The signing was in conjunction with Alcoa's announcement to spend $400m on an efficiency upgrade to its Pinjarra refinery.
The agreements include those relating to the supply of steam, operations and maintenance and the sale of land.
"The activities of Alinta and Alcoa are highly complementary. Alinta has the retailing expertise and over 470,000 customers, whilst Alcoa's base load refinery steam requirements provide an extremely efficient platform for the generation and sale of competitively priced electricity," said Tony Howarth, chairman of Alinta.
Customer demand for the output of the first co-generation unit has been strong. To date, Alinta have pre-sold over 110 MW of capacity from the first unit to be located at the
Pinjarra refinery site. Alinta expects to begin supply of electricity in the second quarter of 2005.