Background

IEA GHG is considering carrying out a study to assess the performance, costs and potential for bioenergy plants with CO2 capture and storage (CCS). Such plants can be considered to have negative nt emissions of CO2. IEA GHG is also considering assessing the relative merits of a broad range of greenhouse gas abatement options, including bio-energy plants with and without CCS.

One of the key issues in studies on bio-energy is the plant size. It has been suggested that CCS may be economically unattractive for relatively small scale biomass plants because of high costs of CO2 transportation. However, some of the authors of the IPCC Special Report on CCS (SRCCS) indicated that plants using 1000 MWth or more of purpose grown biomass could be feasible. This scale of bioenergy plant is much larger than the 30-70 MWe plants considered appropriate for Spain in an earlier study by IEAGHG.

The aim of this report is to provide a critical review and comparison of the key technical and economic assumptions presented in published papers on bio-energy plants, principally those referenced in the IPCC SRCCS.

Conclusions

The optimum size of bio-energy plants depends on the fraction of land around the plant which is devoted to biomass production, biomass yields per hectare, the relationship between biomass transportation distance and costs, and costs and economies of scale in the bio-energy conversion plant. The optimum size therefore depends on the characteristics of the site and the level of technology development.

A wide range of assumptions have been made in published bio-energy studies, resulting in different optimum plant sizes. Some of the studies which focused on particularly large plant sizes did not take into account the effects on costs of increased biomass transportation distances. The addition of CO2 capture and transportation will increase capital costs and is likely to increase the economic optimum plant size.

Recommendations

Any future studies by IEA GHG on the relative merits of GHG abatement options should include assessment of bio-energy plants at a range of different sites worldwide. The studies also need to be based on a clearly defined timeframe and assumptions regarding future technological improvements.