First, I don't know for sure whether the subsidy will cover 100% of the production costs. The subsidy in the contracts is a “per unit of power” subsidy. The exact amount is in U.S. dollars. I don't know whether that covers the totality of the production costs, or whether the production costs will be higher. I presume the production costs will be higher than the subsidy. Hence, I'm not convinced that, as you say, taxpayers will be subsidizing 100% of the cost of the batteries.
Based on what we have seen in the contracts, and in the Trillium Network study, we estimate that the payback for these battery plants—their direct, indirect and induced benefits—should be recovered by increased taxes paid to the feds and the Ontario government over a 20-year period.