The cheapest chargers Daniel could find were $10 at the time of this writing. They would take around 5 hours to charge a typical 11 Watt-hour smartphone battery under bright sunlight.

Part 1: What is the levelized cost of electricity from this system, if its used to charge an 11 Wh battery every day of the year? Use a modest individual capital charge factor of 0.15; you may neglect all costs other than the $10 purchase price. [...$/kWh ]

Part 2: What is the mitigation cost for Daniel to use this sytem instead of using grid electricity? Assume grid electricity costs $0.20/kWh, with 0.5 kg CO₂e emitted per kWh. Answer in dollars per ton of CO₂. [... $/tCO2]