NT Power Generation Pty Ltd v Power & Water Authority

The dispute in *NT Power Generation Pty Ltd v Power & Water Authority* concerned the interpretation of a contract for the sale of electricity. NT Power Generation Pty Ltd (NT Power) was the seller and the Power and Water Authority (PAWA) was the buyer. The case was heard in the High Court of Australia.

The central legal issue before the High Court was whether PAWA was entitled to recover from NT Power certain payments made under the contract, which PAWA alleged were made under a mistake of fact. Specifically, PAWA contended that it had mistakenly overpaid NT Power for electricity supplied due to an incorrect calculation of the "market price" as defined in the contract.

The High Court, in a joint judgment delivered by McHugh and Kirby JJ, held that PAWA was not entitled to recover the payments. Their Honours reasoned that the contract contained a clear mechanism for determining the market price, and that PAWA had made payments in accordance with that mechanism. The Court found that PAWA's belief that it had overpaid was not a mistake of fact in the relevant sense, but rather a misunderstanding of its contractual obligations or a misinterpretation of the contract's terms. The principle applied was that a party cannot recover money paid under a contract if the payment was made voluntarily and with full knowledge of the facts, even if that party later believes they have made an error in calculation or interpretation.

Consequently, the High Court dismissed PAWA's appeal.