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    Rights: The University of Waikato
    Published 10 June 2008 Referencing Hub media

    Peter Hall from Scion explains that residual biomass is material created as a by-product from making something else.

    Residual biomass is a term that is used to describe waste products from biomass resources that can be used to produce energy. Wood off-cuts left behind in the forest are a good example of this. However, energy demands outnumber what can be supplied by using residual biomass. In order to supply a growing demand of renewable energy resources, residual biomass could be supplemented through purpose-grown products.


    The residual biomass is material which is created as a by-product from making something else. So the logging residue and the sawmill residues are a by-product of creating sawn timber. So the material that is created there is a residual or, in some cases, possibly even a waste. However, if there is an efficient way of converting, say, wood into liquid fuels and we need to meet a large part of the demand for liquid fuels, there isn't enough residual material to make enough liquid fuel to meet our demand. So you then have to purpose-grow a section of either forest, or possibly agricultural crop, and the sole aim of that crop is to make energy as opposed to food or timber or something else.

    Within biomass, the logical route is to use all of the waste resources first. Now, there’s a hierarchy of costs and volumes and risks associated with using those materials, and this little graph is hopefully a way of explaining it. Down here, we have waste cooking oil, and this is looking at meeting liquid fuel demand from a variety of resources. You can make biodiesel out of waste cooking oil, and you can do it very cheaply, but there is only a very small quantity of waste cooking oil around, there is only about 5 millions litres nationally. Now 5 million litres might sound like a very big number, but this is what happens when you look at the demand for liquid fuels, versus the ability of making liquid fuels out of residual material. And these two graphs – on this top one this is our first residue resource and how much liquid fuel we could make out of it in terms of hundreds of litres, the cost of doing it, and there is some risk around doing it, cause it… there’s still some technology development to do to make it work. And there’s a whole lot of other things we can make into liquid fuels from the various waste resources, but the problem is that, if you just focus on residuals, and you put in the issue of demand, these are the same resources. When you put them on a scale where you've got the demand for liquid fuel – this country uses, just petrol and diesel, about 6.3 billion litres a year, if you put jet fuel for planes in there, it’s nearer to 7.8 billion litres a year of liquid fuels, so it’s really a lot – and residual biomass simply cannot meet that demand, so you have to look at purpose-growing it from somewhere if you want to increase the amount of that demand that you are going to meet from biomass or carbon neutral fuels. And it’s a very similar picture for heat. The demand scale isn't quite as large and the biomass can make a bigger contribution, but you can only use it once – you can either use it for biomass, you can use it for heat or for liquid fuels. So if you are trying to make a dent in both the heat and liquid fuel demand, then the logical route is that you have to purpose-grow something somewhere.

    KQED QUEST, some rights reserved
    Paul Brooker