Any guaranty under this subchapter shall apply only to so much of the principal amount of any loan as does not exceed 75 percent of the aggregate cost of the project with respect to which the loan is made, except that any guarantee made for a loan to an electric, housing, or other cooperative, or to a municipality (as defined in section
796
(7) of title
16), may apply to so much of the principal amount of the loan as does not exceed 90 percent of the aggregate cost of the project. In determining the aggregate cost of a project for purposes of the preceding sentence, there shall be excluded the cost of constructing electrical transmission lines to the extent that the cost of constructing such lines exceeds 25 percent of the aggregate cost of the project (as determined without regard to this sentence); except that the Secretary may waive or limit the application of this sentence with respect to any project located in the State of Hawaii upon a finding that such project is remote from the area of primary consumption, that a transmission line is required before the geothermal reservoir can be developed, and that the particular transmission line involved will be used for more than the plant which is the subject of the loan guarantee. In the case of a guaranty for the purposes specified in subsection (b)(5) of this section, the aggregate cost of the project shall be deemed to be that portion of the total cost of construction and operation which is directly related to the utilization of geothermal energy within the structure or facility in question, except that the aggregate cost of the project with respect to which the loan is made may be the total cost including construction and operation in cases where the facility or structure has been located near a geothermal energy resource predominantly for the purpose of utilizing geothermal energy, or as determined by the Secretary of Energy the economic viability of the project is substantially dependent upon the performance of the geothermal reservoir.