<p>Substitute products, in economics, are&#xa0;goods that can be used in place of each other to satisfy the same basic need or want.&#xa0;Demand for the less expensive alternative rises as a result of people switching to the other substitute as the price of the first one rises. Renewable energy comes from natural resources that replenish more quickly than they are depleted. Two examples of such constantly replenishing sources are sunlight and wind. Sunlight and wind are two examples of such sources that are always being replenished. Numerous renewable energy sources surround us. The study examines a third-order equation that combines Cournot's price model for replacement products for deteriorating items with Cournot's price-dependent renewable energy demand. The optimal demand and manufacturing lot size are option variables. The price break-even point has been determined, the law of demand has been validated, and the maximum profit from the three different elements has been computed. The price break even point is 1724. 6368 and the highest possible profit is 253,550.05 with the corresponding demand of 2987.4595 units. To cut carbon emissions, costs associated with transportation, carbon emissions, investments in green technology, and renewable energy are introduced. The purpose of this paper is to determine the ideal demand and production lot size in order to maximise total profit. The applicability of this concept is illustrated by numerical examples. A sensitivity analysis of the best solutions is provided to assess the stability of this proposed model. Visual Basic 6.0 is used to generate the data.</p>