the char and cooking would reduce biomass consumption, but it would not increase it either. It seems like a win-win situation, however there is still the matter of convincing the project and then the market to accept the proposal. Regards Crispin
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