Renewable Energy Technology Assessments - Kauai Island Utility ...

Kaua’i Island Utility Cooperative
Renewable Energy Technology Assessments
3.0 Renewable Energy Technology
Options
production and power facility that would optimize the production of ethanol from higher
value feedstocks, while producing power from waste biomass (such as bagasse).
Although there are many potential feedstocks for ethanol production, sugarcane is
one of the most attractive given its high yields and the historical production of the crop
on the island. Similar to banagrass discussed earlier, if all 140,000 acres zoned for
agriculture on Kauai were used to grow sugarcane yielding 2,070 gallons of ethanol per
acre per year, approximately 290 million gallons of ethanol could be produced each
year. 17 More realistically, if only 20 percent of this land was available (an amount equal
to 28,000 acres, less than the amount of land used for sugarcane in the mid-1990s), about
58 million gallons of ethanol per year could be produced. For comparison, Kauai
consumed 32.3 million gallons of gasoline in 2003. 18 Kauai could easily supply 10
percent of its transportation fuel use from ethanol and have remaining fuel for export or
other use, including power generation. Assuming power generation from 50 million
gallons at a heat rate of 8,000 Btu/kWh (HHV), approximately 525 GWh/yr of energy
could be produced from a 75 MW baseload power plant.
Gasoline is generally reserved for use as transportation fuel but can be used for
power generation in some applications. Ethanol could be blended relatively easily with
gasoline for power applications, if the power conversion technology can burn the blend.
Ethanol can also be mixed with diesel; however it has poor solubility and other issues
that have limited this application. Further research and development is underway to
explore these issues.
It should be noted that for power generation, it is generally more efficient and cost
effective to burn the biomass directly rather than convert biomass to ethanol and then
burn the ethanol in an engine or turbine. That said, ethanol could be used to displace
fuels in existing power plants with minimal modifications to the power plant, similar to
solid biomass cofiring (discussed earlier). Given that all of KIUC’s existing thermal
capacity is designed to burn liquid fuels, this may be attractive; however, there are
limitations on which units are compatible. The nearest term application for KIUC would
be to replace diesel fuel combusted in the 10 MW thermal steam plant at Port Allen. This
would likely require burner modifications to the boiler and some fuel system changes, but
these should be straightforward and relatively low cost. Assuming 100 percent firing of
ethanol and operation similar to historical patterns 19 , this plant would generate about 50
GWh/yr consuming approximately 5.6 million gallons of ethanol. Assuming ethanol is
supplied by a third party, this project could be implemented quickly, at low capital cost,
17 Yield data from Stillwater Associates, “Hawaii Ethanol Alternatives”, available at:
http://www.hawaii.gov/dbedt/ert/ewg/ethanol-stillwater.pdf.
18 State of Hawaii Department of Taxation, “Liquid Fuel Tax Base & Tax Collections”, 2003.
19 9,000 Btu/kWh (HHV) heat rate and a capacity factor of 60 percent
21 March 2005 3-26 Black & Veatch