We used discounted cash flow analysis to calculate daily user cost based on capital, operation and maintenance, and electricity expenses (separate from operation). The expenses or revenue are amortized. Specifically, initial capital costs are distributed over the lifetime of the system, with a discount rate adjusting for the diminishing value of money over time. For capital costs of OP, a learning curve equation was used to conservatively estimate costs at scale to produce 10,000 units. Operation and maintenance costs were estimated for consumables and replacement parts, and labor costs were estimated based on operator wages and hours of labor. Electricity requirements were estimated based on the energy needs of each unit within the OP and typical electricity costs per kilowatt-hour. The total cost is adjusted to account for income tax obligations (at a tax rate of 20 -35%). The objective of this analysis is to estimate the daily user fee necessary to account for the full costs of the system (e.g., meeting annual operating expenses while accounting for initial capital requirements). Details on the modeling procedures for costs are described in the Supporting Information (Section S2).